Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Lumninous Infrared Galaxy Candidates

Science.gov (United States)

Griffith, Roger L.; Kirkpatrick, J. Davy; Eisenhardt, Peter R. M.; Gelino, Christopher R.; Cushing, Michael C.; Benford, Dominic; Blain, Andrew; Bridge, Carrie R.; Cohen, Martin; Cutri, Roc M.;

A Spitzer Infrared Radius for the Transiting Extrasolar Planet HD 209458 b

Science.gov (United States)

Richardson, L. Jeremy; Harrington, Joseph; Seager, Sara; Deming, Drake

2007-01-01

We have measured the infrared transit of the extrasolar planet HD 209458 b using the Spitzer Space Telescope. We observed two primary eclipse events (one partial and one complete transit) using the 24 micrometer array of the Multiband Imaging Photometer for Spitzer (MIPS). We analyzed a total of 2392 individual images (10-second integrations) of the planetary system, recorded before, during, and after transit. We perform optimal photometry on the images and use the local zodiacal light as a short-term flux reference. At this long wavelength, the transit curve has a simple box-like shape, allowing robust solutions for the stellar and planetary radii independent of stellar limb darkening, which is negligible at 24 micrometers. We derive a stellar radius of R(sub *) = 1.06 plus or minus 0.07 solar radius, a planetary radius of R(sub p) = 1.26 plus or minus 0.08 R(sub J), and a stellar mass of 1.17 solar mass. Within the errors, our results agree with the measurements at visible wavelengths. The 24 micrometer radius of the planet therefore does not differ significantly compared to the visible result. We point out the potential for deriving extrasolar transiting planet radii to high accuracy using transit photometry at slightly shorter IR wavelengths where greater photometric precision is possible.

SPITZER OBSERVATIONS OF THE λ ORIONIS CLUSTER. II. DISKS AROUND SOLAR-TYPE AND LOW-MASS STARS

International Nuclear Information System (INIS)

Hernandez, Jesus; Morales-Calderon, Maria; Calvet, Nuria; Hartmann, L.; Muzerolle, J.; Gutermuth, R.; Luhman, K. L.; Stauffer, J.

2010-01-01

We present IRAC/MIPS Spitzer Space Telescope observations of the solar-type and the low-mass stellar population of the young (∼5 Myr) λ Orionis cluster. Combining optical and Two Micron All Sky Survey photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 M sun to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with 'evolved disks' (with smaller excesses than optically thick disk systems), and 'transitional disk' candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from ∼6% for K-type stars (R C - J C - J>4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the λ Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as ∼5 Myr.

Spitzer Observations of the X-ray Sources of NGC 4485/90

Science.gov (United States)

Vazquez, Gerardo A.; Colbert, E.; Hornschemeier, A.; Malhotra, S.; Roberts, T.; Ward, M.

2006-06-01

The mechanism for forming (or igniting) so-called Ultra-Luminous X- ray sources (ULXs) is very poorly understood. In order to investigate the stellar and gaseous environment of ULXs, we have observed the nearby starburst galaxy system NGC 4485/90 with Spitzer's IRAC and IRS instruments. High-quality mid-infrared images and spectra are used to characterize the stellar history of stars near the ULXs, and the ionization state of the surrounding gas. NGC 4485/90 fortuitively hosts six ULXs, and we have analyzed IRAC images and IRS spectra of all six regions. We also observed two "comparison" regions with no X-ray sources. Here we present our preliminary findings on the similarities and differences between the stellar and gaseous components near the ULXs.

Spitzer ultra faint survey program (surfs up). I. An overview

Energy Technology Data Exchange (ETDEWEB)

Bradač, Maruša; Huang, Kuang-Han; Cain, Benjamin; Hall, Nicholas; Lubin, Lori [Department of Physics, University of California, Davis, CA 95616 (United States); Ryan, Russell; Casertano, Stefano [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Lemaux, Brian C. [Aix Marseille Université, CNRS, LAM (Laboratoire d' Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Schrabback, Tim; Hildebrandt, Hendrik [Argelander-Institut für Astronomie, Auf Dem Hügel 71, D-53121 Bonn (Germany); Gonzalez, Anthony H. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States); Allen, Steve; Von der Linden, Anja [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305-4060 (United States); Gladders, Mike [The University of Chicago, The Kavli Institute for Cosmological Physics, 933 East 56th Street, Chicago, IL 60637 (United States); Hinz, Joannah; Zaritsky, Dennis [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Treu, Tommaso, E-mail: marusa@physics.ucdavis.edu [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

2014-04-20

Spitzer UltRa Faint SUrvey Program is a joint Spitzer and Hubble Space Telescope Exploration Science program using 10 galaxy clusters as cosmic telescopes to study z ≳ 7 galaxies at intrinsically lower luminosities, enabled by gravitational lensing, than blank field surveys of the same exposure time. Our main goal is to measure stellar masses and ages of these galaxies, which are the most likely sources of the ionizing photons that drive reionization. Accurate knowledge of the star formation density and star formation history at this epoch is necessary to determine whether these galaxies indeed reionized the universe. Determination of the stellar masses and ages requires measuring rest-frame optical light, which only Spitzer can probe for sources at z ≳ 7, for a large enough sample of typical galaxies. Our program consists of 550 hr of Spitzer/IRAC imaging covering 10 galaxy clusters with very well-known mass distributions, making them extremely precise cosmic telescopes. We combine our data with archival observations to obtain mosaics with ∼30 hr exposure time in both 3.6 μm and 4.5 μm in the central 4' × 4' field and ∼15 hr in the flanking fields. This results in 3σ sensitivity limits of ∼26.6 and ∼26.2 AB magnitudes for the central field in the IRAC 3.6 and 4.5 μm bands, respectively. To illustrate the survey strategy and characteristics we introduce the sample, present the details of the data reduction and demonstrate that these data are sufficient for in-depth studies of z ≳ 7 sources (using a z = 9.5 galaxy behind MACS J1149.5+2223 as an example). For the first cluster of the survey (the Bullet Cluster) we have released all high-level data mosaics and IRAC empirical point-spread function models. In the future we plan to release these data products for the entire survey.

Exoplanet Characterization With Spitzer Eclipses

Science.gov (United States)

Harrington, Joseph

We will analyze our existing Spitzer eclipse data for 11 exoplanets (GJ 436b, WASP-8b, WASP-29b, WASP-11b, TrES-1, WASP-34b, WASP-43b, HD 209458b, HAT-P-30b, HAT-P-13b, and WASP-12b) along with all other Spitzer eclipse and transit data for these systems (723 hours of total data). In combination with transit results, these measurements reveal the surface fluxes emitted by the planets' atmospheres in the six Spitzer bandpasses (3.6, 4.5, 5.8, 8.0, 16, and 24 1-4m), as well as orbital eccentricity and in a few cases possibly even precession rate. The fluxes, in turn, can constrain atmospheric composition and thermal profiles. We propose here to analyze data for these planets using Monte Carlo-driven, radiative-transfer, model-fitting codes; to conduct aggregate analyses; and to develop and share statistical modeling tools. Secondary eclipses provide us with a unique way to characterize exoplanetary atmospheres. Since other techniques like spectroscopy divide the planetary signal into many channels, they require very high signal-to-noise ratio (S/N) and are only possible for a few planets. Broadband eclipse photometry is thus the only technique that can measure dozens of atmospheres and identify the mechanisms that cause planets at a given irradiation level to behave so differently from one another. Until JWST becomes available, the broad variety of Spitzer data that we already have in hand, along with observations from the Hubble Space Telescope and possibly SOFIA, are our best way to understand the wide diversity of exoplanetary atmospheres. Since 2010, the team has produced six papers from a new, highly modular pipeline that implements optimal methods for analysis of Spitzer photometric time series, and our efficiency is increasing. The sensitivity needed for these measurements is up to 100 times better than Spitzer's design criteria, so careful treatment of systematic error is critically important and first-order approximations rarely work. The new pipeline

Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

Energy Technology Data Exchange (ETDEWEB)

Blum, R. D. [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Srinivasan, S.; Kemper, F.; Ling, B. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Volk, K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2014-11-01

K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

International Nuclear Information System (INIS)

Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

2014-01-01

K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

THE SPITZER -HETDEX EXPLORATORY LARGE-AREA SURVEY

Energy Technology Data Exchange (ETDEWEB)

Papovich, C.; Shipley, H. V.; Mehrtens, N.; Lanham, C.; DePoy, D. L.; Kawinwanichakij, L. [Department of Physics and Astronomy, Texas A and M University, College Station, TX, 77843-4242 (United States); Lacy, M. [North American ALMA Science Center, NRAO Headquarters, Charlottesville, VA 22903 (United States); Ciardullo, R.; Gronwall, C. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Finkelstein, S. L.; Drory, N.; Gebhardt, K.; Hill, G. J.; Jogee, S. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Bassett, R. [International Centre for Radio Astronomy Research, University of Western Australia, 7 Fairway, Crawley, WA 6009 (Australia); Behroozi, P. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Blanc, G. A. [Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago (Chile); Jong, R. S. de [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Gawiser, E. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Hopp, U., E-mail: papovich@physics.tamu.edu, E-mail: papovich@tamu.edu [Max-Planck-Institut für Extraterrestrische Physik, D-85741, Garching (Germany); and others

2016-06-01

We present post-cryogenic Spitzer imaging at 3.6 and 4.5 μ m with the Infrared Array Camera (IRAC) of the Spitzer /HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ≈24 deg{sup 2} of the Sloan Digital Sky Survey “Stripe 82” region, and falls within the footprints of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R ∼ 800 spectroscopy will produce ∼200,000 redshifts from the Ly α emission for galaxies in the range 1.9 <  z  < 3.5, and an additional ∼200,000 redshifts from the [O ii] emission for galaxies at z  < 0.5. When combined with deep ugriz images from the Dark Energy Camera, K -band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, the presence of active galactic nuclei, and environment over a co-moving volume of ∼0.5 Gpc{sup 3} at 1.9 <  z  < 3.5. Here, we discuss the properties of the SHELA IRAC data set, including the data acquisition, reduction, validation, and source catalogs. Our tests show that the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 μ m images. The catalogs reach limiting sensitivities of 1.1  μ Jy at both 3.6 and 4.5 μ m (1 σ , for R = 2″ circular apertures). As a demonstration of the science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of the Spitzer Exploratory programs, we provide all of the images and catalogs as part of the publication.

THE SPITZER -HETDEX EXPLORATORY LARGE-AREA SURVEY

International Nuclear Information System (INIS)

Papovich, C.; Shipley, H. V.; Mehrtens, N.; Lanham, C.; DePoy, D. L.; Kawinwanichakij, L.; Lacy, M.; Ciardullo, R.; Gronwall, C.; Finkelstein, S. L.; Drory, N.; Gebhardt, K.; Hill, G. J.; Jogee, S.; Bassett, R.; Behroozi, P.; Blanc, G. A.; Jong, R. S. de; Gawiser, E.; Hopp, U.

2016-01-01

We present post-cryogenic Spitzer imaging at 3.6 and 4.5 μ m with the Infrared Array Camera (IRAC) of the Spitzer /HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ≈24 deg 2 of the Sloan Digital Sky Survey “Stripe 82” region, and falls within the footprints of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R ∼ 800 spectroscopy will produce ∼200,000 redshifts from the Ly α emission for galaxies in the range 1.9 <  z  < 3.5, and an additional ∼200,000 redshifts from the [O ii] emission for galaxies at z  < 0.5. When combined with deep ugriz images from the Dark Energy Camera, K -band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, the presence of active galactic nuclei, and environment over a co-moving volume of ∼0.5 Gpc 3 at 1.9 <  z  < 3.5. Here, we discuss the properties of the SHELA IRAC data set, including the data acquisition, reduction, validation, and source catalogs. Our tests show that the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 μ m images. The catalogs reach limiting sensitivities of 1.1  μ Jy at both 3.6 and 4.5 μ m (1 σ , for R = 2″ circular apertures). As a demonstration of the science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of the Spitzer Exploratory programs, we provide all of the images and catalogs as part of the publication.

LUMINOUS BURIED ACTIVE GALACTIC NUCLEI AS A FUNCTION OF GALAXY INFRARED LUMINOSITY REVEALED THROUGH SPITZER LOW-RESOLUTION INFRARED SPECTROSCOPY

International Nuclear Information System (INIS)

Imanishi, Masatoshi

2009-01-01

We present the results of Spitzer Infrared Spectrograph 5-35 μm low-resolution spectroscopic energy diagnostics of ultraluminous infrared galaxies (ULIRGs) at z> 0.15, classified optically as non-Seyferts. Based on the equivalent widths of polycyclic aromatic hydrocarbon emission and the optical depths of silicate dust absorption features, we searched for signatures of intrinsically luminous, but optically elusive, buried active galactic nuclei (AGNs) in these optically non-Seyfert ULIRGs. We then combined the results with those of non-Seyfert ULIRGs at z IR 12 L sun . We found that the energetic importance of buried AGNs clearly increases with galaxy infrared luminosity, becoming suddenly discernible in ULIRGs with L IR > 10 12 L sun . For ULIRGs with buried AGN signatures, a significant fraction of infrared luminosities can be accounted for by the detected buried AGN and modestly obscured (A V < 20 mag) starburst activity. The implied masses of spheroidal stellar components in galaxies for which buried AGNs become important roughly correspond to the value separating red massive and blue less-massive galaxies in the local universe. Our results may support the widely proposed AGN-feedback scenario as the origin of galaxy downsizing phenomena, where galaxies with currently larger stellar masses previously had higher AGN energetic contributions and star formation originating infrared luminosities, and have finished their major star formation more quickly, due to stronger AGN feedback.

SPITZER IRS SPECTRA OF DEBRIS DISKS IN THE SCORPIUS–CENTAURUS OB ASSOCIATION

Energy Technology Data Exchange (ETDEWEB)

Jang-Condell, Hannah [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Chen, Christine H.; Mittal, Tushar; Lisse, Carey M. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Manoj, P. [Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Rd., Mumbai 400005 (India); Watson, Dan [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Nesvold, Erika; Kuchner, Marc [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

2015-08-01

We analyze spectra obtained with the Spitzer Infrared Spectrograph (IRS) of 110 B-, A-, F-, and G-type stars with optically thin infrared excess in the Scorpius–Centaurus OB association. The ages of these stars range from 11 to 17 Myr. We fit the infrared excesses observed in these sources by Spitzer IRS and the Multiband Imaging Photometer for Spitzer (MIPS) to simple dust models according to Mie theory. We find that nearly all of the objects in our study can be fit by one or two belts of dust. Dust around lower mass stars appears to be closer in than around higher mass stars, particularly for the warm dust component in the two-belt systems, suggesting a mass-dependent evolution of debris disks around young stars. For those objects with stellar companions, all dust distances are consistent with truncation of the debris disk by the binary companion. The gaps between several of the two-belt systems can place limits on the planets that might lie between the belts, potentially constraining the mass and locations of planets that may be forming around these stars.

On the Nature of Bright Infrared Sources in the Small Magellanic Cloud: Interpreting MSX through the Lens of Spitzer

Science.gov (United States)

Kraemer, Kathleen E.; Sloan, G. C.

2015-01-01

We compare infrared observations of the Small Magellanic Cloud (SMC) by the Midcourse Space Experiment (MSX) and the Spitzer Space Telescope to better understand what components of a metal-poor galaxy dominate radiative processes in the infrared. The SMC, at a distance of ~60 kpc and with a metallicity of ~0.1-0.2 solar, can serve as a nearby proxy for metal-poor galaxies at high redshift. The MSX Point Source Catalog contains 243 objects in the SMC that were detected at 8.3 microns, the most sensitive MSX band. Multi-epoch, multi-band mapping with Spitzer, supplemented with observations from the Two-Micron All-Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE), provides variability information, and, together with spectra from Spitzer for ~15% of the sample, enables us to determine what these luminous sources are. How many remain simple point sources? What fraction break up into multiple stars? Which are star forming regions, with both bright diffuse emission and point sources? How do evolved stars and stellar remnants contribute at these wavelengths? What role do young stellar objects and HII regions play? Answering these questions sets the stage for understanding what we will see with the James Webb Space Telescope (JWST).

SPITZER IRS SPECTRA OF LUMINOUS 8 μm SOURCES IN THE LARGE MAGELLANIC CLOUD: TESTING COLOR-BASED CLASSIFICATIONS

International Nuclear Information System (INIS)

Buchanan, Catherine L.; Kastner, Joel H.; Hrivnak, Bruce J.; Sahai, Raghvendra

2009-01-01

We present archival Spitzer Infrared Spectrograph (IRS) spectra of 19 luminous 8 μm selected sources in the Large Magellanic Cloud (LMC). The object classes derived from these spectra and from an additional 24 spectra in the literature are compared with classifications based on Two Micron All Sky Survey (2MASS)/MSX (J, H, K, and 8 μm) colors in order to test the 'JHK8' (Kastner et al.) classification scheme. The IRS spectra confirm the classifications of 22 of the 31 sources that can be classified under the JHK8 system. The spectroscopic classification of 12 objects that were unclassifiable in the JHK8 scheme allow us to characterize regions of the color-color diagrams that previously lacked spectroscopic verification, enabling refinements to the JHK8 classification system. The results of these new classifications are consistent with previous results concerning the identification of the most infrared-luminous objects in the LMC. In particular, while the IRS spectra reveal several new examples of asymptotic giant branch (AGB) stars with O-rich envelopes, such objects are still far outnumbered by carbon stars (C-rich AGB stars). We show that Spitzer IRAC/MIPS color-color diagrams provide improved discrimination between red supergiants and oxygen-rich and carbon-rich AGB stars relative to those based on 2MASS/MSX colors. These diagrams will enable the most luminous IR sources in Local Group galaxies to be classified with high confidence based on their Spitzer colors. Such characterizations of stellar populations will continue to be possible during Spitzer's warm mission through the use of IRAC [3.6]-[4.5] and 2MASS colors.

Spitzer ’s View of the Candidate Cluster and Protocluster Catalog (CCPC)

Energy Technology Data Exchange (ETDEWEB)

Franck, J. R.; McGaugh, S. S. [Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106 (United States)

2017-02-10

The Candidate Cluster and Protocluster Catalog contains 218 galaxy overdensities composed of more than 2000 galaxies with spectroscopic redshifts spanning the first few Gyr after the Big Bang (2.0 ≤ z < 6.6). We use Spitzer archival data to track the underlying stellar mass of these overdense regions in various temporal cross sections by building rest-frame near-infrared luminosity functions (LFs) across the span of redshifts. This exercise maps the stellar growth of protocluster galaxies, as halos in the densest environments should be the most massive from hierarchical accretion. The characteristic apparent magnitude, m *( z ), is relatively flat from 2.0 ≤ z < 6.6, consistent with a passive evolution of an old stellar population. This trend maps smoothly to lower redshift results of cluster galaxies from other works. We find no difference in the LFs of galaxies in the field versus protoclusters at a given redshift apart from their density.

Hunting Elusive SPRITEs with Spitzer

Science.gov (United States)

Kohler, Susanna

2017-05-01

In recent years, astronomers have developed many wide-field imaging surveys in which the same targets are observed again and again. This new form of observing has allowed us to discover optical and radio transients explosive or irregular events with durations ranging from seconds to years. The dynamic infrared sky, however, has remained largely unexplored until now.Infrared ExplorationExample of a transient: SPIRITS 14ajc was visible when imaged by SPIRITS in 2014 (left) but it wasnt there during previous imaging between 2004 and 2008 (right). The bottom frame shows the difference between the two images. [Adapted from Kasliwal et al. 2017]Why hunt for infrared transients? Optical wavelengths dont allow us to observe events that are obscured, such that their own structure or their surroundings hide them from our view. Both supernovae and luminous red novae (associated with stellar mergers) are discoverable as infrared transients, and there may well be new types of transients in infrared that we havent seen before!To explore this uncharted territory, a team of scientists developed SPIRITS, the Spitzer Infrared Intensive Transients Survey. Begun in 2014, SPIRITS is a five-year long survey that uses the Spitzer Space Telescope to conduct a systematic search for mid-infrared transients in nearby galaxies.In a recent publication led by Mansi Kasliwal (Caltech and the Carnegie Institution for Science), the SPIRITS team has now detailed how their survey works and what theyve discovered in its first year.The light curves of SPRITEs (red stars) lie in the mid-infared luminosity gap between novae (orange) and supernovae (blue). [Kasliwal et al. 2017]Mystery TransientsKasliwal and collaborators used Spitzer to monitor 190 nearby galaxies. In SPIRITS first year, they found over 1958 variable stars and 43 infrared transient sources. Of these 43 transients, 21 were known supernovae, 4 were in the luminosity range of novae, and 4 had optical counterparts. The remaining 14 events

Inferring Temperature Inversions in Hot Jupiters Via Spitzer Emission Spectroscopy

Science.gov (United States)

Garhart, Emily; Deming, Drake; Mandell, Avi

2016-10-01

We present a systematic study of 35 hot Jupiter secondary eclipses, including 16 hot Jupiters never before characterized via emission, observed at the 3.6 μm and 4.5 μm bandpasses of Warm Spitzer in order to classify their atmospheric structure, namely, the existence of temperature inversions. This is a robust study in that these planets orbit stars with a wide range of compositions, temperatures, and activity levels. This diverse sample allows us to investigate the source of planetary temperature inversions, specifically, its correlation with stellar irradiance and magnetic activity. We correct for systematic and intra-pixel sensitivity effects with a pixel level decorrelation (PLD) method described in Deming et al. (2015). The relationship between eclipse depths and a best-fit blackbody function versus stellar activity, a method described in Knutson et al. (2010), will ultimately enable us to appraise the current hypotheses of temperature inversions.

A SPITZER SURVEY OF PROTOPLANETARY DISK DUST IN THE YOUNG SERPENS CLOUD : HOW DO DUST CHARACTERISTICS EVOLVE WITH TIME?

NARCIS (Netherlands)

Oliveira, Isa; Pontoppidan, Klaus M.; Merin, Bruno; van Dishoeck, Ewine F.; Lahuis, Fred; Geers, Vincent C.; Jorgensen, Jes K.; Olofsson, Johan; Augereau, Jean-Charles; Brown, Joanna M.

2010-01-01

We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35 mu m) spectra of a complete flux-limited sample (>= 3 mJy at 8 mu m) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and

A SPITZER c2d LEGACY SURVEY TO IDENTIFY AND CHARACTERIZE DISKS WITH INNER DUST HOLES

International Nuclear Information System (INIS)

Merin, Bruno; Brown, Joanna M.; Herczeg, Gregory J.; Van Dishoeck, Ewine F.; Oliveira, Isa; Lahuis, Fred; Bottinelli, Sandrine; Augereau, Jean-Charles; Olofsson, Johan; Evans, Neal J.; Harvey, Paul M.; Cieza, Lucas; Spezzi, Loredana; Prusti, Timo; Alcala, Juan M.; Blake, Geoffrey A.; Bayo, Amelia; Geers, Vincent G.; Walter, Frederick M.; Chiu, Kuenley

2010-01-01

Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 μm feature strength above the continuum declines for holes with radii larger than ∼7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases.

THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE

International Nuclear Information System (INIS)

Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Comerón, Sebastien; Gadotti, Dimitri A.; Kim, Taehyun; Buta, Ron; Sheth, Kartik; Muñoz-Mateos, Juan Carlos; Zaritsky, Dennis; Hinz, Joannah L.; Ho, Luis; Knapen, Johan; Cisternas, Mauricio; Athanassoula, E.; Bosma, Albert; Laine, Seppo; Regan, Michael; De Paz, Armando Gil; Menendez-Delmestre, Karin

2015-01-01

The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (<40 Mpc) galaxies. We describe the S 4 G data analysis pipeline 4, which is dedicated to two-dimensional structural surface brightness decompositions of 3.6 μm images, using GALFIT3.0. Besides automatic 1-component Sérsic fits, and 2-component Sérsic bulge + exponential disk fits, we present human-supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sérsic index and bulge-to-total light ratio (B/T), confirming earlier results. Here, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page (www.oulu.fi/astronomy/S4G-PIPELINE4/MAIN). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK-EDIT) used in data preparation. A detailed analysis of the bulge, disk, and bar parameters derived from multi-component decompositions will be published separately

The NASA Spitzer Space Telescope.

Science.gov (United States)

Gehrz, R D; Roellig, T L; Werner, M W; Fazio, G G; Houck, J R; Low, F J; Rieke, G H; Soifer, B T; Levine, D A; Romana, E A

2007-01-01

The National Aeronautics and Space Administration's Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991-2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer's expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/.

VLT/SINFONI Observations of Spitzer /MIPSGAL 24 μ m Circumstellar Shells: Revealing the Natures of Their Central Sources

Energy Technology Data Exchange (ETDEWEB)

Silva, K. M. [Physics and Astronomy Department, University of Hawaii Hilo, 200 W Kawili Street, Hilo, HI 96720 (United States); Flagey, N. [Canada–France–Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743 (United States); Noriega-Crespo, A. [Space Telescope Science Institue, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Carey, S. [Infrared Processing Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Ingallinera, A., E-mail: silvakm@hawaii.edu [INAF-Osservatorio Astrofisico di Catania, Via Santa Sofia 78, I-95123 Catania (Italy)

2017-03-01

We present Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared H - and K -band spectra of potential central stars within the inner 8″-by-8″ regions of 55 MIPSGAL “bubbles” (MBs), sub-arcminute circumstellar shells discovered in the mid-IR survey of the Galactic plane with Spitzer /MIPS. At magnitudes brighter than 15, we detect a total of 230 stars in the K band and 179 stars in the H band. We spectrally identify 145 stars in all but three MBs, with average magnitudes of 13.8 and 12.7 respectively, using spectral libraries and previous studies of near-IR stellar spectra. We also use tabulated intrinsic stellar magnitudes and colors to derive distances and extinction values, and to better constrain the classifications of the stars. We reliably identify the central sources for 21 of the 55 MBs, which we classify as follows: one Wolf–Rayet, three luminous blue variable candidates, four early-type (O to F), and 15 late-type (G to M) stars. The 21 central sources are, on average, one magnitude fainter than these in the most recent study of MBs, and we notice a significant drop in the fraction of massive star candidates. For the 34 remaining MBs in our sample, we are unable to identify the central sources due to confusion, low spectroscopic signal-to-noise ratio, and/or lack of detections in the images near the centers of the bubbles. We discuss how our findings compare with previous studies and support the trend, for the most part, between the shells’ morphologies in the mid-IR and central sources spectral types.

NEW DEBRIS DISKS AROUND YOUNG, LOW-MASS STARS DISCOVERED WITH THE SPITZER SPACE TELESCOPE

International Nuclear Information System (INIS)

Plavchan, Peter; Werner, M. W.; Stapelfeldt, K. R.; Chen, C. H.; Su, K. Y. L.; Stauffer, J. R.; Song, I.

2009-01-01

We present 24 μm and 70 μm Multiband Imaging Photometer for Spitzer (MIPS) observations of 70 A through M-type dwarfs with estimated ages from 8 Myr to 1.1 Gyr, as part of a Spitzer guaranteed time program, including a re-analysis of some previously published source photometry. Our sample is selected from stars with common youth indicators such as lithium abundance, X-ray activity, chromospheric activity, and rapid rotation. We compare our MIPS observations to empirically derived K s -[24] colors as a function of the stellar effective temperature to identify 24 μm and 70 μm excesses. We place constraints or upper limits on dust temperatures and fractional infrared luminosities with a simple blackbody dust model. We confirm the previously published 70 μm excesses for HD 92945, HD 112429, and AU Mic, and provide updated flux density measurements for these sources. We present the discovery of 70 μm excesses for five stars: HD 7590, HD 10008, HD 59967, HD 73350, and HD 135599. HD 135599 is also a known Spitzer IRS (InfraRed Spectrograph) excess source, and we confirm the excess at 24 μm. We also present the detection of 24 μm excesses for 10 stars: HD 10008, GJ 3400A, HD 73350, HD 112429, HD 123998, HD 175742, AT Mic, BO Mic, HD 358623 and Gl 907.1. We find that large 70 μm excesses are less common around stars with effective temperatures of less than 5000 K (3.7 +7.6 -1.1 %) than around stars with effective temperatures between 5000 K and 6000 K (21.4 +9.5 -5.7 %), despite the cooler stars having a younger median age in our sample (12 Myr vs. 340 Myr). We find that the previously reported excess for TWA 13A at 70 μm is due to a nearby background galaxy, and the previously reported excess for HD 177724 is due to saturation of the near-infrared photometry used to predict the mid-infrared stellar flux contribution. In the Appendix, we present an updated analysis of dust grain removal timescales due to grain-grain collisions and radiation pressure, Poynting

Bright galaxies at z=9-11 from pure-parallel HST observations: Building a unique sample for JWST with Spitzer/IRAC

Science.gov (United States)

Bouwens, Rychard; Morashita, Takahiro; Stefanon, Mauro; Magee, Dan

2018-05-01

The combination of observations taken by Hubble and Spitzer revealed the unexpected presence of sources as bright as our own Milky Way as early as 400 Myr after the Big Bang, potentially highlighting a new highly efficient regime for star formation in L>L* galaxies at very early times. Yet, the sample of high-quality z>8 galaxies with both HST and Spitzer/IRAC imaging is still small, particularly at the highest luminosities. We propose here to remedy this situation and use Spitzer/IRAC to efficiently follow up the most promising z>8 sources from our Hubble Brightest of Reionizing Galaxies (BoRG) survey, which covers a footprint on the sky similar to CANDELS, provides a deeper search than ground-based surveys like UltraVISTA, and is robust against cosmic variance because of its 210 independent lines of sight. The proposed new 3.6 micron observations will continue our Spitzer cycle 12 and 13 BORG911 programs, targeting 15 additional fields, leveraging over 200 new HST orbits to identify a final sample of about 8 bright galaxies at z >= 8.5. For optimal time use (just 20 hours), our goal is to readily discriminate between z>8 sources (undetected or marginally detected in IRAC) and z 2 interlopers (strongly detected in IRAC) with just 1-2 hours per pointing. The high-quality candidates that we will identify with IRAC will be ideal targets for further studies investigating the ionization state of the distant universe through near-IR Keck/VLT spectroscopy. They will also be uniquely suited to measurement of the redshift and stellar population properties through JWST/NIRSPEC observations, with the potential to elucidate how the first generations of stars are assembled in the earliest stages of the epoch of reionization.

THE SPITZER LOCAL VOLUME LEGACY: SURVEY DESCRIPTION AND INFRARED PHOTOMETRY

International Nuclear Information System (INIS)

Dale, D. A.; Cohen, S. A.; Johnson, L. C.; Schuster, M. D.; Calzetti, D.; Engelbracht, C. W.; Kennicutt, R. C.; Block, M.; Marble, A. R.; Gil de Paz, A.; Lee, J. C.; Begum, A.; Dalcanton, J. J.; Funes, J. G.; Gordon, K. D.; Johnson, B. D.; Sakai, S.; Skillman, E. D.; Van Zee, L.; Walter, F.

2009-01-01

The survey description and the near-, mid-, and far-infrared flux properties are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a Spitzer Space Telescope legacy program that surveys the local universe out to 11 Mpc, built upon a foundation of ultraviolet, Hα, and Hubble Space Telescope imaging from 11HUGS (11 Mpc Hα and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby Galaxy Survey Treasury). LVL covers an unbiased, representative, and statistically robust sample of nearby star-forming galaxies, exploiting the highest extragalactic spatial resolution achievable with Spitzer. As a result of its approximately volume-limited nature, LVL augments previous Spitzer observations of present-day galaxies with improved sampling of the low-luminosity galaxy population. The collection of LVL galaxies shows a large spread in mid-infrared colors, likely due to the conspicuous deficiency of 8 μm polycyclic aromatic hydrocarbon emission from low-metallicity, low-luminosity galaxies. Conversely, the far-infrared emission tightly tracks the total infrared emission, with a dispersion in their flux ratio of only 0.1 dex. In terms of the relation between the infrared-to-ultraviolet ratio and the ultraviolet spectral slope, the LVL sample shows redder colors and/or lower infrared-to-ultraviolet ratios than starburst galaxies, suggesting that reprocessing by dust is less important in the lower mass systems that dominate the LVL sample. Comparisons with theoretical models suggest that the amplitude of deviations from the relation found for starburst galaxies correlates with the age of the stellar populations that dominate the ultraviolet/optical luminosities.

A SPITZER TRANSMISSION SPECTRUM FOR THE EXOPLANET GJ 436b, EVIDENCE FOR STELLAR VARIABILITY, AND CONSTRAINTS ON DAYSIDE FLUX VARIATIONS

International Nuclear Information System (INIS)

Knutson, Heather A.; Madhusudhan, Nikku; Cowan, Nicolas B.; Christiansen, Jessie L.; Agol, Eric; Deming, Drake; Desert, Jean-Michel; Charbonneau, David; Henry, Gregory W.; Homeier, Derek; Laughlin, Gregory; Langton, Jonathan; Seager, Sara

2011-01-01

In this paper, we describe a uniform analysis of eight transits and eleven secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5, and 8.0 μm bands using the IRAC instrument on the Spitzer Space Telescope between UT 2007 June 29 and UT 2009 February 4. We find that the best-fit transit depths for visits in the same bandpass can vary by as much as 8% of the total (4.7σ significance) from one epoch to the next. Although we cannot entirely rule out residual detector effects or a time-varying, high-altitude cloud layer in the planet's atmosphere as the cause of these variations, we consider the occultation of active regions on the star in a subset of the transit observations to be the most likely explanation. We find that for the deepest 3.6 μm transit the in-transit data have a higher standard deviation than the out-of-transit data, as would be expected if the planet occulted a star spot. We also compare all published transit observations for this object and find that transits observed in the infrared typically have smaller timing offsets than those observed in visible light. In this case, the three deepest Spitzer transits are all measured within a period of five days, consistent with a single epoch of increased stellar activity. We reconcile the presence of magnetically active regions with the lack of significant visible or infrared flux variations from the star by proposing that the star's spin axis is tilted with respect to our line of sight and that the planet's orbit is therefore likely to be misaligned. In contrast to the results reported by Beaulieu et al., we find no convincing evidence for methane absorption in the planet's transmission spectrum. If we exclude the transits that we believe to be most affected by stellar activity, we find that we prefer models with enhanced CO and reduced methane, consistent with GJ 436b's dayside composition from Stevenson et al. It is also possible that all transits are significantly affected by this

THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE

Energy Technology Data Exchange (ETDEWEB)

Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Comerón, Sebastien [Astronomy and Space Physics, University of Oulu, FI-90014 (Finland); Gadotti, Dimitri A.; Kim, Taehyun [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Buta, Ron [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Sheth, Kartik; Muñoz-Mateos, Juan Carlos [National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Zaritsky, Dennis; Hinz, Joannah L. [University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 (United States); Ho, Luis [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Knapen, Johan; Cisternas, Mauricio [Instituto de Astrofísica de Canarias, E-38205 La Laguna (Spain); Athanassoula, E.; Bosma, Albert [Aix Marseille Universite, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Laine, Seppo [Spitzer Science Center—Caltech, MS 314-6, Pasadena, CA 91125 (United States); Regan, Michael [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); De Paz, Armando Gil [Departamento de Astrofísica, Universidad Complutense de Madrid, Madrid E-28040 (Spain); Menendez-Delmestre, Karin [Observatorio do Valongo, Universidade Federal de Rio de Janeiro, Ladeira Pedro Antonio, 43, Saude CEP 20080-090, Rio de Janeiro—RJ (Brazil); and others

2015-07-20

The Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (<40 Mpc) galaxies. We describe the S{sup 4}G data analysis pipeline 4, which is dedicated to two-dimensional structural surface brightness decompositions of 3.6 μm images, using GALFIT3.0. Besides automatic 1-component Sérsic fits, and 2-component Sérsic bulge + exponential disk fits, we present human-supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sérsic index and bulge-to-total light ratio (B/T), confirming earlier results. Here, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page (www.oulu.fi/astronomy/S4G-PIPELINE4/MAIN). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK-EDIT) used in data preparation. A detailed analysis of the bulge, disk, and bar parameters derived from multi-component decompositions will be published separately.

RETENTION OF STELLAR-MASS BLACK HOLES IN GLOBULAR CLUSTERS

International Nuclear Information System (INIS)

Morscher, Meagan; Umbreit, Stefan; Farr, Will M.; Rasio, Frederic A.

2013-01-01

Globular clusters should be born with significant numbers of stellar-mass black holes (BHs). It has been thought for two decades that very few of these BHs could be retained through the cluster lifetime. With masses ∼10 M ☉ , BHs are ∼20 times more massive than an average cluster star. They segregate into the cluster core, where they may eventually decouple from the remainder of the cluster. The small-N core then evaporates on a short timescale. This is the so-called Spitzer instability. Here we present the results of a full dynamical simulation of a globular cluster containing many stellar-mass BHs with a realistic mass spectrum. Our Monte Carlo simulation code includes detailed treatments of all relevant stellar evolution and dynamical processes. Our main finding is that old globular clusters could still contain many BHs at present. In our simulation, we find no evidence for the Spitzer instability. Instead, most of the BHs remain well mixed with the rest of the cluster, with only the innermost few tens of BHs segregating significantly. Over the 12 Gyr evolution, fewer than half of the BHs are dynamically ejected through strong binary interactions in the cluster core. The presence of BHs leads to long-term heating of the cluster, ultimately producing a core radius on the high end of the distribution for Milky Way globular clusters (and those of other galaxies). A crude extrapolation from our model suggests that the BH-BH merger rate from globular clusters could be comparable to the rate in the field.

EARLY-TYPE GALAXIES WITH TIDAL DEBRIS AND THEIR SCALING RELATIONS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G)

International Nuclear Information System (INIS)

Kim, Taehyun; Sheth, Kartik; Muñoz-Mateos, Juan-Carlos; Hinz, Joannah L.; Zaritsky, Dennis; Lee, Myung Gyoon; Gadotti, Dimitri A.; Knapen, Johan H.; Schinnerer, Eva; Ho, Luis C.; Madore, Barry F.; Laurikainen, Eija; Salo, Heikki; Athanassoula, E.; Bosma, Albert; De Swardt, Bonita; Comerón, Sébastien; Regan, Michael W.; Menéndez-Delmestre, Karín; De Paz, Armando Gil

2012-01-01

Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early-type galaxies (T ≤ 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). The tidal debris includes features such as shells, ripples, and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, were used to quantify the residual tidal features. The tidal debris contributes ∼3%-10% to the total 3.6 μm luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the fundamental plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early-type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase mixing so that their structural properties become similar to those of the non-interacting early-type galaxies.

Characterizing stellar and exoplanetary environments

CERN Document Server

Khodachenko, Maxim

2015-01-01

In this book an international group of specialists discusses studies of exoplanets subjected to extreme stellar radiation and plasma conditions. It is shown that such studies will help us to understand how terrestrial planets and their atmospheres, including the early Venus, Earth and Mars, evolved during the host star’s active early phase. The book presents an analysis of findings from Hubble Space Telescope observations of transiting exoplanets, as well as applications of advanced numerical models for characterizing the upper atmosphere structure and stellar environments of exoplanets. The authors also address detections of atoms and molecules in the atmosphere of “hot Jupiters” by NASA’s Spitzer telescope. The observational and theoretical investigations and discoveries presented are both timely and important in the context of the next generation of space telescopes. 
 The book is divided into four main parts, grouping chapters on exoplanet host star radiation and plasma environments, exoplanet u...

METALLICITY AND AGE OF THE STELLAR STREAM AROUND THE DISK GALAXY NGC 5907

Energy Technology Data Exchange (ETDEWEB)

Laine, Seppo; Grillmair, Carl J.; Capak, Peter [Spitzer Science Center-Caltech, MS 314-6, Pasadena, CA 91125 (United States); Arendt, Richard G. [CRESST/UMBC/NASA GSFC, Code 665, Greenbelt, MD 20771 (United States); Romanowsky, Aaron J. [Department of Physics and Astronomy, San José State University, One Washington Square, San Jose, CA 95192 (United States); Martínez-Delgado, David [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Ashby, Matthew L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Davies, James E. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Majewski, Stephen R. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Brodie, Jean P.; Arnold, Jacob A. [University of California Observatories and Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); GaBany, R. Jay, E-mail: seppo@ipac.caltech.edu [Black Bird Observatory, 5660 Brionne Drive, San Jose, CA 95118 (United States)

2016-09-01

Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby ( d  = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μ m Spitzer /Infrared Array Camera observations. Combining the near-infrared 3.6 μ m data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ∼60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of −0.3 inferred along the brightest parts of the stream.

Central Stars of Mid-Infrared Nebulae Discovered with Spitzer and WISE

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.

2017-02-01

Searches for compact mid-IR nebulae with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), accompanied by spectroscopic observations of central stars of these nebulae led to the discovery of many dozens of massive stars at different evolutionary stages, of which the most numerous are candidate luminous blue variables (LBVs). In this paper, we give a census of candidate and confirmed Galactic LBVs revealed with Spitzer and WISE, and present some new results of spectroscopic observations of central stars of mid-IR nebulae.

The Demographics and Properties of Wide-Orbit, Planetary-Mass Companions from PSF Fitting of Spitzer/IRAC Images

Science.gov (United States)

Martinez, Raquel; Kraus, Adam L.

2017-06-01

Over the past decade, a growing population of planetary-mass companions ( 100 AU) from their host stars, challenging existing models of both star and planet formation. It is unclear whether these systems represent the low-mass extreme of stellar binary formation or the high-mass and wide-orbit extreme of planet formation theories, as various proposed formation pathways inadequately explain the physical and orbital aspects of these systems. Even so, determining which scenario best reproduces the observed characteristics of the PMCs will come once a statistically robust sample of directly-imaged PMCs are found and studied.We are developing an automated pipeline to search for wide-orbit PMCs to young stars in Spitzer/IRAC images. A Markov Chain Monte Carlo (MCMC) algorithm is the backbone of our novel point spread function (PSF) subtraction routine that efficiently creates and subtracts χ2-minimizing instrumental PSFs, simultaneously measuring astrometry and infrared photometry of these systems across the four IRAC channels (3.6 μm, 4.5 μm, 5.8 μm, and 8 μm). In this work, we present the results of a Spitzer/IRAC archival imaging study of 11 young, low-mass (0.044-0.88 M⊙ K3.5-M7.5) stars known to have faint, low-mass companions in 3 nearby star-forming regions (Chameleon, Taurus, and Upper Scorpius). We characterize the systems found to have low-mass companions with non-zero [I1] - [I4] colors, potentially signifying the presence of a circum(sub?)stellar disk. Plans for future pipeline improvements and paths forward will also be discussed. Once this computational foundation is optimized, the stage is set to quickly scour the nearby star-forming regions already imaged by Spitzer, identify potential candidates for further characterization with ground- or space-based telescopes, and increase the number of widely-separated PMCs known.

Revealing Fact or Fiction in Spitzer Exoplanet Phase Curve Trends

Science.gov (United States)

Bean, Jacob; Parmentier, Vivien; Mansfield, Megan; Cowan, Nicolas; Kempton, Eliza; Desert, Jean-Michel; Swain, Mark; Dang, Lisa; Bell, Taylor; Keating, Dylan; Zellem, Robert; Fortney, Jonathan; Line, Michael; Kreidberg, Laura; Stevenson, Kevin

2018-05-01

The constraints on energy transport in exoplanet atmospheres from phase curve observations is sure to be one of Spitzer's enduring legacies. However, with phase curves for 17 planets now observed we find that the previously observed trends are not coming into sharper focus. Instead, these trends in hot spot offset and day-night flux contrast vs. the fundamental planetary parameters expected to control the energy transport (e.g., irradiation and rotational period) are becoming more uncertain due to the recent discovery of outliers. At the same time, there is a growing understanding that a number of factors like magnetic fields, aerosols, and molecular chemistry could be confounding the search for these correlations. We propose a final phase curve program to advance our understanding of energy transport in transiting exoplanet atmospheres and to cement Spitzer's legacy on this topic. This program tackles the outstanding questions in this area with a comprehensive, two-pronged approach: (1) a survey of an additional 10 high signal-to-noise planets that span a broad parameter space and (2) a search for magnetic field-induced variability in the planet HAT-P-7b. The expanded survey will bring additional statistical power to the search for trends and will enable us to determine if the recently-detected outliers are indeed oddities or are instead actually representative of the intrinsic sample diversity. The variability search will test the hypothesis that the atmospheric dynamics of the partially ionized atmospheres of close-in planets are influenced by magnetic fields, which could explain the observed scatter around the existing trends. All observations will be performed at 4.5 microns, which is the consensus best channel for these measurements. The dataset from this program will provide vital context for JWST observations and will not be superseded until ARIEL flies more than a decade from now.

Spitzer Digs Up Galactic Fossil

Science.gov (United States)

2004-01-01

with stars, infrared images (middle and right), reveal a never-before-seen bundle of stars, called a globular cluster. The left panel is from the California Institute of Technology's Digitized Sky Survey; the middle panel includes images from the NASA-funded Two Micron All-Sky Survey and the University of Wyoming Infrared Observatory (circle inset); and the right panel is from NASA's Spitzer Space Telescope. The Two Micron All-Sky Survey false-color image was obtained using near-infrared wavelengths ranging from 1.3 to 2.2 microns. The University of Wyoming Observatory false-color image was captured on July 31, 2004, at wavelengths ranging from 1.2 to 2.2 microns. The Spitzer false-color image composite was taken on April 21, 2004, by its infrared array camera. It is composed of images obtained at four mid-infrared wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

SPITZER OBSERVATIONS OF BOW SHOCKS AND OUTFLOWS IN RCW 38

Energy Technology Data Exchange (ETDEWEB)

Winston, E. [ESA-ESTEC (SRE-SA), Keplerlaan 1, 2201 AZ Noordwijk ZH (Netherlands); Wolk, S. J.; Bourke, T. L.; Spitzbart, B. [Harvard Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Megeath, S. T. [Ritter Observatory, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft Ave., Toledo, OH 43606 (United States); Gutermuth, R., E-mail: ewinston@rssd.esa.int [Five Colleges Astronomy Department, Smith College, Northampton, MA 01027 (United States)

2012-01-10

We report Spitzer observations of five newly identified bow shocks in the massive star-forming region RCW 38. Four are visible at Infrared Array Camera (IRAC) wavelengths, the fifth is only visible at 24 {mu}m. Chandra X-ray emission indicates that winds from the central O5.5 binary, IRS 2, have caused an outflow to the northeast and southwest of the central subcluster. The southern lobe of hot ionized gas is detected in X-rays; shocked gas and heated dust from the shock front are detected with Spitzer at 4.5 and 24 {mu}m. The northern outflow may have initiated the present generation of star formation, based on the filamentary distribution of the protostars in the central subcluster. Further, the bow-shock driving star, YSO 129, is photo-evaporating a pillar of gas and dust. No point sources are identified within this pillar at near- to mid-IR wavelengths. We also report on IRAC 3.6 and 5.8 {mu}m observations of the cluster DBS2003-124, northeast of RCW 38, where 33 candidate young stellar objects (YSOs) are identified. One star associated with the cluster drives a parsec-scale jet. Two Herbig-Haro objects associated with the jet are visible at IRAC and Multiband Imaging Photometer for Spitzer (MIPS) wavelengths. The jet extends over a distance of {approx}3 pc. Assuming a velocity of 100 km s{sup -1} for the jet material gives an age of 3 Multiplication-Sign 10{sup 4} yr, indicating that the star (and cluster) are likely to be very young, with a similar or possibly younger age than RCW 38, and that star formation is ongoing in the extended RCW 38 region.

SPITZER OBSERVATIONS OF BOW SHOCKS AND OUTFLOWS IN RCW 38

International Nuclear Information System (INIS)

Winston, E.; Wolk, S. J.; Bourke, T. L.; Spitzbart, B.; Megeath, S. T.; Gutermuth, R.

2012-01-01

We report Spitzer observations of five newly identified bow shocks in the massive star-forming region RCW 38. Four are visible at Infrared Array Camera (IRAC) wavelengths, the fifth is only visible at 24 μm. Chandra X-ray emission indicates that winds from the central O5.5 binary, IRS 2, have caused an outflow to the northeast and southwest of the central subcluster. The southern lobe of hot ionized gas is detected in X-rays; shocked gas and heated dust from the shock front are detected with Spitzer at 4.5 and 24 μm. The northern outflow may have initiated the present generation of star formation, based on the filamentary distribution of the protostars in the central subcluster. Further, the bow-shock driving star, YSO 129, is photo-evaporating a pillar of gas and dust. No point sources are identified within this pillar at near- to mid-IR wavelengths. We also report on IRAC 3.6 and 5.8 μm observations of the cluster DBS2003-124, northeast of RCW 38, where 33 candidate young stellar objects (YSOs) are identified. One star associated with the cluster drives a parsec-scale jet. Two Herbig-Haro objects associated with the jet are visible at IRAC and Multiband Imaging Photometer for Spitzer (MIPS) wavelengths. The jet extends over a distance of ∼3 pc. Assuming a velocity of 100 km s –1 for the jet material gives an age of 3 × 10 4 yr, indicating that the star (and cluster) are likely to be very young, with a similar or possibly younger age than RCW 38, and that star formation is ongoing in the extended RCW 38 region.

THE SPITZER INFRARED SPECTROGRAPH DEBRIS DISK CATALOG. II. SILICATE FEATURE ANALYSIS OF UNRESOLVED TARGETS

Energy Technology Data Exchange (ETDEWEB)

Mittal, Tushar [Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720-4767 (United States); Chen, Christine H. [Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218 (United States); Jang-Condell, Hannah [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Manoj, P. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005 (India); Sargent, Benjamin A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Watson, Dan M. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Lisse, Carey M., E-mail: cchen@stsci.edu [Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States)

2015-01-10

During the Spitzer Space Telescope cryogenic mission, astronomers obtained Infrared Spectrograph (IRS) observations of hundreds of debris disk candidates that have been compiled in the Spitzer IRS Debris Disk Catalog. We have discovered 10 and/or 20 μm silicate emission features toward 120 targets in the catalog and modeled the IRS spectra of these sources, consistent with MIPS 70 μm observations, assuming that the grains are composed of silicates (olivine, pyroxene, forsterite, and enstatite) and are located either in a continuous disk with power-law size and surface density distributions or thin rings that are well-characterized using two separate dust grain temperatures. For systems better fit by the continuous disk model, we find that (1) the dust size distribution power-law index is consistent with that expected from a collisional cascade, q = 3.5-4.0, with a large number of values outside this range, and (2) the minimum grain size, a {sub min}, increases with stellar luminosity, L {sub *}, but the dependence of a {sub min} on L {sub *} is weaker than expected from radiation pressure alone. In addition, we also find that (3) the crystalline fraction of dust in debris disks evolves as a function of time with a large dispersion in crystalline fractions for stars of any particular stellar age or mass, (4) the disk inner edge is correlated with host star mass, and (5) there exists substantial variation in the properties of coeval disks in Sco-Cen, indicating that the observed variation is probably due to stochasticity and diversity in planet formation.

COLORS OF ELLIPTICALS FROM GALEX TO SPITZER

Energy Technology Data Exchange (ETDEWEB)

Schombert, James M., E-mail: jschombe@uoregon.edu [Department of Physics, University of Oregon, Eugene, OR 97403 (United States)

2016-12-01

Multi-color photometry is presented for a large sample of local ellipticals selected by morphology and isolation. The sample uses data from the Galaxy Evolution Explorer ( GALEX ), Sloan Digital Sky Survey (SDSS), Two Micron All-Sky Survey (2MASS), and Spitzer to cover the filters NUV , ugri , JHK and 3.6 μ m. Various two-color diagrams, using the half-light aperture defined in the 2MASS J filter, are very coherent from color to color, meaning that galaxies defined to be red in one color are always red in other colors. Comparison to globular cluster colors demonstrates that ellipticals are not composed of a single age, single metallicity (e.g., [Fe/H]) stellar population, but require a multi-metallicity model using a chemical enrichment scenario. Such a model is sufficient to explain two-color diagrams and the color–magnitude relations for all colors using only metallicity as a variable on a solely 12 Gyr stellar population with no evidence of stars younger than 10 Gyr. The [Fe/H] values that match galaxy colors range from −0.5 to +0.4, much higher (and older) than population characteristics deduced from Lick/IDS line-strength system studies, indicating an inconsistency between galaxy colors and line indices values for reasons unknown. The NUV colors have unusual behavior, signaling the rise and fall of the UV upturn with elliptical luminosity. Models with blue horizontal branch tracks can reproduce this behavior, indicating the UV upturn is strictly a metallicity effect.

COLORS OF ELLIPTICALS FROM GALEX TO SPITZER

International Nuclear Information System (INIS)

Schombert, James M.

2016-01-01

Multi-color photometry is presented for a large sample of local ellipticals selected by morphology and isolation. The sample uses data from the Galaxy Evolution Explorer ( GALEX ), Sloan Digital Sky Survey (SDSS), Two Micron All-Sky Survey (2MASS), and Spitzer to cover the filters NUV , ugri , JHK and 3.6 μ m. Various two-color diagrams, using the half-light aperture defined in the 2MASS J filter, are very coherent from color to color, meaning that galaxies defined to be red in one color are always red in other colors. Comparison to globular cluster colors demonstrates that ellipticals are not composed of a single age, single metallicity (e.g., [Fe/H]) stellar population, but require a multi-metallicity model using a chemical enrichment scenario. Such a model is sufficient to explain two-color diagrams and the color–magnitude relations for all colors using only metallicity as a variable on a solely 12 Gyr stellar population with no evidence of stars younger than 10 Gyr. The [Fe/H] values that match galaxy colors range from −0.5 to +0.4, much higher (and older) than population characteristics deduced from Lick/IDS line-strength system studies, indicating an inconsistency between galaxy colors and line indices values for reasons unknown. The NUV colors have unusual behavior, signaling the rise and fall of the UV upturn with elliptical luminosity. Models with blue horizontal branch tracks can reproduce this behavior, indicating the UV upturn is strictly a metallicity effect.

The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects. III. CH4

NARCIS (Netherlands)

Oberg, Karin I.; Boogert, A. C. Adwin; Pontoppidan, Klaus M.; Blake, Geoffrey A.; Evans, Neal J.; Lahuis, Fred; van Dishoeck, Ewine F.

2008-01-01

CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH4 toward low-mass star-forming regions as well. Infrared spectra

SPRITE: the Spitzer proposal review website

Science.gov (United States)

Crane, Megan K.; Storrie-Lombardi, Lisa J.; Silbermann, Nancy A.; Rebull, Luisa M.

2008-07-01

The Spitzer Science Center (SSC), located on the campus of the California Institute of Technology, supports the science operations of NASA's infrared Spitzer Space Telescope. The SSC issues an annual Call for Proposals inviting investigators worldwide to submit Spitzer Space Telescope proposals. The Spitzer Proposal Review Website (SPRITE) is a MySQL/PHP web database application designed to support the SSC proposal review process. Review panel members use the software to view, grade, and write comments about the proposals, and SSC support team members monitor the grading and ranking process and ultimately generate a ranked list of all the proposals. The software is also used to generate, edit, and email award letters to the proposers. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration.

Emergent Exoplanet Flux: Review of the Spitzer Results

OpenAIRE

Deming, Drake

2008-01-01

Observations using the Spitzer Space Telescope provided the first detections of photons from extrasolar planets. Spitzer observations are allowing us to infer the temperature structure, composition, and dynamics of exoplanet atmospheres. The Spitzer studies extend from many hot Jupiters, to the hot Neptune orbiting GJ436. Here I review the current status of Spitzer secondary eclipse observations, and summarize the results from the viewpoint of what is robust, what needs more work, and what th...

THE c2d SPITZER SPECTROSCOPIC SURVEY OF ICES AROUND LOW-MASS YOUNG STELLAR OBJECTS. IV. NH3 AND CH3OH

International Nuclear Information System (INIS)

Bottinelli, Sandrine; Van Dishoeck, Ewine F.; Lahuis, Fred; Boogert, A. C. Adwin; Bouwman, Jordy; Beckwith, Martha; Oeberg, Karin I.; Linnartz, Harold; Pontoppidan, Klaus M.; Blake, Geoffrey A.; Evans, Neal J.

2010-01-01

NH 3 and CH 3 OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH 3 CN and CH 3 OCH 3 . Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the ∼8-10 μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH 3 - and CH 3 OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ∼9 μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH 3 ν 2 umbrella mode and derive abundances with respect to water between ∼2% and 15%. Simultaneously, we also revisited the case of CH 3 OH ice by studying the ν 4 C-O stretch mode of this molecule at ∼9.7 μm in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 μm data analysis. Our study indicates that NH 3 is present primarily in H 2 O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH 3 OH being in an almost pure methanol ice, or mixed mainly with CO or CO 2 , consistent with its formation through hydrogenation on grains. Finally, we use our derived NH 3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of

Spitzer Infrared Spectrograph Observations of the Galactic Center: Quantifying the Extreme Ultraviolet/Soft X-ray Fluxes

Science.gov (United States)

Simpson, Janet P.

2018-04-01

It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of H II regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal H II regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5 Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.

REPEATABILITY OF SPITZER/IRAC EXOPLANETARY ECLIPSES WITH INDEPENDENT COMPONENT ANALYSIS

Energy Technology Data Exchange (ETDEWEB)

Morello, G.; Waldmann, I. P.; Tinetti, G., E-mail: giuseppe.morello.11@ucl.ac.uk [Department of Physics and Astronomy, University College London, Gower Street, WC1E6BT (United Kingdom)

2016-04-01

objectivity, as it does not use prior information about the instrument systematics, making it a promising method to analyze data from other observatories. The self-consistency of individual measurements of eclipse depth and phase curve slope over a span of more than three years proves the stability of Warm Spitzer/IRAC photometry within the error bars, at the level of 1 part in 10{sup 4} in stellar flux.

REPEATABILITY OF SPITZER/IRAC EXOPLANETARY ECLIPSES WITH INDEPENDENT COMPONENT ANALYSIS

International Nuclear Information System (INIS)

Morello, G.; Waldmann, I. P.; Tinetti, G.

2016-01-01

objectivity, as it does not use prior information about the instrument systematics, making it a promising method to analyze data from other observatories. The self-consistency of individual measurements of eclipse depth and phase curve slope over a span of more than three years proves the stability of Warm Spitzer/IRAC photometry within the error bars, at the level of 1 part in 10 4 in stellar flux

The formation of a Spitzer bubble RCW 79 triggered by a cloud-cloud collision

Science.gov (United States)

Ohama, Akio; Kohno, Mikito; Hasegawa, Keisuke; Torii, Kazufumi; Nishimura, Atsushi; Hattori, Yusuke; Hayakawa, Takahiro; Inoue, Tsuyoshi; Sano, Hidetoshi; Yamamoto, Hiroaki; Tachihara, Kengo; Fukui, Yasuo

2018-05-01

Understanding the mechanism of O-star formation is one of the most important current issues in astrophysics. Also an issue of keen interest is how O stars affect their surroundings and trigger secondary star formation. An H II region RCW 79 is one of the typical Spitzer bubbles alongside RCW 120. New observations of CO J = 1-0 emission with Mopra and NANTEN2 revealed that molecular clouds are associated with RCW 79 in four velocity components over a velocity range of 20 km s-1. We hypothesize that two of the clouds collided with each other and the collision triggered the formation of 12 O stars inside the bubble and the formation of 54 low-mass young stellar objects along the bubble wall. The collision is supported by observational signatures of bridges connecting different velocity components in the colliding clouds. The whole collision process happened over a timescale of ˜3 Myr. RCW 79 has a larger size by a factor of 30 in the projected area than RCW 120 with a single O star, and the large size favored formation of the 12 O stars due to the greater accumulated gas in the collisional shock compression.

Probing the Dusty Stellar Populations of the Local Volume Galaxies with JWST /MIRI

Energy Technology Data Exchange (ETDEWEB)

Jones, Olivia C.; Meixner, Margaret [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Justtanont, Kay [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden); Glasse, Alistair [UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)

2017-05-20

The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope ( JWST ) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer -IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)–Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (grams), and the grid of YSO models by Robitaille et al., we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes to explore the JWST /MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.

SPITZER OBSERVATIONS OF OGLE-2015-BLG-1212 REVEAL A NEW PATH TOWARD BREAKING STRONG MICROLENS DEGENERACIES

DEFF Research Database (Denmark)

Bozza, V.; Shvartzvald, Y.; Udalski, A.

2016-01-01

Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively break a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter s...

A SPITZER MIPS STUDY OF 2.5-2.0 M{sub Sun} STARS IN SCORPIUS-CENTAURUS

Energy Technology Data Exchange (ETDEWEB)

Chen, Christine H.; Bitner, Martin [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Pecaut, Mark; Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Su, Kate Y. L., E-mail: cchen@stsci.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2012-09-10

We have obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 {mu}m and 70 {mu}m observations of 215 nearby, Hipparcos B- and A-type common proper-motion single and binary systems in the nearest OB association, Scorpius-Centaurus. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 {mu}m B+A-type disk fractions of 17/67 (25{sup +6}{sub -5}%), 36/131 (27{sup +4}{sub -4}%), and 23/95 (24{sup +5}{sub -4}%) for Upper Scorpius ({approx}11 Myr), Upper Centaurus Lupus ({approx}15 Myr), and Lower Centaurus Crux ({approx}17 Myr), respectively, somewhat smaller disk fractions than previously obtained for F- and G-type members. We confirm previous IRAS excess detections and present new discoveries of 51 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L{sub IR}/L{sub *} = 10{sup -6} to 10{sup -2} and grain temperatures ranging from T{sub gr} = 40 to 300 K. In addition, we confirm that the 24 {mu}m and 70 {mu}m excesses (or fractional infrared luminosities) around B+A-type stars are smaller than those measured toward F+G-type stars and hypothesize that the observed disk property dependence on stellar mass may be the result of a higher stellar companion fraction around B- and A-type stars at 10-200 AU. Finally, we note that the majority of the ScoCen 24 {mu}m excess sources also possess 12 {mu}m excess, indicating that Earth-like planets may be forming via collisions in the terrestrial planet zone at {approx}10-100 Myr.

Optical Monitoring of Young Stellar Objects

Science.gov (United States)

Kar, Aman; Jang-Condell, Hannah; Kasper, David; Findlay, Joseph; Kobulnicky, Henry A.

2018-06-01

Observing Young Stellar Objects (YSOs) for variability in different wavelengths enables us to understand the evolution and structure of the protoplanetary disks around stars. The stars observed in this project are known YSOs that show variability in the Infrared. Targets were selected from the Spitzer Space Telescope Young Stellar Object Variability (YSOVAR) Program, which monitored star-forming regions in the mid-infrared. The goal of our project is to investigate any correlation between the variability in the infrared versus the optical. Infrared variability of YSOs is associated with the heating of the protoplanetary disk while accretion signatures are observed in the H-alpha region. We used the University of Wyoming’s Red Buttes Observatory to monitor these stars for signs of accretion using an H-alpha narrowband filter and the Johnson-Cousins filter set, over the Summer of 2017. We perform relative photometry and inspect for an image-to-image variation by observing these targets for a period of four months every two to three nights. The study helps us better understand the link between accretion and H-alpha activity and establish a disk-star connection.

LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Kryukova, E.; Megeath, S. T.; Allen, T. S. [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Pipher, J. [Department of Physics and Astronomy, University of Rochester, Rochester, NY (United States); Allen, L. E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Myers, P. C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Muzerolle, J. [Space Telescope Science Institute, Baltimore, MD (United States)

2012-08-15

We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 {mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 {mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L{sub Sun} and show a tail extending toward luminosities above 100 L{sub Sun }. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L{sub Sun }. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity

LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

International Nuclear Information System (INIS)

Kryukova, E.; Megeath, S. T.; Allen, T. S.; Gutermuth, R. A.; Pipher, J.; Allen, L. E.; Myers, P. C.; Muzerolle, J.

2012-01-01

We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 μm spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 μm), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L ☉ and show a tail extending toward luminosities above 100 L ☉ . The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L ☉ . Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity functions to those

STELLAR MASSES AND STAR FORMATION RATES OF LENSED, DUSTY, STAR-FORMING GALAXIES FROM THE SPT SURVEY

Energy Technology Data Exchange (ETDEWEB)

Ma, Jingzhe; Gonzalez, Anthony H. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Spilker, J. S.; Marrone, D. P. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Strandet, M. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69 D-53121 Bonn (Germany); Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aravena, M. [Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Béthermin, M.; Breuck, C. de; Gullberg, B. [European Southern Observatory, Karl Schwarzschild Straße 2, D-85748 Garching (Germany); Bothwell, M. S. [Cavendish Laboratory, University of Cambridge, JJ Thompson Avenue, Cambridge CB3 0HA (United Kingdom); Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Chapman, S. C. [Dalhousie University, Halifax, Nova Scotia (Canada); Fassnacht, C. D. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Greve, T. R. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Hezaveh, Y. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Malkan, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Saliwanchik, B. R., E-mail: jingzhema@ufl.edu [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); and others

2015-10-10

To understand cosmic mass assembly in the universe at early epochs, we primarily rely on measurements of the stellar masses and star formation rates (SFRs) of distant galaxies. In this paper, we present stellar masses and SFRs of six high-redshift (2.8 ≤ z ≤ 5.7) dusty, star-forming galaxies (DSFGs) that are strongly gravitationally lensed by foreground galaxies. These sources were first discovered by the South Pole Telescope (SPT) at millimeter wavelengths and all have spectroscopic redshifts and robust lens models derived from Atacama Large Millimeter/submillimeter Array observations. We have conducted follow-up observations to obtain multi-wavelength imaging data using the Hubble Space Telescope (HST), Spitzer, Herschel, and the Atacama Pathfinder EXperiment. We use the high-resolution HST/Wide Field Camera 3 images to disentangle the background source from the foreground lens in Spitzer/IRAC data. The detections and upper limits provide important constraints on the spectral energy distributions (SEDs) for these DSFGs, yielding stellar masses, IR luminosities, and SFRs. The SED fits of six SPT sources show that the intrinsic stellar masses span a range more than one order of magnitude with a median value ∼5 ×10{sup 10} M{sub ⊙}. The intrinsic IR luminosities range from 4 × 10{sup 12} L{sub ⊙} to 4 × 10{sup 13} L{sub ⊙}. They all have prodigious intrinsic SFRs of 510–4800 M{sub ⊙} yr{sup −1}. Compared to the star-forming main sequence (MS), these six DSFGs have specific SFRs that all lie above the MS, including two galaxies that are a factor of 10 higher than the MS. Our results suggest that we are witnessing ongoing strong starburst events that may be driven by major mergers.

THE SPITZER DEEP, WIDE-FIELD SURVEY

International Nuclear Information System (INIS)

Ashby, M. L. N.; Brodwin, M.; Stern, D.; Griffith, R.; Eisenhardt, P.; Gorjian, V.; Kozlowski, S.; Kochanek, C. S.; Bock, J. J.; Borys, C.; Brand, K.; Grogin, N. A.; Brown, M. J. I.; Cool, R.; Cooray, A.; Croft, S.; Dey, A.; Eisenstein, D.; Gonzalez, A. H.; Ivison, R. J.

2009-01-01

The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of 10 deg. 2 in the Booetes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Spitzer Cycle 4 Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit-for the first time-the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z ∼ 3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS data sets will thus be especially useful for characterizing galaxy evolution beyond z ∼ 1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 x 10 5 distinct sources detected to the average 5σ, 4''-diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 μm, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 minute integration time of the SDWFS IRAC imaging, >50% of isolated Faint Images of the Radio Sky at Twenty cm radio sources and >80% of on-axis XBooetes sources are detected out to 8.0 μm. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.

Variability of Massive Young Stellar Objects in Cygnus-X

Science.gov (United States)

Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

2013-01-01

Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

Physical Characterization of Warm Spitzer Observed Near-Earth Objects

NARCIS (Netherlands)

Thomas, C. A.; Emery, J. P.; Trilling, D. E.; Delbo, M.; Hora, J. L.; Mueller, M.

2012-01-01

We have undertaken a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program. The combination of Spitzer derived albedos and diameters with spectroscopic data will enhance our understanding of the NEO population.

THE ATMOSPHERES OF THE HOT-JUPITERS KEPLER-5b AND KEPLER-6b OBSERVED DURING OCCULTATIONS WITH WARM-SPITZER AND KEPLER

Energy Technology Data Exchange (ETDEWEB)

Desert, Jean-Michel; Charbonneau, David; Fressin, Francois; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Madhusudhan, Nikku [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Knutson, Heather A. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Deming, Drake [Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Borucki, William J. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Brown, Timothy M. [Las Cumbres Observatory Global Telescope, Goleta, CA 93117 (United States); Caldwell, Douglas [SETI Institute, Mountain View, CA 94043 (United States); Ford, Eric B. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Gilliland, Ronald L. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Marcy, Geoffrey W. [Berkeley Astronomy Department, University of California, Berkeley, CA 94720 (United States); Seager, Sara, E-mail: jdesert@cfa.harvard.edu [Massachusetts Institute of Technology, Cambridge, MA 02159 (United States)

2011-11-01

This paper reports the detection and the measurements of occultations of the two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent stars. The observations are obtained in the near-infrared with Warm-Spitzer Space Telescope and at optical wavelengths by combining more than a year of Kepler photometry. The investigation consists of constraining the eccentricities of these systems and of obtaining broadband emergent photometric data for individual planets. For both targets, the occultations are detected at the 3{sigma} level at each wavelength with mid-occultation times consistent with circular orbits. The brightness temperatures of these planets are deduced from the infrared observations and reach T{sub Spitzer} = 1930 {+-} 100 K and T{sub Spitzer} = 1660 {+-} 120 K for Kepler-5b and Kepler-6b, respectively. We measure optical geometric albedos A{sub g} in the Kepler bandpass and find A{sub g} = 0.12 {+-} 0.04 for Kepler-5b and A{sub g} = 0.11 {+-} 0.04 for Kepler-6b, leading to upper an limit for the Bond albedo of A{sub B} {<=} 0.17 in both cases. The observations for both planets are best described by models for which most of the incident energy is redistributed on the dayside, with only less than 10% of the absorbed stellar flux redistributed to the nightside of these planets.

MN48: a new Galactic bona fide luminous blue variable revealed by Spitzer and SALT

Science.gov (United States)

Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

2016-07-01

In this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star MN48 disclosed via detection of a mid-infrared circular shell around it with the Spitzer Space Telescope. Follow-up optical spectroscopy of MN48 with the Southern African Large Telescope (SALT) carried out in 2011-2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (LBVs). The LBV status of MN48 was further supported by photometric monitoring which shows that in 2009-2011 this star has brightened by ≈0.9 and 1 mag in the V and Ic bands, respectively, then faded by ≈1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. The detected changes in the spectrum and brightness of MN48 make this star the 18th known Galactic bona fide LBV and increase the percentage of LBVs associated with circumstellar nebulae to more than 70 per cent. We discuss the possible birth place of MN48 and suggest that this star might have been ejected either from a putative star cluster embedded in the H II region IRAS 16455-4531 or the young massive star cluster Westerlund 1.

LOW FALSE POSITIVE RATE OF KEPLER CANDIDATES ESTIMATED FROM A COMBINATION OF SPITZER AND FOLLOW-UP OBSERVATIONS

International Nuclear Information System (INIS)

Désert, Jean-Michel; Brown, Timothy M.; Charbonneau, David; Torres, Guillermo; Fressin, François; Ballard, Sarah; Latham, David W.; Bryson, Stephen T.; Borucki, William J.; Knutson, Heather A.; Batalha, Natalie M.; Deming, Drake; Ford, Eric B.; Fortney, Jonathan J.; Gilliland, Ronald L.; Seager, Sara

2015-01-01

NASA’s Kepler mission has provided several thousand transiting planet candidates during the 4 yr of its nominal mission, yet only a small subset of these candidates have been confirmed as true planets. Therefore, the most fundamental question about these candidates is the fraction of bona fide planets. Estimating the rate of false positives of the overall Kepler sample is necessary to derive the planet occurrence rate. We present the results from two large observational campaigns that were conducted with the Spitzer Space Telescope during the the Kepler mission. These observations are dedicated to estimating the false positive rate (FPR) among the Kepler candidates. We select a sub-sample of 51 candidates, spanning wide ranges in stellar, orbital, and planetary parameter space, and we observe their transits with Spitzer at 4.5 μm. We use these observations to measures the candidate’s transit depths and infrared magnitudes. An authentic planet produces an achromatic transit depth (neglecting the modest effect of limb darkening). Conversely a bandpass-dependent depth alerts us to the potential presence of a blending star that could be the source of the observed eclipse: a false positive scenario. For most of the candidates (85%), the transit depths measured with Kepler are consistent with the transit depths measured with Spitzer as expected for planetary objects, while we find that the most discrepant measurements are due to the presence of unresolved stars that dilute the photometry. The Spitzer constraints on their own yield FPRs between 5% and depending on the Kepler Objects of Interest. By considering the population of the Kepler field stars, and by combining follow-up observations (imaging) when available, we find that the overall FPR of our sample is low. The measured upper limit on the FPR of our sample is 8.8% at a confidence level of 3σ. This observational result, which uses the achromatic property of planetary transit signals that is not investigated

LOW FALSE POSITIVE RATE OF KEPLER CANDIDATES ESTIMATED FROM A COMBINATION OF SPITZER AND FOLLOW-UP OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Désert, Jean-Michel; Brown, Timothy M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Charbonneau, David; Torres, Guillermo; Fressin, François; Ballard, Sarah; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Bryson, Stephen T.; Borucki, William J. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Knutson, Heather A. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Batalha, Natalie M. [San Jose State University, San Jose, CA 95192 (United States); Deming, Drake [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Ford, Eric B. [University of Florida, Gainesville, FL 32611 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Gilliland, Ronald L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Seager, Sara, E-mail: desert@colorado.edu [Massachusetts Institute of Technology, Cambridge, MA 02159 (United States)

2015-05-01

NASA’s Kepler mission has provided several thousand transiting planet candidates during the 4 yr of its nominal mission, yet only a small subset of these candidates have been confirmed as true planets. Therefore, the most fundamental question about these candidates is the fraction of bona fide planets. Estimating the rate of false positives of the overall Kepler sample is necessary to derive the planet occurrence rate. We present the results from two large observational campaigns that were conducted with the Spitzer Space Telescope during the the Kepler mission. These observations are dedicated to estimating the false positive rate (FPR) among the Kepler candidates. We select a sub-sample of 51 candidates, spanning wide ranges in stellar, orbital, and planetary parameter space, and we observe their transits with Spitzer at 4.5 μm. We use these observations to measures the candidate’s transit depths and infrared magnitudes. An authentic planet produces an achromatic transit depth (neglecting the modest effect of limb darkening). Conversely a bandpass-dependent depth alerts us to the potential presence of a blending star that could be the source of the observed eclipse: a false positive scenario. For most of the candidates (85%), the transit depths measured with Kepler are consistent with the transit depths measured with Spitzer as expected for planetary objects, while we find that the most discrepant measurements are due to the presence of unresolved stars that dilute the photometry. The Spitzer constraints on their own yield FPRs between 5% and depending on the Kepler Objects of Interest. By considering the population of the Kepler field stars, and by combining follow-up observations (imaging) when available, we find that the overall FPR of our sample is low. The measured upper limit on the FPR of our sample is 8.8% at a confidence level of 3σ. This observational result, which uses the achromatic property of planetary transit signals that is not investigated

SPARC: MASS MODELS FOR 175 DISK GALAXIES WITH SPITZER PHOTOMETRY AND ACCURATE ROTATION CURVES

Energy Technology Data Exchange (ETDEWEB)

Lelli, Federico; McGaugh, Stacy S. [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Schombert, James M., E-mail: federico.lelli@case.edu [Department of Physics, University of Oregon, Eugene, OR 97403 (United States)

2016-12-01

We introduce SPARC ( Spitzer Photometry and Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6  μ m and high-quality rotation curves from previous H i/H α studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (∼5 dex), and surface brightnesses (∼4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass–H i mass relation and the stellar radius–H i radius relation have significant intrinsic scatter, while the H i   mass–radius relation is extremely tight. We build detailed mass models and quantify the ratio of baryonic to observed velocity ( V {sub bar}/ V {sub obs}) for different characteristic radii and values of the stellar mass-to-light ratio (ϒ{sub ⋆}) at [3.6]. Assuming ϒ{sub ⋆} ≃ 0.5 M {sub ⊙}/ L {sub ⊙} (as suggested by stellar population models), we find that (i) the gas fraction linearly correlates with total luminosity; (ii) the transition from star-dominated to gas-dominated galaxies roughly corresponds to the transition from spiral galaxies to dwarf irregulars, in line with density wave theory; and (iii)  V {sub bar}/ V {sub obs} varies with luminosity and surface brightness: high-mass, high-surface-brightness galaxies are nearly maximal, while low-mass, low-surface-brightness galaxies are submaximal. These basic properties are lost for low values of ϒ{sub ⋆} ≃ 0.2 M {sub ⊙}/ L {sub ⊙} as suggested by the DiskMass survey. The mean maximum-disk limit in bright galaxies is ϒ{sub ⋆} ≃ 0.7 M {sub ⊙}/ L {sub ⊙} at [3.6]. The SPARC data are publicly available and represent an ideal test bed for models of galaxy formation.

Discovering Massive z > 1 Galaxy Clusters with Spitzer and SPTpol

Science.gov (United States)

Bleem, Lindsey; Brodwin, Mark; Ashby, Matthew; Stalder, Brian; Klein, Matthias; Gladders, Michael; Stanford, Spencer; Canning, Rebecca

2018-05-01

We propose to obtain Spitzer/IRAC imaging of 50 high-redshift galaxy cluster candidates derived from two new completed SZ cluster surveys by the South Pole Telescope. Clusters from the deep SPTpol 500-square-deg main survey will extend high-redshift SZ cluster science to lower masses (median M500 2x10^14Msun) while systems drawn from the wider 2500-sq-deg SPTpol Extended Cluster Survey are some of the rarest most massive high-z clusters in the observable universe. The proposed small 10 h program will enable (1) confirmation of these candidates as high-redshift clusters, (2) measurements of the cluster redshifts (sigma_z/(1+z) 0.03), and (3) estimates of the stellar masses of the brightest cluster members. These observations will yield exciting and timely targets for the James Webb Space Telescope--and, combined with lower-z systems--will both extend cluster tests of dark energy to z>1 as well as enable studies of galaxy evolution in the richest environments for a mass-limited cluster sample from 0

Physical characterization of Near Earth Objects with Spitzer

Science.gov (United States)

Trilling, David; Hora, Joseph; Mommert, Michael; Chesley, Steve; Emery, Joshua; Fazio, Giovanni; Harris, Alan; Mueller, Migo; Smith, Howard

2018-05-01

We propose here an efficient, flux-limited survey of 426 optically discovered NEOs in order to measure their diameters and albedos. We include only targets not previously detected by Spitzer or NEOWISE and includes all NEOs available to Spitzer in Cycle 14. This program will maintain the fraction of all known NEOs with measured diameters and albedos at around 20% even in the face of increasingly successful NEO discovery surveys. By the conclusion of this program nearly 3500 NEOs will have measured diameters and albedos, with nearly 3000 of those observations being made by Spitzer and our team. We will determine an independent size distribution of NEOs at 100 meters that is free from albedo assumptions, addressing a current controversy. We will also derive, through our albedo measurements, the compositional distribution of NEOs as a function of size. We will measure or constrain lightcurves for more than 400 NEOs, thus constraining their shapes in addition to sizes and compositions. This catalog will enable a number of other science cases to be pursued by us and other researchers. Our team has unmatched experience observing NEOs with Spitzer.

A MODEL FOR (QUASI-)PERIODIC MULTIWAVELENGTH PHOTOMETRIC VARIABILITY IN YOUNG STELLAR OBJECTS

Energy Technology Data Exchange (ETDEWEB)

Kesseli, Aurora Y. [Boston University, 725 Commonwealth Ave, Boston, MA 02215 (United States); Petkova, Maya A.; Wood, Kenneth; Gregory, Scott G. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD (United Kingdom); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States); Hillenbrand, L. A. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Stauffer, J. R.; Morales-Calderon, M.; Rebull, L. [Spitzer Science Center, California Institute of Technology, CA 91125 (United States); Alencar, S. H. P., E-mail: aurorak@bu.com [Departamento de Física—ICEx—UFMG, Av. Antônio Carlos, 6627, 30270-901, Belo Horizonte, MG (Brazil)

2016-09-01

We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.

Unveiling the structure of barred galaxies at 3.6 μm with the Spitzer survey of stellar structure in galaxies (S4G). I. Disk breaks

International Nuclear Information System (INIS)

Kim, Taehyun; Lee, Myung Gyoon; Gadotti, Dimitri A.; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Athanassoula, E.; Bosma, Albert; Madore, Barry F.; Ho, Luis C.; Elmegreen, Bruce; Knapen, Johan H.; Cisternas, Mauricio; Erroz-Ferrer, Santiago; Zaritsky, Dennis; Comerón, Sébastien; Laurikainen, Eija; Salo, Heikki; Holwerda, Benne; Hinz, Joannah L.; Buta, Ron

2014-01-01

We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r br /R bar , varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r br /R bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

THE SPITZER-WISE SURVEY OF THE ECLIPTIC POLES

International Nuclear Information System (INIS)

Jarrett, T. H.; Masci, F.; Cutri, R. M.; Marsh, K.; Padgett, D.; Tsai, C. W.; Cohen, M.; Wright, E.; Petty, S.; Stern, D.; Eisenhardt, P.; Mainzer, A.; Ressler, M.; Benford, D.; Blain, A.; Carey, S.; Surace, J.; Lonsdale, C.; Skrutskie, M.; Stanford, S.

2011-01-01

We have carried out a survey of the north and south ecliptic poles, EP-N and EP-S, respectively, with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE). The primary objective was to cross-calibrate WISE with the Spitzer and Midcourse Space Experiment (MSX) photometric systems by developing a set of calibration stars that are common to these infrared missions. The ecliptic poles were continuous viewing zones for WISE due to its polar-crossing orbit, making these areas ideal for both absolute and internal calibrations. The Spitzer IRAC and MIPS imaging survey covers a complete area of 0.40 deg 2 for the EP-N and 1.28 deg 2 for the EP-S. WISE observed the whole sky in four mid-infrared bands, 3.4, 4.6, 12, and 22 μm, during its eight-month cryogenic mission, including several hundred ecliptic polar passages; here we report on the highest coverage depths achieved by WISE, an area of ∼1.5 deg 2 for both poles. Located close to the center of the EP-N, the Sy-2 galaxy NGC 6552 conveniently functions as a standard calibrator to measure the red response of the 22 μm channel of WISE. Observations from Spitzer-IRAC/MIPS/IRS-LL and WISE show that the galaxy has a strong red color in the mid-infrared due to star-formation and the presence of an active galactic nucleus (AGN), while over a baseline >1 year the mid-IR photometry of NGC 6552 is shown to vary at a level less than 2%. Combining NGC 6552 with the standard calibrator stars, the achieved photometric accuracy of the WISE calibration, relative to the Spitzer and MSX systems, is 2.4%, 2.8%, 4.5%, and 5.7% for W1 (3.4 μm), W2 (4.6 μm), W3 (12 μm), and W4 (22 μm), respectively. The WISE photometry is internally stable to better than 0.1% over the cryogenic lifetime of the mission. The secondary objective of the Spitzer-WISE Survey was to explore the poles at greater flux-level depths, exploiting the higher angular resolution Spitzer observations and the exceptionally deep (in total

THE DYNAMICAL EVOLUTION OF STELLAR BLACK HOLES IN GLOBULAR CLUSTERS

Energy Technology Data Exchange (ETDEWEB)

Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl; Rasio, Frederic A.; Umbreit, Stefan, E-mail: m.morscher@u.northwestern.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, Evanston, IL (United States)

2015-02-10

Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters (GCs) may have formed hundreds to thousands of stellar-mass black holes (BHs), the remnants of stars with initial masses from ∼20-100 M {sub ☉}. Birth kicks from supernova explosions may eject some BHs from their birth clusters, but most should be retained. Using a Monte Carlo method we investigate the long-term dynamical evolution of GCs containing large numbers of stellar BHs. We describe numerical results for 42 models, covering a broad range of realistic initial conditions, including up to 1.6 × 10{sup 6} stars. In almost all models we find that significant numbers of BHs (up to ∼10{sup 3}) are retained all the way to the present. This is in contrast to previous theoretical expectations that most BHs should be ejected dynamically within a few gigayears The main reason for this difference is that core collapse driven by BHs (through the Spitzer {sup m}ass segregation instability{sup )} is easily reverted through three-body processes, and involves only a small number of the most massive BHs, while lower-mass BHs remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar BHs does not lead to a long-term physical separation of most BHs into a dynamically decoupled inner core, as often assumed previously. Combined with the recent detections of several BH X-ray binary candidates in Galactic GCs, our results suggest that stellar BHs could still be present in large numbers in many GCs today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

Ultradeep Infrared Array Camera Observations of Sub-L* z ~ 7 and z ~ 8 Galaxies in the Hubble Ultra Deep Field: the Contribution of Low-Luminosity Galaxies to the Stellar Mass Density and Reionization

Science.gov (United States)

Labbé, I.; González, V.; Bouwens, R. J.; Illingworth, G. D.; Oesch, P. A.; van Dokkum, P. G.; Carollo, C. M.; Franx, M.; Stiavelli, M.; Trenti, M.; Magee, D.; Kriek, M.

2010-01-01

We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z ~ 7 z 850-dropout galaxies and 5z ~ 8 Y 105-dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6 μm and 4.5 μm. None of the galaxies are detected to [3.6] ≈ 26.9 (AB, 2σ), but a stacking analysis reveals a robust detection for the z 850-dropouts and an upper limit for the Y 105-dropouts. We construct average broadband spectral energy distributions using the stacked Advanced Camera for Surveys (ACS), WFC3, and IRAC fluxes and fit stellar population synthesis models to derive mean redshifts, stellar masses, and ages. For the z 850-dropouts, we find z = 6.9+0.1 -0.1, (U - V)rest ≈ 0.4, reddening AV = 0, stellar mass langM*rang = 1.2+0.3 -0.6 × 109 M sun (Salpeter initial mass function). The best-fit ages ~300 Myr, M/LV ≈ 0.2, and SSFR ~1.7 Gyr-1 are similar to values reported for luminous z ~ 7 galaxies, indicating the galaxies are smaller but not much younger. The sub-L* galaxies observed here contribute significantly to the stellar mass density and under favorable conditions may have provided enough photons for sustained reionization at 7 dropouts have stellar masses that are uncertain by 1.5 dex due to the near-complete reliance on far-UV data. Adopting the 2σ upper limit on the M/L(z = 8), the stellar mass density to M UV,AB Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #11563, 9797. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through contract 125790 issued by JPL/Caltech. Based on service mode observations collected at the European Southern Observatory, Paranal, Chile (ESO Program

SPITZER IMAGING OF STRONGLY LENSED HERSCHEL-SELECTED DUSTY STAR-FORMING GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Ma, Brian; Cooray, Asantha; Calanog, J. A.; Nayyeri, H.; Timmons, N.; Casey, C. [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Baes, M. [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent (Belgium); Chapman, S. [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2 (Canada); Dannerbauer, H. [Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu-CNRS-Université Paris Diderot, CE-Saclay, pt courrier 131, F-91191 Gif-sur-Yvette (France); Da Cunha, E. [Center for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn VIC 3122 (Australia); De Zotti, G. [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Dunne, L.; Michałowski, M. J.; Oteo, I. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Farrah, D. [Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States); Fu, Hai [Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States); Gonzalez-Nuevo, J. [Departamento de Fisica, Universidad de Oviedo C/ Calvo Sotelo, s/n, E-33007 Oviedo (Spain); Magdis, G. [Department of Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Riechers, D. A. [Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853 (United States); Scott, D. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); and others

2015-11-20

We present the rest-frame optical spectral energy distribution (SED) and stellar masses of six Herschel-selected gravitationally lensed dusty, star-forming galaxies (DSFGs) at 1 < z < 3. These galaxies were first identified with Herschel/SPIRE imaging data from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). The targets were observed with Spitzer/IRAC at 3.6 and 4.5 μm. Due to the spatial resolution of the IRAC observations at the level of 2″, the lensing features of a background DSFG in the near-infrared are blended with the flux from the foreground lensing galaxy in the IRAC imaging data. We make use of higher resolution Hubble/WFC3 or Keck/NIRC2 Adaptive Optics imaging data to fit light profiles of the foreground lensing galaxy (or galaxies) as a way to model the foreground components, in order to successfully disentangle the foreground lens and background source flux densities in the IRAC images. The flux density measurements at 3.6 and 4.5 μm, once combined with Hubble/WFC3 and Keck/NIRC2 data, provide important constraints on the rest-frame optical SED of the Herschel-selected lensed DSFGs. We model the combined UV- to millimeter-wavelength SEDs to establish the stellar mass, dust mass, star formation rate, visual extinction, and other parameters for each of these Herschel-selected DSFGs. These systems have inferred stellar masses in the range 8 × 10{sup 10}–4 × 10{sup 11} M{sub ⊙} and star formation rates of around 100 M{sub ⊙} yr{sup −1}. This puts these lensed submillimeter systems well above the SFR-M* relation observed for normal star-forming galaxies at similar redshifts. The high values of SFR inferred for these systems are consistent with a major merger-driven scenario for star formation.

SPITZER IRAC PHOTOMETRY FOR TIME SERIES IN CROWDED FIELDS

Energy Technology Data Exchange (ETDEWEB)

Novati, S. Calchi; Beichman, C. [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Gould, A.; Fausnaugh, M.; Gaudi, B. S.; Pogge, R. W.; Wibking, B.; Zhu, W.; Poleski, R. [Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Yee, J. C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Bryden, G.; Henderson, C. B.; Shvartzvald, Y. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Carey, S. [Spitzer, Science Center, MS 220-6, California Institute of Technology, Pasadena, CA (United States); Udalski, A.; Pawlak, M.; Szymański, M. K.; Skowron, J.; Mróz, P.; Kozłowski, S. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Collaboration: Spitzer team; OGLE group; and others

2015-12-01

We develop a new photometry algorithm that is optimized for the Infrared Array Camera (IRAC) Spitzer time series in crowded fields and that is particularly adapted to faint or heavily blended targets. We apply this to the 170 targets from the 2015 Spitzer microlensing campaign and present the results of three variants of this algorithm in an online catalog. We present detailed accounts of the application of this algorithm to two difficult cases, one very faint and the other very crowded. Several of Spitzer's instrumental characteristics that drive the specific features of this algorithm are shared by Kepler and WFIRST, implying that these features may prove to be a useful starting point for algorithms designed for microlensing campaigns by these other missions.

A Statistical Approach to Exoplanetary Molecular Spectroscopy Using Spitzer Eclipses

Science.gov (United States)

Deming, Drake; Garhart, Emily; Burrows, Adam; Fortney, Jonathan; Knutson, Heather; Todorov, Kamen

2018-01-01

Secondary eclipses of exoplanets observed using the Spitzer Space Telescope measure the total emission emergent from exoplanetary atmospheres integrated over broad photometric bands. Spitzer photometry is excellent for measuring day side temperatures, but is less well suited to the detection of molecular absorption or emission features. Even for very hot exoplanets, it can be difficult to attain the accuracy on eclipse depth that is needed to unambiguously interpret the Spitzer results in terms of molecular absorption or emission. However, a statistical approach, wherein we seek deviations from a simple blackbody planet as a function of the planet's equilibrium temperature, shows promise for defining the nature and strength of molecular absorption in ensembles of planets. In this paper, we explore such an approach using secondary eclipses observed for tens of hot exoplanets during Spitzer's Cycles 10, 12, and 13. We focus on the possibility that the hottest planets exhibit molecular features in emission, due to temperature inversions.

THE SPITZER SURVEY OF INTERSTELLAR CLOUDS IN THE GOULD BELT. IV. LUPUS V AND VI OBSERVED WITH IRAC AND MIPS

International Nuclear Information System (INIS)

Spezzi, Loredana; Vernazza, Pierre; Merin, Bruno; Allen, Lori E.; Evans, Neal J. II; Harvey, Paul M.; Joergensen, Jes K.; Bourke, Tyler L.; Peterson, Dawn; Cieza, Lucas A.; Dunham, Michael M.; Huard, Tracy L.; Tothill, Nick F. H.

2011-01-01

We present Gould's Belt (GB) Spitzer IRAC and MIPS observations of the Lupus V and VI clouds and discuss them in combination with near-infrared (2MASS) data. Our observations complement those obtained for other Lupus clouds within the frame of the Spitzer C ore to Disk(c2d) Legacy Survey. We found 43 young stellar object (YSO) candidates in Lupus V and 45 in Lupus VI, including two transition disks, using the standard c2d/GB selection method. None of these sources was classified as a pre-main-sequence star from previous optical, near-IR, and X-ray surveys. A large majority of these YSO candidates appear to be surrounded by thin disks (Class III; ∼79% in Lupus V and ∼87% in Lupus VI). These Class III abundances differ significantly from those observed for the other Lupus clouds and c2d/GB surveyed star-forming regions, where objects with optically thick disks (Class II) dominate the young population. We investigate various scenarios that can explain this discrepancy. In particular, we show that disk photoevaporation due to nearby OB stars is not responsible for the high fraction of Class III objects. The gas surface densities measured for Lupus V and VI lie below the star formation threshold (A V ∼ 8.6 mag), while this is not the case for other Lupus clouds. Thus, few Myr older age for the YSOs in Lupus V and VI with respect to other Lupus clouds is the most likely explanation of the high fraction of Class III objects in these clouds, while a higher characteristic stellar mass might be a contributing factor. Better constraints on the age and binary fraction of the Lupus clouds might solve the puzzle but require further observations.

SPATIAL VARIATIONS OF PAH PROPERTIES IN M17SW REVEALED BY SPITZER /IRS SPECTRAL MAPPING

Energy Technology Data Exchange (ETDEWEB)

Yamagishi, M. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Chuo-ku, Sagamihara 252-5210 (Japan); Kaneda, H.; Ishihara, D.; Oyabu, S.; Suzuki, T.; Nishimura, A.; Kohno, M. [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Onaka, T.; Ohashi, S. [Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Nagayama, T.; Matsuo, M. [Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan); Umemoto, T.; Minamidani, T.; Fujita, S. [Nobeyama Radio Observatory, National Astronomical Observatory of Japan (NAOJ), National Institutes of Natural Sciences (NINS), 462-2, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305 (Japan); Tsuda, Y., E-mail: yamagish@ir.isas.jaxa.jp [Graduate School of Science and Engineering, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-0042 (Japan)

2016-12-20

We present Spitzer /IRS mid-infrared spectral maps of the Galactic star-forming region M17 as well as IRSF/SIRIUS Br γ and Nobeyama 45 m/FOREST {sup 13}CO ( J = 1–0) maps. The spectra show prominent features due to polycyclic aromatic hydrocarbons (PAHs) at wavelengths of 6.2, 7.7, 8.6, 11.3, 12.0, 12.7, 13.5, and 14.2  μ m. We find that the PAH emission features are bright in the region between the H ii region traced by Br γ and the molecular cloud traced by {sup 13}CO, supporting that the PAH emission originates mostly from photo-dissociation regions. Based on the spatially resolved Spitzer /IRS maps, we examine spatial variations of the PAH properties in detail. As a result, we find that the interband ratio of PAH 7.7  μ m/PAH 11.3  μ m varies locally near M17SW, but rather independently of the distance from the OB stars in M17, suggesting that the degree of PAH ionization is mainly controlled by local conditions rather than the global UV environments determined by the OB stars in M17. We also find that the interband ratios of the PAH 12.0  μ m, 12.7  μ m, 13.5  μ m, and 14.2  μ m features to the PAH 11.3  μ m feature are high near the M17 center, which suggests structural changes of PAHs through processing due to intense UV radiation, producing abundant edgy irregular PAHs near the M17 center.

The Carnegie-Spitzer-IMACS redshift survey of galaxy evolution since z = 1.5. I. Description and methodology

Energy Technology Data Exchange (ETDEWEB)

Kelson, Daniel D.; Williams, Rik J.; Dressler, Alan; McCarthy, Patrick J.; Shectman, Stephen A.; Mulchaey, John S.; Villanueva, Edward V.; Crane, Jeffrey D.; Quadri, Ryan F. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2014-03-10

We describe the Carnegie-Spitzer-IMACS (CSI) Survey, a wide-field, near-IR selected spectrophotometric redshift survey with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on Magellan-Baade. By defining a flux-limited sample of galaxies in Spitzer Infrared Array Camera 3.6 μm imaging of SWIRE fields, the CSI Survey efficiently traces the stellar mass of average galaxies to z ∼ 1.5. This first paper provides an overview of the survey selection, observations, processing of the photometry and spectrophotometry. We also describe the processing of the data: new methods of fitting synthetic templates of spectral energy distributions are used to derive redshifts, stellar masses, emission line luminosities, and coarse information on recent star formation. Our unique methodology for analyzing low-dispersion spectra taken with multilayer prisms in IMACS, combined with panchromatic photometry from the ultraviolet to the IR, has yielded high-quality redshifts for 43,347 galaxies in our first 5.3 deg{sup 2} of the SWIRE XMM-LSS field. We use three different approaches to estimate our redshift errors and find robust agreement. Over the full range of 3.6 μm fluxes of our selection, we find typical redshift uncertainties of σ {sub z}/(1 + z) ≲ 0.015. In comparisons with previously published spectroscopic redshifts we find scatters of σ {sub z}/(1 + z) = 0.011 for galaxies at 0.7 ≤ z ≤ 0.9, and σ {sub z}/(1 + z) = 0.014 for galaxies at 0.9 ≤ z ≤ 1.2. For galaxies brighter and fainter than i = 23 mag, we find σ {sub z}/(1 + z) = 0.008 and σ {sub z}/(1 + z) = 0.022, respectively. Notably, our low-dispersion spectroscopy and analysis yields comparable redshift uncertainties and success rates for both red and blue galaxies, largely eliminating color-based systematics that can seriously bias observed dependencies of galaxy evolution on environment.

ULTRAVIOLET+INFRARED STAR FORMATION RATES: HICKSON COMPACT GROUPS WITH SWIFT AND SPITZER

International Nuclear Information System (INIS)

Tzanavaris, P.; Hornschemeier, A. E.; Immler, S.; Gallagher, S. C.; Johnson, K. E.; Reines, A. E.; Gronwall, C.; Hoversten, E.; Charlton, J. C.

2010-01-01

We present Swift UVOT ultraviolet (UV; 1600-3000 A) data with complete three-band UV photometry for a sample of 41 galaxies in 11 nearby ( -1 ) Hickson Compact Groups (HCGs) of galaxies. We use UVOT uvw2-band (2000 A) photometry to estimate the dust-unobscured component, SFR UV , of the total star formation rate, SFR TOTAL . We use Spitzer MIPS 24 μm photometry to estimate SFR IR , the component of SFR TOTAL that suffers dust extinction in the UV and is re-emitted in the IR. By combining the two components, we obtain SFR TOTAL estimates for all HCG galaxies. We obtain total stellar mass, M * , estimates by means of Two Micron All Sky Survey K s -band luminosities, and use them to calculate specific star formation rates, SSFR ≡ SFR TOTAL /M * . SSFR values show a clear and significant bimodality, with a gap between low (∼ -11 yr -1 ) and high-SSFR (∼>1.2 x 10 -10 yr -1 ) systems. We compare this bimodality to the previously discovered bimodality in α IRAC , the MIR activity index from a power-law fit to the Spitzer IRAC 4.5-8 μm data for these galaxies. We find that all galaxies with α IRAC ≤ 0 ( >0) are in the high- (low-) SSFR locus, as expected if high levels of star-forming activity power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. Consistent with this finding, all elliptical/S0 galaxies are in the low-SSFR locus, while 22 out of 24 spirals/irregulars are in the high-SSFR locus, with two borderline cases. We further divide our sample into three subsamples (I, II, and III) according to decreasing H I richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and α IRAC bimodality, 12 out of 15 type I (11 out of 12 type III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. We use the Spitzer Infrared Nearby Galaxy Survey (SINGS) to construct a comparison subsample of galaxies that (1) match HCG galaxies in J-band total

Understanding the formation and evolution of early-type galaxies based on newly developed single-burst stellar population synthesis models in the infrared

Science.gov (United States)

Roeck, Benjamin

2015-12-01

The detailed study of the different stellar populations which can be observed in galaxies is one of the most promising methods to shed light on the evolutionary histories of galaxies. So far, stellar population analysis has been carried out mainly in the optical wavelength range. The infrared spectral range, on the other hand, has been poorly studied so far, although it provides very important insights, particularly into the cooler stellar populations which are present in galaxies. However, in the last years, space telescopes like the Spitzer Space Telescope or the Wide-field Infrared Survey Explorer and instruments like the spectrograph X-Shooter on the Very Large Telescope have collected more and more photometric and spectroscopic data in this wavelength range. In order to analyze these observations, it is necessary to dispose of reliable and accurate stellar population models in the infrared. Only a small number of stellar population models in the infrared exist in the literature. They are mostly based on theoretical stellar libraries and very often cover only the near-infrared wavelength range at a rather low resolution. Hence, we developed new single-burst stellar population models between 8150 and 50000Å which are exclusively based on 180 spectra from the empirical Infrared Telescope Facility stellar library. We computed our single stellar population models for two different sets of isochrones and various types of initial mass functions of different slopes. Since the stars of the Infrared Telescope Facility library present only a limited coverage of the stellar atmospheric parameter space, our models are of sufficient quality only for ages larger than 1 Gyr and metallicities between [Fe/H] = 0.40 and 0.26. By combining our single stellar population models in the infrared with the extended medium-resolution Isaac Newton Telescope library of empirical spectra in the optical spectral range, we created the first single stellar population models covering the

The kilometer-sized Main Belt asteroid population revealed by Spitzer

Science.gov (United States)

Ryan, E. L.; Mizuno, D. R.; Shenoy, S. S.; Woodward, C. E.; Carey, S. J.; Noriega-Crespo, A.; Kraemer, K. E.; Price, S. D.

2015-06-01

Aims: Multi-epoch Spitzer Space Telescope 24 μm data is utilized from the MIPSGAL and Taurus Legacy surveys to detect asteroids based on their relative motion. Methods: Infrared detections are matched to known asteroids and average diameters and albedos are derived using the near Earth asteroid thermal model (NEATM) for 1865 asteroids ranging in size from 0.2 to 169 km. A small subsample of these objects was also detected by IRAS or MSX and the single wavelength albedo and diameter fits derived from these data are within the uncertainties of the IRAS and/or MSX derived albedos and diameters and available occultation diameters, which demonstrates the robustness of our technique. Results: The mean geometric albedo of the small Main Belt asteroids in this sample is pV = 0.134 with a sample standard deviation of 0.106. The albedo distribution of this sample is far more diverse than the IRAS or MSX samples. The cumulative size-frequency distribution of asteroids in the Main Belt at small diameters is directly derived and a 3σ deviation from the fitted size-frequency distribution slope is found near 8 km. Completeness limits of the optical and infrared surveys are discussed. Tables 1-3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A42

Recent SPIRITS discoveries of Infrared Transients and Variables with Spitzer/IRAC

Science.gov (United States)

Jencson, J. E.; Kasliwal, M. M.; Adams, S.; Cook, D.; Tinyanont, S.; Kwan, S.; Prince, T.; Lau, R. M.; Perley, D.; Masci, F.; Helou, G.; Armus, L.; Surace, J.; Dyk, S. D. Van; Cody, A.; Boyer, M. L.; Bond, H. E.; Monson, A.; Bally, J.; Khan, R.; Levesque, E.; Fox, O.; Williams, R.; Whitelock, P. A.; Mohamed, S.; Gehrz, R. D.; Amodeo, S.; Shenoy, D.; Carlon, R.; Cass, A.; Corgan, D.; Dykhoff, D.; Faella, J.; Gburek, T.; Smith, N.; Cantiello, M.; Langer, N.; Ofek, E.; Johansson, J.; Parthasarathy, M.; Hsiao, E.; Phillips, M.; Morrell, N.; Gonzalez, C.; Contreras, C.

2018-04-01

We report the discoveries of mid-infrared transients/strong variables found in the course of the Spitzer InfraRed Intensive Transients Survey (SPIRITS) using Spitzer Early Release Data (ATel #6644, #7929, #8688, #8940, #9434, #10171, #10172, #10488, #10903).

Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

International Nuclear Information System (INIS)

Wit, Julien de; Lewis, Nikole K.; Knutson, Heather A.; Batygin, Konstantin; Fuller, Jim; Antoci, Victoria; Fulton, Benjamin J.; Laughlin, Gregory; Deming, Drake; Shporer, Avi; Cowan, Nicolas B.; Agol, Eric; Burrows, Adam S.; Fortney, Jonathan J.; Langton, Jonathan; Showman, Adam P.

2017-01-01

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μ m observations with the Spitzer Space Telescope . The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μ m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.

Efficient Mosaicking of Spitzer Space Telescope Images

Science.gov (United States)

Jacob, Joseph; Makovoz, David; Eisenhardt, Peter

2007-01-01

A parallel version of the MOPEX software, which generates mosaics of infrared astronomical images acquired by the Spitzer Space Telescope, extends the capabilities of the prior serial version. In the parallel version, both the input image space and the output mosaic space are divided among the available parallel processors. This is the only software that performs the point-source detection and the rejection of spurious imaging effects of cosmic rays required by Spitzer scientists. This software includes components that implement outlier-detection algorithms that can be fine-tuned for a particular set of image data by use of a number of adjustable parameters. This software has been used to construct a mosaic of the Spitzer Infrared Array Camera Shallow Survey, which comprises more than 17,000 exposures in four wavelength bands from 3.6 to 8 m and spans a solid angle of about 9 square degrees. When this software was executed on 32 nodes of the 1,024-processor Cosmos cluster computer at NASA s Jet Propulsion Laboratory, a speedup of 8.3 was achieved over the serial version of MOPEX. The performance is expected to improve dramatically once a true parallel file system is installed on Cosmos.

The Stellar Populations of Two Ultra-diffuse Galaxies from Optical and Near-infrared Photometry

Science.gov (United States)

Pandya, Viraj; Romanowsky, Aaron J.; Laine, Seppo; Brodie, Jean P.; Johnson, Benjamin D.; Glaccum, William; Villaume, Alexa; Cuillandre, Jean-Charles; Gwyn, Stephen; Krick, Jessica; Lasker, Ronald; Martín-Navarro, Ignacio; Martinez-Delgado, David; van Dokkum, Pieter

2018-05-01

We present observational constraints on the stellar populations of two ultra-diffuse galaxies (UDGs) using optical through near-infrared (NIR) spectral energy distribution (SED) fitting. Our analysis is enabled by new Spitzer-IRAC 3.6 and 4.5 μm imaging, archival optical imaging, and the prospector fully Bayesian SED fitting framework. Our sample contains one field UDG (DGSAT I), one Virgo cluster UDG (VCC 1287), and one Virgo cluster dwarf elliptical for comparison (VCC 1122). We find that the optical–NIR colors of the three galaxies are significantly different from each other. We infer that VCC 1287 has an old (≳7.7 Gyr) and surprisingly metal-poor ([Z/Z ⊙] ≲ ‑1.0) stellar population, even after marginalizing over uncertainties on diffuse interstellar dust. In contrast, the field UDG DGSAT I shows evidence of being younger than the Virgo UDG, with an extended star formation history and an age posterior extending down to ∼3 Gyr. The stellar metallicity of DGSAT I is sub-solar but higher than that of the Virgo UDG, with [Z/{Z}ȯ ]=-{0.63}-0.62+0.35; in the case of exactly zero diffuse interstellar dust, DGSAT I may even have solar metallicity. With VCC 1287 and several Coma UDGs, a general picture is emerging where cluster UDGs may be “failed” galaxies, but the field UDG DGSAT I seems more consistent with a stellar feedback-induced expansion scenario. In the future, our approach can be applied to a large and diverse sample of UDGs down to faint surface brightness limits, with the goal of constraining their stellar ages, stellar metallicities, and circumstellar and diffuse interstellar dust content.

Spitzer - Hot & Colorful Student Activities

Science.gov (United States)

McDonald, D.; Rebull, L. M.; DeWolf, C.; Guastella, P.; Johnson, C. H.; Schaefers, J.; Spuck, T.; McDonald, J. G., III; DeWolf, T.; Brock, S.; Boerma, J.; Bemis, G.; Paulsen, K.; Yueh, N.; Peter, A.; Wassmer, W.; Haber, R.; Scaramucci, A.; Butchart, J.; Holcomb, A.; Karns, B.; Kennedy, S.; Siegel, R.; Weiser, S.

2009-01-01

In this poster, we present the results of several activities developed for the general science student to explore infrared light. The first activity involved measuring infrared radiation using an updated version of Newton's experiment of splitting white light and finding IR radiation. The second used Leslie's cube to allow students to observe different radiators, while the third used a modern infrared thermometer to measure and identify IR sources in an enclosed box. The last activity involved students making false-color images from narrow-band filter images from data sets from Spitzer Space Telescope, STScI Digitized Sky Survey and other sources. Using computer programs like Adobe Photoshop and free software such as ds9, Spot and Leopard, poster-like images were created by the students. This research is funded by the Spitzer Science Center (SSC) and the National Optical Astronomy Observatory (NOAO). Please see our companion poster, Johnson et al., on the science aspect of this program, and another poster on the educational aspects, Guastella et al.

The Size Distribution of Very Small Near Earth Objects As Measured by Warm Spitzer

NARCIS (Netherlands)

Trilling, David E.; Hora, J.; Burt, B.; Delbo, M.; Emery, J.; Fazio, G.; Fuentes, C.; Harris, A.; Mueller, M.; Mommert, M.; Smith, H.

2013-01-01

We have carried out a pilot search for Near Earth Objects (NEOs) with 84 hours of Warm Spitzer time in April, 2013. Results are obtained through a multi-step process: implanting synthetic objects in the Spitzer data stream; processing the Spitzer data; linking non-sidereal sources to form plausible

SPITZER OBSERVATIONS OF GJ 3470 b: A VERY LOW-DENSITY NEPTUNE-SIZE PLANET ORBITING A METAL-RICH M DWARF

International Nuclear Information System (INIS)

Demory, Brice-Olivier; Seager, Sara; Torres, Guillermo; Neves, Vasco; Santos, Nuno; Rogers, Leslie; Gillon, Michaël; Horch, Elliott; Sullivan, Peter; Bonfils, Xavier; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Mayor, Michel; Udry, Stephane; Smalley, Barry

2013-01-01

We present Spitzer/IRAC 4.5 μm transit photometry of GJ 3470 b, a Neptune-size planet orbiting an M1.5 dwarf star with a 3.3 day period recently discovered in the course of the HARPS M-dwarf survey. We refine the stellar parameters by employing purely empirical mass-luminosity and surface brightness relations constrained by our updated value for the mean stellar density, and additional information from new near-infrared spectroscopic observations. We derive a stellar mass of M * = 0.539 +0.047 -0.043 M sun and a radius of R * = 0.568 +0.037 -0.031 R sun . We determine the host star of GJ 3470 b to be metal-rich, with a metallicity of [Fe/H] = +0.20 ± 0.10 and an effective temperature of T eff = 3600 ± 100 K. The revised stellar parameters yield a planetary radius R p = 4.83 -0.21 +0.22 R ⊕ that is 13% larger than the value previously reported in the literature. We find a planetary mass M p = 13.9 +1.5 -1.4 M ⊕ that translates to a very low planetary density, ρ p = 0.72 +0.13 -0.12 g cm –3 , which is 33% smaller than the original value. With a mean density half of that of GJ 436 b, GJ 3470 b is an example of a very low-density low-mass planet, similar to Kepler-11 d, Kepler-11 e, and Kepler-18 c, but orbiting a much brighter nearby star that is more conducive to follow-up studies.

Spitzer secondary eclipses of Qatar-1b

Science.gov (United States)

Garhart, Emily; Deming, Drake; Mandell, Avi; Knutson, Heather; Fortney, Jonathan J.

2018-02-01

Aims: Previous secondary eclipse observations of the hot Jupiter Qatar-1b in the Ks band suggest that it may have an unusually high day side temperature, indicative of minimal heat redistribution. There have also been indications that the orbit may be slightly eccentric, possibly forced by another planet in the system. We investigate the day side temperature and orbital eccentricity using secondary eclipse observations with Spitzer. Methods: We observed the secondary eclipse with Spitzer/IRAC in subarray mode, in both 3.6 and 4.5 μm wavelengths. We used pixel-level decorrelation to correct for Spitzer's intra-pixel sensitivity variations and thereby obtain accurate eclipse depths and central phases. Results: Our 3.6 μm eclipse depth is 0.149 ± 0.051% and the 4.5 μm depth is 0.273 ± 0.049%. Fitting a blackbody planet to our data and two recent Ks band eclipse depths indicates a brightness temperature of 1506 ± 71 K. Comparison to model atmospheres for the planet indicates that its degree of longitudinal heat redistribution is intermediate between fully uniform and day-side only. The day side temperature of the planet is unlikely to be as high (1885 K) as indicated by the ground-based eclipses in the Ks band, unless the planet's emergent spectrum deviates strongly from model atmosphere predictions. The average central phase for our Spitzer eclipses is 0.4984 ± 0.0017, yielding e cos ω = -0.0028 ± 0.0027. Our results are consistent with a circular orbit, and we constrain e cos ω much more strongly than has been possible with previous observations. Tables of the lightcurve data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A55

Spitzer observations of dust emission from H II regions in the Large Magellanic Cloud

Energy Technology Data Exchange (ETDEWEB)

Stephens, Ian W. [Now at Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA. (United States); Evans, Jessica Marie; Xue, Rui; Chu, You-Hua; Gruendl, Robert A.; Segura-Cox, Dominique M., E-mail: ianws@bu.edu [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

2014-04-01

Massive stars can alter physical conditions and properties of their ambient interstellar dust grains via radiative heating and shocks. The H II regions in the Large Magellanic Cloud (LMC) offer ideal sites to study the stellar energy feedback effects on dust because stars can be resolved, and the galaxy's nearly face-on orientation allows us to unambiguously associate H II regions with their ionizing massive stars. The Spitzer Space Telescope survey of the LMC provides multi-wavelength (3.6-160 μm) photometric data of all H II regions. To investigate the evolution of dust properties around massive stars, we have analyzed spatially resolved IR dust emission from two classical H II regions (N63 and N180) and two simple superbubbles (N70 and N144) in the LMC. We produce photometric spectral energy distributions (SEDs) of numerous small subregions for each region based on its stellar distributions and nebular morphologies. We use DustEM dust emission model fits to characterize the dust properties. Color-color diagrams and model fits are compared with the radiation field (estimated from photometric and spectroscopic surveys). Strong radial variations of SEDs can be seen throughout the regions, reflecting the available radiative heating. Emission from very small grains drastically increases at locations where the radiation field is the highest, while polycyclic aromatic hydrocarbons (PAHs) appear to be destroyed. PAH emission is the strongest in the presence of molecular clouds, provided that the radiation field is low.

Soap, A Free-code Tool To Study The Impact Of Stellar Activity

Science.gov (United States)

Boisse, Isabelle; Bonfils, X.; Santos, N.

2011-09-01

Dark spots and bright plages are present on the surface of all stars, even low-active stars (like the Sun in its low-active phase). Their appearance and disappearance on the stellar photosphere, combined with the stellar rotation, may lead to errors and uncertainties in the characterization of planets both in radial velocimetry and photometry. SOAP is a tool offered to the community (Boisse, Bonfils and Santos, in prep.) that enables to simulate spots and plages on rotating stars and computes their impact on RV and photometric measurements. This talk will discuss the challenges related to the knowledge of stellar activity for the next decade: detect telluric planets in the habitable zone of their stars (from G to M dwarfs), understand the activity in the low-mass end of M dwarf (on which will focus future projects like Elektra, SPIRou or CARMENES), limitation to the sum of different transit observations in order to characterize the atmospheric components (from the ground or with Spitzer, JWST), planets around young stars,... and how this can be simulated with SOAP in order to search for indices and corrections. IB and NCS would like to thank the support by the European Research Council/European Community under the FP7 through a Starting Grant, as well from Fundacao para a Ciencia e a Tecnologia (FCT), Portugal.

Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

Energy Technology Data Exchange (ETDEWEB)

Wit, Julien de [Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Lewis, Nikole K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Knutson, Heather A.; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Fuller, Jim [TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125 (United States); Antoci, Victoria [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Fulton, Benjamin J. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Laughlin, Gregory [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Deming, Drake [Department of Astronomy, University of Maryland at College Park, College Park, MD 20742 (United States); Shporer, Avi [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91009 (United States); Cowan, Nicolas B. [Department of Physics, Department of Earth and Planetary Sciences, McGill University, 3550 rue University, Montreal, QC H3A 2A7 (Canada); Agol, Eric [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Burrows, Adam S. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Fortney, Jonathan J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Langton, Jonathan [Department of Physics, Principia College, Elsah, IL 62028 (United States); Showman, Adam P. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)

2017-02-20

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μ m observations with the Spitzer Space Telescope . The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μ m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.

SOAP: A Tool for the Fast Computation of Photometry and Radial Velocity Induced by Stellar Spots

Science.gov (United States)

Boisse, I.; Bonfils, X.; Santos, N. C.; Figueira, P.

2013-04-01

Dark spots and bright plages are present on the surface of dwarf stars from spectral types F to M, even in their low-active phase (like the Sun). Their appearance and disappearance on the stellar photosphere, combined with the stellar rotation, may lead to errors and uncertainties in the characterization of planets both in radial velocity (RV) and photometry. Spot Oscillation and Planet (SOAP) is a tool offered to the community that enables to simulate spots and plages on rotating stars and computes their impact on RV and photometric measurements. This tool will help to understand the challenges related to the knowledge of stellar activity for the next decade: detect telluric planets in the habitable zone of their stars (from G to M dwarfs), understand the activity in the low-mass end of M dwarf (on which future projects, like SPIRou or CARMENES, will focus), limitation to the characterization of the exoplanetary atmosphere (from the ground or with Spitzer, JWST), search for planets around young stars. These can be simulated with SOAP in order to search for indices and corrections to the effect of activity.

SPITZER OBSERVATIONS OF YOUNG RED QUASARS

International Nuclear Information System (INIS)

Urrutia, Tanya; Lacy, Mark; Spoon, Henrik; Glikman, Eilat; Petric, Andreea; Schulz, Bernhard

2012-01-01

We present mid-infrared spectra and photometry of 13 redshift 0.4 < z < 1 dust reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic active galactic nucleus (AGN) luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from Hubble Space Telescope imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass-bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example, in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the [O III]5007 Å emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample.

THE SPITZER INFRARED SPECTROGRAPH DEBRIS DISK CATALOG. I. CONTINUUM ANALYSIS OF UNRESOLVED TARGETS

Energy Technology Data Exchange (ETDEWEB)

Chen, Christine H. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Mittal, Tushar [Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720-4767 (United States); Kuchner, Marc [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771 (United States); Forrest, William J.; Watson, Dan M. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Lisse, Carey M. [Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States); Manoj, P. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005 (India); Sargent, Benjamin A., E-mail: cchen@stsci.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2014-04-01

During the Spitzer Space Telescope cryogenic mission, Guaranteed Time Observers, Legacy Teams, and General Observers obtained Infrared Spectrograph (IRS) observations of hundreds of debris disk candidates. We calibrated the spectra of 571 candidates, including 64 new IRAS and Multiband Imaging Photometer for Spitzer (MIPS) debris disks candidates, modeled their stellar photospheres, and produced a catalog of excess spectra for unresolved debris disks. For 499 targets with IRS excess but without strong spectral features (and a subset of 420 targets with additional MIPS 70 μm observations), we modeled the IRS (and MIPS data) assuming that the dust thermal emission was well-described using either a one- or two-temperature blackbody model. We calculated the probability for each model and computed the average probability to select among models. We found that the spectral energy distributions for the majority of objects (∼66%) were better described using a two-temperature model with warm (T {sub gr} ∼ 100-500 K) and cold (T {sub gr} ∼ 50-150 K) dust populations analogous to zodiacal and Kuiper Belt dust, suggesting that planetary systems are common in debris disks and zodiacal dust is common around host stars with ages up to ∼1 Gyr. We found that younger stars generally have disks with larger fractional infrared luminosities and higher grain temperatures and that higher-mass stars have disks with higher grain temperatures. We show that the increasing distance of dust around debris disks is inconsistent with self-stirred disk models, expected if these systems possess planets at 30-150 AU. Finally, we illustrate how observations of debris disks may be used to constrain the radial dependence of material in the minimum mass solar nebula.

Spitzer spectral line mapping of the HH211 outflow

DEFF Research Database (Denmark)

Dionatos, Odyssefs; Nisini, Brunella; Cabrit, Sylvie

2010-01-01

of emission line diagnostics and an existing grid of molecular shock models. The physical properties of the warm gas are compared against other molecular jet tracers and to the results of a similar study towards the L1448-C outflow. Results: We have detected and mapped the v=0-0 S(0) - S(7) H2 lines and fine...... compared to solar abundances by a factor ~10-50. Conclusions: Spitzer spectral mapping observations reveal for the first time a cool H$_2$ component towards the CO jet of HH211 consistent with the CO material being fully molecular and warm at ~ 300 K. The maps also reveal for the first time the existence...... uncertainties on jet speed and shock conditions are too large for a definite conclusion....

Growth of a Massive Young Stellar Object Fed by a Gas Flow from a Companion Gas Clump

Energy Technology Data Exchange (ETDEWEB)

Chen, Xi; Shen, Zhiqiang [Shanghai Astronomical Observatories, Chinese Academy of Science, Nandan Rd. 80, Shanghai (China); Ren, Zhiyuan [National Astronomical Observatories, Chinese Academy of Science, Chaoyang District Datun Rd. A20, Beijing (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Rd., Nanjing, Jiangsu 210093 (China)

2017-02-01

We present a Submillimeter Array (SMA) observation toward the young massive double-core system G350.69-0.49. This system consists of a northeast (NE) diffuse gas bubble and a southwest (SW) massive young stellar object (MYSO), both clearly seen in the Spitzer images. The SMA observations reveal a gas flow between the NE bubble and the SW MYSO in a broad velocity range from 5 to 30 km s{sup −1} with respect to the system velocity. The gas flow is well confined within the interval between the two objects and traces a significant mass transfer from the NE gas bubble to the SW massive core. The transfer flow can supply the material accreted onto the SW MYSO at a rate of 4.2×10{sup −4} M{sub ⊙} yr{sup −1}. The whole system therefore suggests a mode for the mass growth in the MYSO from a gas transfer flow launched from its companion gas clump, despite the driving mechanism of the transfer flow not being fully determined from the current data.

SPITZER SPACE TELESCOPE MID-IR LIGHT CURVES OF NEPTUNE

Energy Technology Data Exchange (ETDEWEB)

Stauffer, John; Rebull, Luisa; Carey, Sean J.; Krick, Jessica; Ingalls, James G.; Lowrance, Patrick; Glaccum, William [Spitzer Science Center (SSC), California Institute of Technology, Pasadena, CA 91125 (United States); Marley, Mark S. [NASA Ames Research Center, Space Sciences and Astrobiology Division, MS245-3, Moffett Field, CA 94035 (United States); Gizis, John E. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Simon, Amy A. [NASA Goddard Space Flight Center, Solar System Exploration Division (690.0), 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Wong, Michael H. [University of California, Department of Astronomy, Berkeley CA 94720-3411 (United States)

2016-11-01

We have used the Spitzer Space Telescope in 2016 February to obtain high cadence, high signal-to-noise, 17 hr duration light curves of Neptune at 3.6 and 4.5 μ m. The light curve duration was chosen to correspond to the rotation period of Neptune. Both light curves are slowly varying with time, with full amplitudes of 1.1 mag at 3.6 μ m and 0.6 mag at 4.5 μ m. We have also extracted sparsely sampled 18 hr light curves of Neptune at W1 (3.4 μ m) and W2 (4.6 μ m) from the Wide-feld Infrared Survey Explorer ( WISE )/ NEOWISE archive at six epochs in 2010–2015. These light curves all show similar shapes and amplitudes compared to the Spitzer light curves but with considerable variation from epoch to epoch. These amplitudes are much larger than those observed with Kepler / K 2 in the visible (amplitude ∼0.02 mag) or at 845 nm with the Hubble Space Telescope ( HST ) in 2015 and at 763 nm in 2016 (amplitude ∼0.2 mag). We interpret the Spitzer and WISE light curves as arising entirely from reflected solar photons, from higher levels in Neptune’s atmosphere than for K 2. Methane gas is the dominant opacity source in Neptune’s atmosphere, and methane absorption bands are present in the HST 763 and 845 nm, WISE W1, and Spitzer 3.6 μ m filters.

SPITZER OBSERVATIONS OF GJ 3470 b: A VERY LOW-DENSITY NEPTUNE-SIZE PLANET ORBITING A METAL-RICH M DWARF

Energy Technology Data Exchange (ETDEWEB)

Demory, Brice-Olivier; Seager, Sara [Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 (United States); Torres, Guillermo [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Neves, Vasco; Santos, Nuno [Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Rogers, Leslie [Department of Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Gillon, Michaeel [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout, 17, Bat. B5C, Liege 1 (Belgium); Horch, Elliott [Department of Physics, 501 Crescent Street, Southern Connecticut State University, New Haven, CT 06515 (United States); Sullivan, Peter [Department of Physics and Kavli Institute for Astrophysics and Space Research, MIT, 77 Massachusetts Avenue, Cambridge, MA 02138 (United States); Bonfils, Xavier; Delfosse, Xavier; Forveille, Thierry [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Lovis, Christophe; Mayor, Michel; Udry, Stephane [Observatoire de Geneve, Universite de Geneve, 51 ch. des Maillettes, CH-1290 Versoix (Switzerland); Smalley, Barry, E-mail: demory@mit.edu [Astrophysics Group, Keele University, Staffordshire, ST55BG (United Kingdom)

2013-05-10

We present Spitzer/IRAC 4.5 {mu}m transit photometry of GJ 3470 b, a Neptune-size planet orbiting an M1.5 dwarf star with a 3.3 day period recently discovered in the course of the HARPS M-dwarf survey. We refine the stellar parameters by employing purely empirical mass-luminosity and surface brightness relations constrained by our updated value for the mean stellar density, and additional information from new near-infrared spectroscopic observations. We derive a stellar mass of M{sub *}= 0.539{sup +0.047}{sub -0.043} M{sub sun} and a radius of R{sub *}= 0.568{sup +0.037}{sub -0.031} R{sub sun}. We determine the host star of GJ 3470 b to be metal-rich, with a metallicity of [Fe/H] = +0.20 {+-} 0.10 and an effective temperature of T{sub eff} = 3600 {+-} 100 K. The revised stellar parameters yield a planetary radius R{sub p}= 4.83{sub -0.21}{sup +0.22} R{sub Circled-Plus} that is 13% larger than the value previously reported in the literature. We find a planetary mass M{sub p}= 13.9{sup +1.5}{sub -1.4} M{sub Circled-Plus} that translates to a very low planetary density, {rho}{sub p}= 0.72{sup +0.13}{sub -0.12} g cm{sup -3}, which is 33% smaller than the original value. With a mean density half of that of GJ 436 b, GJ 3470 b is an example of a very low-density low-mass planet, similar to Kepler-11 d, Kepler-11 e, and Kepler-18 c, but orbiting a much brighter nearby star that is more conducive to follow-up studies.

The SAGE-Spec Spitzer Legacy program: the life-cycle of dust and gas in the Large Magellanic Cloud. Point source classification - III

Science.gov (United States)

Jones, O. C.; Woods, P. M.; Kemper, F.; Kraemer, K. E.; Sloan, G. C.; Srinivasan, S.; Oliveira, J. M.; van Loon, J. Th.; Boyer, M. L.; Sargent, B. A.; McDonald, I.; Meixner, M.; Zijlstra, A. A.; Ruffle, P. M. E.; Lagadec, E.; Pauly, T.; Sewiło, M.; Clayton, G. C.; Volk, K.

2017-09-01

The Infrared Spectrograph (IRS) on the Spitzer Space Telescope observed nearly 800 point sources in the Large Magellanic Cloud (LMC), taking over 1000 spectra. 197 of these targets were observed as part of the SAGE-Spec Spitzer Legacy program; the remainder are from a variety of different calibration, guaranteed time and open time projects. We classify these point sources into types according to their infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, using a decision-tree classification method. We then refine the classification using supplementary information from the astrophysical literature. We find that our IRS sample is comprised substantially of YSO and H II regions, post-main-sequence low-mass stars: (post-)asymptotic giant branch stars and planetary nebulae and massive stars including several rare evolutionary types. Two supernova remnants, a nova and several background galaxies were also observed. We use these classifications to improve our understanding of the stellar populations in the LMC, study the composition and characteristics of dust species in a variety of LMC objects, and to verify the photometric classification methods used by mid-IR surveys. We discover that some widely used catalogues of objects contain considerable contamination and others are missing sources in our sample.

THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

International Nuclear Information System (INIS)

Megeath, S. T.; Kryukova, E.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Myers, P. C.; Fazio, G. G.; Allen, L. E.; Flaherty, K.; Hartmann, L.; Pipher, J. L.; Stauffer, J.; Young, E. T.

2016-01-01

We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc −2 to over 10,000 pc −2 , with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc −2 , we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions

THE SPITZER SURVEY OF INTERSTELLAR CLOUDS IN THE GOULD BELT. III. A MULTI-WAVELENGTH VIEW OF CORONA AUSTRALIS

International Nuclear Information System (INIS)

Peterson, Dawn E.; Bourke, Tyler L.; Forbrich, Jan; Patten, Brian M.; Caratti o Garatti, Alessio; Gutermuth, Robert A.; Joergensen, Jes K.; Allen, Lori E.; Dunham, Michael M.; Harvey, Paul M.; Evans, Neal J.; MerIn, Bruno; Chapman, Nicholas L.; Cieza, Lucas A.; Huard, Tracy L.; Knez, Claudia; Prager, Brian

2011-01-01

We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg 2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as sources distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star formation rate is computed to be 12 M sun Myr -1 , similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc -2 . In addition, we analyze outflows and jets in CrA by means of new CO and H 2 data. We present 1.3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H 2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a CO(2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, which is east-west oriented and originates in the SMA 2 region and likely driven by SMA 2 or IRS 7A.

SPITZER IRAC SECONDARY ECLIPSE PHOTOMETRY OF THE TRANSITING EXTRASOLAR PLANET HAT-P-1b

International Nuclear Information System (INIS)

Todorov, Kamen; Deming, Drake; Harrington, Jospeph; Stevenson, Kevin B.; Bowman, William C.; Nymeyer, Sarah; Fortney, Jonathan J.; Bakos, Gaspar A.

2010-01-01

We report Spitzer/IRAC photometry of the transiting giant exoplanet HAT-P-1b during its secondary eclipse. This planet lies near the postulated boundary between the pM and pL-class of hot Jupiters, and is important as a test of models for temperature inversions in hot Jupiter atmospheres. We derive eclipse depths for HAT-P-1b, in units of the stellar flux, that are: 0.080% ± 0.008% [3.6 μm], 0.135% ± 0.022% [4.5 μm], 0.203% ± 0.031% [5.8 μm], and 0.238% ± 0.040% [8.0 μm]. These values are best fit using an atmosphere with a modest temperature inversion, intermediate between the archetype inverted atmosphere (HD 209458b) and a model without an inversion. The observations also suggest that this planet is radiating a large fraction of the available stellar irradiance on its dayside, with little available for redistribution by circulation. This planet has sometimes been speculated to be inflated by tidal dissipation, based on its large radius in discovery observations, and on a non-zero orbital eccentricity allowed by the radial velocity data. The timing of the secondary eclipse is very sensitive to orbital eccentricity, and we find that the central phase of the eclipse is 0.4999 ± 0.0005. The difference between the expected and observed phase indicates that the orbit is close to circular, with a 3σ limit of |e cos ω| < 0.002.

A SPITZER CENSUS OF STAR FORMATION ACTIVITY IN THE PIPE NEBULA

International Nuclear Information System (INIS)

Forbrich, Jan; Lada, Charles J.; Muench, August A.; Alves, Joao; Lombardi, Marco

2009-01-01

The Pipe Nebula, a large nearby molecular cloud, lacks obvious signposts of star formation in all but one of more than 130 dust extinction cores that have been identified within it. In order to quantitatively determine the current level of star formation activity in the Pipe Nebula, we analyzed 13 deg 2 of sensitive mid-infrared maps of the entire cloud, obtained with the Multiband Imaging Photometer for Spitzer at wavelengths of 24 μm and 70 μm, to search for candidate young stellar objects (YSOs) in the high-extinction regions. We argue that our search is complete for class I and typical class II YSOs with luminosities of L bol ∼ 0.2 L sun and greater. We find only 18 candidate YSOs in the high-extinction regions of the entire Pipe cloud. Twelve of these sources are previously known members of a small cluster associated with Barnard 59, the largest and most massive dense core in the cloud. With only six candidate class I and class II YSOs detected toward extinction cores outside of this cluster, our findings emphatically confirm the notion of an extremely low level of star formation activity in the Pipe Nebula. The resulting star formation efficiency for the entire cloud mass is only ∼0.06%.

Visible photometry of NEOs in support of a Warm Spitzer program

Science.gov (United States)

Trilling, David E.; Jones, Sarah; Penprase, Bryan; Emery, Josh; Harris, Alan; Spahr, Tim; Delbo, Marco

2009-08-01

Near Earth Objects (NEOs) may act as dynamical and compositional tracers of the history of near-Earth space. However, despite their scientific importance, key characteristics of the NEO population -- such as the size distribution, mix of albedos and mineralogies, and contributions from so-called dead or dormant comets -- remain largely unexplored; some 99% of all presently known NEOs are essentially uncharacterized. We have been awarded 500 hours of Warm Spitzer time to study some 700 NEOs. The Spitzer data will allow us to measure thermal fluxes and, in combination with optical data, derive albedos and diameters for a large fraction of all known NEOs. Remarkably, the primary uncertainty in our Spitzer results will derive from a lack of good optical photometry for our targets. Fortunately, our targets are generally bright, and obtaining good V band measurements of them requires only a modest amount of time on modest aperture telescopes. We propose here for 36 hours of SMARTS 1.3-m time or 54 hours of SMARTS 0.9-m time to obtain visible photometry of the 72 southern moderately bright ``B'' semester targets in our Warm Spitzer program. These program is ideal for queue/service observing because each observation requires only ~30 minutes and our targets are all over the sky.

The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer

Energy Technology Data Exchange (ETDEWEB)

Agol, E.; /Washington U., Seattle, Astron. Dept. /Santa Barbara, KITP /UC, Santa Barbara; Cowan, Nicolas B.; /Washington U., Seattle, Astron. Dept.; Knutson, Heather A.; /UC, Berkeley, Astron. Dept.; Deming, Drake; /NASA, Goddard; Steffen, Jason H.; /Fermilab; Henry, Gregory W.; /Tennessee State U.; Charbonneau, David; /Harvard-Smithsonian Ctr. Astrophys.

2010-07-01

We present observations of six transits and six eclipses of the transiting planet system HD 189733 taken with the Spitzer Space Telescope IRAC camera at 8 microns, as well as a re-analysis of previously published data. We use several novel techniques in our data analysis, the most important of which is a new correction for the detector 'ramp' variation with a double-exponential function which performs better and is a better physical model for this detector variation. Our main scientific findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hours before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, which is in good agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 seconds, which is mostly accounted for by a 31 second light travel time delay and 33 second delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot

Brown dwarf distances and atmospheres: Spitzer Parallaxes and the Keck/NIRSPEC upgrade

Science.gov (United States)

Martin, Emily C.

2018-01-01

Advances in infrared technology have been essential towards improving our understanding of the solar neighborhood, revealing a large population of brown dwarfs, which span the mass regime between planets and stars. My thesis combines near-infrared (NIR) spectroscopic and astrometric analysis of nearby low-mass stars and brown dwarfs with instrumentation work to upgrade the NIRSPEC instrument for the Keck II Telescope. I will present results from a program using Spitzer/IRAC data to measure precise locations and distances to 22 of the coldest and closest brown dwarfs. These distances allow us to constrain absolute physical properties, such as mass, radius, and age, of free-floating planetary-mass objects through comparison to atmospheric and evolutionary models. NIR spectroscopy combined with the Spitzer photometry reveals a detailed look into the atmospheres of brown dwarfs and gaseous extrasolar planets. Additionally, I will discuss the improvements we are making to the NIRSPEC instrument at Keck. NIRSPEC is a NIR echelle spectrograph, capable of R~2000 and R~25,000 observations in the 1-5 μm range. As part of the upgrade, I performed detector characterization, optical design of a new slit-viewing camera, mechanical testing, and electronics design. NIRSPEC’s increased efficiency will allow us to obtain moderate- and high-resolution NIR spectra of objects up to a magnitude fainter than the current NIRSPEC design. Finally, I will demonstrate the utility of a NIR laser frequency comb as a high-resolution calibrator. This new technology will revolutionize precision radial velocity measurements in the coming decade.

Emerging Massive Star Clusters Revealed: High-Resolution Imaging of NGC 4449 from the Radio to the Ultraviolet

Science.gov (United States)

Reines, Amy E.; Johnson, Kelsey E.; Goss, W. M.

2008-06-01

We present a multi-wavelength study of embedded massive clusters in the nearby (3.9 Mpc) starburst galaxy NGC 4449 in an effort to uncover the earliest phases of massive cluster evolution. By combining high-resolution imaging from the radio to the ultraviolet, we reveal these clusters to be in the process of emerging from their gaseous and dusty birth cocoons. We use Very Large Array (VLA) observations at centimeter wavelengths to identify young clusters surrounded by ultra-dense H II regions, detectable via their production of thermal free-free radio continuum. Ultraviolet, optical and infrared observations are obtained from the Hubble and Spitzer Space Telescope archives for comparison. We detect 39 compact radio sources toward NGC 4449 at 3.6 cm using the highest resolution (1farcs3) and sensitivity (~12 μJy) VLA image of the galaxy to date. We reliably identify 13 thermal radio sources and derive their physical properties using both nebular emission from the H II regions and spectral energy distribution fitting to the stellar continuum. These radio-detected clusters have ages lsim5 Myr and stellar masses of order 104 M sun. The measured extinctions are quite low: 12 of the 13 thermal radio sources have A V lsim 1.5, while the most obscured source has A V ≈ 4.3. By combining results from the nebular and stellar emission, we find an I-band excess that is anti-correlated with cluster age and an apparent mass-age correlation. Additionally, we find evidence that local processes such as supernovae and stellar winds likely play an important role in triggering the current bursts of star formation within NGC 4449.

Spitzer Observations of GRB Hosts: A Legacy Approach

Science.gov (United States)

Perley, Daniel; Tanvir, Nial; Hjorth, Jens; Berger, Edo; Laskar, Tanmoy; Michalowski, Michal; Chary, Ranga-Ram; Fynbo, Johan; Levan, Andrew

2012-09-01

The host galaxies of long-duration GRBs are drawn from uniquely broad range of luminosities and redshifts. Thus they offer the possibility of studying the evolution of star-forming galaxies without the limitations of other luminosity-selected samples, which typically are increasingly biased towards the most massive systems at higher redshift. However, reaping the full benefits of this potential requires careful attention to the selection biases affecting host identification. To this end, we propose observations of a Legacy sample of 70 GRB host galaxies (an additional 70 have already been observed by Spitzer), in order to constrain the mass and luminosity function in GRB-selected galaxies at high redshift, including its dependence on redshift and on properties of the afterglow. Crucially, and unlike previous Spitzer surveys, this sample is carefully designed to be uniform and free of optical selection biases that have caused previous surveys to systematically under-represent the role of luminous, massive hosts. We also propose to extend to larger, more powerfully constraining samples the study of two science areas where Spitzer observations have recently shown spectacular success: the hosts of dust-obscured GRBs (which promise to further our understanding of the connection between GRBs and star-formation in the most luminous galaxies), and the evolution of the mass-metallicity relation at z>2 (for which GRB host observations provide particularly powerful constraints on high-z chemical evolution).

IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

International Nuclear Information System (INIS)

Günther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L.; Gutermuth, R. A.; Allen, L.; Megeath, S. T.; Pipher, J. L.

2012-01-01

IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N H /A K ratio compared with the diffuse interstellar medium.

IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

Energy Technology Data Exchange (ETDEWEB)

Guenther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Allen, L. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Megeath, S. T. [Department of Physics and Astronomy, MS-113, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Pipher, J. L., E-mail: hguenther@cfa.harvard.edu [Department of Physics and Astronomy, University of Rochester, 500 Wilson Boulevard, Rochester, NY 14627 (United States)

2012-10-01

IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N{sub H}/A{sub K} ratio compared with the diffuse interstellar medium.

DEBRIS DISKS AROUND SOLAR-TYPE STARS: OBSERVATIONS OF THE PLEIADES WITH THE SPITZER SPACE TELESCOPE

International Nuclear Information System (INIS)

Sierchio, J. M.; Rieke, G. H.; Su, K. Y. L.; Plavchan, P.; Stauffer, J. R.; Gorlova, N. I.

2010-01-01

We present Spitzer MIPS observations at 24 μm of 37 solar-type stars in the Pleiades and combine them with previous observations to obtain a sample of 71 stars. We report that 23 stars, or 32% ± 6.8%, have excesses at 24 μm at least 10% above their photospheric emission. We compare our results with studies of debris disks in other open clusters and with a study of A stars to show that debris disks around solar-type stars at 115 Myr occur at nearly the same rate as around A-type stars. We analyze the effects of binarity and X-ray activity on the excess flux. Stars with warm excesses tend not to be in equal-mass binary systems, possibly due to clearing of planetesimals by binary companions in similar orbits. We find that the apparent anti-correlations in the incidence of excess and both the rate of stellar rotation and also the level of activity as judged by X-ray emission are statistically weak.

SPITZER OBSERVATIONS OF PASSIVE AND STAR-FORMING EARLY-TYPE GALAXIES: AN INFRARED COLOR-COLOR SEQUENCE

International Nuclear Information System (INIS)

Temi, Pasquale; Brighenti, Fabrizio; Mathews, William G.

2009-01-01

We describe the infrared properties of a large sample of early-type galaxies, comparing data from the Spitzer archive with Ks-band emission from the Two Micron All Sky Survey. While most representations of this data result in correlations with large scatter, we find a remarkably tight relation among colors formed by ratios of luminosities in Spitzer-Multiband Imaging Photometer bands (24, 70, and 160 μm) and the Ks band. Remarkably, this correlation among E and S0 galaxies follows that of nearby normal galaxies of all morphological types. In particular, the tight infrared color-color correlation for S0 galaxies alone follows that of the entire Hubble sequence of normal galaxies, roughly in order of galaxy type from ellipticals to spirals to irregulars. The specific star formation rate (SFR) of S0 galaxies estimated from the 24 μm luminosity increases with decreasing K-band luminosity (or stellar mass) from essentially zero, as with most massive ellipticals, to rates typical of irregular galaxies. Moreover, the luminosities of the many infrared-luminous S0 galaxies can significantly exceed those of the most luminous (presumably post-merger) E galaxies. SFRs in the most infrared-luminous S0 galaxies approach 1-10 solar masses per year. Consistently, with this picture we find that while most early-type galaxies populate an infrared red sequence, about 24% of the objects (mostly S0s) are in an infrared blue cloud together with late-type galaxies. For those early-type galaxies also observed at radio frequencies, we find that the far-infrared luminosities correlate with the mass of neutral and molecular hydrogen, but the scatter is large. This scatter suggests that the star formation may be intermittent or that similar S0 galaxies with cold gaseous disks of nearly equal mass can have varying radial column density distributions that alter the local and global SFRs.

A LARGE, MASSIVE, ROTATING DISK AROUND AN ISOLATED YOUNG STELLAR OBJECT

International Nuclear Information System (INIS)

Quanz, Sascha P.; Beuther, Henrik; Steinacker, Juergen; Linz, Hendrik; Krause, Oliver; Henning, Thomas; Birkmann, Stephan M.; Zhang Qizhou

2010-01-01

We present multi-wavelength observations and a radiative transfer model of a newly discovered massive circumstellar disk of gas and dust which is one of the largest disks known today. Seen almost edge-on, the disk is resolved in high-resolution near-infrared (NIR) images and appears as a dark lane of high opacity intersecting a bipolar reflection nebula. Based on molecular line observations, we estimate the distance to the object to be 3.5 kpc. This leads to a size for the dark lane of ∼10,500 AU but due to shadowing effects the true disk size could be smaller. In Spitzer/IRAC 3.6 μm images, the elongated shape of the bipolar reflection nebula is still preserved and the bulk of the flux seems to come from disk regions that can be detected due to the slight inclination of the disk. At longer IRAC wavelengths, the flux is mainly coming from the central regions penetrating directly through the dust lane. Interferometric observations of the dust continuum emission at millimeter wavelengths with the Submillimeter Array confirm this finding as the peak of the unresolved millimeter-emission coincides perfectly with the peak of the Spitzer/IRAC 5.8 μm flux and the center of the dark lane seen in the NIR images. Simultaneously acquired CO data reveal a molecular outflow along the northern part of the reflection nebula which seems to be the outflow cavity. An elongated gaseous disk component is also detected and shows signs of rotation. The emission is perpendicular to the molecular outflow and thus parallel to but even more extended than the dark lane in the NIR images. Based on the dust continuum and the CO observations, we estimate a disk mass of up to a few solar masses depending on the underlying assumptions. Whether the disk-like structure is an actual accretion disk or rather a larger-scale flattened envelope or pseudodisk is difficult to discriminate with the current data set. The existence of HCO + /H 13 CO + emission proves the presence of dense gas in the disk

The Spectral Energy Distributions of z ~ 8 Galaxies from the IRAC Ultra Deep Fields: Emission Lines, Stellar Masses, and Specific Star Formation Rates at 650 Myr

Science.gov (United States)

Labbé, I.; Oesch, P. A.; Bouwens, R. J.; Illingworth, G. D.; Magee, D.; González, V.; Carollo, C. M.; Franx, M.; Trenti, M.; van Dokkum, P. G.; Stiavelli, M.

2013-11-01

Using new ultradeep Spitzer/InfraRed Array Camera (IRAC) photometry from the IRAC Ultra Deep Field program, we investigate the stellar populations of a sample of 63 Y-dropout galaxy candidates at z ~ 8, only 650 Myr after the big bang. The sources are selected from HST/ACS+WFC3/IR data over the Hubble Ultra Deep Field (HUDF), two HUDF parallel fields, and wide area data over the CANDELS/GOODS-South. The new Spitzer/IRAC data increase the coverage in [3.6] and [4.5] to ~120h over the HUDF reaching depths of ~28 (AB,1σ). The improved depth and inclusion of brighter candidates result in direct >=3σ InfraRed Array Camera (IRAC) detections of 20/63 sources, of which 11/63 are detected at >=5σ. The average [3.6]-[4.5] colors of IRAC detected galaxies at z ~ 8 are markedly redder than those at z ~ 7, observed only 130 Myr later. The simplest explanation is that we witness strong rest-frame optical emission lines (in particular [O III] λλ4959, 5007 + Hβ) moving through the IRAC bandpasses with redshift. Assuming that the average rest-frame spectrum is the same at both z ~ 7 and z ~ 8 we estimate a rest-frame equivalent width of {W}_{[O\\,\\scriptsize{III}]\\ \\lambda \\lambda 4959,5007+H\\beta }=670^{+260}_{-170} Å contributing 0.56^{+0.16}_{-0.11} mag to the [4.5] filter at z ~ 8. The corresponding {W}_{H\\alpha }=430^{+160}_{-110} Å implies an average specific star formation rate of sSFR=11_{-5}^{+11} Gyr-1 and a stellar population age of 100_{-50}^{+100} Myr. Correcting the spectral energy distribution for the contribution of emission lines lowers the average best-fit stellar masses and mass-to-light ratios by ~3 ×, decreasing the integrated stellar mass density to \\rho ^*(z=8,M_{\\rm{UV}}Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #11563, 9797. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of

A Cometary Bow Shock and Mid-Infrared Emission Variations Revealed in Spitzer Observations of HD 34078 and IC 405

OpenAIRE

France, Kevin; McCandliss, Stephan R.; Lupu, Roxana E.

2006-01-01

We present new infrared observations of the emission/reflection nebula IC 405 obtained with the Spitzer Space Telescope. Infrared images in the four IRAC bands (3.6, 4.5, 5.8, and 8.0 um) and two MIPS bands (24 and 70 um) are complemented by IRS spectroscopy (5-30 um) of two nebular filaments. The IRAC (8.0 um) and MIPS imaging shows evidence of a bow shock associated with the runaway O9.5V star, HD 34078, created by the interaction between the star and nebular material. The ratio of emission...

OPEN CLUSTERS IN THE MILKY WAY OUTER DISK: NEWLY DISCOVERED AND UNSTUDIED CLUSTERS IN THE SPITZER GLIMPSE-360, CYG-X, AND SMOG SURVEYS

International Nuclear Information System (INIS)

Zasowski, G.; Beaton, R. L.; Hamm, K. K.; Majewski, S. R.; Patterson, R. J.; Babler, B.; Churchwell, E.; Meade, M.; Whitney, B. A.; Benjamin, R. A.; Watson, C.

2013-01-01

Open stellar clusters are extremely valuable probes of Galactic structure, star formation, kinematics, and chemical abundance patterns. Near-infrared (NIR) data have enabled the detection of hundreds of clusters hidden from optical surveys, and mid-infrared (MIR) data are poised to offer an even clearer view into the most heavily obscured parts of the Milky Way. We use new MIR images from the Spitzer GLIMPSE-360, Cyg-X, and SMOG surveys to visually identify a large number of open cluster candidates in the outer disk of the Milky Way (65° < l < 265°). Using NIR color-magnitude diagrams, stellar isochrones, and stellar reddening estimates, we derive cluster parameters (metallicity, distance, reddening) for those objects without previous identification and/or parameters in the literature. In total, we present coordinates and sizes of 20 previously unknown open cluster candidates; for 7 of these we also present metallicity, distance, and reddening values. In addition, we provide the first estimates of these values for nine clusters that had been previously cataloged. We compare our cluster sizes and other derived parameters to those in the open cluster catalog of Dias et al. and find strong similarities except for a higher mean reddening for our objects, which signifies our increased detection sensitivity in regions of high extinction. The results of this cluster search and analysis demonstrate the ability of MIR imaging and photometry to augment significantly the current census of open clusters in the Galaxy

On the mid-infrared variability of candidate eruptive variables (exors): A comparison between Spitzer and WISE data

Energy Technology Data Exchange (ETDEWEB)

Antoniucci, S.; Giannini, T.; Li Causi, G.; Lorenzetti, D., E-mail: simone.antoniucci@oa-roma.inaf.it, E-mail: teresa.giannini@oa-roma.inaf.it, E-mail: gianluca.licausi@oa-roma.inaf.it, E-mail: dario.lorenzetti@oa-roma.inaf.it [INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monte Porzio (Italy)

2014-02-10

Aiming to statistically study the variability in the mid-IR of young stellar objects, we have compared the 3.6, 4.5, and 24 μm Spitzer fluxes of 1478 sources belonging to the C2D (Cores to Disks) legacy program with the WISE fluxes at 3.4, 4.6, and 22 μm. From this comparison, we have selected a robust sample of 34 variable sources. Their variations were classified per spectral Class (according to the widely accepted scheme of Class I/flat/II/III protostars), and per star forming region. On average, the number of variable sources decreases with increasing Class and is definitely higher in Perseus and Ophiuchus than in Chamaeleon and Lupus. According to the paradigm Class ≡ Evolution, the photometric variability can be considered to be a feature more pronounced in less evolved protostars, and, as such, related to accretion processes. Moreover, our statistical findings agree with the current knowledge of star formation activity in different regions. The 34 selected variables were further investigated for similarities with known young eruptive variables, namely the EXors. In particular, we analyzed (1) the shape of the spectral energy distribution, (2) the IR excess over the stellar photosphere, (3) magnitude versus color variations, and (4) output parameters of model fitting. This first systematic search for EXors ends up with 11 bona fide candidates that can be considered as suitable targets for monitoring or future investigations.

Young Stars in the Camelopardalis Dust and Molecular Clouds. VI. YSOs Verified by Spitzer and Akari Infrared Photometry

Directory of Open Access Journals (Sweden)

Straižys V.

2010-06-01

Full Text Available Using photometric data of infrared surveys, young stellar object (YSO status is verified for 141 objects selected in our previous papers in the Cassiopeia and Camelopardalis segment of the Milky Way bounded by Galactic coordinates (l, b = (132-158°, ±12°. The area includes the known star- forming regions in the emission nebulae W3, W4 and W5 and the massive YSO AFGL490. Spectral energy distribution (SED curves between 700 nm and 160 μm, constructed from the GSC 2, 2MASS, IRAS, MSX, Spitzer and AKARI data, are used to estimate the evolutionary stages of these stars. We confirm the YSO status for most of the objects. If all of the investigated objects were YSOs, 45% of them should belong to Class I, 41% to class II and 14% to Class III. However, SEDs of some of these objects can be affected by nearby extended infrared sources, like compact H II regions, infrared clusters or dusty galaxies.

THE SPECTRAL ENERGY DISTRIBUTIONS OF z ∼ 8 GALAXIES FROM THE IRAC ULTRA DEEP FIELDS: EMISSION LINES, STELLAR MASSES, AND SPECIFIC STAR FORMATION RATES AT 650 MYR

Energy Technology Data Exchange (ETDEWEB)

Labbé, I.; Bouwens, R. J.; Franx, M. [Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands); Oesch, P. A.; Illingworth, G. D.; Magee, D.; González, V. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Carollo, C. M. [Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland); Trenti, M. [Kavli Institute for Cosmology and Institute of Astronomy, University of Cambridge, Cambridge (United Kingdom); Van Dokkum, P. G. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Stiavelli, M. [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2013-11-10

Using new ultradeep Spitzer/InfraRed Array Camera (IRAC) photometry from the IRAC Ultra Deep Field program, we investigate the stellar populations of a sample of 63 Y-dropout galaxy candidates at z ∼ 8, only 650 Myr after the big bang. The sources are selected from HST/ACS+WFC3/IR data over the Hubble Ultra Deep Field (HUDF), two HUDF parallel fields, and wide area data over the CANDELS/GOODS-South. The new Spitzer/IRAC data increase the coverage in [3.6] and [4.5] to ∼120h over the HUDF reaching depths of ∼28 (AB,1σ). The improved depth and inclusion of brighter candidates result in direct ≥3σ InfraRed Array Camera (IRAC) detections of 20/63 sources, of which 11/63 are detected at ≥5σ. The average [3.6]-[4.5] colors of IRAC detected galaxies at z ∼ 8 are markedly redder than those at z ∼ 7, observed only 130 Myr later. The simplest explanation is that we witness strong rest-frame optical emission lines (in particular [O III] λλ4959, 5007 + Hβ) moving through the IRAC bandpasses with redshift. Assuming that the average rest-frame spectrum is the same at both z ∼ 7 and z ∼ 8 we estimate a rest-frame equivalent width of contributing 0.56{sup +0.16}{sub -0.11} mag to the [4.5] filter at z ∼ 8. The corresponding W{sub Hα}=430{sup +160}{sub -110} Å implies an average specific star formation rate of sSFR=11{sub -5}{sup +11} Gyr{sup –1} and a stellar population age of 100{sub -50}{sup +100} Myr. Correcting the spectral energy distribution for the contribution of emission lines lowers the average best-fit stellar masses and mass-to-light ratios by ∼3 ×, decreasing the integrated stellar mass density to ρ{sup *}(z=8,M{sub UV}<-18)=0.6{sup +0.4}{sub -0.3}×10{sup 6} M{sub sun} Mpc{sup –3}.

THE STELLAR MASS–HALO MASS RELATION FOR LOW-MASS X-RAY GROUPS AT 0.5< z< 1 IN THE CDFS WITH CSI

International Nuclear Information System (INIS)

Patel, Shannon G.; Kelson, Daniel D.; Williams, Rik J.; Mulchaey, John S.; Dressler, Alan; McCarthy, Patrick J.; Shectman, Stephen A.

2015-01-01

Since z∼1, the stellar mass density locked in low-mass groups and clusters has grown by a factor of ∼8. Here, we make the first statistical measurements of the stellar mass content of low-mass X-ray groups at 0.5stellar-to-halo mass scales for wide-field optical and infrared surveys. Groups are selected from combined Chandra and XMM-Newton X-ray observations in the Chandra Deep Field South. These ultra-deep observations allow us to identify bona fide low-mass groups at high redshift and enable measurements of their total halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise ∼3%–4% of the total mass of group halos with masses 10 12.8 stellar-to-halo mass ratio decreases toward higher halo masses, consistent with other work in the local and high redshift universe. The observed scatter about the stellar–halo mass relation is σ∼0.25 dex, which is relatively small and suggests that total group stellar mass can serve as a rough proxy for halo mass. We find no evidence for any significant evolution in the stellar–halo mass relation since z≲1. Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly leads to such halos growing in number density and hosting increasing shares of quiescent galaxies

STELLAR MEMBERSHIP AND DUSTY DEBRIS DISKS IN THE α PERSEI CLUSTER

International Nuclear Information System (INIS)

Zuckerman, B.; Melis, Carl; Rhee, Joseph H.; Schneider, Adam; Song, Inseok

2012-01-01

Because of its proximity to the Galactic plane, reliable identification of members of the α Persei cluster is often problematic. Based primarily on membership evaluations contained in six published papers, we constructed a mostly complete list of high-fidelity members of spectral type G and earlier that lie within 3 arc degrees of the cluster center. α Persei was the one nearby, rich, young open cluster not surveyed with the Spitzer Space Telescope. We examined the first and final data releases of the Wide-field Infrared Survey Explorer and found 11, or perhaps 12, α Per cluster members that have excess mid-infrared emission above the stellar photosphere attributable to an orbiting dusty debris disk. The most unusual of these is V488 Per, a K-type star with an excess IR luminosity 16% (or more) of the stellar luminosity; this is a larger excess fraction than that of any other known dusty main-sequence star. Much of the dust that orbits V488 Per is at a temperature of ∼800 K; if these grains radiate like blackbodies, then they lie only ∼0.06 AU from the star. The dust is probably the aftermath of a collision of two planetary embryos or planets with small semimajor axes; such orbital radii are similar to those of many of the transiting planets discovered by the Kepler satellite.

A SPITZER CENSUS OF TRANSITIONAL PROTOPLANETARY DISKS WITH AU-SCALE INNER HOLES

International Nuclear Information System (INIS)

Muzerolle, James; Allen, Lori E.; Megeath, S. Thomas; Hernandez, Jesus; Gutermuth, Robert A.

2010-01-01

Protoplanetary disks with AU-scale inner clearings, often referred to as transitional disks, provide a unique sample for understanding disk dissipation mechanisms and possible connections to planet formation. Observations of young stellar clusters with the Spitzer Space Telescope have amassed mid-infrared (IR) spectral energy distributions (SEDs) for thousands of star-disk systems from which transition disks can be identified. From a sample of eight relatively nearby young regions (d ∼ 0) to select for robust optically thick outer disks, and 3.6-5.8 μm spectral slope and 5.8 μm continuum excess limits to select for optically thin or zero continuum excess from the inner few AU of the disks. We also identified two additional categories representing more ambiguous cases: 'warm excess' objects with transition-like SEDs but moderate excess at 5.8 μm, and 'weak excess' objects with smaller 24 μm excess that may be optically thin or exhibit advanced dust grain growth and settling. From existing Hα emission measurements, we find evidence for different accretion activity among the three categories, with a majority of the classical and warm excess transition objects still accreting gas through their inner holes and onto the central stars, while a smaller fraction of the weak transition objects are accreting at detectable rates. We find a possible age dependence on the frequency of classical transition objects, with fractions relative to the total population of disks in a given region of a few percent at 1-2 Myr rising to 10%-20% at 3-10 Myr. The trend is even stronger if the weak and warm excess objects are included. This relationship may be due to a dependence of the outer disk clearing timescale with stellar age, suggesting a variety of clearing mechanisms working at different times, or it may reflect that a smaller fraction of all disks actually undergo an inner clearing phase at younger ages. Classical transition disks appear to be less common, and weak transition

UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. II. PHOTOMETRIC REDSHIFTS, STELLAR MASSES, AND STAR FORMATION RATES

International Nuclear Information System (INIS)

Barro, G.; Perez-Gonzalez, P. G.; Gallego, J.; Villar, V.; Zamorano, J.; Ashby, M. L. N.; Kajisawa, M.; Yamada, T.; Miyazaki, S.

2011-01-01

Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 μm selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] ≤ 23.75 (85% completeness level of the IRAC survey) over 0.48 deg 2 . The typical photometric redshift accuracy is Δz/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 μm data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z ∼> 1.5 observed when only MIPS 24 μm data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

SPITZER SECONDARY ECLIPSES OF WASP-18b

International Nuclear Information System (INIS)

Nymeyer, Sarah; Harrington, Joseph; Hardy, Ryan A.; Stevenson, Kevin B.; Campo, Christopher J.; Blecic, Jasmina; Bowman, William C.; Britt, Christopher B. T.; Cubillos, Patricio; Madhusudhan, Nikku; Collier-Cameron, Andrew; Maxted, Pierre F. L.; Loredo, Thomas J.; Hellier, Coel; Anderson, David R.; Gillon, Michael; Hebb, Leslie; Wheatley, Peter J.; Pollacco, Don

2011-01-01

The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera in the 3.6 μm and 5.8 μm bands on 2008 December 20, and in the 4.5 μm and 8.0 μm bands on 2008 December 24. We report eclipse depths of 0.30% ± 0.02%, 0.39% ± 0.02%, 0.37% ± 0.03%, 0.41% ± 0.02%, and brightness temperatures of 3100 ± 90, 3310 ± 130, 3080 ± 140, and 3120 ± 110 K in order of increasing wavelength. WASP-18b is one of the hottest planets yet discovered—as hot as an M-class star. The planet's pressure-temperature profile most likely features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day side to the night side of the planet.

SPITZER PARALLAX of OGLE-2015-BLG-0966

DEFF Research Database (Denmark)

Street, R. A.; Udalski, A.; Novati, S. Calchi

2016-01-01

We report the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 M⊙ M dwarf lying 2.5-3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real...

Kepler-93b: A terrestrial world measured to within 120 km, and a test case for a new Spitzer observing mode

Energy Technology Data Exchange (ETDEWEB)

Ballard, Sarah [University of Washington, Seattle, WA 98195 (United States); Chaplin, William J.; Davies, Guy R.; Campante, Tiago L.; Handberg, Rasmus; Elsworth, Yvonne; Hekker, Saskia [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Charbonneau, David; Fressin, Francois; Zeng, Li [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Désert, Jean-Michel [Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder CO 80309 (United States); Werner, Michael W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States); Aguirre, Victor Silva; Christensen-Dalsgaard, Jørgen; Metcalfe, Travis S.; Karoff, Christoffer [Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, Sarbani [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Stello, Dennis; Bedding, Timothy R. [Sydney Institute for Astronomy, School of Physics, University of Sydney 2006 (Australia); Gilliland, Ronald L., E-mail: sarahba@uw.edu [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); and others

2014-07-20

We present the characterization of the Kepler-93 exoplanetary system, based on three years of photometry gathered by the Kepler spacecraft. The duration and cadence of the Kepler observations, in tandem with the brightness of the star, enable unusually precise constraints on both the planet and its host. We conduct an asteroseismic analysis of the Kepler photometry and conclude that the star has an average density of 1.652 ± 0.006 g cm{sup –3}. Its mass of 0.911 ± 0.033 M{sub ☉} renders it one of the lowest-mass subjects of asteroseismic study. An analysis of the transit signature produced by the planet Kepler-93b, which appears with a period of 4.72673978 ± 9.7 × 10{sup –7} days, returns a consistent but less precise measurement of the stellar density, 1.72{sub −0.28}{sup +0.02} g cm{sup –3}. The agreement of these two values lends credence to the planetary interpretation of the transit signal. The achromatic transit depth, as compared between Kepler and the Spitzer Space Telescope, supports the same conclusion. We observed seven transits of Kepler-93b with Spitzer, three of which we conducted in a new observing mode. The pointing strategy we employed to gather this subset of observations halved our uncertainty on the transit radius ratio R{sub P} /R{sub *}. We find, after folding together the stellar radius measurement of 0.919 ± 0.011 R{sub ☉} with the transit depth, a best-fit value for the planetary radius of 1.481 ± 0.019 R{sub ⊕}. The uncertainty of 120 km on our measurement of the planet's size currently renders it one of the most precisely measured planetary radii outside of the solar system. Together with the radius, the planetary mass of 3.8 ± 1.5 M{sub ⊕} corresponds to a rocky density of 6.3 ± 2.6 g cm{sup –3}. After applying a prior on the plausible maximum densities of similarly sized worlds between 1 and 1.5 R{sub ⊕}, we find that Kepler-93b possesses an average density within this group.

DEEP CHANDRA OBSERVATIONS OF THE CRAB-LIKE PULSAR WIND NEBULA G54.1+0.3 AND SPITZER SPECTROSCOPY OF THE ASSOCIATED INFRARED SHELL

International Nuclear Information System (INIS)

Temim, Tea; Slane, Patrick; Raymond, John C.; Reynolds, Stephen P.; Borkowski, Kazimierz J.

2010-01-01

G54.1+0.3 is a young pulsar wind nebula (PWN), closely resembling the Crab, for which no thermal shell emission has been detected in X-rays. Recent Spitzer observations revealed an infrared (IR) shell containing a dozen point sources arranged in a ring-like structure, previously proposed to be young stellar objects. An extended knot of emission located in the NW part of the shell appears to be aligned with the pulsar's X-ray jet, suggesting a possible interaction with the shell material. Surprisingly, the IR spectrum of the knot resembles the spectrum of freshly formed dust in Cas A, and is dominated by an unidentified dust emission feature at 21 μm. The spectra of the shell also contain various emission lines and show that some are significantly broadened, suggesting that they originate in rapidly expanding supernova (SN) ejecta. We present the first evidence that the PWN is driving shocks into expanding SN ejecta and we propose an alternative explanation for the origin of the IR emission in which the shell is composed entirely of SN ejecta. In this scenario, the freshly formed SN dust is being heated by early-type stars belonging to a cluster in which the SN exploded. Simple dust models show that this interpretation can give rise to the observed shell emission and the IR point sources.

Stellar Physics 2: Stellar Evolution and Stability

CERN Document Server

Bisnovatyi-Kogan, Gennady S

2011-01-01

"Stellar Physics" is a an outstanding book in the growing body of literature on star formation and evolution. Not only does the author, a leading expert in the field, very thoroughly present the current state of knowledge on stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 1000 entries makes this book an unparalleled reference source. "Stellar Evolution and Stability" is the second of two volumes and can be read, as can the first volume "Fundamental Concepts and Stellar Equilibrium," as a largely independent work. It traces in great detail the evolution of protostars towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to supernovae explosions, gamma-ray bursts and black hole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars. This second edition is carefully updated in the areas of pre...

THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

International Nuclear Information System (INIS)

Salmon, Brett; Papovich, Casey; Tilvi, Vithal; Finkelstein, Steven L.; Finlator, Kristian; Behroozi, Peter; Lu, Yu; Wechsler, Risa H.; Dahlen, Tomas; Ferguson, Henry C.; Davé, Romeel; Dekel, Avishai; Dickinson, Mark; Giavalisco, Mauro; Long, James; Mobasher, Bahram; Reddy, Naveen; Somerville, Rachel S.

2015-01-01

Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M ⋆ a with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M ☉ yr –1 ) < 0.3-0.4 dex, for galaxies with log M * /M ☉ > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot gas ), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation

Dayside atmospheric structure of HD209458b from Spitzer eclipses

Science.gov (United States)

Reinhard, Matthew; Harrington, Joseph; Challener, Ryan; Cubillos, Patricio; Blecic, Jasmina

2017-10-01

HD209458b is a hot Jupiter with a radius of 1.26 ± 0.08 Jupiter radii (Richardson et al, 2006) and a mass of 0.64 ± 0.09 Jupiter masses (Snellen et al, 2010). The planet orbits a G0 type star with an orbital period of 3.52472 ± 2.81699e-05 days, and a relatively low eccentricity of 0.0082 +0.0078/-0.0082 (Wang and Ford 2013). We report the analysis of observations of HD209458b during eclipse, taken in the 3.6 and 4.5 micron channels by the Spitzer Space Telescope's Infrared Array Camera (Program 90186). We produce a photometric light curve of the eclipses in both channels, using our Photometry for Orbits Eclipses and Transits (POET) code, and calculate the brightness temperatures and eclipse depths. We also present best estimates of the atmospheric parameters of HD209458b using our Bayesian Atmospheric Radiative Transfer (BART) code. These are some preliminary results of what will be an analysis of all available Spitzer data for HD209458b. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work was supported by NASA Planetary Atmospheres grant NX12AI69G and NASA Astrophysics Data Analysis Program grant NNX13AF38G.

ExploreNEOs: The Warm Spitzer Near Earth Object Survey

NARCIS (Netherlands)

Trilling, D. E.; Hora, J. L.; Mueller, M.; Thomas, C. A.; Harris, A. W.; Hagen, A. R.; Mommert, M.; Benner, L.; Bhattacharya, B.; Bottke, W. F.; Chesley, S.; Delbo, M.; Emery, J. P.; Fazio, G.; Kistler, J. L.; Mainzer, A.; Morbidelli, A.; Penprase, B.; Smith, H. A.; Spahr, T. B.; Stansberry, J. A.

2012-01-01

We have observed some 600 near Earth objects (NEOs) at 3.6 and 4.5 microns with the Warm Spitzer Space Telescope. We derive the albedo and diameter for each NEO to characterize global properties of the NEO population, among other goals.

SUBMILLIMETER ARRAY AND SPITZER OBSERVATIONS OF BOK GLOBULE CB 17: A CANDIDATE FIRST HYDROSTATIC CORE?

Energy Technology Data Exchange (ETDEWEB)

Chen Xuepeng; Arce, Hector G.; Dunham, Michael M. [Department of Astronomy, Yale University, Box 208101, New Haven, CT 06520-8101 (United States); Zhang Qizhou; Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Launhardt, Ralf; Schmalzl, Markus; Henning, Thomas, E-mail: xuepeng.chen@yale.edu [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2012-06-01

We present high angular resolution Submillimeter Array (SMA) and Spitzer observations toward the Bok globule CB 17. SMA 1.3 mm dust continuum images reveal within CB 17 two sources with an angular separation of {approx}21'' ({approx}5250 AU at a distance of {approx}250 pc). The northwestern continuum source, referred to as CB 17 IRS, dominates the infrared emission in the Spitzer images, drives a bipolar outflow extending in the northwest-southeast direction, and is classified as a low-luminosity Class 0/I transition object (L{sub bol} {approx} 0.5 L{sub Sun }). The southeastern continuum source, referred to as CB 17 MMS, has faint dust continuum emission in the SMA 1.3 mm observations ({approx}6{sigma} detection; {approx}3.8 mJy), but is not detected in the deep Spitzer infrared images at wavelengths from 3.6 to 70 {mu}m. Its bolometric luminosity and temperature, estimated from its spectral energy distribution, are {<=}0.04 L{sub Sun} and {<=}16 K, respectively. The SMA CO (2-1) observations suggest that CB 17 MMS may drive a low-velocity molecular outflow ({approx}2.5 km s{sup -1}), extending in the east-west direction. Comparisons with prestellar cores and Class 0 protostars suggest that CB 17 MMS is more evolved than prestellar cores but less evolved than Class 0 protostars. The observed characteristics of CB 17 MMS are consistent with the theoretical predictions from radiative/magnetohydrodynamical simulations of a first hydrostatic core, but there is also the possibility that CB 17 MMS is an extremely low luminosity protostar deeply embedded in an edge-on circumstellar disk. Further observations are needed to study the properties of CB 17 MMS and to address more precisely its evolutionary stage.

VizieR Online Data Catalog: Deconvolved Spitzer images of 89 protostars (Velusamy+, 2014)

Science.gov (United States)

Velusamy, T.; Langer, W. D.; Thompson, T.

2016-03-01

The sample of Class 0 protostars, H2 jets, and outflow sour selected for HiRes deconvolution of Spitzer images are listed in Table1. The majority of our target protostellar objects were selected from "The Youngest Protostars" webpage hosted by the University of Kent (http://astro.kent.ac.uk/protostars/old/), which are based on the young Class 0 objects compiled by Froebrich 2005 (cat. J/ApJS/156/169). In addition to these objects, our sample includes some Herbig-Haro (HH) sources and a few well known jet outflow sources. Our sample also includes one high-mass protostar (IRAS20126+4104; cf. Caratti o Garatti et al., 2008A&A...485..137C) to demonstrate the use of HiRes for such sources. Our choice for target selection was primarily based on the availability of Spitzer images in IRAC and MIPS bands in the archives and the feasibility for reprocessing based on the published Spitzer images wherever available. (1 data file).

Spitzer mid-infrared spectra of cool-core galaxy clusters

NARCIS (Netherlands)

de Messières, G.E.; O'Connell, R.W.; McNamara, B.R.; Donahue, M.; Nulsen, P.E.J.; Voit, G.M.; Wise, M.W.; Smith, B.; Higdon, J.; Higdon, S.; Bastian, N.

2010-01-01

We have obtained mid-infrared spectra of nine cool-core galaxy clusters with the Infrared Spectrograph aboard the Spitzer Space Telescope. X-ray, ultraviolet and optical observations have demonstrated that each of these clusters hosts a cooling flow which seems to be fueling vigorous star formation

SPIRITS: Uncovering Unusual Infrared Transients with Spitzer

International Nuclear Information System (INIS)

Kasliwal, Mansi M.; Jencson, Jacob E.; Tinyanont, Samaporn; Cao, Yi; Cook, David; Bally, John; Masci, Frank; Armus, Lee; Cody, Ann Marie; Bond, Howard E.; Contreras, Carlos; Dykhoff, Devin A.; Amodeo, Samuel; Carlon, Robert L.; Cass, Alexander C.; Corgan, David T.; Faella, Joseph; Boyer, Martha; Cantiello, Matteo; Fox, Ori D.

2017-01-01

We present an ongoing, five-year systematic search for extragalactic infrared transients, dubbed SPIRITS—SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer /IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate-luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between −11 and −14 (Vega-mag) and [3.6]–[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from <0.1 mag yr −1 to >7 mag yr −1 . SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a protostellar merger.

SPIRITS: Uncovering Unusual Infrared Transients with Spitzer

Energy Technology Data Exchange (ETDEWEB)

Kasliwal, Mansi M.; Jencson, Jacob E.; Tinyanont, Samaporn; Cao, Yi; Cook, David [Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Bally, John [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Masci, Frank; Armus, Lee [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Cody, Ann Marie [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Bond, Howard E. [Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Contreras, Carlos [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Dykhoff, Devin A.; Amodeo, Samuel; Carlon, Robert L.; Cass, Alexander C.; Corgan, David T.; Faella, Joseph [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S. E., University of Minnesota, Minneapolis, MN 55455 (United States); Boyer, Martha [NASA Goddard Space Flight Center, MC 665, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Cantiello, Matteo [Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010 (United States); Fox, Ori D. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

2017-04-20

We present an ongoing, five-year systematic search for extragalactic infrared transients, dubbed SPIRITS—SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer /IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate-luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between −11 and −14 (Vega-mag) and [3.6]–[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from <0.1 mag yr{sup −1} to >7 mag yr{sup −1}. SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a protostellar merger.

RELICS of the Cosmic Dawn

Science.gov (United States)

Bradac, Marusa; Coe, Dan; Strait, Victoria; Salmon, Brett; Hoag, Austin; Bradley, Larry; Ryan, Russell; Dawson, Will; Zitrin, Adi; Jones, Christine; Sharon, Keren; Trenti, Michele; Stark, Daniel; Oesch, Pascal; Lam, Danel; Carrasco Nunez, Daniela Patricia; Paterno-Mahler, Rachel; Frye, Brenda

2018-05-01

When did galaxies start forming stars? What is the role of distant galaxies in galaxy formation models and epoch of reionization? Recent observations indicate at least two critical puzzles in these studies. (1) First galaxies might have started forming stars earlier than previously thought (knowledge of stellar masses, ages, and star formation rates at this epoch requires measuring both rest-frame UV and optical light, which only Spitzer and HST can probe at z 6-11 for a large enough sample of typical galaxies. To address this cosmic puzzle, we propose to complete deep Spitzer imaging of the fields behind the 10 most powerful cosmic telescopes selected using HST, Spitzer, and Planck data from the RELICS and SRELICS programs (Reionization Lensing Cluster Survey; 41 clusters, 190 HST orbits, 440 Spitzer hours). 6 clusters out of 10 are still lacking deep data. This proposal will be a valuable Legacy complement to the existing IRAC deep surveys, and it will open up a new parameter space by probing the ordinary yet magnified population with much improved sample variance. The program will allow us to study stellar properties of a large number, 60 galaxies at z 6-11. Deep Spitzer data will be crucial to unambiguously measure their stellar properties (age, SFR, M*). Finally this proposal will establish the presence (or absence) of an unusually early established stellar population, as was recently observed in MACS1149JD at z 9. If confirmed in a larger sample, this result will require a paradigm shift in our understanding of the earliest star formation.

Spitzer Secondary Eclipse Depths with Multiple Intrapixel Sensitivity Correction Methods Observations of WASP-13b, WASP-15b, WASP-16b, WASP-62b, and HAT-P-22b

Science.gov (United States)

Kilpatrick, Brian M.; Lewis, Nikole K.; Kataria, Tiffany; Deming, Drake; Ingalls, James G.; Krick, Jessica E.; Tucker, Gregory S.

2017-01-01

We measure the 4.5 μm thermal emission of five transiting hot Jupiters, WASP-13b, WASP-15b, WASP-16b, WASP-62b, and HAT-P-22b using channel 2 of the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. Significant intrapixel sensitivity variations in Spitzer IRAC data require careful correction in order to achieve precision on the order of several hundred parts per million (ppm) for the measurement of exoplanet secondary eclipses. We determine eclipse depths by first correcting the raw data using three independent data reduction methods. The Pixel Gain Map (PMAP), Nearest Neighbors (NNBR), and Pixel Level Decorrelation (PLD) each correct for the intrapixel sensitivity effect in Spitzer photometric time-series observations. The results from each methodology are compared against each other to establish if they reach a statistically equivalent result in every case and to evaluate their ability to minimize uncertainty in the measurement. We find that all three methods produce reliable results. For every planet examined here NNBR and PLD produce results that are in statistical agreement. However, the PMAP method appears to produce results in slight disagreement in cases where the stellar centroid is not kept consistently on the most well characterized area of the detector. We evaluate the ability of each method to reduce the scatter in the residuals as well as in the correlated noise in the corrected data. The NNBR and PLD methods consistently minimize both white and red noise levels and should be considered reliable and consistent. The planets in this study span equilibrium temperatures from 1100 to 2000 K and have brightness temperatures that require either high albedo or efficient recirculation. However, it is possible that other processes such as clouds or disequilibrium chemistry may also be responsible for producing these brightness temperatures.

SPITZER SECONDARY ECLIPSE DEPTHS WITH MULTIPLE INTRAPIXEL SENSITIVITY CORRECTION METHODS OBSERVATIONS OF WASP-13b, WASP-15b, WASP-16b, WASP-62b, AND HAT-P-22b

Energy Technology Data Exchange (ETDEWEB)

Kilpatrick, Brian M.; Tucker, Gregory S. [Department of Physics, Box 1843, Brown University, Providence, RI 02904 (United States); Lewis, Nikole K. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Kataria, Tiffany [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Deming, Drake [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Ingalls, James G.; Krick, Jessica E., E-mail: brian_kilpatrick@brown.edu, E-mail: nlewis@stsci.org, E-mail: tiffany.kataria@jpl.nasa.gov, E-mail: ddeming@astro.umd.edu, E-mail: krick@ipac.caltech.edu [Spitzer Science Center, Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91125 (United States)

2017-01-01

We measure the 4.5 μ m thermal emission of five transiting hot Jupiters, WASP-13b, WASP-15b, WASP-16b, WASP-62b, and HAT-P-22b using channel 2 of the Infrared Array Camera (IRAC) on the Spitzer Space Telescope . Significant intrapixel sensitivity variations in Spitzer IRAC data require careful correction in order to achieve precision on the order of several hundred parts per million (ppm) for the measurement of exoplanet secondary eclipses. We determine eclipse depths by first correcting the raw data using three independent data reduction methods. The Pixel Gain Map (PMAP), Nearest Neighbors (NNBR), and Pixel Level Decorrelation (PLD) each correct for the intrapixel sensitivity effect in Spitzer photometric time-series observations. The results from each methodology are compared against each other to establish if they reach a statistically equivalent result in every case and to evaluate their ability to minimize uncertainty in the measurement. We find that all three methods produce reliable results. For every planet examined here NNBR and PLD produce results that are in statistical agreement. However, the PMAP method appears to produce results in slight disagreement in cases where the stellar centroid is not kept consistently on the most well characterized area of the detector. We evaluate the ability of each method to reduce the scatter in the residuals as well as in the correlated noise in the corrected data. The NNBR and PLD methods consistently minimize both white and red noise levels and should be considered reliable and consistent. The planets in this study span equilibrium temperatures from 1100 to 2000 K and have brightness temperatures that require either high albedo or efficient recirculation. However, it is possible that other processes such as clouds or disequilibrium chemistry may also be responsible for producing these brightness temperatures.

Spitzer Observations of M33 & M83 and the Hot Star, Hii Region Connection

Science.gov (United States)

Rubin, R.; Simpson, J.; Colgan, S.; Dufour, R.; Citron, R.; Ray, K.; Erickson, E.; Haas, M.; Pauldrach, A.

2007-05-01

H II regions play a crucial role in the measurement of current interstellar abundances. They also serve as laboratories for atomic physics and provide fundamental data about heavy element abundances that serve to constrain models of galactic chemical evolution. We observed emission lines of [S IV] 10.5, H (7-6) 12.4, [Ne II] 12.8, [Ne III] 15.6, & [S III] 18.7 micron cospatially with the Spitzer Space Telescope using the Infrared Spectrograph (IRS) in short-high mode (SH). Here we concentrate on the galaxy M33 and compare the results with our earlier similar study of M83. In each of these substantially face-on spirals, we observed ˜25 H II regions, covering a full range of galactocentric radii (RG). For most of the M33 H II regions, we were able to measure the H (7-6) line while none were detectable in M83. This limited our M83 study to a determination of the Ne++/Ne+, /, and S3+/S++ abundance ratios vs. RG. Angular brackets denote fractional ionizations. As well as having the addition of fluxes for the H(7-6) line, the M33 H II regions are generally of much higher ionization than those in M83, resulting in larger Ne++/Ne+ and S3+/ S++ abundance ratios. For M33, in addition to what we derived for those nebulae in M83, we are also able to derive Ne/H, S/H and Ne/S vs. RG. Important advantages compared with prior optical studies are: 1) the IR lines have a weak and similar electron temperature (Te) dependence while optical lines vary exponentially with Te and 2) the IR lines suffer far less from interstellar extinction. Additionally, these data may be used as constraints on the ionizing spectral energy distribution for the stars exciting these nebulae by comparing the above ionic ratios with predictions using stellar atmosphere models from several different non-LTE model sets. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407

A SPITZER SURVEY FOR DUST IN TYPE IIn SUPERNOVAE

International Nuclear Information System (INIS)

Fox, Ori D.; Chevalier, Roger A.; Skrutskie, Michael F.; Soderberg, Alicia M.; Filippenko, Alexei V.; Ganeshalingam, Mohan; Silverman, Jeffrey M.; Smith, Nathan; Steele, Thea N.

2011-01-01

Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (>100 days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low SN IIn rate (<10% of all core-collapse SNe), few IR observations exist for this subclass. The handful of isolated studies, however, show late-time IR emission from warm dust that, in some cases, extends for five or six years post-discovery. While previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted the Type IIn subclass. This paper presents results from a warm Spitzer/IRAC survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc between 1999 and 2008 that have remained unobserved by Spitzer more than 100 days post-discovery. The detection of late-time emission from 10 targets (∼15%) nearly doubles the database of existing mid-IR observations of SNe IIn. Although optical spectra show evidence for new dust formation in some cases, the data show that in most cases the likely origin of the mid-IR emission is pre-existing dust, which is continuously heated by optical emission generated by ongoing circumstellar interaction between the forward shock and circumstellar medium. Furthermore, an emerging trend suggests that these SNe decline at ∼1000-2000 days post-discovery once the forward shock overruns the dust shell. The mass-loss rates associated with these dust shells are consistent with luminous blue variable progenitors.

STAR FORMATION AT 4 < z < 6 FROM THE SPITZER LARGE AREA SURVEY WITH HYPER-SUPRIME-CAM (SPLASH)

Energy Technology Data Exchange (ETDEWEB)

Steinhardt, Charles L.; Capak, Peter; Masters, Dan; Petric, Andreea [Caltech, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Speagle, Josh S.; Silverman, John D. [Kavli IPMU, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8583 (Japan); Carollo, Marcella [ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich (Switzerland); Dunlop, James [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Hashimoto, Yasuhiro [National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 11677, Taiwan R.O.C. (China); Hsieh, Bau-Ching; Lin, Lihwai; Lin, Yen-Ting [ASIAA Sinica, AS/NTU. No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, R.O.C. (China); Ilbert, Olivier; Le Fevre, Olivier [Laboratoire d' Astrophysique de Marseille, 38 rue Frederic Joliot Curie, F-13388 Marseille (France); Le Floc' h, Emeric [Service d' Astrophysique, CEA-Saclay, Orme des Merisiers, Bat. 709, F-91191 Gif-sur-Yvette (France); Lee, Nicholas; Sanders, Dave [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); McCracken, Henry J. [Institut d' Astrophysique de Paris, 98 bis boulevard Arago, F-75014 Paris (France); Nagao, Tohru [Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Salvato, Mara [Max Planck Institute for Extraterrestrial Physics (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); and others

2014-08-20

Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam observations on the 1.8 deg{sup 2} Cosmological Evolution Survey we estimate the masses and star formation rates of 3398 M {sub *} > 10{sup 10} M {sub ☉} star-forming galaxies at 4 < z < 6 with a substantial population up to M {sub *} ≳ 10{sup 11.5} M {sub ☉}. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the ''main sequence'' of star-forming galaxies) extends to z ∼ 6. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to z ∼ 6 or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.

Young stellar population and star formation history ofW4 HII region/Cluster Complex

Science.gov (United States)

Panwar, Neelam

2018-04-01

The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to thei! r immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

Diogenite-like Features in the Spitzer IRS (5-35 micrometers) Spectrum of 956 ELISA

Science.gov (United States)

Lim, Lucy F.; Emery, Joshua P.; Moskovitz, Nicholas A.

2009-01-01

We report preliminary results from the Spitzer Infrared Spectrograph (IRS) observations of the V-type asteroid 956 Elisa. Elisa was observed as part of a campaign to measure the 5.2-38 micron spectra of small basaltic asteroids with the Spitzer IRS. Targets include members of the dynamical family of the unique large differentiated asteroid 4 Vesta ("Vesroids"), several outer-main-belt basaltic asteroids whose orbits exclude them from originating on 4 Vesta, and the basaltic near-Earth asteroid 4055 Magellan.

THE SPITZER HIGH-REDSHIFT RADIO GALAXY SURVEY

International Nuclear Information System (INIS)

De Breuck, Carlos; Galametz, Audrey; Vernet, Joel; Seymour, Nick; Stern, Daniel; Eisenhardt, P. R. M.; Willner, S. P.; Fazio, G. G.; Lacy, Mark; Rettura, Alessandro; Rocca-Volmerange, Brigitte

2010-01-01

We present results from a comprehensive imaging survey of 70 radio galaxies at redshifts 1 3 μ m /S 1.6 μ m versus S 5 μ m /S 3 μ m criterion, we identify 42 sources where the rest-frame 1.6 μm emission from the stellar population can be measured. For these radio galaxies, the median stellar mass is high, 2 x 10 11 M sun , and remarkably constant within the range 1 3, there is tentative evidence for a factor of two decrease in stellar mass. This suggests that radio galaxies have assembled the bulk of their stellar mass by z ∼ 3, but confirmation by more detailed decomposition of stellar and active galactic nucleus (AGN) emission is needed. The rest-frame 500 MHz radio luminosities are only marginally correlated with stellar mass but are strongly correlated with the rest-frame 5 μm hot dust luminosity. This suggests that the radio galaxies have a large range of Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz imaging of 14 radio galaxies and find that radio core dominance-an indicator of jet orientation-is strongly correlated with hot dust luminosity. While all of our targets were selected as narrow-lined, type 2 AGNs, this result can be understood in the context of orientation-dependent models if there is a continuous distribution of orientations from obscured type 2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio galaxies have nearby (<6'') companions whose mid-IR colors are suggestive of their being AGNs. This may indicate an association between radio galaxy activity and major mergers.

Young stellar population and ongoing star formation in the H II complex Sh2-252

Science.gov (United States)

Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.

2013-07-01

In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it

Measuring the Evolution of Stellar Populations And Gas Metallicity in Galaxies with Far-Infrared Space Spectroscopy

Science.gov (United States)

Stacey, Gordon

We propose a study of the evolution of stellar populations and gas metallicities in about 80 nearby star forming galaxies based on mining the NASA data archives for observations of the [NIII] 57 µm, [OIII] 52 µm and/or 88 µm, [NII] 122 and [CII] 158 µm far-infrared (FIR) fine- structure lines and other archives for thermal radio continuum. These lines are powerful probes of both stellar populations and gas properties and our primary science derives from these tracers. For sources that show both signs of active galactic nuclei (AGN) and star formation, we will take advantage of the readily available NASA Spitzer IRS data base that includes mid-IR [NeII] 12.8 µm, [NeIII] 15.6 µm and [NeV] 14.3 µm, [OIV] 25.9 µm and PAH observations. These complementary data reveal the relative fractions of the FIR line emission that might arise from star formation and the narrow line regions (NLR) associated with an AGN, thereby providing a robust set of observations to compare with star formation models. Subsets of the FIR lines have been detected from hundreds of nearby galaxies. From both theoretical studies and the results of these pioneering observations we know that these lines can be powerful probes of stellar populations and star formation in galaxies. Here we plan to use various combinations of the lines to constrain (1) the age of the stellar populations (through lines that trace the hardness of the stellar radiation fields, hence stellar spectral type), (2) the degree of processing of the interstellar medium (through lines that trace growth of secondary to primary element abundances for example, the N/O ratio), (3) the efficiency of star formation (through growth in absolute abundances of N and O, the N/H and O/H ratios), and (4) the current day mass function of upper main sequence stars. Surprisingly, there has been no systematic study of the large sample of these line detections made with PACS on Herschel in order to truly assess and calibrate their diagnostic

Stellar Sources of Gamma-ray Bursts

OpenAIRE

Luchkov, B. I.

2011-01-01

Correlation analysis of Swift gamma-ray burst coordinates and nearby star locations (catalog Gliese) reveals 4 coincidences with good angular accuracy. The random probability is 4\\times 10^{-5}, so evidencing that coincident stars are indeed gamma-ray burst sources. Some additional search of stellar gamma-ray bursts is discussed.

A Spitzer Survey for Dust in Type IIn Supernovae

Science.gov (United States)

Fox, Ori D.; Chevalier, Roger A.; Skrutskie, Michael F.; Soderberg, Alicia M.; Filippenko, Alexei V.; Ganeshalingam, Mohan; Silverman, Jeffrey M.; Smith, Nathan; Steele, Thea N.

2011-01-01

Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (greater than 100 days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low SN IIn rate (less than 10% of all core-collapse SNe), few IR observations exist for this subclass. The handful of isolated studies, however, show late-time IR emission from warm dust that, in some cases, extends for five or six years post-discovery. While previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted the Type IIn subclass. This article presents results from a warm Spitzer/IRAC survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc between 1999 and 2008 that have remained unobserved by Spitzer more than 100 days postdiscovery. The detection of late-time emission from ten targets (approximately 15%) nearly doubles the database of existing mid-IR observations of SNe IIn. Although optical spectra show evidence for new dust formation in some cases, the data show that in most cases the likely origin of the mid-IR emission is pre-existing dust, which is continuously heated by optical emission generated by ongoing circumstellar interaction between the forward shock and circumstellar medium. Furthermore, an emerging trend suggests that these SNe decline at approximately 1000-2000 days post-discovery once the forward shock overruns the dust shell. The mass-loss rates associated with these dust shells are consistent with luminous blue variable (LBV) progenitors.

THE TAURUS SPITZER SURVEY: NEW CANDIDATE TAURUS MEMBERS SELECTED USING SENSITIVE MID-INFRARED PHOTOMETRY

International Nuclear Information System (INIS)

Rebull, L. M.; Padgett, D. L.; McCabe, C.-E.; Noriega-Crespo, A.; Carey, S. J.; Brooke, T.; Hillenbrand, L. A.; Stapelfeldt, K. R.; Angione, J. R.; Huard, T.; Terebey, S.; Audard, M.; Baldovin-Saavedra, C.; Monin, J.-L.; Menard, F.; Bouvier, J.; Fukagawa, M.; Guedel, M.; Knapp, G. R.; Allen, L. E.

2010-01-01

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid- and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our ∼44 deg 2 map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ∼20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%-20% in Taurus members. Of the objects for which we have spectroscopy, seven are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and active galactic nuclei.

ExploreNEOs: The Warm Spitzer Near Earth Object survey

NARCIS (Netherlands)

Mueller, M.; Trilling, D. E.; Hora, J. L.; Harris, A. W.; Benner, L. A. M.; Bhattacharya, B.; Bottke, W. F.; Chesley, S.; Delbó, M.; Emery, J. P.; Fazio, G.; Hagen, A. R.; Kistler, J. L.; Mainzer, A.; Mommert, M.; Morbidelli, A.; Penprase, B.; Smith, H. A.; Spahr, T. B.; Stansberry, J. A.; Thomas, C. A.

2011-01-01

We are carrying out the ExploreNEOs project in which we observe more than 600 near Earth Objects (NEOs) at 3.6 and 4.5 microns with Warm Spitzer. For each NEO we derive diameter and albedo. We present our results to date, which include studies of individual objects, results for our entire observed

Robert Spitzer and psychiatric classification: technical challenges and ethical dilemmas.

Science.gov (United States)

Jacob, K S

2016-01-01

Dr Robert Leopold Spitzer (May 22, 1932-December 25, 2015), the architect of modern psychiatric diagnostic criteria and classification, died recently at the age of 83 in Seattle. Under his leadership, the American Psychiatric Association's (APA) Diagnostic and Statistical Manuals (DSM) became the international standard.

RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S4G IRAC 3.6 AND 4.5 μm IMAGES. I. CORRECTING FOR CONTAMINATION BY POLYCYCLIC AROMATIC HYDROCARBONS, HOT DUST, AND INTERMEDIATE-AGE STARS

International Nuclear Information System (INIS)

Meidt, Sharon E.; Schinnerer, Eva; Knapen, Johan H.; Bosma, Albert; Athanassoula, E.; Sheth, Kartik; Muñoz-Mateos, Juan-Carlos; Buta, Ronald J.; Zaritsky, Dennis; Hinz, Joannah L.; Skibba, Ramin A.; Laurikainen, Eija; Salo, Heikki; Elmegreen, Debra; Elmegreen, Bruce G.; Gadotti, Dimitri A.; Regan, Michael; Ho, Luis C.; Madore, Barry F.; Gil de Paz, Armando

2012-01-01

With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 μm images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 μm bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 μm, which is dominated by the broad PAH feature. Using the measured 3.6 μm/8 μm ratio to select individual contaminants, we find that hot dust and PAHs together contribute between ∼5% and 15% to the integrated light at 3.6 μm, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information

HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Gruendl, Robert A.; Chu, Y.-H.

2009-01-01

Archival Spitzer Infrared Array Camera (IRAC) and MIPS observations of the Large Magellanic Cloud (LMC) have been used to search for young stellar objects (YSOs). We have carried out independent aperture photometry of these data and merged the results from different passbands to produce a photometric catalog. To verify our methodology we have also analyzed the data from the SAGE and SWIRE Legacy programs; our photometric measurements are in general agreement with the photometry released by these programs. A detailed completeness analysis for our photometric catalog of the LMC shows that the 90% completeness limits are, on average, 16.0, 15.0, 14.3, 13.1, and 9.2 mag at 3.6, 4.5, 5.8, 8.0, and 24 μm, respectively. Using our mid-infrared photometric catalogs and two simple selection criteria, [4.5]-[8.0]>2.0 to exclude normal and evolved stars and [8.0]>14-([4.5]-[8.0]) to exclude background galaxies, we have identified a sample of 2910 sources in the LMC that could potentially be YSOs. We then used the Spitzer observations complemented by optical and near-infrared data to carefully assess the nature of each source. To do so we simultaneously considered multiwavelength images and photometry to assess the source morphology, spectral energy distribution (SED) from the optical through the mid-infrared wavelengths, and the surrounding interstellar environment to determine the most likely nature of each source. From this examination of the initial sample, we suggest that 1172 sources are most likely YSOs. We have also identified 1075 probable background galaxies, consistent with the expected number estimated from the SWIRE survey. Spitzer IRS observations of 269 of the brightest YSOs from our sample have confirmed that ∼>95% are indeed YSOs. An examination of color-color and color-magnitude diagrams shows no simple criteria in color-magnitude space that can unambiguously separate the LMC YSOs from all asymptotic giant branch (AGB)/post-AGB stars, planetary nebulae, and

RELICS of the Cosmic Dawn

Science.gov (United States)

Bradac, Marusa; Coe, Dan; Huang, Kuang-Han; Salmon, Brett; Hoag, Austin; Bradley, Larry; Ryan, Russell; Dawson, Will; Zitrin, Adi; Jones, Christine; Sharon, Keren; Trentu, Michele; Stark, Daniel; Bouwens, Rychard; Oesch, Pascal; Lam, Daniel; Patricia Carasco Nunez, Daniela; Paterno-Mahler, Rachel; Strait, Victoria

2017-10-01

When did galaxies start forming stars? What is the role of distant galaxies in galaxy formation models and epoch of reionization? Recent observations indicate at least two critical puzzles in these studies. (1) First galaxies might have started forming stars earlier than previously thought (Big Bang). (2) It is still unclear what is their star formation history and whether these galaxies can reionize the Universe. Accurate knowledge of stellar masses, ages, and star formation rates at this epoch requires measuring both rest-frame UV and optical light, which only Spitzer and HST can probe at z 6-11 for a large enough sample of typical galaxies. To address this cosmic puzzle, we propose Spitzer imaging of the fields behind the most powerful cosmic telescopes selected using HST, Spitzer, and Planck data from the RELICS and SRELICS programs (Reionization Lensing Cluster Survey; 41 clusters, 190 HST orbits, 550 Spitzer hours). This proposal will be a valuable Legacy complement to the existing IRAC deep surveys, and it will open up a new parameter space by probing the ordinary yet magnified population with much improved sample variance. The program will allow us to study stellar properties of a large number, 20 galaxies at z 6-11. Deep Spitzer data will be crucial to unambiguously measure their stellar properties (age, SFR, M*). Finally this proposal is a unique opportunity to establish the presence (or absence) of an unusually early established stellar population, as was recently observed in MACS1149JD at z 9. If confirmed, this result will require a paradigm shift in our understanding of the earliest star formation.

The Fourier-Kelvin Stellar Interferometer (FKSI): Infrared Detection and Characterization of Exozodiacal Dust to Super-Earths, A Progress Report

Science.gov (United States)

Danchi, W.

2010-01-01

The Fourier-Kelvin Stellar Interferometer (FKSI) is a structurally connected infrared space interferometer with 0.5 m diameter telescopes on a 12.5 m baseline, and is passively cooled to approx.60K. The FKSI operates in the thermal infrared from 3-8 microns in a nulling (or starlight suppressing) mode for the detection and characterization of exoplanets, debris disks, extrasolar zodiacal dust levels. The FKSI will have the highest angular resolution of any infrared space instrument ever made with its nominal resolution of 40 mas at a 5 micron center wavelength. This resolution exceeds that of Spitzer by a factor of 38 and JWST by a factor of 5. The FKSI mission is conceived as a "probe class" or "mid-sized" strategic mission that utilizes technology advances from flagship projects like JWST, SIM, Spitzer, and the technology programs of TPF-I/Darwin. During the past year we began investigating an enhanced version of FKSI with 1-2 m diameter telescopes, passively cooled to 40K, on a 20-m baseline, with a sunshade giving a +/- 45 degree Field-of-Regard. This enhanced design is capable of detecting and characterizing the atmospheres of many 2 Earth-radius super-Earths and a few Earth-twins. We will report progress on the design of the enhanced mission concept and current status of the technologies needed for this mission.

Star Formation Rates and Stellar Masses of z = 7-8 Galaxies from IRAC Observations of the WFC3/IR Early Release Science and the HUDF Fields

Science.gov (United States)

Labbé, I.; González, V.; Bouwens, R. J.; Illingworth, G. D.; Franx, M.; Trenti, M.; Oesch, P. A.; van Dokkum, P. G.; Stiavelli, M.; Carollo, C. M.; Kriek, M.; Magee, D.

2010-06-01

We investigate the Spitzer/IRAC properties of 36 z ~ 7 z 850-dropout galaxies and three z ~ 8 Y 098 galaxies derived from deep/wide-area WFC3/IR data of the Early Release Science, the ultradeep HUDF09, and wide-area NICMOS data. We fit stellar population synthesis models to the spectral energy distributions to derive mean redshifts, stellar masses, and ages. The z ~ 7 galaxies are best characterized by substantial ages (>100 Myr) and M/LV ≈ 0.2. The main trend with decreasing luminosity is that of bluing of the far-UV slope from β ~ -2.0 to β ~ -3.0. This can be explained by decreasing metallicity, except for the lowest luminosity galaxies (0.1L* z = 3), where low metallicity and smooth star formation histories (SFHs) fail to match the blue far-UV and moderately red H - [3.6] color. Such colors may require episodic SFHs with short periods of activity and quiescence ("on-off" cycles) and/or a contribution from emission lines. The stellar mass of our sample of z ~ 7 star-forming galaxies correlates with star formation rate (SFR) according to log M* = 8.70(±0.09) + 1.06(±0.10)log SFR, implying that star formation may have commenced at z > 10. No galaxies are found with SFRs much higher or lower than the past averaged SFR suggesting that the typical star formation timescales are probably a substantial fraction of the Hubble time. We report the first IRAC detection of Y 098-dropout galaxies at z ~ 8. The average rest-frame U - V ≈ 0.3 (AB) of the three galaxies are similar to faint z ~ 7 galaxies, implying similar M/L. The stellar mass density to M UV,AB Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 11563, 9797. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through contract 125790 issued by JPL/Caltech. Based on service

Discovery of a new Wolf-Rayet star and a candidate star cluster in the Large Magellanic Cloud with Spitzer

Science.gov (United States)

Gvaramadze, V. V.; Chené, A.-N.; Kniazev, A. Y.; Schnurr, O.; Shenar, T.; Sander, A.; Hainich, R.; Langer, N.; Hamann, W.-R.; Chu, Y.-H.; Gruendl, R. A.

2014-08-01

We report the first-ever discovery of a Wolf-Rayet (WR) star in the Large Magellanic Cloud via detection of a circular shell with the Spitzer Space Telescope. Follow-up observations with Gemini-South resolved the central star of the shell into two components separated from each other by ≈2 arcsec (or ≈0.5 pc in projection). One of these components turns out to be a WN3 star with H and He lines both in emission and absorption (we named it BAT99 3a using the numbering system based on extending the Breysacher et al. catalogue). Spectroscopy of the second component showed that it is a B0 V star. Subsequent spectroscopic observations of BAT99 3a with the du Pont 2.5-m telescope and the Southern African Large Telescope revealed that it is a close, eccentric binary system, and that the absorption lines are associated with an O companion star. We analysed the spectrum of the binary system using the non-LTE Potsdam WR (POWR) code, confirming that the WR component is a very hot (≈90 kK) WN star. For this star, we derived a luminosity of log L/ L⊙ = 5.45 and a mass-loss rate of 10- 5.8 M⊙ yr- 1, and found that the stellar wind composition is dominated by helium with 20 per cent of hydrogen. Spectroscopy of the shell revealed an He III region centred on BAT99 3a and having the same angular radius (≈15 arcsec) as the shell. We thereby add a new example to a rare class of high-excitation nebulae photoionized by WR stars. Analysis of the nebular spectrum showed that the shell is composed of unprocessed material, implying that the shell was swept-up from the local interstellar medium. We discuss the physical relationship between the newly identified massive stars and their possible membership of a previously unrecognized star cluster.

The COSMOS2015 galaxy stellar mass function . Thirteen billion years of stellar mass assembly in ten snapshots

Science.gov (United States)

Davidzon, I.; Ilbert, O.; Laigle, C.; Coupon, J.; McCracken, H. J.; Delvecchio, I.; Masters, D.; Capak, P.; Hsieh, B. C.; Le Fèvre, O.; Tresse, L.; Bethermin, M.; Chang, Y.-Y.; Faisst, A. L.; Le Floc'h, E.; Steinhardt, C.; Toft, S.; Aussel, H.; Dubois, C.; Hasinger, G.; Salvato, M.; Sanders, D. B.; Scoville, N.; Silverman, J. D.

2017-09-01

We measure the stellar mass function (SMF) and stellar mass density of galaxies in the COSMOS field up to z 6. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper Suprime-Cam. At z> 2.5 we use new precise photometric redshifts with error σz = 0.03(1 + z) and an outlier fraction of 12%, estimated by means of the unique spectroscopic sample of COSMOS ( 100 000 spectroscopic measurements in total, more than one thousand having robust zspec> 2.5). The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the completeness at high z with respect to previous UltraVISTA catalogues (e.g. our sample is >75% complete at 1010 ℳ⊙ and z = 5). We also identify passive galaxies through a robust colour-colour selection, extending their SMF estimate up to z = 4. Our work provides a comprehensive view of galaxy-stellar-mass assembly between z = 0.1 and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from ΛCDM simulations, finding that at z> 3 both functions decline with a similar slope in thehigh-mass end. This feature could be explained assuming that mechanisms quenching star formation in massive haloes become less effective at high redshifts; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as it moves towards higher redshifts, with α decreasing from -1.47+0.02-0.02 at z ≃ 0.1 to -2.11+0.30-0.13 at z ≃ 5. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best

Size and Albedo of Irregular Saturnian Satellites from Spitzer Observations

NARCIS (Netherlands)

Mueller, Michael; Grav, T.; Trilling, D.; Stansberry, J.; Sykes, M.

2008-01-01

Using MIPS onboard the Spitzer Space Telescope, we observed the thermal emission (24 and, for some targets, 70 um) of eight irregular satellites of Saturn: Albiorix, Siarnaq, Paaliaq, Kiviuq, Ijiraq, Tarvos, Erriapus, and Ymir. We determined the size and albedo of all targets. An analysis of

THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

Energy Technology Data Exchange (ETDEWEB)

Salmon, Brett; Papovich, Casey; Tilvi, Vithal [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy Texas A and M University, College Station, TX 77843 (United States); Finkelstein, Steven L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Finlator, Kristian [DARK fellow, Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Behroozi, Peter; Lu, Yu; Wechsler, Risa H. [Physics Department, Stanford University, Particle Astrophysics, SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology Stanford, CA 94305 (United States); Dahlen, Tomas; Ferguson, Henry C. [Space Telescope Science Institute, Baltimore, MD (United States); Davé, Romeel [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Dekel, Avishai [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Dickinson, Mark [National Optical Astronomy Observatories, Tucson, AZ (United States); Giavalisco, Mauro [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Long, James [Department of Statistics, Texas A and M University, College Station, TX 77843-3143 (United States); Mobasher, Bahram; Reddy, Naveen [Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States); Somerville, Rachel S., E-mail: bsalmon@physics.tamu.edu [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States)

2015-02-01

Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M{sub ⋆}{sup a} with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M {sub ☉} yr{sup –1}) < 0.3-0.4 dex, for galaxies with log M {sub *}/M {sub ☉} > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot {sub gas}), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation.

ULTRADEEP INFRARED ARRAY CAMERA OBSERVATIONS OF SUB-L* z ∼ 7 AND z ∼ 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD: THE CONTRIBUTION OF LOW-LUMINOSITY GALAXIES TO THE STELLAR MASS DENSITY AND REIONIZATION

International Nuclear Information System (INIS)

Labbe, I.; Gonzalez, V.; Bouwens, R. J.; Illingworth, G. D.; Magee, D.; Oesch, P. A.; Carollo, C. M.; Van Dokkum, P. G.; Franx, M.; Stiavelli, M.; Trenti, M.; Kriek, M.

2010-01-01

We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z ∼ 7 z 850 -dropout galaxies and 5z ∼ 8 Y 105 -dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6 μm and 4.5 μm. None of the galaxies are detected to [3.6] ∼ 26.9 (AB, 2σ), but a stacking analysis reveals a robust detection for the z 850 -dropouts and an upper limit for the Y 105 -dropouts. We construct average broadband spectral energy distributions using the stacked Advanced Camera for Surveys (ACS), WFC3, and IRAC fluxes and fit stellar population synthesis models to derive mean redshifts, stellar masses, and ages. For the z 850 -dropouts, we find z = 6.9 +0.1 -0.1 , (U - V) rest ∼ 0.4, reddening A V = 0, stellar mass (M*) = 1.2 +0.3 -0.6 x 10 9 M sun (Salpeter initial mass function). The best-fit ages ∼300 Myr, M/L V ∼ 0.2, and SSFR ∼1.7 Gyr -1 are similar to values reported for luminous z ∼ 7 galaxies, indicating the galaxies are smaller but not much younger. The sub-L* galaxies observed here contribute significantly to the stellar mass density and under favorable conditions may have provided enough photons for sustained reionization at 7 +0.1 -0.2 Y 105 -dropouts have stellar masses that are uncertain by 1.5 dex due to the near-complete reliance on far-UV data. Adopting the 2σ upper limit on the M/L(z = 8), the stellar mass density to M UV,AB +1.4 -1.8 x 10 6 M sun Mpc -3 to ρ*(z = 8) 5 M sun Mpc -3 , following ∝(1 + z) -6 over 3 < z < 8. Lower masses at z = 8 would signify more dramatic evolution, which can be established with deeper IRAC observations, long before the arrival of the James Webb Space Telescope.

SPITZER IRAC COLOR DIAGNOSTICS FOR EXTENDED EMISSION IN STAR-FORMING REGIONS

International Nuclear Information System (INIS)

Ybarra, Jason E.; Tapia, Mauricio; Román-Zúñiga, Carlos G.; Lada, Elizabeth A.

2014-01-01

The infrared data from the Spitzer Space Telescope are an invaluable tool for identifying physical processes in star formation. In this study, we calculate the Infrared Array Camera (IRAC) color space of UV fluorescent H 2 and polycyclic aromatic hydrocarbon (PAH) emission in photodissociation regions (PDRs) using the Cloudy code with PAH opacities from Draine and Li. We create a set of color diagnostics that can be applied to study the structure of PDRs and to distinguish between FUV-excited and shock-excited H 2 emission. To test this method, we apply these diagnostics to Spitzer IRAC data of NGC 2316. Our analysis of the structure of the PDR is consistent with previous studies of the region. In addition to UV excited emission, we identify shocked gas that may be part of an outflow originating from the cluster

SPITZER IRAC COLOR DIAGNOSTICS FOR EXTENDED EMISSION IN STAR-FORMING REGIONS

Energy Technology Data Exchange (ETDEWEB)

Ybarra, Jason E.; Tapia, Mauricio; Román-Zúñiga, Carlos G. [Instituto de Astronomía, Universidad Nacional Autónoma de Mexíco, Unidad Académica en Ensenada, Km 103 Carr. Tijuana-Ensenada, 22860 Ensenada BC (Mexico); Lada, Elizabeth A., E-mail: jybarra@astro.unam.mx [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States)

2014-10-20

The infrared data from the Spitzer Space Telescope are an invaluable tool for identifying physical processes in star formation. In this study, we calculate the Infrared Array Camera (IRAC) color space of UV fluorescent H{sub 2} and polycyclic aromatic hydrocarbon (PAH) emission in photodissociation regions (PDRs) using the Cloudy code with PAH opacities from Draine and Li. We create a set of color diagnostics that can be applied to study the structure of PDRs and to distinguish between FUV-excited and shock-excited H{sub 2} emission. To test this method, we apply these diagnostics to Spitzer IRAC data of NGC 2316. Our analysis of the structure of the PDR is consistent with previous studies of the region. In addition to UV excited emission, we identify shocked gas that may be part of an outflow originating from the cluster.

Stellarator-Spheromak

International Nuclear Information System (INIS)

Moroz, P.E.

1997-03-01

A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with very high β (pressure/magnetic pressure) of the confined plasma

The Low-mass Population in the Young Cluster Stock 8: Stellar Properties and Initial Mass Function

Energy Technology Data Exchange (ETDEWEB)

Jose, Jessy; Herczeg, Gregory J.; Fang, Qiliang [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, Beijing 100871 (China); Samal, Manash R. [Graduate Institute of Astronomy, National Central University 300, Jhongli City, Taoyuan County 32001, Taiwan (China); Panwar, Neelam, E-mail: jessyvjose1@gmail.com [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India)

2017-02-10

The evolution of H ii regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution, and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6 and 4.5 μ m photometry from UKIDSS and Spitzer -IRAC. We use multicolor criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of ∼6.5 (∼3.0 Myr) with an observed age spread of ∼0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ∼0.15 dex. The intrinsic age spread in the cluster is ∼0.2 dex. The fraction of young stellar objects surrounded by disks is ∼35%. The K -band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The initial mass function (IMF) of Stock 8 has a Salpeter-like slope at >0.5 M {sub ⊙} and flattens and peaks at ∼0.4 M {sub ⊙}, below which it declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of the IMF due to the proximity of massive stars around the cluster.

High-angular-resolution stellar imaging with occultations from the Cassini spacecraft - III. Mira

Science.gov (United States)

Stewart, Paul N.; Tuthill, Peter G.; Nicholson, Philip D.; Hedman, Matthew M.

2016-04-01

We present an analysis of spectral and spatial data of Mira obtained by the Cassini spacecraft, which not only observed the star's spectra over a broad range of near-infrared wavelengths, but was also able to obtain high-resolution spatial information by watching the star pass behind Saturn's rings. The observed spectral range of 1-5 microns reveals the stellar atmosphere in the crucial water-bands which are unavailable to terrestrial observers, and the simultaneous spatial sampling allows the origin of spectral features to be located in the stellar environment. Models are fitted to the data, revealing the spectral and spatial structure of molecular layers surrounding the star. High-resolution imagery is recovered revealing the layered and asymmetric nature of the stellar atmosphere. The observational data set is also used to confront the state-of-the-art cool opacity-sampling dynamic extended atmosphere models of Mira variables through a detailed spectral and spatial comparison, revealing in general a good agreement with some specific departures corresponding to particular spectral features.

Estimate of stellar masses from their QPO frequencies

Indian Academy of Sciences (India)

For such a system, the stellar radius is very close to the marginally stable orbit ... The phenomenon of quasiperiodic oscillations was discovered in 1985 by ... QPOs are revealed in a power–density spectrum as a broad peak covering many.

The Magellanic Bridge Cluster NGC 796: Deep Optical AO Imaging Reveals the Stellar Content and Initial Mass Function of a Massive Open Cluster

Science.gov (United States)

Kalari, Venu M.; Carraro, Giovanni; Evans, Christopher J.; Rubio, Monica

2018-04-01

NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5–1/10 Z⊙ Magellanic Bridge, allowing us to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griHα imaging of NGC 796 (at 0.″5, which is ∼0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of {20}-5+12 Myr from isochronal fitting of the cluster main sequence in the color–magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope α = 1.99 ± 0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the Hα emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990 ± 200 M⊙, and a core radius of 1.4 ± 0.3 pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.

Assessment of global stellarator confinement: Status of the international stellarator confinement scaling data base

International Nuclear Information System (INIS)

Dinklage, A.; Beidler, C.D.; Dose, V.; Geiger, J.; Kus, A.; Preuss, R.; Ascasibar, E.; Tribaldos, V.; Harris, J.H.; Murakami, S.; Sano, F.; Okamura, S.; Suzuki, Y.; Watanabe, K.Y.; Yamada, H.; Yokoyama, M.; Stroth, U.; Talmadge, J.

2005-01-01

Different stellarator/heliotron devices along with their respective flexibility cover a large magnetic configuration space. Since the ultimate goal of stellarator research aims at an alternative fusion reactor concept, the exploration of the most promising configurations requires a comparative assessment of the plasma performance and how different aspects of a 3D configuration influence it. Therefore, the International Stellarator Confinement Database (ISCDB) has been re- initiated in 2004 and the ISS95 database has been extended to roughly 3000 discharges from eight different devices. Further data-sets are continuously added. A revision of a data set restricted to comparable scenarios lead to the ISS04 scaling law which confirmed ISS95 but also revealed clearly the necessity to incorporate configuration descriptive parameters. In other words, an extension beyond the set of regression parameters used for ISS95/ISS04 appears to be necessary and candidates, such as the elongation are investigated. Since grouping of data is a key-issue for deriving ISS04, basic assumptions are revised, e.g. the dependence on the heating scheme. Moreover, an assessment of statistical approaches is investigated with respect to their impact on the scaling. A crucial issue is the weighting of data groups which is discussed in terms of error-in-variable techniques and Bayesian model comparison. The latter is employed for testing scaling ansatzes depending on scaling invariance principles hence allowing the assessment of applicability of theory-based scaling laws on stellarator confinement. 1. ISCDB resources are jointly hosted by NIFS and IPP, see http://iscdb.nifs.ac.jp and http://www.ipp.mpg.de/ISS. (author)

A NEARBY GAMMA-RAY BURST HOST PROTOTYPE FOR z ∼ 7 LYMAN-BREAK GALAXIES: SPITZER-IRS AND X-SHOOTER SPECTROSCOPY OF THE HOST GALAXY OF GRB 031203

International Nuclear Information System (INIS)

Watson, D.; French, J.; Hjorth, J.; Malesani, D.; Fynbo, J. P. U.; Castro Cerón, J. M.; Christensen, L.; O'Halloran, B.; Michałowski, M.; Gordon, K. D.; Covino, S.; Reinfrank, R. F.

2011-01-01

Gamma-ray burst (GRB) host galaxies have been studied extensively in optical photometry and spectroscopy. Here we present the first mid-infrared spectrum of a GRB host, HG 031203. It is one of the nearest GRB hosts at z = 0.1055, allowing both low- and high-resolution spectroscopy with the Spitzer Infrared Spectrograph (IRS). Medium-resolution UV to K-band spectroscopy with the X-shooter spectrograph on the Very Large Telescope is also presented, along with Spitzer IRAC and MIPS photometry, as well as radio and submillimeter observations. These data allow us to construct a UV to radio spectral energy distribution with almost complete spectroscopic coverage from 0.3 to 35 μm of a GRB host galaxy for the first time, potentially valuable as a template for future model comparisons. The IRS spectra show strong, high-ionization fine structure line emission indicative of a hard radiation field in the galaxy—in particular the [S IV]/[S III] and [Ne III]/[Ne II] ratios—suggestive of strong ongoing star formation and a very young stellar population. The absence of any polycyclic aromatic hydrocarbon emission supports these conclusions, as does the probable hot peak dust temperature, making HG 031203 similar to the prototypical blue compact dwarf galaxy (BCD), II Zw 40. The selection of HG 031203 via the presence of a GRB suggests that it might be a useful analog of very young star-forming galaxies in the early universe, and hints that local BCDs may be used as more reliable analogs of star formation in the early universe than typical local starbursts. We look at the current debate on the ages of the dominant stellar populations in z ∼ 7 and z ∼ 8 galaxies in this context. The nebular line emission is so strong in HG 031203 that at z ∼ 7, it can reproduce the spectral energy distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 μm fluxes without the need to invoke a 4000 Å break. Indeed, photometry of HG 031203 shows elevation of the broadband V

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

Energy Technology Data Exchange (ETDEWEB)

Saral, G.; Audard, M. [Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix (Switzerland); Hora, J. L.; Martínez-Galarza, J. R.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Motte, F. [Institut de Plantologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes—CNRS-INSU, BP 53, F-38041 Grenoble Cedex 9 (France); Nguyen-Luong, Q. [National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saygac, A. T. [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

2017-04-20

We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color–magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH ii regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H ii regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

BOOK REVIEW: Stellarator and Heliotron Devices

Science.gov (United States)

Johnson, John L.

1999-02-01

Pfirsch-Schlüter current driven magnetic islands and the interpretation of sawtooth instabilities in Heliotron E. The treatment of particle orbits in Chapter 6 includes a derivation of drift equations, a discussion of the characteristics of trapped particle confinement in a heliotron and one of the Monte Carlo method for studying transport phenomena. A good treatment of neoclassical transport in a stellarator, with emphasis on the relation between parallel viscosity driven fluxes and bootstrap current, is given in Chapter 7. This is the best treatment I have found, outside of the original references, but it is still demanding. In addition, a radial electric field is introduced into the energy transport equations. The treatment of heating and confinement of heliotron plasmas in Chapter 8 is a good combination of providing results from experiments on the Heliotron E and DR heliotrons and the ATF and CHS stellarators and showing how theoretical interpretation is formulated. The discussions of ray tracing and energy absorption for both ECRH and ICRF heating techniques, as well as a treatment of neutral beam injection, are very clear. Measurements of bootstrap current and plasma rotation, as well as the density limits associated with pellet injection, are discussed. The chapter ends with a discussion of what may be the author's favourite topic, pressure gradient driven turbulence, in which he describes mixing length and scale invariance techniques. Finally, a discussion of the characteristics of a steady state fusion reactor, including a treatment of the containment, slowing down and energy transfer of the alpha particles, one of the toroidal Alfvén modes driven by these particles and some physics of divertors are given in Chapter 9. A reviewer is usually expected to find some faults. I had no problem in finding one as soon as I received the book: indeed, I did not like its title. I have always maintained that Lyman Spitzer defined a stellarator as any toroidal device in

STELLAR ATMOSPHERES, ATMOSPHERIC EXTENSION, AND FUNDAMENTAL PARAMETERS: WEIGHING STARS USING THE STELLAR MASS INDEX

Energy Technology Data Exchange (ETDEWEB)

Neilson, Hilding R.; Lester, John B. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4 (Canada); Baron, Fabien; Norris, Ryan; Kloppenborg, Brian, E-mail: neilson@astro.utoronto.ca [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States)

2016-10-20

One of the great challenges of understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology, and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star’s effective temperature, radius, and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.

Bulk Densities of Binary Asteroids from the Warm Spitzer NEO Survey

NARCIS (Netherlands)

Kistler, John; Trilling, D. E.; Mueller, M.; Hora, J. L.; Harris, A. W.; Bhattacharya, B.; Bottke, W. F.; Chesley, S.; Emery, J. P.; Fazo, G.; Mainzer, A.; Penprase, B.; Smith, H. A.; Spahr, T. B.; Stansberry, J. A.; Thomas, C. A.

2010-01-01

The Warm Spitzer NEO survey, ExploreNEOs, will observe approximately 700 Near Earth Asteroids. Several of these objects are known to be binary asteroid systems. Binary systems are interesting due to the unique opportunity they present for determining the masses and densities of their constituent

The fundamentals of stellar astrophysics

International Nuclear Information System (INIS)

Collins, G.W. II.

1989-01-01

A broad overview of theoretical stellar astrophysics is presented in a textbook intended for graduate students. Chapters are devoted to fundamental principles, assumptions, theorems, and polytropes; energy sources and sinks; the flow of energy through the star and the construction of stellar models; the theory of stellar evolution; relativistic stellar structure; the structure of distorted stars; stellar pulsation and oscillation. Also discussed are the flow of radiation through the stellar atmosphere, the solution of the radiative-transfer equation, the environment of the radiation field, the construction of a stellar model atmosphere, the formation and shape of spectral lines, LTE breakdown, illuminated and extended stellar atmospheres, and the transfer of polarized radiation. Diagrams, graphs, and sample problems are provided. 164 refs

Physical Properties of Asteroid (10302) 1989 ML, a Potential Spacecraft Target, from Spitzer Observations

Science.gov (United States)

Mueller, Michael; Harris, A. W.

2006-09-01

We report on results from recent Spitzer observations of near-Earth asteroid (10302) 1989 ML, which is among the lowest-ranking objects in terms of the specific momentum Δv required to reach it from Earth. It was originally considered as a target for Hayabusa and is now under consideration as a target of the planned ESA mission Don Quijote. Unfortunately, little is known about the physical properties of 1989 ML, in particular its size and albedo are unknown. Its exhibits an X type reflection spectrum, so depending on its albedo, 1989 ML may be an E, M, or P type asteroid. Provisional results from thermal-infrared observations carried out with Spitzer indicate that the albedo of 1989 ML is compatible with an M- or E-type classification. We will discuss our results and their implications for the physical properties and the rotation period of 1989 ML, and its importance as a potential spacecraft target. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

SPITZER OBSERVATIONS OF HOTSPOTS IN RADIO LOBES

International Nuclear Information System (INIS)

Werner, Michael W.; Murphy, David W.; Livingston, John H.; Gorjian, Varoujan; Jones, Dayton L.; Meier, David L.; Lawrence, Charles R.

2012-01-01

We have carried out a systematic search with Spitzer Warm Mission and archival data for infrared emission from the hotspots in radio lobes that have been described by Hardcastle et al. These hotspots have been detected with both radio and X-ray observations, but an observation at an intermediate frequency in the infrared can be critical to distinguish between competing models for particle acceleration and radiation processes in these objects. Between the archival and warm mission data, we report detections of 18 hotspots; the archival data generally include detections at all four IRAC bands, the Warm Mission data only at 3.6 μm. Using a theoretical formalism adopted from Godfrey et al., we fit both archival and warm mission spectral energy distributions (SEDs)—including radio, X-ray, and optical data from Hardcastle as well as the Spitzer data—with a synchrotron self-Compton (SSC) model, in which the X-rays are produced by Compton scattering of the radio frequency photons by the energetic electrons which radiate them. With one exception, an SSC model requires that the magnetic field be less or much less than the equipartition value which minimizes total energy and has comparable amounts of energy in the magnetic field and in the energetic particles. This conclusion agrees with those of comparable recent studies of hotspots, and with the analysis presented by Hardcastle et al. We also show that the infrared data rule out the simplest synchrotron-only models for the SEDs. We briefly discuss the implications of these results and of alternate interpretations of the data.

Computational Laboratory Astrophysics to Enable Transport Modeling of Protons and Hydrogen in Stellar Winds, the ISM, and other Astrophysical Environments

Science.gov (United States)

Schultz, David

As recognized prominently by the APRA program, interpretation of NASA astrophysical mission observations requires significant products of laboratory astrophysics, for example, spectral lines and transition probabilities, electron-, proton-, or heavy-particle collision data. Availability of these data underpin robust and validated models of astrophysical emissions and absorptions, energy, momentum, and particle transport, dynamics, and reactions. Therefore, measured or computationally derived, analyzed, and readily available laboratory astrophysics data significantly enhances the scientific return on NASA missions such as HST, Spitzer, and JWST. In the present work a comprehensive set of data will be developed for the ubiquitous proton-hydrogen and hydrogen-hydrogen collisions in astrophysical environments including ISM shocks, supernova remnants and bubbles, HI clouds, young stellar objects, and winds within stellar spheres, covering the necessary wide range of energy- and charge-changing channels, collision energies, and most relevant scattering parameters. In addition, building on preliminary work, a transport and reaction simulation will be developed incorporating the elastic and inelastic collision data collected and produced. The work will build upon significant previous efforts of the principal investigators and collaborators, will result in a comprehensive data set required for modeling these environments and interpreting NASA astrophysical mission observations, and will benefit from feedback from collaborators who are active users of the work proposed.

QUASI-STELLAR OBJECT SELECTION ALGORITHM USING TIME VARIABILITY AND MACHINE LEARNING: SELECTION OF 1620 QUASI-STELLAR OBJECT CANDIDATES FROM MACHO LARGE MAGELLANIC CLOUD DATABASE

International Nuclear Information System (INIS)

Kim, Dae-Won; Protopapas, Pavlos; Alcock, Charles; Trichas, Markos; Byun, Yong-Ik; Khardon, Roni

2011-01-01

We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies ∼80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million light curves, and found 1620 QSO candidates. During the selection none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.

Dynamic Young Stars and their Disks: A Temporal View of NGC 2264 with Spitzer and CoRoT*

Directory of Open Access Journals (Sweden)

Cody Ann Marie

2014-01-01

Full Text Available Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 (“CSI 2264”– a joint30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway.

Compact stellarators as reactors

International Nuclear Information System (INIS)

Lyon, J.F.; Valanju, P.; Zarnstorff, M.C.; Hirshman, S.; Spong, D.A.; Strickler, D.; Williamson, D.E.; Ware, A.

2001-01-01

Two types of compact stellarators are examined as reactors: two- and three-field-period (M=2 and 3) quasi-axisymmetric devices with volume-average =4-5% and M=2 and 3 quasi-poloidal devices with =10-15%. These low-aspect-ratio stellarator-tokamak hybrids differ from conventional stellarators in their use of the plasma-generated bootstrap current to supplement the poloidal field from external coils. Using the ARIES-AT model with B max =12T on the coils gives Compact Stellarator reactors with R=7.3-8.2m, a factor of 2-3 smaller R than other stellarator reactors for the same assumptions, and neutron wall loadings up to 3.7MWm -2 . (author)

SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Bonanos, A. Z.; Massa, D. L.; Sewilo, M.

2009-01-01

We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 μm in the UBVIJHK s +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ∼900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L sun ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

Luck Reveals Stellar Explosion's First Moments

Science.gov (United States)

2008-05-01

Through a stroke of luck, astronomers have witnessed the first violent moments of a stellar explosion known as a supernova. Astronomers have seen thousands of these stellar explosions, but all previous supernovae were discovered days after the event had begun. This is the first time scientists have been able to study a supernova from its very beginning. Seeing one just moments after the event began is a major breakthrough that points the way to unraveling longstanding mysteries about how such explosions really work. Galaxy Before Supernova Explosion NASA's Swift satellite took these images of SN 2007uy in galaxy NGC 2770 before SN 2008D exploded. An X-ray image is on the left; image at right is in visible light. CREDIT: NASA/Swift Science Team/Stefan Immler. Large Image With Labels Large Image Without Labels Galaxy After Supernova Explosion On January 9, 2008, Swift caught a bright X-ray burst from an exploding star. A few days later, SN 2008D appeared in visible light. CREDIT: NASA/Swift Science Team/Stefan Immler. Large Image With Labels Large Image Without Labels "For years, we have dreamed of seeing a star just as it was exploding," said team leader Alicia Soderberg, a Hubble and Carnegie-Princeton Fellow at Princeton University. "This newly-born supernova is going to be the Rosetta Stone of supernova studies for years to come." Theorists had predicted for four decades that a bright burst of X-rays should be produced as the shock wave from a supernova blasts out of the star and through dense material surrounding the star. However, in order to see this burst, scientists faced the nearly-impossible challenge of knowing in advance where to point their telescopes to catch a supernova in the act of exploding. On January 9, luck intervened. Soderberg and her colleagues were making a scheduled observation of the galaxy NGC 2770, 88 million light-years from Earth, using the X-ray telescope on NASA's Swift satellite. During that observation, a bright burst of X

DEEP JHKs AND SPITZER IMAGING OF FOUR ISOLATED MOLECULAR CLOUD CORES

International Nuclear Information System (INIS)

Chapman, Nicholas L.; Mundy, Lee G.

2009-01-01

We present observations in eight wavebands from 1.25 to 24 μm of four dense cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the young stellar object (YSO) population of these cores and to measure the mid-infrared extinction law. With our combined near-infrared and Spitzer photometry, we classify each source in the cores as, among other things, background stars, galaxies, or embedded YSOs. L1152 contains three YSOs and L1228 has seven, but neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper limit of 7 x 10 -5 to 5 x 10 -4 L sun for any undiscovered YSOs in our cores. We also compute the line-of-sight extinction law toward each background star. These measurements are averaged spatially, to create χ 2 maps of the changes in the mid-infrared extinction law throughout our cores, and also in different ranges of extinction. From the χ 2 maps, we identify two small regions in L1152 and L1228 where the outflows in those cores appear to be destroying the larger dust grains, thus altering the extinction law in those regions. On average, however, our extinction law is relatively flat from 3.6 to 24 μm for all ranges of extinction and in all four cores. From 3.6 to 8 μm, this law is consistent with a dust model that includes larger dust grains than the diffuse interstellar medium, which suggests grain growth has occurred in our cores. At 24 μm, our extinction law is two to four times higher than predicted by dust models. However, it is similar to other empirical measurements.

Stellar populations a guide from low to high redshift

CERN Document Server

Renzini, Alvio

2011-01-01

This up-to-date reference on stellar populations and development models includes coverage of distant galaxies, chemical evolution and supernovae. Written by highly acclaimed authorities in the field, the book makes use of specific problems to reveal the ""kitchen secrets.""

A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

Science.gov (United States)

van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

2018-04-01

Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

Science.gov (United States)

van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

2018-06-01

Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

Stellar magnetic activity

International Nuclear Information System (INIS)

Schrijver, C.J.

1986-01-01

The stellar emission in the chromospheric Ca II H+K lines is compared with the coronal soft X-ray emission, measuring the effects of non-radiative heating in the outer atmosphere at temperatures differing two orders of magnitude. The comparison of stellar flux densities in Ca II H+K and X-rays is extended to fluxes from the transition-region and the high-temperature chromosphere. The stellar magnetic field is probably generated in the differentially rotating convective envelope. The relation between rotation rate and the stellar level of activity measured in chromospheric, transition-region, and coronal radiative diagnostics is discovered. X-ray observations of the binary λ Andromedae are discussed. The departure of M-type dwarfs from the main relations, and the implications for the structure of the chromospheres of these stars are discussed. Variations of the average surface flux densities of the Sun during the 11-year activity cycle agree with flux-flux relations derived for other cool stars, suggesting that the interpretation of the stellar relations may be furthered by studying the solar analogue in more detail. (Auth.)

sunstardb: A Database for the Study of Stellar Magnetism and the Solar-stellar Connection

Science.gov (United States)

Egeland, Ricky

2018-05-01

The “solar-stellar connection” began as a relatively small field of research focused on understanding the processes that generate magnetic fields in stars and sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time-series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g., luminosity, differential rotation, and the depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time-series keyed by individual named stars. The organization of the data eliminates the need for the problematic catalog cross-matching operations inherent when building an analysis data set from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

Serendipitous discovery of an infrared bow shock near PSR J1549–4848 with Spitzer

Energy Technology Data Exchange (ETDEWEB)

Wang, Zhongxiang [Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Kaplan, David L. [Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States); Slane, Patrick [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Morrell, Nidia [Las Campanas Observatory, Observatories of the Carnegie Institution of Washington, La Serena (Chile); Kaspi, Victoria M. [Department of Physics, McGill University, 3600 University Street, Montreal, QC H3A 2T8 (Canada)

2013-06-01

We report on the discovery of an infrared cometary nebula around PSR J1549–4848 in our Spitzer survey of a few middle-aged radio pulsars. Following the discovery, multi-wavelength imaging and spectroscopic observations of the nebula were carried out. We detected the nebula in Spitzer Infrared Array Camera 8.0, Multiband Imaging Photometer for Spitzer 24 and 70 μm imaging, and in Spitzer IRS 7.5-14.4 μm spectroscopic observations, and also in the Wide-field Infrared Survey Explorer all-sky survey at 12 and 22 μm. These data were analyzed in detail, and we find that the nebula can be described with a standard bow shock shape, and that its spectrum contains polycyclic aromatic hydrocarbon and H{sub 2} emission features. However, it is not certain which object drives the nebula. We analyze the field stars and conclude that none of them can be the associated object because stars with a strong wind or mass ejection that usually produce bow shocks are much brighter than the field stars. The pulsar is approximately 15'' away from the region in which the associated object is expected to be located. In order to resolve the discrepancy, we suggest that a highly collimated wind could be emitted from the pulsar and produce the bow shock. X-ray imaging to detect the interaction of the wind with the ambient medium- and high-spatial resolution radio imaging to determine the proper motion of the pulsar should be carried out, which will help verify the association of the pulsar with the bow shock nebula.

Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

Energy Technology Data Exchange (ETDEWEB)

Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

2014-06-01

A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

Spitzer Secondary Eclipses of HAT-P-13b

Science.gov (United States)

Hardy, Ryan A.; Harrington, J.; Hardin, M. R.; Madhusudhan, N.; Cubillos, P.; Blecic, J.; Bakos, G.; Hartman, J. D.

2013-10-01

HAT-P-13 b is a transiting hot Jupiter with a slightly eccentric orbit (e = 0.010) inhabiting a two-planet system. The two-planet arrangement provides an opportunity to probe the interior structure of HAT-P-13b. Under equilibrium-tide theory and confirmation that the apsides of planets b and c are in alignment, a measurement of the planet's eccentricity can be related to the planet's tidal Love number k2, which describes the central condensation of the planet's mass and its deformation under tidal effects. A measurement of k2 could constrain interior models of HAT-P-13b. HAT-P-13b's orbit is configured favorably for refinement of the eccentricity by secondary eclipse timing observations, which provide direct measurements of ecosω. In 2010, Spitzer observed two secondary eclipses of HAT-P-13b in the 3.6- and 4.5-μm IRAC bandpasses. We present secondary eclipse times and depths; joint models of the HAT-P-13 system that incorporate transit photometry and radial velocity data; and constraints on the atmospheric chemistry of HAT-P-13b that suggest solar-abundance composition without a thermal inversion. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, which provided support for this work. This work was supported in part by NASA Planetary Atmospheres Grant NNX13AF38G.

Intrinsic Turbulence Stabilization in a Stellarator

Directory of Open Access Journals (Sweden)

P. Xanthopoulos

2016-06-01

Full Text Available The magnetic surfaces of modern stellarators are characterized by complex, carefully optimized shaping and exhibit locally compressed regions of strong turbulence drive. Massively parallel computer simulations of plasma turbulence reveal, however, that stellarators also possess two intrinsic mechanisms to mitigate the effect of this drive. In the regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the strongest fluctuations form narrow bandlike structures on the magnetic surfaces. Thanks to this localization, the average transport through the surface is significantly smaller than that predicted at locations of peak turbulence. This feature results in a numerically observed upshift of the onset of turbulence on the surface towards higher ion temperature gradients as compared with the prediction from the most unstable regions. In a second regime lacking scale separation, the localization is lost and the fluctuations spread out on the magnetic surface. Nonetheless, stabilization persists through the suppression of the large eddies (relative to the equilibrium scale, leading to a reduced stiffness for the heat flux dependence on the ion temperature gradient. These fundamental differences with tokamak turbulence are exemplified for the QUASAR stellarator [G. H. Neilson et al., IEEE Trans. Plasma Sci. 42, 489 (2014].

Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies

Science.gov (United States)

Papovich, Casey J.; Rudnick, G.; Le Floc'h, E.; van Dokkum, P. G.; Rieke, G. H.; Taylor, E. N.; Armus, L.; Gawiser, E.; Marcillac, D.; Huang, J.; Franx, M.

2007-05-01

We study the 24, 70, and 160 μm properties of high-redshift galaxies. Our primary interest is to improve the constraints on the total infrared (IR) luminosities, L(IR), of these galaxies. We combine Spitzer data in the southern Extended Chandra Deep Field with a Ks-band-selected galaxy sample with photometric redshifts from the Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure the average 70 and 160 μm flux densities of 1.5 250 μJy and 1.5 250 μJy have S(70)/S(24) flux ratios comparable to sources with X-ray detections or red rest-frame IR colors, suggesting that warm dust possibly heated by AGN produces high 24 μm emission. Based on the average 24-160 μm flux densities, 24 μm-selected galaxies at 1.5 rate observed in low redshift galaxies, suggesting that high redshift galaxies have star formation efficiencies and feedback processes comparable to lower redshift analogs. Support for this work was provided by NASA through the Spitzer Space Telescope Fellowship Program, through a contract issued by JPL, Caltech under a contract with NASA.

An Observational Study of Blended Young Stellar Clusters in the Galactic Plane - Do Massive Stars form First?

Science.gov (United States)

Martínez-Galarza, Rafael; Protopapas, Pavlos; Smith, Howard A.; Morales, Esteban

2018-01-01

From an observational point of view, the early life of massive stars is difficult to understand partly because star formation occurs in crowded clusters where individual stars often appear blended together in the beams of infrared telescopes. This renders the characterization of the physical properties of young embedded clusters via spectral energy distribution (SED) fitting a challenging task. Of particular relevance for the testing of star formation models is the question of whether the claimed universality of the IMF (references) is reflected in an equally universal integrated galactic initial mass function (IGIMF) of stars. In other words, is the set of all stellar masses in the galaxy sampled from a single universal IMF, or does the distribution of masses depend on the environment, making the IGIMF different from the canonical IMF? If the latter is true, how different are the two? We present a infrared SED analysis of ~70 Spitzer-selected, low mass ($facilities.

The impact of endorsing Spitzer's proposed criteria for PTSD in the forthcoming DSM-V on male and female Veterans.

Science.gov (United States)

Miller, Lyndsey N; Chard, Kathleen M; Schumm, Jeremiah A; O'Brien, Carol

2011-06-01

This study explored differences between Spitzer's proposed model of posttraumatic stress disorder (PTSD) and the current DSM-IV diagnostic classification scheme in 353 Veterans. The majority of Veterans (89%) diagnosed with PTSD as specified in the DSM-IV also met Spitzer's proposed criteria. Veterans who met both DSM-IV and Spitzer's proposed criteria had significantly higher Clinician Administered PTSD Scale severity scores than Veterans only meeting DSM-IV criteria. Logistic regression indicated that being African American and having no comorbid diagnosis of major depressive disorder or history of a substance use disorder were found to predict those Veterans who met current, but not proposed criteria. These findings have important implications regarding proposed changes to the diagnostic classification criteria for PTSD in the forthcoming DSM-V. Copyright © 2011 Elsevier Ltd. All rights reserved.

Neoclassical transport in stellarators - a comparison of conventional stellarator/torsatrons with the advanced stellarator, Wendelstein 7X

Energy Technology Data Exchange (ETDEWEB)

Beidler, C D [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)

1991-01-01

A general expression for the magnitude of a stellarator's magnetic field, in terms of a Fourier decomposition, is too complicated to lend itself easily to analytic transport calculations. The great majority of stellarator-type devices, however, may be accurately described if one retains only those harmonics with m=0 and m=1. In the long-mean-free-path regime an analytical approximation to the particle's bounce-averaged kinetic equation can then be found. Using a numerical solution of this equation, it is possible to calculate the particle and heat fluxes due to helical-ripple transport in stellarators throughout the entire long-mean-free-path regime. 3 figs.

Revealing the Formation of Stellar-mass Black Hole Binaries: The Need for Deci-Hertz Gravitational-wave Observatories

Energy Technology Data Exchange (ETDEWEB)

Chen, Xian [Astronomy Department, School of Physics, Peking University, 100871 Beijing (China); Amaro-Seoane, Pau, E-mail: xian.chen@pku.edu.cn, E-mail: pau@ice.cat [Institut de Ciències de l’Espai (CSIC-IEEC) at Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona (Spain)

2017-06-10

The formation of compact stellar-mass binaries is a difficult, but interesting problem in astrophysics. There are two main formation channels: in the field via binary star evolution, or in dense stellar systems via dynamical interactions. The Laser Interferometer Gravitational-wave Observatory (LIGO) has detected black hole binaries (BHBs) via their gravitational radiation. These detections provide us with information about the physical parameters of the system. It has been claimed that when the Laser Interferometer Space Antenna (LISA) is operating, the joint observation of these binaries with LIGO will allow us to derive the channels that lead to their formation. However, we show that for BHBs in dense stellar systems dynamical interactions could lead to high eccentricities such that a fraction of the relativistic mergers are not audible to LISA. A non-detection by LISA puts a lower limit of about 0.005 on the eccentricity of a BHB entering the LIGO band. On the other hand, a deci-Hertz observatory, like DECIGO or Tian Qin, would significantly enhance the chances of a joint detection and shed light on the formation channels of these binaries.

The Value of Change: Surprises and Insights in Stellar Evolution

Science.gov (United States)

Bildsten, Lars

2018-01-01

Astronomers with large-format cameras regularly scan the sky many times per night to detect what's changing, and telescopes in space such as Kepler and, soon, TESS obtain very accurate brightness measurements of nearly a million stars over time periods of years. These capabilities, in conjunction with theoretical and computational efforts, have yielded surprises and remarkable new insights into the internal properties of stars and how they end their lives. I will show how asteroseismology reveals the properties of the deep interiors of red giants, and highlight how astrophysical transients may be revealing unusual thermonuclear outcomes from exploding white dwarfs and the births of highly magnetic neutron stars. All the while, stellar science has been accelerated by the availability of open source tools, such as Modules for Experiments in Stellar Astrophysics (MESA), and the nearly immediate availability of observational results.

NEWLY IDENTIFIED EXTENDED GREEN OBJECTS (EGOs) FROM THE SPITZER GLIMPSE II SURVEY. II. MOLECULAR CLOUD ENVIRONMENTS

Energy Technology Data Exchange (ETDEWEB)

Chen Xi; Gan Conggui; Shen Zhiqiang [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Ellingsen, Simon P.; Titmarsh, Anita [School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania (Australia); He Jinhua, E-mail: chenxi@shao.ac.cn [Key Laboratory for the Structure and Evolution of Celestial Objects, Yunnan Astronomical Observatory/National Astronomical Observatory, Chinese Academy of Sciences, P.O. Box 110, Kunming 650011, Yunnan Province (China)

2013-06-01

We have undertaken a survey of molecular lines in the 3 mm band toward 57 young stellar objects using the Australia Telescope National Facility Mopra 22 m radio telescope. The target sources were young stellar objects with active outflows (extended green objects (EGOs)) newly identified from the GLIMPSE II survey. We observe a high detection rate (50%) of broad line wing emission in the HNC and CS thermal lines, which combined with the high detection rate of class I methanol masers toward these sources (reported in Paper I) further demonstrates that the GLIMPSE II EGOs are associated with outflows. The physical and kinematic characteristics derived from the 3 mm molecular lines for these newly identified EGOs are consistent with these sources being massive young stellar objects with ongoing outflow activity and rapid accretion. These findings support our previous investigations of the mid-infrared properties of these sources and their association with other star formation tracers (e.g., infrared dark clouds, methanol masers and millimeter dust sources) presented in Paper I. The high detection rate (64%) of the hot core tracer CH{sub 3}CN reveals that the majority of these new EGOs have evolved to the hot molecular core stage. Comparison of the observed molecular column densities with predictions from hot core chemistry models reveals that the newly identified EGOs from the GLIMPSE II survey are members of the youngest hot core population, with an evolutionary time scale of the order of 10{sup 3} yr.

Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars

NARCIS (Netherlands)

Ignace, R.; Cassinelli, J.P.; Tracy, G.; Churchwell, E.B.; Lamers, H.J.G.L.M.

2007-01-01

We report on neon abundances derived from Spitzer high resolution spectral data of eight Wolf-Rayet (WR) stars using the forbidden line of [Ne III] 15.56 μm. Our targets include four WN stars of subtypes 4-7, and four WC stars of subtypes 4-7. We derive ion fraction abundances γ of Ne2+ for the

LUMINOUS AND HIGH STELLAR MASS CANDIDATE GALAXIES AT z ≈ 8 DISCOVERED IN THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY

International Nuclear Information System (INIS)

Yan Haojing; Finkelstein, Steven L.; Huang, Kuang-Han; Ryan, Russell E.; Ferguson, Henry C.; Koekemoer, Anton M.; Grogin, Norman A.; Dickinson, Mark; Newman, Jeffrey A.; Somerville, Rachel S.; Davé, Romeel; Faber, S. M.; Papovich, Casey; Guo Yicheng; Giavalisco, Mauro; Lee, Kyoung-soo; Reddy, Naveen; Siana, Brian D.; Cooray, Asantha R.; Hathi, Nimish P.

2012-01-01

One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z ≈ 8. Its two-tiered ''wide and deep'' strategy bridges significant gaps in existing near-infrared surveys. Here we report on z ≈ 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 arcmin 2 to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J 1 mag brighter than any previously known F105W-dropouts. We derive constraints on the bright end of the rest-frame ultraviolet luminosity function of galaxies at z ≈ 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z ≈ 8. Their derived stellar masses are on the order of a few × 10 9 M ☉ , from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z ≈ 8. The high number density of very luminous and very massive galaxies at z ≈ 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.

STELLAR MASSES OF LYMAN BREAK GALAXIES, Lyα EMITTERS, AND RADIO GALAXIES IN OVERDENSE REGIONS AT z = 4-6

International Nuclear Information System (INIS)

Overzier, Roderik A.; Shu Xinwen; Zheng Wei; Rettura, Alessandro; Zirm, Andrew; Ford, Holland; Bouwens, Rychard J.; Illingworth, Garth D.; Miley, George K.; Venemans, Bram; White, Richard L.

2009-01-01

We present new information on galaxies in the vicinity of luminous radio galaxies (RGs) and quasars at z≅4, 5, and 6. These fields were previously found to contain overdensities of Lyman Break Galaxies (LBGs) or spectroscopic Lyα emitters, which were interpreted as evidence for clusters-in-formation ('protoclusters'). We use Hubble Space Telescope and Spitzer data to infer stellar masses from stellar synthesis models calibrated against the Millennium Run simulations, and contrast our results with large samples of LBGs in more average environments as probed by the Great Observatories Origins Deep Survey (GOODS). The following results were obtained. First, LBGs in both overdense regions and in the field at z = 4-5 lie on a very similar sequence in a z'-[3.6] versus 3.6 μm color-magnitude diagram. This is interpreted as a sequence in stellar mass (M * ∼ 10 9 -10 11 M sun ) in which galaxies become increasingly red due to dust and age as their star formation rate (SFR) increases, while their specific SFR stays constant. Second, the two RGs are among the most massive objects (M * ∼ 10 11 M sun ) known to exist at z ≅ 4-5, and are extremely rare based on the low number density of such objects as estimated from the ∼25x larger area GOODS survey. We suggest that the presence of the massive (radio) galaxies and associated supermassive black holes has been boosted through rapid accretion of gas or merging inside overdense regions. Third, the total stellar mass found in the z = 4 protocluster TN1338 accounts for 4, based on a comparison with the massive X-ray cluster Cl1252 at z = 1.2. Although future near-infrared observations should determine whether any massive galaxies are currently being missed by our UV/Lyα selections, one possible explanation for this mass difference is that TN1338 evolves into a smaller cluster than Cl1252. This raises the interesting question of whether the most massive protocluster regions at z > 4 remain yet to be discovered.

THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7

International Nuclear Information System (INIS)

Gonzalez, Valentino; Bouwens, Rychard J.; Illingworth, Garth; Labbe, Ivo; Franx, Marijn; Kriek, Mariska; Brammer, Gabriel B.

2010-01-01

We use a robust sample of 11 z ∼ 7 galaxies (z 850 dropouts) to estimate the stellar mass density (SMD) of the universe when it was only ∼750 Myr old. We combine the very deep optical to near-infrared photometry from the Hubble Space Telescope Advanced Camera for Surveys and NICMOS cameras with mid-infrared Spitzer Infrared Array Camera (IRAC) imaging available through the GOODS program. After carefully removing the flux from contaminating foreground sources, we have obtained reliable photometry in the 3.6 μm and 4.5 μm IRAC channels. The spectral shapes of these sources, including their rest-frame optical colors, strongly support their being at z ∼ 7 with a mean photometric redshift of (z) = 7.2 ± 0.5. We use Bruzual and Charlot synthetic stellar population models to constrain their stellar masses and star formation histories. We find stellar masses that range over (0.1-12) x 10 9 M sun and average ages from 20 Myr to 425 Myr with a mean of ∼300 Myr, suggesting that in some of these galaxies most of the stars were formed at z > 8 (and probably at z ∼> 10). The best fits to the observed SEDs are consistent with little or no dust extinction, in agreement with recent results at z ∼ 4-8. The star formation rates (SFRs) are in the range from 5 to 20 M sun yr -1 . From this sample, we measure an SMD of 6.6 +5.4 -3.3 x 10 5 M sun Mpc -3 to a limit of M UV,AB z=3 ). Combined with a fiducial lower limit for their ages (80 Myr), this implies a maximum SFR density of 0.008 M sun yr -1 Mpc -3 . This is well below the critical level needed to reionize the universe at z ∼ 8 using standard assumptions. However, this result is based on luminous sources (>L*) and does not include the dominant contribution of the fainter galaxies. Strikingly, we find that the specific SFR is constant from z ∼ 7 to z ∼ 2 but drops substantially at more recent times.

Models for stellar flares

International Nuclear Information System (INIS)

Cram, L.E.; Woods, D.T.

1982-01-01

We study the response of certain spectral signatures of stellar flares (such as Balmer line profiles and the broad-band continuum) to changes in atmospheric structure which might result from physical processes akin to those thought to occur in solar flares. While each physical process does not have a unique signature, we can show that some of the observed properties of stellar flares can be explained by a model which involves increased pressures and temperatures in the flaring stellar chromosphere. We suggest that changes in stellar flare area, both with time and with depth in the atmosphere, may play an important role in producing the observed flare spectrum

Spitzer/IRS Observations Of Multiple Main-Belt And Binary Near-Earth Asteroids

Science.gov (United States)

Enriquez, J. Emilio; Marchis, F.; Emery, J. P.; Im, S.

2010-10-01

Since the discovery of Ida's companion in 1993, 195 companions of asteroids have been discovered. To understand the formation process of these interesting bodies, their physical properties such as their bulk density, size, shape, and surface roughness need to be determined. During the Spitzer Cycle-4, we obtained IRS thermal emission spectra (5-42 um) of 23 known binary systems. The majority of asteroids are from the main-belt (16), while the rest are NEOs (7). After extracting the thermal spectra, we used a modified Standard Thermal Model (STM) to calculate their equivalent diameter (from 0.8 km to 237 km), their albedo (from 0.04 for C-type to 0.394 for a V-type) and their beaming factor related to the surface roughness and thermal inertia. We derive their emissivity spectra, which is useful to detect silicate features. Combining these measurements with 3D-models of these multiple asteroid systems obtained by lightcurve inversion, we should be able to derive an accurate estimate of their bulk-density and contrast them with their taxonomic classes. Preliminary studies by Marchis et al. (2008)1, suggested a relationship between bulk density and the taxonomic class of asteroids, which varies from 0.9 g/cc for C-complex to 2.4 g/cc for S-complex asteroids. The National Science Foundation supported this research under award number AAG-0807468. It was conducted with the Spitzer space telescope, which is operated by JPL under a contract with NASA. 1 Marchis et al. , 2008, "Mid-infrared Spectra of Binary Asteroids With Spitzer/IRS", 40th DPS Meeting, Bulletin of the American Astronomical Society, 40, 508

Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star

Energy Technology Data Exchange (ETDEWEB)

Van Grootel, V.; Gillon, M.; Scuflaire, R. [Institut d' Astrophysique et de Géophysique, Université de Liège, 17 Allée du 6 Août, B-4000 Liège (Belgium); Valencia, D. [Department of Physical and Environmental Sciences, University of Toronto, 1265 Military Trail, Toronto, ON, M1C 1A4 (Canada); Madhusudhan, N.; Demory, B.-O.; Queloz, D. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Dragomir, D. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr. Suite 102, Goleta, CA 93117 (United States); Howe, A. R.; Burrows, A. S. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Deming, D. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Ehrenreich, D.; Lovis, C.; Mayor, M.; Pepe, F.; Segransan, D.; Udry, S. [Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, CH-1290 Sauverny (Switzerland); Seager, S., E-mail: valerie.vangrootel@ulg.ac.be [Department of Earth, Atmospheric and Planetary Sciences, Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)

2014-05-01

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass (M {sub *} = 0.77 ± 0.05 M {sub ☉}) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-High Resolution Echelle Spectrometer (Keck-HIRES) radial velocities and Microvariability and Oscillations of STars (MOST) and Spitzer photometry. HD 97658 b is a massive (M{sub P}=7.55{sub −0.79}{sup +0.83} M{sub ⊕}) and large (R{sub P}=2.247{sub −0.095}{sup +0.098}R{sub ⊕} at 4.5 μm) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, of at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for upcoming space missions such as the Transiting Exoplanet Survey Satellite (TESS), the Characterizing Exoplanet Satellite (CHEOPS), the Planetary Transits and Oscillations of stars (PLATO), and the James Webb Space Telescope to characterize thoroughly its structure and atmosphere.

CRYSTALLINE SILICATES IN EVOLVED STARS. I. SPITZER/INFRARED SPECTROGRAPH SPECTROSCOPY OF IRAS 16456-3542, 18354-0638, AND 23239+5754

Energy Technology Data Exchange (ETDEWEB)

Jiang, B. W.; Zhang, Ke [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Li, Aigen [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Lisse, C. M., E-mail: bjiang@bnu.edu.cn, E-mail: kzhang@caltech.edu, E-mail: lia@missouri.edu, E-mail: carey.lisse@jhuapl.edu [Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 (United States)

2013-03-01

We report the Spitzer Infrared Spectrograph (IRS) observations of three evolved stars: IRAS 16456-3542, 18354-0638, and 23239+5754. The 9.9-37.2 {mu}m Spitzer/IRS high-resolution spectra of these three sources exhibit rich sets of enstatite-dominated crystalline silicate emission features. IRAS 16456-3542 is extremely rich in crystalline silicates, with >90% of its silicate mass in crystalline form, the highest to date ever reported for crystalline silicate sources.

Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

International Nuclear Information System (INIS)

Chen, C.-H. Rosie; Indebetouw, Remy; Muller, Erik; Kawamura, Akiko; Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie; Sewiło, Marta; Whitney, Barbara A.; Meade, Marilyn R.; Fukui, Yasuo; Madden, Suzanne C.; Oliveira, Joana M.; Van Loon, Jacco Th.; Robitaille, Thomas P.

2014-01-01

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M ☉ , <<45 M ☉ found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10 20 cm –2 , but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

Energy Technology Data Exchange (ETDEWEB)

Chen, C.-H. Rosie; Indebetouw, Remy [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Muller, Erik; Kawamura, Akiko [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Sewiło, Marta [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Whitney, Barbara A.; Meade, Marilyn R. [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Fukui, Yasuo [Department of Astrophysics, Nagoya University, Furocho, Chikusaku, Nagoya 464-8602 (Japan); Madden, Suzanne C. [CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Oliveira, Joana M.; Van Loon, Jacco Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Robitaille, Thomas P., E-mail: rchen@mpifr-bonn.mpg.de [Max Planck Institute for Astronomy, D-69117 Heidelberg (Germany)

2014-04-20

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M {sub ☉}, <<45 M {sub ☉} found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10{sup 20} cm{sup –2}, but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

Stellar structure and evolution

International Nuclear Information System (INIS)

Kippernhahn, R.; Weigert, A.

1990-01-01

This book introduces the theory of the internal structure of stars and their evolution in time. It presents the basic physics of stellar interiors, methods for solving the underlying equations, and the most important results necessary for understanding the wide variety of stellar types and phenomena. The evolution of stars is discussed from their birth through normal evolution to possibly spectacular final stages. Chapters on stellar oscillations and rotation are included

Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

Science.gov (United States)

Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Forbes, Duncan; Hargis, Jonathan R.; Peter, Annika; Pucha, Ragadeepika; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

2018-06-01

We discuss our ongoing observational program to comprehensively map the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. Our results will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. This program has already yielded the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB, and at least two additional candidate satellites. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

Infrared Extinction and Stellar Populations in the Milky Way Midplane

Science.gov (United States)

Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

2012-01-01

The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

Double-helix stellarator

International Nuclear Information System (INIS)

Moroz, P.E.

1997-09-01

A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A ∼ 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-β MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications

Cold disks : Spitzer spectroscopy of disks around young stars with large gaps

NARCIS (Netherlands)

Blake, G. A.; Dullemond, C. P.; Merin, B.; Augereau, J. C.; Boogert, A. C. A.; Evans, N. J.; Geers, V. C.; Lahuis, F.; Kessler-Silacci, J. E.; Pontoppidan, K. M.; van Dishoeck, E. F.; Brown, J.M.

2007-01-01

We have identified four circumstellar disks with a deficit of dust emission from their inner 15-50 AU. All four stars have F-G spectral type and were uncovered as part of the Spitzer Space Telescope "Cores to Disks" Legacy Program Infrared Spectrograph (IRS) first-look survey of similar to 100 pre -

Spitzer Imaging of Planck-Herschel Dusty Proto-Clusters at z=2-3

Science.gov (United States)

Cooray, Asantha; Ma, Jingzhe; Greenslade, Joshua; Kubo, Mariko; Nayyeri, Hooshang; Clements, David; Cheng, Tai-An

2018-05-01

We have recently introduced a new proto-cluster selection technique by combing Herschel/SPIRE imaging data and Planck/HFIk all-sky survey point source catalog. These sources are identified as Planck point sources with clumps of Herschel source over-densities with far-IR colors comparable to z=0 ULIRGS redshifted to z=2 to 3. The selection is sensitive to dusty starbursts and obscured QSOs and we have recovered couple of the known proto-clusters and close to 30 new proto-clusters. The candidate proto-clusters selected from this technique have far-IR flux densities several times higher than those that are optically selected, such as using LBG selection, implying that the member galaxies are in a special phase of heightened dusty starburst and dusty QSO activity. This far-IR luminous phase may be short but likely to be necessary piece to understand the whole stellar mass assembly history of clusters. Moreover, our photo-clusters are missed in optical selections, suggesting that optically selected proto-clusters alone do not provide adequate statistics and a comparison of the far-IR and optical selected clusters may reveal the importance of the dusty stellar mass assembly. Here, we propose IRAC observations of six of the highest priority new proto-clusters, to establish the validity of the technique and to determine the total stellar mass through SED models. For a modest observing time the science program will have a substantial impact on an upcoming science topic in cosmology with implications for observations with JWST and WFIRST to understand the mass assembly in the universe.

The Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) Survey: Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

Science.gov (United States)

Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Peter, Annika; Price, Paul A.; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

2017-01-01

We discuss the first results of our observational program to comprehensively map nearly the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. These will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. We will detail our discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

SPITZER, GAIA, AND THE POTENTIAL OF THE MILKY WAY

International Nuclear Information System (INIS)

Price-Whelan, Adrian M.; Johnston, Kathryn V.

2013-01-01

Near-future data from ESA's Gaia mission will provide precise, full phase-space information for hundreds of millions of stars out to heliocentric distances of ∼10 kpc. This ''horizon'' for full phase-space measurements is imposed by the Gaia parallax errors degrading to worse than 10%, and could be significantly extended by an accurate distance indicator. Recent work has demonstrated how Spitzer observations of RR Lyrae stars can be used to make distance estimates accurate to 2%, effectively extending the Gaia, precise-data horizon by a factor of 10 in distance and a factor of 1000 in volume. This Letter presents one approach to exploit data of such accuracy to measure the Galactic potential using small samples of stars associated with debris from satellite destruction. The method is tested with synthetic observations of 100 stars from the end point of a simulation of satellite destruction: the shape, orientation, and depth of the potential used in the simulation are recovered to within a few percent. The success of this simple test with such a small sample in a single debris stream suggests that constraints from multiple streams could be combined to examine the Galaxy's dark matter halo in even more detail—a truly unique opportunity that is enabled by the combination of Spitzer and Gaia with our intimate perspective on our own Galaxy

GALAXY FORMATION WITH COLD GAS ACCRETION AND EVOLVING STELLAR INITIAL MASS FUNCTION

International Nuclear Information System (INIS)

Kang Xi; Lin, W. P.; Skibba, Ramin; Chen, D. N.

2010-01-01

The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the ΛCDM model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models (SAMs) of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0. In addition, there is a strong correlation between star formation rate (SFR) and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using an SAM that includes (1) cold gas accretion in massive halos at high redshift; (2) tidal stripping of stellar mass from satellite galaxies; and (3) an evolving stellar initial mass function (IMF; bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from (1) and (2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, while the combined effects of (1) and (3) can reproduce the correlation between SFR and stellar mass for star-forming galaxies across a wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.

VizieR Online Data Catalog: Spitzer observations of Taurus members (Luhman+, 2010)

Science.gov (United States)

Luhman, K. L.; Allen, P. R.; Espaillat, C.; Hartmann, L.; Calvet, N.

2016-03-01

For our census of the disk population in Taurus, we use images at 3.6, 4.5, 5.8, and 8.0um obtained with Spitzer's Infrared Array Camera (IRAC) and images at 24um obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The cameras produced images with FWHM=1.6"-1.9" from 3.6 to 8.0um and FWHM=5.9" at 24um. The available data were obtained through Guaranteed Time Observations for PID = 6, 36, 37 (G. Fazio), 53 (G. Rieke), 94 (C. Lawrence), 30540 (G. Fazio, J. Houck), and 40302 (J. Houck), Director's Discretionary Time for PID = 462 (L. Rebull), Legacy programs for PID = 139, 173 (N. Evans), and 30816 (D. Padgett), and General Observer programs for PID = 3584 (D. Padgett), 20302 (P. Andre), 20386 (P. Myers), 20762 (J. Swift), 30384 (T. Bourke), 40844 (C. McCabe), and 50584 (D. Padgett). The IRAC and MIPS observations were performed through 180 and 137 Astronomical Observation Requests (AORs), respectively. The characteristics of the resulting images are summarized in Tables 1 and 2. (6 data files).

SPITZER PARALLAX OF OGLE-2015-BLG-0966: A COLD NEPTUNE IN THE GALACTIC DISK

Energy Technology Data Exchange (ETDEWEB)

Street, R. A.; Bachelet, E. [LCOGT, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Novati, S. Calchi [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Hundertmark, M. P. G.; Jørgensen, U. G. [Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5, DK-1350—Copenhagen K (Denmark); Zhu, W.; Gould, A. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Yee, J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tsapras, Y. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), D-69120 Heidelberg (Germany); Bennett, D. P. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Dominik, M. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Andersen, M. I. [Niels Bohr Institute and Dark Cosmology Centre, University of Copenhagen, Juliane Mariesvej 30, DK-2100—Copenhagen Ø (Denmark); Bozza, V. [Dipartimento di Fisica “E.R. Caianiello,” Università di Salerno, Via Giovanni Paolo II 132, I-84084, Fisciano (Italy); Bramich, D. M. [Qatar Environment and Energy Research Institute, Qatar Foundation, P.O. Box 5825, Doha (Qatar); Collaboration: RoboNet Project and MiNDSTEp Consortium; OGLE Project; Spitzer Team; MOA Collaboration; KMTNet Modeling Team; and others

2016-03-10

We report the detection of a cold Neptune m{sub planet} = 21 ± 2 M{sub ⊕} orbiting a 0.38 M{sub ⊙} M dwarf lying 2.5–3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near to mid-disk and are clearly not in the Galactic bulge.

Ripple transport in helical-axis advanced stellarators - a comparison with classical stellarator/torsatrons

International Nuclear Information System (INIS)

Beidler, C.D.; Hitchon, W.N.G.

1993-08-01

Calculations of the neoclassical transport rates due to particles trapped in the helical ripples of a stellarator's magnetic field are carried out, based on solutions of the bounce-averaged kinetic equation. These calculations employ a model for the magnetic field strength, B, which is an accurate approximation to the actual B for a wide variety of stellarator-type devices, among which are Helical-Axis Advanced Stellarators (Helias) as well as conventional stellarators and torsatrons. Comparisons are carried out in which it is shown that the Helias concept leads to significant reductions in neoclassical transport rates throughout the entire long-mean-free-path regime, with the reduction being particularly dramatic in the ν -1 regime. These findings are confirmed by numerical simulations. Further, it is shown that the behavior of deeply trapped particles in Helias can be fundamentally different from that in classical stellarator/torsatrons; as a consequence, the beneficial effects of a radial electric field on the transport make themselves felt at lower collision frequency than is usual. (orig.)

Convection and stellar oscillations

DEFF Research Database (Denmark)

Aarslev, Magnus Johan

2017-01-01

for asteroseismology, because of the challenges inherent in modelling turbulent convection in 1D stellar models. As a result of oversimplifying the physics near the surface, theoretical calculations systematically overestimate the oscillation frequencies. This has become known as the asteroseismic surface effect. Due...... to lacking better options, this frequency difference is typically corrected for with ad-hoc formulae. The topic of this thesis is the improvement of 1D stellar convection models and the effects this has on asteroseismic properties. The source of improvements is 3D simulations of radiation...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them...

Stellarator Research Opportunities: A report of the National Stellarator Coordinating Committee

Energy Technology Data Exchange (ETDEWEB)

Gates, David A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Anderson, David [University of Wisconsin-Madison

2017-06-01

This document is the product of a stellarator community workshop, organized by the National Stellarator Coordinating Committee and referred to as Stellcon, that was held in Cambridge, Massachusetts in February 2016, hosted by MIT. The workshop was widely advertised, and was attended by 40 scientists from 12 different institutions including national labs, universities and private industry, as well as a representative from the Department of Energy. The final section of this document describes areas of community wide consensus that were developed as a result of the discussions held at that workshop. Areas where further study would be helpful to generate a consensus path forward for the US stellarator program are also discussed. The program outlined in this document is directly responsive to many of the strategic priorities of FES as articulated in “Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)” [2]. The natural disruption immunity of the stellarator directly addresses “Elimination of transient events that can be deleterious to toroidal fusion plasma confinement devices” an area of critical importance for the U.S. fusion energy sciences enterprise over the next decade. Another critical area of research “Strengthening our partnerships with international research facilities,” is being significantly advanced on the W7-X stellarator in Germany and serves as a test-bed for development of successful international collaboration on ITER. This report also outlines how materials science as it relates to plasma and fusion sciences, another critical research area, can be carried out effectively in a stellarator. Additionally, significant advances along two of the Research Directions outlined in the report; “Burning Plasma Science: Foundations - Next-generation research capabilities”, and “Burning Plasma Science: Long pulse - Sustainment of Long-Pulse Plasma Equilibria” are proposed.

Stellarator Research Opportunities: A Report of the National Stellarator Coordinating Committee

Science.gov (United States)

Gates, D. A.; Anderson, D.; Anderson, S.; Zarnstorff, M.; Spong, D. A.; Weitzner, H.; Neilson, G. H.; Ruzic, D.; Andruczyk, D.; Harris, J. H.; Mynick, H.; Hegna, C. C.; Schmitz, O.; Talmadge, J. N.; Curreli, D.; Maurer, D.; Boozer, A. H.; Knowlton, S.; Allain, J. P.; Ennis, D.; Wurden, G.; Reiman, A.; Lore, J. D.; Landreman, M.; Freidberg, J. P.; Hudson, S. R.; Porkolab, M.; Demers, D.; Terry, J.; Edlund, E.; Lazerson, S. A.; Pablant, N.; Fonck, R.; Volpe, F.; Canik, J.; Granetz, R.; Ware, A.; Hanson, J. D.; Kumar, S.; Deng, C.; Likin, K.; Cerfon, A.; Ram, A.; Hassam, A.; Prager, S.; Paz-Soldan, C.; Pueschel, M. J.; Joseph, I.; Glasser, A. H.

2018-02-01

This document is the product of a stellarator community workshop, organized by the National Stellarator Coordinating Committee and referred to as Stellcon, that was held in Cambridge, Massachusetts in February 2016, hosted by MIT. The workshop was widely advertised, and was attended by 40 scientists from 12 different institutions including national labs, universities and private industry, as well as a representative from the Department of Energy. The final section of this document describes areas of community wide consensus that were developed as a result of the discussions held at that workshop. Areas where further study would be helpful to generate a consensus path forward for the US stellarator program are also discussed. The program outlined in this document is directly responsive to many of the strategic priorities of FES as articulated in "Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)" [1]. The natural disruption immunity of the stellarator directly addresses "Elimination of transient events that can be deleterious to toroidal fusion plasma confinement devices" an area of critical importance for the US fusion energy sciences enterprise over the next decade. Another critical area of research "Strengthening our partnerships with international research facilities," is being significantly advanced on the W7-X stellarator in Germany and serves as a test-bed for development of successful international collaboration on ITER. This report also outlines how materials science as it relates to plasma and fusion sciences, another critical research area, can be carried out effectively in a stellarator. Additionally, significant advances along two of the Research Directions outlined in the report; "Burning Plasma Science: Foundations - Next-generation research capabilities", and "Burning Plasma Science: Long pulse - Sustainment of Long-Pulse Plasma Equilibria" are proposed.

Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

Science.gov (United States)

Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

2013-05-01

Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

A comparison of LBGs, DRGs, and BzK galaxies: their contribution to the stellar mass density in the GOODS-MUSIC sample

Science.gov (United States)

Grazian, A.; Salimbeni, S.; Pentericci, L.; Fontana, A.; Nonino, M.; Vanzella, E.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Santini, P.

2007-04-01

Context: The classification scheme for high redshift galaxies is complex at the present time, with simple colour-selection criteria (i.e. EROs, IEROs, LBGs, DRGs, BzKs), resulting in ill-defined properties for the stellar mass and star formation rate of these distant galaxies. Aims: The goal of this work is to investigate the properties of different classes of high-z galaxies, focusing in particular on the stellar masses of LBGs, DRGs, and BzKs, in order to derive their contribution to the total mass budget of the distant Universe. Methods: We used the GOODS-MUSIC catalog, containing ~3000 Ks-selected (~10 000 z-selected) galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8~μm band, with spectroscopic or accurate photometric redshifts. We selected samples of BM/BX/LBGs, DRGs, and BzK galaxies to discuss the overlap and the limitations of these criteria, which can be overridden by a selection criterion based on physical parameters. We then measured the stellar masses of these galaxies and computed the stellar mass density (SMD) for the different samples up to redshift ≃4. Results: We show that the BzK-PE criterion is not optimal for selecting early type galaxies at the faint end. On the other hand, BzK-SF is highly contaminated by passively evolving galaxies at red z-Ks colours. We find that LBGs and DRGs contribute almost equally to the global SMD at z≥ 2 and, in general, that star-forming galaxies form a substantial fraction of the universal SMD. Passively evolving galaxies show a strong negative density evolution from redshift 2 to 3, indicating that we are witnessing the epoch of mass assembly of such objects. Finally we have indications that by pushing the selection to deeper magnitudes, the contribution of less massive DRGs could overtake that of LBGs. Deeper surveys, like the HUDF, are required to confirm this suggestion.

The “Building Blocks” of Stellar Halos

Directory of Open Access Journals (Sweden)

Kyle A. Oman

2017-08-01

Full Text Available The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the apostle project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ∼0.2–0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.

Metal-rich, Metal-poor: Updated Stellar Population Models for Old Stellar Systems

Science.gov (United States)

Conroy, Charlie; Villaume, Alexa; van Dokkum, Pieter G.; Lind, Karin

2018-02-01

We present updated stellar population models appropriate for old ages (>1 Gyr) and covering a wide range in metallicities (‑1.5 ≲ [Fe/H] ≲ 0.3). These models predict the full spectral variation associated with individual element abundance variation as a function of metallicity and age. The models span the optical–NIR wavelength range (0.37–2.4 μm), include a range of initial mass functions, and contain the flexibility to vary 18 individual elements including C, N, O, Mg, Si, Ca, Ti, and Fe. To test the fidelity of the models, we fit them to integrated light optical spectra of 41 Galactic globular clusters (GCs). The value of testing models against GCs is that their ages, metallicities, and detailed abundance patterns have been derived from the Hertzsprung–Russell diagram in combination with high-resolution spectroscopy of individual stars. We determine stellar population parameters from fits to all wavelengths simultaneously (“full spectrum fitting”), and demonstrate explicitly with mock tests that this approach produces smaller uncertainties at fixed signal-to-noise ratio than fitting a standard set of 14 line indices. Comparison of our integrated-light results to literature values reveals good agreement in metallicity, [Fe/H]. When restricting to GCs without prominent blue horizontal branch populations, we also find good agreement with literature values for ages, [Mg/Fe], [Si/Fe], and [Ti/Fe].

The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud Observed with IRAC and MIPS

Science.gov (United States)

Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jorgensen, Jes K.;

Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions

Directory of Open Access Journals (Sweden)

Douglas Rubin

2011-01-01

Full Text Available The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates >10-5M⨀yr−1 in the vicinity of ~1″. For present-day mass functions of the form, dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass ≲7M⨀ and a power-law slope ≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

Principles of Stellar Interferometry

CERN Document Server

Glindemann, Andreas

2011-01-01

Over the last decade, stellar interferometry has developed from a specialist tool to a mainstream observing technique, attracting scientists whose research benefits from milliarcsecond angular resolution. Stellar interferometry has become part of the astronomer’s toolbox, complementing single-telescope observations by providing unique capabilities that will advance astronomical research. This carefully written book is intended to provide a solid understanding of the principles of stellar interferometry to students starting an astronomical research project in this field or to develop instruments and to astronomers using interferometry but who are not interferometrists per se. Illustrated by excellent drawings and calculated graphs the imaging process in stellar interferometers is explained starting from first principles on light propagation and diffraction wave propagation through turbulence is described in detail using Kolmogorov statistics the impact of turbulence on the imaging process is discussed both f...

Advanced stellarator power plants

International Nuclear Information System (INIS)

Miller, R.L.

1994-01-01

The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies

Compact stellarator coils

International Nuclear Information System (INIS)

Pomphrey, N.; Berry, L.A.; Boozer, A.H.

2001-01-01

Experimental devices to study the physics of high-beta (β>∼4%), low aspect ratio (A<∼4.5) stellarator plasmas require coils that will produce plasmas satisfying a set of physics goals, provide experimental flexibility, and be practical to construct. In the course of designing a flexible coil set for the National Compact Stellarator Experiment, we have made several innovations that may be useful in future stellarator design efforts. These include: the use of Singular Value Decomposition methods for obtaining families of smooth current potentials on distant coil winding surfaces from which low current density solutions may be identified; the use of a Control Matrix Method for identifying which few of the many detailed elements of the stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of Genetic Algorithms for choosing an optimal set of discrete coils from a continuum of potential contours; the evaluation of alternate coil topologies for balancing the tradeoff between physics objective and engineering constraints; the development of a new coil optimization code for designing modular coils, and the identification of a 'natural' basis for describing current sheet distributions. (author)

Use of the stellarator expansion to investigate plasma equilibrium in modular stellarators

International Nuclear Information System (INIS)

Anania, G.; Johnson, J.L.; Weimer, K.E.

1982-11-01

A numerical code utilizing a large-aspect ratio, small-helical-distortion expansion is developed and used to investigate the effect of plasma currents on stellarator equilibrium. Application to modular stellarator configurations shows that a large rotational transform, and hence large coil deformation, is needed to achieve high-beta equilibria

Stellar CME candidates: towards a stellar CME-flare relation

Science.gov (United States)

Paraskevi Moschou, Sofia; Drake, Jeremy J.; Cohen, Ofer; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

2018-06-01

For decades the Sun has been the only star that allowed for direct CME observations. Recently, with the discovery of multiple extrasolar systems, it has become imperative that the role of stellar CMEs be assessed in the context of exoplanetary habitability. Solar CMEs and flares show a higher association with increasing flaring energy, with strong flares corresponding to large and fast CMEs. As argued in earlier studies, extrasolar environments around active stars are potentially dominated by CMEs, as a result of their extreme flaring activity. This has strong implications for the energy budget of the system and the atmospheric erosion of orbiting planets.Nevertheless, with current instrumentation we are unable to directly observe CMEs in even the closest stars, and thus we have to look for indirect techniques and observational evidence and signatures for the eruption of stellar CMEs. There are three major observational techniques for tracing CME signatures in other stellar systems, namely measuring Type II radio bursts, Doppler shifts in UV/optical lines or transient absorption in the X-ray spectrum. We present observations of the most probable stellar CME candidates captured so far and examine the different observational techniques used together with their levels of uncertainty. Assuming that they were CMEs, we try to asses their kinematic and energetic characteristics and place them in an extension of the well-established solar CME-flare energy scaling law. We finish by discussing future observations for direct measurements.

Stellar wind theory

International Nuclear Information System (INIS)

Summers, D.

1980-01-01

The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

Stellarator fusion neutronics research in Australia

International Nuclear Information System (INIS)

Zimin, S.; Cross, R.C.

1997-01-01

The new status of the H-INF Heliac Stellaralor as a National Facility and the signed international Implementing Agreement on 'Collaboration in the Development of the Stellarator Concept' represents a significant encouragement for further fusion research in Australia. In this report the future of fusion research in Australia is discussed with special attention being paid to the importance of Stellarator power plant studies and in particular stellarator fusion neutronics. The main differences between tokamak and stellarator neutronics analyses are identified, namely the neutron wall loading, geometrical modelling and total heating in in-vessel reactor components including toroidal field (TF) coils. Due to the more complicated nature of stellarator neutronics analyses, simplified approaches to fusion neutronics already developed for tokamaks are expected to be even more important and widely used for designing a Conceptual Stellarator Power Plant

SPITZER ULTRA FAINT SURVEY PROGRAM (SURFS UP). II. IRAC-DETECTED LYMAN-BREAK GALAXIES AT 6 ≲ z ≲ 10 BEHIND STRONG-LENSING CLUSTERS

Energy Technology Data Exchange (ETDEWEB)

Huang, Kuang-Han; Bradač, Maruša; Hoag, Austin; Cain, Benjamin; Lubin, L. M.; Knight, Robert I. [University of California Davis, 1 Shields Avenue, Davis, CA 95616 (United States); Lemaux, Brian C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Ryan, R. E. Jr.; Brammer, Gabriel B. [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Castellano, Marco; Amorin, Ricardo; Fontana, Adriano; Merlin, Emiliano [INAF—Osservatorio Astronomico di Roma Via Frascati 33, I-00040 Monte Porzio Catone (Italy); Schmidt, Kasper B. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Schrabback, Tim [Argelander-Institut für Astronomie, Auf Dem Hügel 71, D-53121 Bonn (Germany); Treu, Tommaso [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States); Gonzalez, Anthony H. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States); Linden, Anja von der, E-mail: khhuang@ucdavis.edu, E-mail: astrokuang@gmail.com [Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305 (United States)

2016-01-20

We study the stellar population properties of the IRAC-detected 6 ≲ z ≲ 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a total of 17 galaxy candidates at 6 ≲ z ≲ 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios  ≥ 3 in at least one of the IRAC 3.6 and 4.5 μm channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of ∼1.2–5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M{sub 1600} are between −21.2 and −18.9 mag, while their intrinsic stellar masses are between 2 × 10{sup 8}M{sub ⊙} and 2.9 × 10{sup 9}M{sub ⊙}. We identify two Lyα emitters in our sample from the Keck DEIMOS spectra, one at z{sub Lyα} = 6.76 (in RXJ 1347) and one at z{sub Lyα} = 6.32 (in MACS 0454). We find that 4 out of 17 z ≳ 6 galaxy candidates are favored by z ≲ 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC [3.6]–[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.

The Galactic Distribution of Planets via Spitzer Microlensing Parallax

Science.gov (United States)

Gould, Andrew; Yee, Jennifer; Carey, Sean; Shvartzvald, Yossi

2018-05-01

We will measure the Galactic distribution of planets by obtaining 'microlens parallaxes' of about 200 events, including 3 planetary events, from the comparison of microlens lightcurves observed from Spitzer and Earth, which are separated by >1.5 AU in projection. The proposed observations are part of a campaign that we have conducted with Spitzer since 2014. The planets expected to be identified in this campaign when combined with previous work will yield a first statistically significant measurement of the frequency of planets in the Galactic bulge versus the Galactic disk. As we have demonstrated in three previous programs, the difference in these lightcurves yields both the 'microlens parallax' (ratio of the lens-source relative parallax) to the Einstein radius, and the direction of lens-source relative motion. For planetary events, this measurement directly yields the mass and distance of the planet. This proposal is significantly more sensitive to planets than previous work because it takes advantage of the KMTNet observing strategy that covers >85 sq.deg t >0.4/hr cadence, 24/7 from 3 southern observatories and a alert system KMTNet is implementing for 2019. This same observing program also provides a unique probe of dark objects. It will yield an improved measurement of the isolated-brown-dwarf mass function. Thirteen percent of the observations will specifically target binaries, which will probe systems with dark components (brown dwarfs, neutron stars, black holes) that are difficult or impossible to investigate by other methods. The observations and methods from this work are a test bed for WFIRST microlensing.

The Galactic stellar disc

International Nuclear Information System (INIS)

Feltzing, S; Bensby, T

2008-01-01

The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies.

YOUNG STELLAR OBJECTS IN THE GOULD BELT

Energy Technology Data Exchange (ETDEWEB)

Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Allen, Lori E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Evans II, Neal J.; Harvey, Paul M. [Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); Broekhoven-Fiene, Hannah [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6 (Canada); Cieza, Lucas A. [Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Di Francesco, James; Johnstone, Doug; Matthews, Brenda C. [National Research Council of Canada, Herzberg Astronomy and Astrophysics Programs, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Gutermuth, Robert A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Hatchell, Jennifer [Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Heiderman, Amanda [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Huard, Tracy L. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Kirk, Jason M. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Miller, Jennifer F. [Gemini Observatory, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Peterson, Dawn E. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Young, Kaisa E., E-mail: mdunham@cfa.harvard.edu [Department of Physical Sciences, Nicholls State University, P.O. Box 2022, Thibodaux, LA 70310 (United States)

2015-09-15

We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope “cores to disks” (c2d) and “Gould Belt” (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40–0.78 Myr for Class 0 + I YSOs and 0.26–0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13–0.26 Myr (Class 0) and 0.27–0.52 Myr (Class I). We revisit infrared color–color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.

YOUNG STELLAR OBJECTS IN THE GOULD BELT

International Nuclear Information System (INIS)

Dunham, Michael M.; Allen, Lori E.; Evans II, Neal J.; Harvey, Paul M.; Broekhoven-Fiene, Hannah; Cieza, Lucas A.; Di Francesco, James; Johnstone, Doug; Matthews, Brenda C.; Gutermuth, Robert A.; Hatchell, Jennifer; Heiderman, Amanda; Huard, Tracy L.; Kirk, Jason M.; Miller, Jennifer F.; Peterson, Dawn E.; Young, Kaisa E.

2015-01-01

We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope “cores to disks” (c2d) and “Gould Belt” (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40–0.78 Myr for Class 0 + I YSOs and 0.26–0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13–0.26 Myr (Class 0) and 0.27–0.52 Myr (Class I). We revisit infrared color–color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs

Quasisymmetry equations for conventional stellarators

International Nuclear Information System (INIS)

Pustovitov, V.D.

1994-11-01

General quasisymmetry condition, which demands the independence of B 2 on one of the angular Boozer coordinates, is reduced to two equations containing only geometrical characteristics and helical field of a stellarator. The analysis is performed for conventional stellarators with a planar circular axis using standard stellarator expansion. As a basis, the invariant quasisymmetry condition is used. The quasisymmetry equations for stellarators are obtained from this condition also in an invariant form. Simplified analogs of these equations are given for the case when averaged magnetic surfaces are circular shifted torii. It is shown that quasisymmetry condition can be satisfied, in principle, in a conventional stellarator by a proper choice of two satellite harmonics of the helical field in addition to the main harmonic. Besides, there appears a restriction on the shift of magnetic surfaces. Thus, in general, the problem is closely related with that of self-consistent description of a configuration. (author)

Stellar formation

CERN Document Server

Reddish, V C

1978-01-01

Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

Energy Technology Data Exchange (ETDEWEB)

Saral, G.; Hora, J. L.; Willis, S. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Gutermuth, R. A. [University of Massachusetts, Department of Astronomy, Amherst, MA 01003 (United States); Saygac, A. T., E-mail: gsaral@cfa.harvard.edu [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

2015-11-01

We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

Optimizing Stellarators for Turbulent Transport

International Nuclear Information System (INIS)

Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.

2010-01-01

Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

SPITZER survey of dust grain processing in stable discs around binary post-AGB stars

NARCIS (Netherlands)

Gielen, C.; van Winckel, H.; Min, M.; Waters, L.B.F.M.; Lloyd Evans, T.

2008-01-01

Aims. We investigate the mineralogy and dust processing in the circumbinary discs of binary post-AGB stars using high-resolution TIMMI2 and SPITZER infrared spectra. Methods: We perform a full spectral fitting to the infrared spectra using the most recent opacities of amorphous and crystalline dust

Stellar Structure and Evolution

CERN Document Server

Kippenhahn, Rudolf; Weiss, Achim

2013-01-01

This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

Spitzer and z' secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b

Energy Technology Data Exchange (ETDEWEB)

Beatty, Thomas G.; Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Collins, Karen A.; Kielkopf, John F. [Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292 (United States); Fortney, Jonathan [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Knutson, Heather [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Bruns, Jacob M. [Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States); Showman, Adam P. [Lunar and Planetary Laboratory, 1629 E. University Blvd., University of Arizona, Tucson, AZ (United States); Eastman, Jason [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Santa Barbara, CA 93117 (United States); Pepper, Joshua [Department of Physics, Lehigh University, Bethlehem, PA 18015 (United States); Siverd, Robert J.; Stassun, Keivan G., E-mail: tbeatty@astronomy.ohio-state.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)

2014-03-10

We present secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b. These observations represent the first constraints on the atmospheric dynamics of a highly irradiated brown dwarf, the atmospheres of irradiated giant planets at high surface gravity, and the atmospheres of brown dwarfs that are dominated by external, rather than internal, energy. Using the Spitzer Space Telescope, we measure secondary eclipse depths of 0.195% ± 0.010% at 3.6 μm and 0.200% ± 0.012% at 4.5 μm. We also find tentative evidence for the secondary eclipse in the z' band with a depth of 0.049% ± 0.023%. These measured eclipse depths are most consistent with an atmosphere model in which there is a strong substellar hotspot, implying that heat redistribution in the atmosphere of KELT-1b is low. While models with a more mild hotspot or even with dayside heat redistribution are only marginally disfavored, models with complete heat redistribution are strongly ruled out. The eclipse depths also prefer an atmosphere with no TiO inversion layer, although a model with TiO inversion is permitted in the dayside heat redistribution case, and we consider the possibility of a day-night TiO cold trap in this object. For the first time, we compare the IRAC colors of brown dwarfs and hot Jupiters as a function of effective temperature. Importantly, our measurements reveal that KELT-1b has a [3.6] – [4.5] color of 0.07 ± 0.11, identical to that of isolated brown dwarfs of similarly high temperature. In contrast, hot Jupiters generally show redder [3.6] – [4.5] colors of ∼0.4, with a very large range from ∼0 to ∼1. Evidently, despite being more similar to hot Jupiters than to isolated brown dwarfs in terms of external forcing of the atmosphere by stellar insolation, KELT-1b appears to have an atmosphere most like that of other brown dwarfs. This suggests that surface gravity is very important in controlling the atmospheric systems of substellar mass bodies.

Results of Compact Stellarator Engineering Trade Studies

International Nuclear Information System (INIS)

Brown, Tom; Bromberg, L.; Cole, M.

2009-01-01

A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study

Results of Compact Stellarator Engineering Trade Studies

International Nuclear Information System (INIS)

Brown, T.; Bromberg, L.; Cole, M.

2009-01-01

A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

A Review of Stellar Abundance Databases and the Hypatia Catalog Database

Science.gov (United States)

Hinkel, Natalie Rose

2018-01-01

The astronomical community is interested in elements from lithium to thorium, from solar twins to peculiarities of stellar evolution, because they give insight into different regimes of star formation and evolution. However, while some trends between elements and other stellar or planetary properties are well known, many other trends are not as obvious and are a point of conflict. For example, stars that host giant planets are found to be consistently enriched in iron, but the same cannot be definitively said for any other element. Therefore, it is time to take advantage of large stellar abundance databases in order to better understand not only the large-scale patterns, but also the more subtle, small-scale trends within the data.In this overview to the special session, I will present a review of large stellar abundance databases that are both currently available (i.e. RAVE, APOGEE) and those that will soon be online (i.e. Gaia-ESO, GALAH). Additionally, I will discuss the Hypatia Catalog Database (www.hypatiacatalog.com) -- which includes abundances from individual literature sources that observed stars within 150pc. The Hypatia Catalog currently contains 72 elements as measured within ~6000 stars, with a total of ~240,000 unique abundance determinations. The online database offers a variety of solar normalizations, stellar properties, and planetary properties (where applicable) that can all be viewed through multiple interactive plotting interfaces as well as in a tabular format. By analyzing stellar abundances for large populations of stars and from a variety of different perspectives, a wealth of information can be revealed on both large and small scales.

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

Science.gov (United States)

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G; Serenelli, Aldo M; Sheffield, Allyson; Li, Ting S; Casagrande, Luca; Johnston, Kathryn V; Laporte, Chervin F P; Price-Whelan, Adrian M; Schönrich, Ralph; Gould, Andrew

2018-03-15

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

A TWO-COMPONENT POWER LAW COVERING NEARLY FOUR ORDERS OF MAGNITUDE IN THE POWER SPECTRUM OF SPITZER FAR-INFRARED EMISSION FROM THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Block, David L.; Puerari, Ivanio; Elmegreen, Bruce G.; Bournaud, Frederic

2010-01-01

Power spectra of Large Magellanic Cloud (LMC) emission at 24, 70, and 160 μm observed with the Spitzer Space Telescope have a two-component power-law structure with a shallow slope of -1.6 at low wavenumber, k, and a steep slope of -2.9 at high k. The break occurs at k -1 ∼ 100-200 pc, which is interpreted as the line-of-sight thickness of the LMC disk. The slopes are slightly steeper for longer wavelengths, suggesting the cooler dust emission is smoother than the hot emission. The power spectrum (PS) covers ∼3.5 orders of magnitude, and the break in the slope is in the middle of this range on a logarithmic scale. Large-scale driving from galactic and extragalactic processes, including disk self-gravity, spiral waves, and bars, presumably causes the low-k structure in what is effectively a two-dimensional geometry. Small-scale driving from stellar processes and shocks causes the high-k structure in a three-dimensional geometry. This transition in dimensionality corresponds to the observed change in PS slope. A companion paper models the observed power law with a self-gravitating hydrodynamics simulation of a galaxy like the LMC.

Including collisions in gyrokinetic tokamak and stellarator simulations

International Nuclear Information System (INIS)

Kauffmann, Karla

2012-01-01

Particle and heat transport in fusion devices often exceed the neoclassical prediction. This anomalous transport is thought to be produced by turbulence caused by microinstabilities such as ion and electron-temperature-gradient (ITG/ETG) and trapped-electron-mode (TEM) instabilities, the latter ones known for being strongly influenced by collisions. Additionally, in stellarators, the neoclassical transport can be important in the core, and therefore investigation of the effects of collisions is an important field of study. Prior to this thesis, however, no gyrokinetic simulations retaining collisions had been performed in stellarator geometry. In this work, collisional effects were added to EUTERPE, a previously collisionless gyrokinetic code which utilizes the δf method. To simulate the collisions, a pitch-angle scattering operator was employed, and its implementation was carried out following the methods proposed in [Takizuka and Abe 1977, Vernay Master's thesis 2008]. To test this implementation, the evolution of the distribution function in a homogeneous plasma was first simulated, where Legendre polynomials constitute eigenfunctions of the collision operator. Also, the solution of the Spitzer problem was reproduced for a cylinder and a tokamak. Both these tests showed that collisions were correctly implemented and that the code is suited for more complex simulations. As a next step, the code was used to calculate the neoclassical radial particle flux by neglecting any turbulent fluctuations in the distribution function and the electric field. Particle fluxes in the neoclassical analytical regimes were simulated for tokamak and stellarator (LHD) configurations. In addition to the comparison with analytical fluxes, a successful benchmark with the DKES code was presented for the tokamak case, which further validates the code for neoclassical simulations. In the final part of the work, the effects of collisions were investigated for slab and toroidal ITGs and

Including collisions in gyrokinetic tokamak and stellarator simulations

Energy Technology Data Exchange (ETDEWEB)

Kauffmann, Karla

2012-04-10

Particle and heat transport in fusion devices often exceed the neoclassical prediction. This anomalous transport is thought to be produced by turbulence caused by microinstabilities such as ion and electron-temperature-gradient (ITG/ETG) and trapped-electron-mode (TEM) instabilities, the latter ones known for being strongly influenced by collisions. Additionally, in stellarators, the neoclassical transport can be important in the core, and therefore investigation of the effects of collisions is an important field of study. Prior to this thesis, however, no gyrokinetic simulations retaining collisions had been performed in stellarator geometry. In this work, collisional effects were added to EUTERPE, a previously collisionless gyrokinetic code which utilizes the {delta}f method. To simulate the collisions, a pitch-angle scattering operator was employed, and its implementation was carried out following the methods proposed in [Takizuka and Abe 1977, Vernay Master's thesis 2008]. To test this implementation, the evolution of the distribution function in a homogeneous plasma was first simulated, where Legendre polynomials constitute eigenfunctions of the collision operator. Also, the solution of the Spitzer problem was reproduced for a cylinder and a tokamak. Both these tests showed that collisions were correctly implemented and that the code is suited for more complex simulations. As a next step, the code was used to calculate the neoclassical radial particle flux by neglecting any turbulent fluctuations in the distribution function and the electric field. Particle fluxes in the neoclassical analytical regimes were simulated for tokamak and stellarator (LHD) configurations. In addition to the comparison with analytical fluxes, a successful benchmark with the DKES code was presented for the tokamak case, which further validates the code for neoclassical simulations. In the final part of the work, the effects of collisions were investigated for slab and toroidal

Size and Albedo of Irregular Saturnian Satellites from Spitzer Observations

Science.gov (United States)

Mueller, Michael; Grav, T.; Trilling, D.; Stansberry, J.; Sykes, M.

2008-09-01

Using MIPS onboard the Spitzer Space Telescope, we observed the thermal emission (24 and, for some targets, 70 um) of eight irregular satellites of Saturn: Albiorix, Siarnaq, Paaliaq, Kiviuq, Ijiraq, Tarvos, Erriapus, and Ymir. We determined the size and albedo of all targets. An analysis of archived MIPS observations of Phoebe reproduces Cassini results very accurately, thereby validating our method. For all targets, the geometric albedo is found to be low, probably below 10% and clearly below 15%. Irregular satellites are much darker than the large regular satellites. Their albedo is, however, quite similar to that of small bodies in the outer Solar System (such as cometary nuclei, Jupiter Trojans, or TNOs). This is consistent with color measurements as well as dynamical considerations which suggest a common origin of the said populations. There appear to be significant object-to-object albedo differences. Similar albedos found for some members of dynamical clusters support the idea that they may have originated in the breakup of a parent body. For three satellites, thermal data at two wavelengths are available, enabling us to constrain their thermal properties. Sub-solar temperatures are similar to that found from Cassini's Phoebe fly-by. This suggests a rather low thermal inertia, as expected for regolith-covered objects. This work is based on observations made with the Spitzer Space Telescope, which is operated by JPL under a contract with NASA. Support for this work was provided by NASA.

SPITZER TRANSITS OF THE SUPER-EARTH GJ1214b AND IMPLICATIONS FOR ITS ATMOSPHERE

Energy Technology Data Exchange (ETDEWEB)

Fraine, Jonathan D.; Deming, Drake [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Gillon, Michaeel; Jehin, Emmanueel [Institute d' Astrophysique et de Geophysique, Universite de Liege, Liege (Belgium); Demory, Brice-Olivier; Benneke, Bjoern; Seager, Sara [Department of Earth, Atmospheric and Planetary Sciences, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Lewis, Nikole K. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Knutson, Heather [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Desert, Jean-Michel, E-mail: jfraine@astro.umd.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

2013-03-10

We observed the transiting super-Earth exoplanet GJ1214b using warm Spitzer at 4.5 {mu}m wavelength during a 20 day quasi-continuous sequence in 2011 May. The goals of our long observation were to accurately define the infrared transit radius of this nearby super-Earth, to search for the secondary eclipse, and to search for other transiting planets in the habitable zone of GJ1214. We here report results from the transit monitoring of GJ1214b, including a reanalysis of previous transit observations by Desert et al. In total, we analyze 14 transits of GJ1214b at 4.5 {mu}m, 3 transits at 3.6 {mu}m, and 7 new ground-based transits in the I+z band. Our new Spitzer data by themselves eliminate cloudless solar composition atmospheres for GJ1214b, and methane-rich models from Howe and Burrows. Using our new Spitzer measurements to anchor the observed transit radii of GJ1214b at long wavelengths, and adding new measurements in I+z, we evaluate models from Benneke and Seager and Howe and Burrows using a {chi}{sup 2} analysis. We find that the best-fit model exhibits an increase in transit radius at short wavelengths due to Rayleigh scattering. Pure water atmospheres are also possible. However, a flat line (no atmosphere detected) remains among the best of the statistically acceptable models, and better than pure water atmospheres. We explore the effect of systematic differences among results from different observational groups, and we find that the Howe and Burrows tholin-haze model remains the best fit, even when systematic differences among observers are considered.

Multiplicity in Early Stellar Evolution

Science.gov (United States)

Reipurth, B.; Clarke, C. J.; Boss, A. P.; Goodwin, S. P.; Rodríguez, L. F.; Stassun, K. G.; Tokovinin, A.; Zinnecker, H.

Observations from optical to centimeter wavelengths have demonstrated that multiple systems of two or more bodies is the norm at all stellar evolutionary stages. Multiple systems are widely agreed to result from the collapse and fragmentation of cloud cores, despite the inhibiting influence of magnetic fields. Surveys of class 0 protostars with millimeter interferometers have revealed a very high multiplicity frequency of about 2/3, even though there are observational difficulties in resolving close protobinaries, thus supporting the possibility that all stars could be born in multiple systems. Near-infrared adaptive optics observations of class I protostars show a lower binary frequency relative to the class 0 phase, a declining trend that continues through the class II/III stages to the field population. This loss of companions is a natural consequence of dynamical interplay in small multiple systems, leading to ejection of members. We discuss observational consequences of this dynamical evolution, and its influence on circumstellar disks, and we review the evolution of circumbinary disks and their role in defining binary mass ratios. Special attention is paid to eclipsing PMS binaries, which allow for observational tests of evolutionary models of early stellar evolution. Many stars are born in clusters and small groups, and we discuss how interactions in dense stellar environments can significantly alter the distribution of binary separations through dissolution of wider binaries. The binaries and multiples we find in the field are the survivors of these internal and external destructive processes, and we provide a detailed overview of the multiplicity statistics of the field, which form a boundary condition for all models of binary evolution. Finally, we discuss various formation mechanisms for massive binaries, and the properties of massive trapezia.

Reduction of the general Spitzer-Haerm problem in plasma physics

International Nuclear Information System (INIS)

Ferreira, A.

1988-01-01

The general Spitzer-Haerm problem is unfolded through a redefinition of the dependent variable into two separate simpler problems. The first takes the form of a second order differential equation, and the second, that of an integration over the solution of the first problem, which provides the distribution function or, directly, the current and the heat flow. It is shown that the current and the heat flow can in general by synthesized from the solutions of the differential equation for two specific forms of the driving term. (author)

The Dynamical Evolution of Stellar-Mass Black Holes in Dense Star Clusters

Science.gov (United States)

Morscher, Maggie

Solar masses. Birth kicks from supernova explosions may eject some black holes from their birth clusters, but most should be retained initially. Using our Monte Carlo code, we have investigated the long-term dynamical evolution of globular clusters containing large numbers of stellar black holes. Our study is the first to explore in detail the dynamics of BHs in clusters through a large number of realistic simulations covering a wide range of initial conditions (cluster masses from 105 -- 106 Solar masses, as well as variation in other key parameters, such as the virial radius, central concentration, and metallicity), that also includes all the required physics. In almost all of our models we find that significant numbers of black holes (up to about a 1000) are retained all the way to the present. This is in contrast to previous theoretical expectations that most black holes should be ejected dynamically within a few Gyr. The main reason for this difference is that core collapse driven by black holes (through the Spitzer "mass segregation instability'') is easily reverted through three-body processes, and involves only a small number of the most massive black holes, while lower-mass black holes remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar black holes does not lead to a long-term physical separation of most black holes into a dynamically decoupled inner core, as often assumed previously; this is one of the most important results of this dissertation. Combined with the recent detections of several black hole X-ray binary candidates in Galactic globular clusters, our results suggest that stellar black holes could still be present in large numbers in many globular clusters today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

Targeted Optimization of Quasi-Symmetric Stellarators

International Nuclear Information System (INIS)

Hegna, Chris C.; Talmadge, J. N.

2016-01-01

The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

Targeted Optimization of Quasi-Symmetric Stellarators

Energy Technology Data Exchange (ETDEWEB)

Hegna, Chris C. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics; Anderson, D. T. [Univ. of Wisconsin, Madison, WI (United States); Talmadge, J. N. [Univ. of Wisconsin, Madison, WI (United States)

2016-10-06

The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

Energy Technology Data Exchange (ETDEWEB)

Jabran Zahid, H. [Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kudritzki, Rolf-Peter; Ho, I-Ting [University of Hawaii at Manoa, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Conroy, Charlie [Department of Astronomy, Harvard University, Cambridge, MA, 02138 (United States); Andrews, Brett, E-mail: zahid@cfa.harvard.edu [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 (United States)

2017-09-20

We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

International Nuclear Information System (INIS)

Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting; Conroy, Charlie; Andrews, Brett

2017-01-01

We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes

Science.gov (United States)

Thilker, David

At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF

Evolution of the stellar mass function in multiple-population globular clusters

Science.gov (United States)

Vesperini, Enrico; Hong, Jongsuk; Webb, Jeremy J.; D'Antona, Franca; D'Ercole, Annibale

2018-05-01

We present the results of a survey of N-body simulations aimed at studying the effects of the long-term dynamical evolution on the stellar mass function (MF) of multiple stellar populations in globular clusters. Our simulations show that if first-(1G) and second-generation (2G) stars have the same initial MF (IMF), the global MFs of the two populations are affected similarly by dynamical evolution and no significant differences between the 1G and 2G MFs arise during the cluster's evolution. If the two populations have different IMFs, dynamical effects do not completely erase memory of the initial differences. Should observations find differences between the global 1G and 2G MFs, these would reveal the fingerprints of differences in their IMFs. Irrespective of whether the 1G and 2G populations have the same global IMF or not, dynamical effects can produce differences between the local (measured at various distances from the cluster centre) 1G and 2G MFs; these differences are a manifestation of the process of mass segregation in populations with different initial structural properties. In dynamically old and spatially mixed clusters, however, differences between the local 1G and 2G MFs can reveal differences between the 1G and 2G global MFs. In general, for clusters with any dynamical age, large differences between the local 1G and 2G MFs are more likely to be associated with differences in the global MF. Our study also reveals a dependence of the spatial mixing rate on the stellar mass, another dynamical consequence of the multiscale nature of multiple-population clusters.

A deep Spitzer survey of circumstellar disks in the young double cluster, h and χ Persei

Energy Technology Data Exchange (ETDEWEB)

Cloutier, Ryan; Currie, Thayne; Jayawardhana, Ray [University of Toronto, 50 St. George Street, Toronto, ON, M5S 2J7 (Canada); Rieke, George H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Kenyon, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02140 (United States); Balog, Zoltan, E-mail: cloutier@cita.utoronto.ca, E-mail: currie@astro.utoronto.ca, E-mail: grieke@as.arizona.edu, E-mail: skenyon@cfa.harvard.edu [Max Planck Institute for Astrophysics, Königstuhl 17, D-69117 Heidelberg (Germany)

2014-12-01

We analyze very deep Infrared Array Camera and Multiband Imaging Photometer for Spitzer (MIPS) photometry of ∼12, 500 members of the 14 Myr old Double Cluster, h and χ Persei, building upon our earlier, shallower Spitzer Cycle 1 studies. Numerous likely members show infrared (IR) excesses at 8 μm and 24 μm, indicative of circumstellar dust. The frequency of stars with 8 μm excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower mass stars). Optical spectroscopy also identifies gas in about 2% of systems, but with no clear trend between the presence of dust and gas. Spectral energy distribution modeling of 18 sources with detections at optical wavelengths through MIPS 24 μm reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, though similar data for all disk-bearing members would provide constraints. Using Monte Carlo simulations, we combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times (τ{sub 0}) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr, respectively. Assuming a revised set of ages for some clusters, these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime than previously thought. In both cases, the transitional disk duration, averaged over multiple evolutionary pathways, is ≈1 Myr. Finally, 24 μm excess frequencies for 4-6 M {sub ☉} stars appear lower than for 1-2.5 M {sub ☉} stars in other 10-30 Myr old clusters.

Exploring the Dust Content of Galactic Winds with Herschel. II. Nearby Dwarf Galaxies*

Science.gov (United States)

McCormick, Alexander; Veilleux, Sylvain; Meléndez, Marcio; Martin, Crystal L.; Bland-Hawthorn, Joss; Cecil, Gerald; Heitsch, Fabian; Müller, Thomas; Rupke, David S. N.; Engelbracht, Chad

2018-03-01

We present results from analysis of deep Herschel Space Observatory observations of six nearby dwarf galaxies known to host galactic-scale winds. The superior far-infrared sensitivity and angular resolution of Herschel have allowed detection of cold circumgalactic dust features beyond the stellar components of the host galaxies traced by Spitzer 4.5 μm images. Comparisons of these cold dust features with ancillary data reveal an imperfect spatial correlation with the ionized gas and warm dust wind components. We find that typically ˜10-20% of the total dust mass in these galaxies resides outside of their stellar disks, but this fraction reaches ˜60% in the case of NGC 1569. This galaxy also has the largest metallicity (O/H) deficit in our sample for its stellar mass. Overall, the small number of objects in our sample precludes drawing strong conclusions on the origin of the circumgalactic dust. We detect no statistically significant trends with star formation properties of the host galaxies, as might be expected if the dust were lifted above the disk by energy inputs from on-going star formation activity. Although a case for dust entrained in a galactic wind is seen in NGC 1569, in all cases, we cannot rule out the possibility that some of the circumgalactic dust might be associated instead with gas accreted or removed from the disk by recent galaxy interaction events, or that it is part of the outer gas-rich portion of the disk that lies below the sensitivity limit of the Spitzer 4.5 μm data.

Stellar photometry and polarimetry

International Nuclear Information System (INIS)

Golay, M.; Serkowski, K.

1976-01-01

A critical review of progress made in stellar photometry and polarimetry over the period 1973-1975 is presented. Reports of photometric measurements from various observatories throughout the world are summarized. The summary of work on stellar polarimetry lists the review papers, the catalogues and lists of standard stars, and descriptions of new observing techniques. (B.R.H.)

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

Science.gov (United States)

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; Serenelli, Aldo M.; Sheffield, Allyson; Li, Ting S.; Casagrande, Luca; Johnston, Kathryn V.; Laporte, Chervin F. P.; Price-Whelan, Adrian M.; Schönrich, Ralph; Gould, Andrew

2018-03-01

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

Physical Properties of Asteroid (10302) 1989 ML, a Potential Spacecraft Target, from Spitzer Observations

NARCIS (Netherlands)

Mueller, Michael; Harris, A. W.

2006-01-01

We report on results from recent Spitzer observations of near-Earth asteroid (10302) 1989 ML, which is among the lowest-ranking objects in terms of the specific momentum Δv required to reach it from Earth. It was originally considered as a target for Hayabusa and is now under consideration as a

On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?

Science.gov (United States)

Cordiner, M. A.; Boogert, A. C. A.; Charnley, S. B.; Justtanont, K.; Cox, N. L. J.; Smith, R. G.; Tielens, A. G. G. M.; Wirstrom, E. S.; Milam, S. N.; Keane, J. V.

2016-01-01

IRAS?19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS?19312+1950 in the range 5-550 microns using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 microns, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: approx. = 0.22 Stellar Mass of material at 280+/-18 K, and ˜1.6 Me of material at 157+/-3 K. The OI 63 micron line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 microns and CO2 at 15 microns. The spectral energy distribution is consistent with a massive, luminous (approx. 2 × 10(exp 4) Stellar Luminosity) central source surrounded by a dense, warm circumstellar disk and envelope of total mass approx. 500-700 Stellar Mass with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.

New Views of a Familiar Beauty

Science.gov (United States)

2005-01-01

[figure removed for brevity, see original site] Figure 1 [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 2Figure 3Figure 4Figure 5 This image composite compares the well-known visible-light picture of the glowing Trifid Nebula (left panel) with infrared views from NASA's Spitzer Space Telescope (remaining three panels). The Trifid Nebula is a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius. The false-color Spitzer images reveal a different side of the Trifid Nebula. Where dark lanes of dust are visible trisecting the nebula in the visible-light picture, bright regions of star-forming activity are seen in the Spitzer pictures. All together, Spitzer uncovered 30 massive embryonic stars and 120 smaller newborn stars throughout the Trifid Nebula, in both its dark lanes and luminous clouds. These stars are visible in all the Spitzer images, mainly as yellow or red spots. Embryonic stars are developing stars about to burst into existence. Ten of the 30 massive embryos discovered by Spitzer were found in four dark cores, or stellar 'incubators,' where stars are born. Astronomers using data from the Institute of Radioastronomy millimeter telescope in Spain had previously identified these cores but thought they were not quite ripe for stars. Spitzer's highly sensitive infrared eyes were able to penetrate all four cores to reveal rapidly growing embryos. Astronomers can actually count the individual embryos tucked inside the cores by looking closely at the Spitzer image taken by its infrared array camera (figure 4). This instrument has the highest spatial resolution of Spitzer's imaging cameras. The Spitzer image from the multiband imaging photometer (figure 5), on the other hand, specializes in detecting cooler materials. Its view highlights the relatively cool core material falling onto the Trifid's growing embryos. The middle panel is a combination of Spitzer

Does the stellar distribution flare? A comparison of stellar scale heights with LAB H I data

Energy Technology Data Exchange (ETDEWEB)

Kalberla, P. M. W.; Kerp, J.; Dedes, L. [Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn (Germany); Haud, U., E-mail: pkalberla@astro.uni-bonn.de [Tartu Observatory, 61602 Tõravere (Estonia)

2014-10-10

The question of whether the stellar populations in the Milky Way take part in the flaring of scale heights as observed for the H I gas is a matter of debate. Standard mass models for the Milky Way assume a constant scale height for each of the different stellar distributions. However, there is mounting evidence that at least some of the stellar distributions reach, at large galactocentric distances, high altitudes, which are incompatible with a constant scale height. We discuss recent observational evidence for stellar flaring and compare it with H I data from the Leiden/Argentine/Bonn survey. Within the systemic and statistical uncertainties we find a good agreement between both.

SPITZER MICROLENS MEASUREMENT OF A MASSIVE REMNANT IN A WELL-SEPARATED BINARY

Energy Technology Data Exchange (ETDEWEB)

Shvartzvald, Y.; Bryden, G.; Henderson, C. B. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Gould, A.; Fausnaugh, M.; Gaudi, B. S.; Pogge, R. W.; Wibking, B.; Zhu, W. [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Han, C. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Bozza, V.; Novati, S. Calchi [Dipartimento di Fisica “E. R. Caianiello,” Università di Salerno, Via Giovanni Paolo II, I-84084 Fisciano (Italy); Friedmann, M. [School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Hundertmark, M. [Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5, DK-1350 Copenhagen K (Denmark); Beichman, C. [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Carey, S. [Spitzer, Science Center, MS 220-6, California Institute of Technology, Pasadena, CA (United States); Kerr, T.; Varricatt, W. [UKIRT, 660 N. Aohoku Place, University Park, Hilo, HI 96720 (United States); Yee, J. C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Collaboration: and; Spitzer team; OGLE group; KMTNet group; Wise group; RoboNet; MiNDSTEp; and others

2015-12-01

We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La,b, with the more massive component having M{sub 1} > 1.35 M{sub ⊙} (80% probability). A main-sequence star in this mass range is ruled out by limits on blue light, meaning that a primary in this mass range must be a neutron star (NS) or black hole (BH). The system has a projected separation r{sub ⊥} = 6.1 ± 0.4 AU and lies in the Galactic bulge. These measurements are based on the “microlens parallax” effect, i.e., comparing the microlensing light curve as seen from Spitzer, which lay at 1.25 AU projected from Earth, to the light curves from four ground-based surveys, three in the optical and one in the near-infrared. Future adaptive optics imaging of the companion by 30 m class telescopes will yield a much more accurate measurement of the primary mass. This discovery both opens the path and defines the challenges to detecting and characterizing BHs and NSs in wide binaries, with either dark or luminous companions. In particular, we discuss lessons that can be applied to future Spitzer and Kepler K2 microlensing parallax observations.

ON THE DISTRIBUTION OF STELLAR MASSES IN GAMMA-RAY BURST HOST GALAXIES

International Nuclear Information System (INIS)

Castro Ceron, J. M.; Michalowski, M. J.; Hjorth, J.; Malesani, D.; Watson, D.; Fynbo, J. P. U.; Gorosabel, J.; Morales Calderon, M.

2010-01-01

We analyze Spitzer images of 30 long-duration gamma-ray burst (GRB) host galaxies. We estimate their total stellar masses (M * ) based on the rest-frame K-band luminosities (L K rest ) and constrain their star formation rates (SFRs; not corrected for dust extinction) based on the rest-frame UV continua. Further, we compute a mean M * /L K rest = 0.45 M sun /L sun . We find that the hosts are low M * , star-forming systems. The median M * in our sample ((M * ) = 10 9.7 M sun ) is lower than that of 'field' galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M * is 10 7 M sun * 11 M sun , while the range spanned by the dust-uncorrected UV SFR is 10 -2 M sun yr -1 sun yr -1 . There is no evidence for intrinsic evolution in the distribution of M * with redshift. We show that extinction by dust must be present in at least 25% of the GRB hosts in our sample and suggest that this is a way to reconcile our finding of a relatively lower UV-based, specific SFR (φ ≡ SFR/M * ) with previous claims that GRBs have some of the highest φ values. We also examine the effect that the inability to resolve the star-forming regions in the hosts has on φ.

WARM SPITZER OBSERVATIONS OF THREE HOT EXOPLANETS: XO-4b, HAT-P-6b, AND HAT-P-8b

Energy Technology Data Exchange (ETDEWEB)

Todorov, Kamen O. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Deming, Drake [Planetary Systems Laboratory, NASA' s Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Knutson, Heather A. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Burrows, Adam [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 05844 (United States); Sada, Pedro V. [Department of Physics and Mathematics, University of Monterrey, Monterrey (Mexico); Cowan, Nicolas B. [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States); Agol, Eric [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Desert, Jean-Michel; Charbonneau, David [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Fortney, Jonathan J.; Laughlin, Gregory [Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Langton, Jonathan [Department of Physics, Principia College, Elsah, IL 62028 (United States); Showman, Adam P.; Lewis, Nikole K. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)

2012-02-10

We analyze Warm Spitzer/Infrared Array Camera observations of the secondary eclipses of three planets, XO-4b, HAT-P-6b, and HAT-P-8b. We measure secondary eclipse amplitudes at 3.6 {mu}m and 4.5 {mu}m for each target. XO-4b exhibits a stronger eclipse depth at 4.5 {mu}m than at 3.6 {mu}m, which is consistent with the presence of a temperature inversion. HAT-P-8b shows a stronger eclipse amplitude at 3.6 {mu}m and is best described by models without a temperature inversion. The eclipse depths of HAT-P-6b can be fitted with models with a small or no temperature inversion. We consider our results in the context of a postulated relationship between stellar activity and temperature inversion and a relationship between irradiation level and planet dayside temperature, as discussed by Knutson et al. and Cowan and Agol, respectively. Our results are consistent with these hypotheses, but do not significantly strengthen them. To measure accurate secondary eclipse central phases, we require accurate ephemerides. We obtain primary transit observations and supplement them with publicly available observations to update the orbital ephemerides of the three planets. Based on the secondary eclipse timing, we set upper boundaries for ecos ({omega}) for HAT-P-6b, HAT-P-8b, and XO-4b and find that the values are consistent with circular orbits.

Wisconsin torsatron/stellarator program, FY 1989

International Nuclear Information System (INIS)

Shohet, J.L.; Anderson, D.T.; Anderson, F.S.B.; Talmadge, J.N.

1988-07-01

This proposal documents recent activities within the University of Wisconsin-Madison Torsatron/Stellarator Laboratory and presents plans for future research activities for a three year period. Research efforts have focused on fundamental stellarator physics issues through experimental investigations on the Interchangeable Module Stellarator (IMS) and the Proto-Cleo Stellarator. Theoretical activities and studies of new configurations are being undertaken to support and broaden the experimental program. Experimental research at the Torsatron Stellarator Laboratory has been primarily concerned with effects induced through electron-cyclotron resonant frequency plasma production and heating in the IMS device. Plasma electric fields have been shown to play a major role in particle transport and confinement in IMS. ECRF heating at 6 kG has produced electron tail populations in agreement with Monte-Carlo models. Electric and magnetic fields have been shown to alter the particle flows to the IMS modular divertors. 48 refs

Introduction to stellar astrophysics. V. 1

International Nuclear Information System (INIS)

Boehm-Vitense, E.

1989-01-01

This textbook introduces basic elements of fundamental astronomy and astrophysics which serve as a foundation for understanding the structure, evolution, and observed properties of stars. The first half of the book explains how stellar motions, distances, luminosities, colours, radii, masses and temperatures are measured or derived. The author then shows how data of these sorts can be arranged to classify stars through their spectra. Stellar rotation and stellar magnetic fields are introduced. Stars with peculiar spectra and pulsating stars also merit special attention. The endpoints of stellar evolutions are briefly described. There is a separate chapter on the Sun and a final one on interstellar absorption. (author)

Stellar Streams Discovered in the Dark Energy Survey

Energy Technology Data Exchange (ETDEWEB)

Shipp, N.; et al.

2018-01-09

We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data covering $\\sim 5000$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $< 1 \\%$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $\\sim 50$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of eleven new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way.

A probable stellar solution to the cosmological lithium discrepancy.

Science.gov (United States)

Korn, A J; Grundahl, F; Richard, O; Barklem, P S; Mashonkina, L; Collet, R; Piskunov, N; Gustafsson, B

2006-08-10

The measurement of the cosmic microwave background has strongly constrained the cosmological parameters of the Universe. When the measured density of baryons (ordinary matter) is combined with standard Big Bang nucleosynthesis calculations, the amounts of hydrogen, helium and lithium produced shortly after the Big Bang can be predicted with unprecedented precision. The predicted primordial lithium abundance is a factor of two to three higher than the value measured in the atmospheres of old stars. With estimated errors of 10 to 25%, this cosmological lithium discrepancy seriously challenges our understanding of stellar physics, Big Bang nucleosynthesis or both. Certain modifications to nucleosynthesis have been proposed, but found experimentally not to be viable. Diffusion theory, however, predicts atmospheric abundances of stars to vary with time, which offers a possible explanation of the discrepancy. Here we report spectroscopic observations of stars in the metal-poor globular cluster NGC 6397 that reveal trends of atmospheric abundance with evolutionary stage for various elements. These element-specific trends are reproduced by stellar-evolution models with diffusion and turbulent mixing. We thus conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars by transporting the lithium deep into the star.

Stellar photospheric abundances as a probe of discs and planets

Science.gov (United States)

Jermyn, Adam S.; Kama, Mihkel

2018-06-01

Protoplanetary discs, debris discs, and disrupted or evaporating planets can all feed accretion on to stars. The photospheric abundances of such stars may then reveal the composition of the accreted material. This is especially likely in B to mid-F type stars, which have radiative envelopes and hence less bulk-photosphere mixing. We present a theoretical framework (CAM), considering diffusion, rotation, and other stellar mixing mechanisms to describe how the accreted material interacts with the bulk of the star. This allows the abundance pattern of the circumstellar material to be calculated from measured stellar abundances and parameters (vrot, Teff). We discuss the λ Boötis phenomenon and the application of CAM on stars hosting protoplanetary discs (HD 100546, HD 163296), debris discs (HD 141569, HD 21997), and evaporating planets (HD 195689/KELT-9).

Progress Toward Attractive Stellarators

International Nuclear Information System (INIS)

Neilson, G.H.; Bromberg, L.; Brown, T.G.; Gates, D.A.; Ku, L.P.; Zarnstorff, M.C.; Boozer, A.H.; Harris, J.H.; Meneghini, O.; Mynick, H.E.; Pomphrey, N.; Reiman, A.H.; Xanthopoulos, P.

2011-01-01

The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

Measurement of the Transverse Spitzer Resistivity during Collisional Magnetic Reconnection

International Nuclear Information System (INIS)

Trintchouk, F.; Yamada, M.; Ji, H.; Kulsrud, R.M.; Carter, T.A.

2000-01-01

Measurement of the transverse resistivity was carried out in a reconnecting current sheet where the mean free path for the Coulomb collision is smaller than the thickness of the sheet. In a collisional neutral sheet without a guide field, the transverse resistivity is directly related to the reconnection rate. A remarkable agreement is found between the measured resistivity and the classical value derived by L. Spitzer. In his calculation the transverse resistivity for the electrons is higher than the parallel resistivity by a factor of 1.96. The measured values have verified this theory to within 30% errors

Stellar magnetic activity and exoplanets

Directory of Open Access Journals (Sweden)

Vidotto A.A.

2017-01-01

Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

Transport in stellarators

International Nuclear Information System (INIS)

Maassberg, H.; Brakel, R.; Burhenn, R.; Gasparino, U.; Grigull, P.; Kick, M.; Kuehner, G.; Ringler, H.; Sardei, F.; Stroth, U.; Weller, A.

1993-01-01

The local electron and ion heat transport as well as the particle and impurity transport properties in stellarators are reviewed. In this context, neoclassical theory is used as a guideline for the comparison of the experimental results of the quite different confinement concepts. At sufficiently high temperatures depending on the specific magnetic configuration, neoclassical predictions are confirmed by experimental findings. The confinement properties in the LMFP collisionality regime are discussed with respect to the next stellarator generation, for which at higher temperatures the neoclassical transport is expected to become more important. (orig.)

Stellar oscillations in planet-hosting giant stars

Energy Technology Data Exchange (ETDEWEB)

Hatzes, Artie P; Zechmeister, Mathias [Thueringer Landessternwarte, Sternwarte 5, D-07778 (Germany)], E-mail: artie@tls-tautenburg.de

2008-10-15

Recently a number of giant extrasolar planets have been discovered around giant stars. These discoveries are important because many of these giant stars have intermediate masses in the range 1.2-3 Msun. Early-type main sequence stars of this mass range have been avoided by radial velocity planet search surveys due the difficulty of getting the requisite radial velocity precision needed for planet discoveries. Thus, giant stars can tell us about planet formation for stars more massive than the sun. However, the determination of stellar masses for giant stars is difficult due to the fact that evolutionary tracks for stars covering a wide range of masses converge to the same region of the H-R diagram. We report here on stellar oscillations in three planet-hosting giant stars: HD 13189, {beta} Gem, and {iota} Dra. Precise stellar radial velocity measurements for these stars show variations whose periods and amplitudes are consistent with solar-like p-mode oscillations. The implied stellar masses for these objects based on the characteristics of the stellar oscillations are consistent with the predictions of stellar isochrones. An investigation of stellar oscillations in planet hosting giant stars offers us the possibility of getting an independent determination of the stellar mass for these objects which is of crucial importance for extrasolar planet studies.

Stellar Dynamics and Star Formation Histories of z ∼ 1 Radio-loud Galaxies

Energy Technology Data Exchange (ETDEWEB)

Barišić, Ivana; Van der Wel, Arjen; Chauké, Priscilla; Van Houdt, Josha; Straatman, Caroline [Max-Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); Bezanson, Rachel [Department of Astrophysics, Princeton University, Princeton, NJ 08544 (United States); Pacifici, Camilla [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Noeske, Kai [experimenta gGmbH, Kranenstraße 14, 74072 Heilbronn (Germany); Muñoz-Mateos, Juan C. [European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago (Chile); Franx, Marijn; Labbé, Ivo; Maseda, Michael V.; Sobral, David [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 AA Leiden (Netherlands); Smolčić, Vernesa [Department of Physics, Faculty of Science, University of Zagreb, Bijenicka cesta 32, 10000 Zagreb (Croatia); Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109 (United States); Brammer, Gabriel [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Calhau, João [Department of Physics, Lancaster University, Lancaster LA1 4 YB (United Kingdom); Van Dokkum, Pieter G. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Gallazzi, Anna [INAF-Osservatorio Astrofsico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Muzzin, Adam, E-mail: barisic@mpia.de [Department of Physics and Astronomy, York University, 4700 Keele Street, Toronto, Ontario, ON MJ3 1P3 (Canada); and others

2017-09-20

We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities ( L {sub 3} {sub GHz} > 10{sup 23} W Hz{sup −1}) at 0.6 < z < 1. This sample is constructed by cross-matching galaxies from the deep VLT/VIMOS LEGA-C spectroscopic survey with the VLA 3 GHz data set. The LEGA-C continuum spectra reveal for the first time stellar velocity dispersions and age indicators of z ∼ 1 radio galaxies. We find that z ∼ 1 radio-loud active galactic nucleus (AGN) occur exclusively in predominantly old galaxies with high velocity dispersions: σ {sub *} > 175 km s{sup −1}, corresponding to black hole masses in excess of 10{sup 8} M {sub ⊙}. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z ∼ 1 is five to 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z ∼ 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black hole masses, radio loudness, and quiescence at z ∼ 1.

Astrospheres and Solar-like Stellar Winds

Directory of Open Access Journals (Sweden)

Wood Brian E.

2004-07-01

Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION

Energy Technology Data Exchange (ETDEWEB)

Sobral, David; Santos, Sérgio [Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT1349-018 Lisbon (Portugal); Matthee, Jorryt; Röttgering, Huub J. A. [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Darvish, Behnam; Mobasher, Bahram; Hemmati, Shoubaneh [Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92521 (United States); Schaerer, Daniel, E-mail: sobral@iastro.pt [Observatoire de Genève, Département d’Astronomie, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix (Switzerland)

2015-08-01

Faint Lyα emitters become increasingly rarer toward the reionization epoch (z ∼ 6–7). However, observations from a very large (∼5 deg{sup 2}) Lyα narrow-band survey at z = 6.6 show that this is not the case for the most luminous emitters, capable of ionizing their own local bubbles. Here we present follow-up observations of the two most luminous Lyα candidates in the COSMOS field: “MASOSA” and “CR7.” We used X-SHOOTER, SINFONI, and FORS2 on the Very Large Telescope, and DEIMOS on Keck, to confirm both candidates beyond any doubt. We find redshifts of z = 6.541 and z = 6.604 for “MASOSA” and “CR7,” respectively. MASOSA has a strong detection in Lyα with a line width of 386 ± 30 km s{sup −1} (FWHM) and with very high EW{sub 0} (>200 Å), but undetected in the continuum, implying very low stellar mass and a likely young, metal-poor stellar population. “CR7,” with an observed Lyα luminosity of 10{sup 43.92±0.05} erg s{sup −1} is the most luminous Lyα emitter ever found at z > 6 and is spatially extended (∼16 kpc). “CR7” reveals a narrow Lyα line with 266 ± 15 km s{sup −1} FWHM, being detected in the near-infrared (NIR) (rest-frame UV; β = −2.3 ± 0.1) and in IRAC/Spitzer. We detect a narrow He ii 1640 Å emission line (6σ, FWHM = 130 ± 30 km s{sup −1}) in CR7 which can explain the clear excess seen in the J-band photometry (EW{sub 0} ∼ 80 Å). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra (He ii/O iii] 1663 Å > 3 and He ii/C iii] 1908 Å > 2.5). We conclude that CR7 is best explained by a combination of a PopIII-like population, which dominates the rest-frame UV and the nebular emission, and a more normal stellar population, which presumably dominates the mass. Hubble Space Telescope/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lyα and He ii emission, and two red components (∼5 kpc away), which

Solar and stellar flares and their impact on planets

Science.gov (United States)

Shibata, Kazunari

Recent observations of the Sun revealed that the solar atmosphere is full of flares and flare-like phenomena, which affect terrestrial environment and our civilization. It has been established that flares are caused by the release of magnetic energy through magnetic reconnection. Many stars show flares similar to solar flares, and such stellar flares especially in stars with fast rotation are much more energetic than solar flares. These are called superflares. The total energy of a solar flare is 1029 - 1032 erg, while that of a superflare is 1033 - 1038 erg. Recently, it was found that superflares (with 1034 - 1035 erg) occur on Sun-like stars with slow rotation with frequency once in 800 - 5000 years. This suggests the possibility of superflares on the Sun. We review recent development of solar and stellar flare research, and briefly discuss possible impacts of superflares on the Earth and exoplanets.

Enhanced-confinement class of stellarators

International Nuclear Information System (INIS)

Mynick, H.E.; Chu, T.K.; Boozer, A.H.

1981-08-01

A class of stellarators has been found in which the transport is reduced by an order of magnitude from transport in conventional stellarators, by localizing the helical ripple to the inside of the torus. The reduction is observed in numerical experiments and explained theoretically

A SPITZER SURVEY OF PROTOPLANETARY DISK DUST IN THE YOUNG SERPENS CLOUD: HOW DO DUST CHARACTERISTICS EVOLVE WITH TIME?

International Nuclear Information System (INIS)

Oliveira, Isa; Van Dishoeck, Ewine F.; Lahuis, Fred; Pontoppidan, Klaus M.; MerIn, Bruno; Geers, Vincent C.; Joergensen, Jes K.; Olofsson, Johan; Augereau, Jean-Charles; Brown, Joanna M.

2010-01-01

We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35 μm) spectra of a complete flux-limited sample (≥3 mJy at 8 μm) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted polycyclic aromatic hydrocarbon (PAH) features), and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs, and silicate features. The presence, strength, and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13 μm flux ratios consistent with cold disks with inner holes or gaps, and 3% of the disks show PAH emission. Comparison with models indicates that dust grains in the surface of these disks have sizes of at least a few μm. The 20 μm silicate feature is sometimes seen in the absence of the 10 μm feature, which may be indicative of very small holes in these disks. No significant difference is found in the distribution of silicate feature shapes and strengths between sources in clusters and in the field. Moreover, the results in Serpens are compared with other well-studied samples: the c2d IRS sample distributed over five clouds and a large sample of disks in the Taurus star-forming region. The remarkably similar distributions of silicate feature characteristics in samples with different environment and median ages-if significant-imply that the dust population in the disk surface results from an equilibrium between dust growth and destructive collision processes

Introduction to stellar structure

CERN Document Server

Maciel, Walter J

2016-01-01

In the first part of this book, the author presents the basic properties of the stellar interior and describes them thoroughly, along with deriving the main stellar structure equations of temperature, density, pressure and luminosity, among others. The process and application of solving these equations is explained, as well as linking these results with actual observations.  The second part of the text describes what happens to a star over time, and how to determine this by solving the same equations at different points during a star’s lifetime. The fate of various stars is quite different depending on their masses, and this is described in the final parts of the book. This text can be used for an upper level undergraduate course or an introductory graduate course on stellar physics.

SDP_golofs01_3: Stellar Disk Evolution

Science.gov (United States)

Olofsson, G.

2010-03-01

n a collaboration between the HSC, P. Harvey (Mission Scientist) and the three instrument consortia we propose to apply the full power of Herschel to investigate the properties of circum-stellar disks. The versatility of Herschel allows us to address several key questions: How do the disks evolve with time? Planets clearly form out of circum-stellar disks and there is growing evidence that the time scale is short, 1 - 10 Myr, for the main accretion phase. During this time period, the stellar radiation and stellar winds clean the disks from most of their dust and gas, eventually making them transparent. However, collisions and evaporation from comet- like bodies will continue to produce dust and gas. This activity declines with time, and we will pursue this scenario by observing a sample of IR excess stars of known age, ranging from a few million years to the age of the sun. Are there analogues to our Kuiper belt around nearby stars? The Kuiper belt is a dust belt surrounding the Sun, located outside the orbit of Neptune, which has a key role in stabilizing orbits of the KE-objects and this dynamical aspect makes it particularly interesting to search for stars that may host KE-belt analogues. Herschel offers a unique sensitivity beyond 100 m and we propose an extensive survey of nearby stars seeking cold dust emission. What will a closer IR look at the "Fabulous Four" (and some other resolved disks) reveal? Several nearby MS stars with IR excesses have circumstellar dust structures that can be resolved by Herschel. Imaging these structures in the six PACS+SPIRE bands will enable us to explore the dust properties, notably the size distribution and albedo.. What is the composition of young disks? We propose a detailed spectroscopic investigation of four bright disks, including a full spectral scan with PACS, an FTS scan at full resolution and HIFI observations of selected frequencies. The aim is to constrain the properties of both the dust and gas components.

THE SPITZER c2d SURVEY OF NEARBY DENSE CORES: JET AND MOLECULAR OUTFLOW ASSOCIATED WITH A YOUNG STELLAR OBJECT IN CORE A OF L1251

International Nuclear Information System (INIS)

Lee, Jeong-Eun; Kim, Il-Suk; Choi, Yunhee; Lee, Ho-Gyu; Shinn, Jong-Ho; Dunham, Michael M.; Evans, Neal J.; Kim, Chang Hee; Bourke, Tyler L.

2010-01-01

A long infrared jet has been discovered by the Spitzer c2d Legacy Program in core A of L1251. It is associated with a very embedded Class 0 object with an accretion luminosity of about 0.9 L sun derived by radiative transfer model fitting to the observed spectral energy distribution. Comparing the observed Infrared Array Camera colors along the infrared jet with those calculated from a model of an admixture of gas with a power-law temperature distribution indicates that the jet is possibly created by a paraboloidal bow shock propagating into the ambient medium of n(H 2 ) = 10 5 cm -3 . In addition, the variation of the power-law index along the jet suggests that the portion of hot gas decreases with distance from the jet engine. The molecular outflow in this region has been mapped for the first time using CO data. From the calculated outflow momentum flux, a very strong lower limit to the average accretion luminosity is 3.6 sin i/cos 3 i L sun , indicative of a decrease in the accretion rate with time.

Near-term directions in the World Stellarator Program

International Nuclear Information System (INIS)

Lyon, J.F.

1990-01-01

Interest in stellarators has increased because of the progress being made in the development of this concept and the inherent advantages of stellarators as candidates for an attractive, steady-state fusion reactor. Three new stellarator experiments started operation in 1988, and three more are scheduled to start in the next few years. In addition, design studies have started on large next-generation stellarator experiments for the mid-1990s. These devices are designed to test four basic approaches to stellarator configuration optimization. Ways in which these devices complement each other in exploring the potential of the stellarator concept and the main issues that they will address during the next decade are described

OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES

International Nuclear Information System (INIS)

Moustakas, John; Kennicutt, Robert C. Jr.; Tremonti, Christy A.; Dale, Daniel A.; Smith, John-David T.; Calzetti, Daniela

2010-01-01

We present intermediate-resolution optical spectrophotometry of 65 galaxies obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS). For each galaxy we obtain a nuclear, circumnuclear, and semi-integrated optical spectrum designed to coincide spatially with mid- and far-infrared spectroscopy from the Spitzer Space Telescope. We make the reduced, spectrophotometrically calibrated one-dimensional spectra, as well as measurements of the fluxes and equivalent widths of the strong nebular emission lines, publicly available. We use optical emission-line ratios measured on all three spatial scales to classify the sample into star-forming, active galactic nuclei (AGNs), and galaxies with a mixture of star formation and nuclear activity. We find that the relative fraction of the sample classified as star forming versus AGN is a strong function of the integrated light enclosed by the spectroscopic aperture. We supplement our observations with a large database of nebular emission-line measurements of individual H II regions in the SINGS galaxies culled from the literature. We use these ancillary data to conduct a detailed analysis of the radial abundance gradients and average H II-region abundances of a large fraction of the sample. We combine these results with our new integrated spectra to estimate the central and characteristic (globally averaged) gas-phase oxygen abundances of all 75 SINGS galaxies. We conclude with an in-depth discussion of the absolute uncertainty in the nebular oxygen abundance scale.

PROTOPLANETARY AND TRANSITIONAL DISKS IN THE OPEN STELLAR CLUSTER IC 2395

Energy Technology Data Exchange (ETDEWEB)

Balog, Zoltan [Max Planck Institute for Astronomy, Heidelberg, D-69117 (Germany); Siegler, Nick [NASA Exoplanet Exploration Program, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Rieke, G. H.; Su, K. Y. L.; Gáspár, András [Steward Observatory, 933 N. Cherry Ave, University of Arizona, Tucson, AZ 85721 (United States); Kiss, L. L. [Konkoly Observatory, Research Center for Astronomy and Earth Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Bell, Cameron P. M. [Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093, Zürich (Switzerland); Vinkó, J. [Dept. of Optics and Quantum Electronics, University of Szeged, H-6720 Szeged (Hungary); Young, E. T., E-mail: balog@mpia-hd.mpg.de [NASA Ames SOFIA Science Center, N211, Mountain View, CA 94043 (United States)

2016-11-20

We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (∼6–10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope , covering the wavelength range from 3.6 to 24 μ m. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii from ∼0.1 to ∼10 au from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively, 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ∼1 to ∼18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 μ m excesses ([8] – [24] ≥ 1.5) increases from (8.4 ± 1.3)% at ∼3 Myr to (46 ± 5)% at ∼10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.

The Resolved Stellar Populations Early Release Science Program

Science.gov (United States)

Gilbert, Karoline; Weisz, Daniel; Resolved Stellar Populations ERS Program Team

2018-06-01

The Resolved Stellar Populations Early Release Science Program (PI D. Weisz) will observe Local Group targets covering a range of stellar density and star formation histories, including a globular cluster, and ultra-faint dwarf galaxy, and a star-forming dwarf galaxy. Using observations of these diverse targets we will explore a broad science program: we will measure star formation histories, the sub-solar stellar initial mass function, and proper motions, perform studies of evolved stars, and map extinction in the target fields. Our observations will be of high archival value for other science such as calibrating stellar evolution models, studying variable stars, and searching for metal-poor stars. We will determine optimal observational setups and develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will also design, test, and release point spread function (PSF) fitting software specific to NIRCam and NIRISS, required for the crowded stellar regime. Prior to the Cycle 2 Call for Proposals, we will release PSF fitting software, matched HST and JWST catalogs, and clear documentation and step-by-step tutorials (such as Jupyter notebooks) for reducing crowded stellar field data and producing resolved stellar photometry catalogs, as well as for specific resolved stellar photometry science applications.

Turbulence optimisation in stellarator experiments

Energy Technology Data Exchange (ETDEWEB)

Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)

2015-05-01

Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.

SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

International Nuclear Information System (INIS)

Daemgen, Sebastian; Bonavita, Mariangela; Jayawardhana, Ray; Lafrenière, David; Janson, Markus

2015-01-01

We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M ☉ and low-mass stars at ∼0.2 M ☉ . We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M Jup . The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3 −4.9 +6.6 %. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M ☉ appear to be multiple. Higher order multiples were found in 1.8 −1.5 +4.2 % of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively

SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Daemgen, Sebastian [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5H 3H4 (Canada); Bonavita, Mariangela [The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Jayawardhana, Ray [Physics and Astronomy, York University, Toronto, Ontario L3T 3R1 (Canada); Lafrenière, David [Department of Physics, University of Montréal, Montréal, QC (Canada); Janson, Markus, E-mail: daemgen@astro.utoronto.ca [Department of Astronomy, Stockholm University, Stockholm (Sweden)

2015-02-01

We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

Olivine Composition of the Mars Trojan 5261 Eureka: Spitzer IRS Data

Science.gov (United States)

Lim, L. F.; Burt, B. J.; Emery, J. P.; Mueller, M.; Rivkin, A. S.; Trilling, D.

2011-01-01

The largest Mars trojan, 5261 Eureka, is one of two prototype "Sa" asteroids in the Bus-Demeo taxonomy. Analysis of its visible/near-IR spectrum led to the conclusion that it might represent either an angritic analog or an olivine-rich composition such as an R chondrite. Spitzer IRS data (5-30 micrometers) have enabled us to resolve this ambiguity. The thermal-IR spectrum exhibits strong olivine reststrahlen features consistent with a composition of approximately equals Fo60-70. Laboratory spectra of R chondrites, brachinites, and chassignites are dominated by similar features.

Infrared Colors of Dwarf-Dwarf Galaxy Interactions

Science.gov (United States)

Liss, Sandra; Stierwalt, Sabrina; Johnson, Kelsey; Patton, Dave; Kallivayalil, Nitya

2015-10-01

We request Spitzer Warm Mission IRAC Channel 1 & 2 imaging for a sample of 60 isolated dwarf galaxy pairs as a key component of a larger, multi-wavelength effort to understand the role low-mass mergers play in galaxy evolution. A systematic study of dwarf-dwarf mergers has never been done, and we wish to characterize the impact such interactions have on fueling star formation in the nearby universe. The Spitzer imaging proposed here will allow us to determine the extent to which the 3.6 and 4.5 mum bands are dominated by stellar light and investigate a) the extent to which interacting pairs show IR excess and b) whether the excess is related to the pair separation. Second, we will use this IR photometry to constrain the processes contributing to the observed color excess and scatter in each system. We will take advantage of the wealth of observations available in the Spitzer Heritage Archive for 'normal' non-interacting dwarfs by comparing the stellar populations of those dwarfs with the likely interacting dwarfs in our sample. Ultimately, we can combine the Spitzer imaging proposed here with our current, ongoing efforts to obtain groundbased optical photometry to model the star formation histories of these dwarfs and to help constrain the timescales and impact dwarf-dwarf mergers have on fueling star formation. The sensitivity and resolution offered by Spitzer are necessary to determine the dust properties of these interacting systems, and how these properties vary as a function of pair separation, mass ratio, and gas fraction.

A catalog of stellar spectrophotometry

Science.gov (United States)

Adelman, S. J.; Pyper, D. M.; Shore, S. N.; White, R. E.; Warren, W. H., Jr.

1989-01-01

A machine-readable catalog of stellar spectrophotometric measurements made with rotating grating scanner is introduced. Consideration is given to the processes by which the stellar data were collected and calibrated with the fluxes of Vega (Hayes and Latham, 1975). A sample page from the spectrophotometric catalog is presented.

The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

Science.gov (United States)

Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

2018-01-01

Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

STAR FORMATION RATES AND STELLAR MASSES OF z = 7-8 GALAXIES FROM IRAC OBSERVATIONS OF THE WFC3/IR EARLY RELEASE SCIENCE AND THE HUDF FIELDS

International Nuclear Information System (INIS)

Labbe, I.; Gonzalez, V.; Bouwens, R. J.; Illingworth, G. D.; Magee, D.; Franx, M.; Trenti, M.; Oesch, P. A.; Carollo, C. M.; Van Dokkum, P. G.; Stiavelli, M.; Kriek, M.

2010-01-01

We investigate the Spitzer/IRAC properties of 36 z ∼ 7 z 850 -dropout galaxies and three z ∼ 8 Y 098 galaxies derived from deep/wide-area WFC3/IR data of the Early Release Science, the ultradeep HUDF09, and wide-area NICMOS data. We fit stellar population synthesis models to the spectral energy distributions to derive mean redshifts, stellar masses, and ages. The z ∼ 7 galaxies are best characterized by substantial ages (>100 Myr) and M/L V ∼ 0.2. The main trend with decreasing luminosity is that of bluing of the far-UV slope from β ∼ -2.0 to β ∼ -3.0. This can be explained by decreasing metallicity, except for the lowest luminosity galaxies (0.1L* z =3 ), where low metallicity and smooth star formation histories (SFHs) fail to match the blue far-UV and moderately red H - [3.6] color. Such colors may require episodic SFHs with short periods of activity and quiescence ('on-off' cycles) and/or a contribution from emission lines. The stellar mass of our sample of z ∼ 7 star-forming galaxies correlates with star formation rate (SFR) according to log M* = 8.70(±0.09) + 1.06(±0.10)log SFR, implying that star formation may have commenced at z > 10. No galaxies are found with SFRs much higher or lower than the past averaged SFR suggesting that the typical star formation timescales are probably a substantial fraction of the Hubble time. We report the first IRAC detection of Y 098 -dropout galaxies at z ∼ 8. The average rest-frame U - V ∼ 0.3 (AB) of the three galaxies are similar to faint z ∼ 7 galaxies, implying similar M/L. The stellar mass density to M UV,AB +0.7 -1.0 x 10 6 M sun Mpc -3 , following log ρ*(z) = 10.6(±0.6) - 4.4(±0.7) log(1 + z) [M sun Mpc -3 ] over 3 < z < 8.

PREFACE: A Stellar Journey A Stellar Journey

Science.gov (United States)

Asplund, M.

2008-10-01

The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

Spitzer Opens New Path to Break Classic Degeneracy for Jupiter-mass Microlensing Planet OGLE-2017-BLG-1140Lb

Science.gov (United States)

Calchi Novati, S.; Skowron, J.; Jung, Y. K.; Beichman, C.; Bryden, G.; Carey, S.; Gaudi, B. S.; Henderson, C. B.; Shvartzvald, Y.; Yee, J. C.; Zhu, W.; Spitzer Team; Udalski, A.; Szymański, M. K.; Mróz, P.; Poleski, R.; Soszyński, I.; Kozłowski, S.; Pietrukowicz, P.; Ulaczyk, K.; Pawlak, M.; Rybicki, K.; Iwanek, P.; OGLE Collaboration; Albrow, M. D.; Chung, S.-J.; Gould, A.; Han, C.; Hwang, K.-H.; Ryu, Y.-H.; Shin, I.-G.; Zang, W.; Cha, S.-M.; Kim, D.-J.; Kim, H.-W.; Kim, S.-L.; Lee, C.-U.; Lee, D.-J.; Lee, Y.; Park, B.-G.; Pogge, R. W.; KMTNet Collaboration

2018-06-01

We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class ({m}p≃ 1.6 {M}{{J}{{u}}{{p}}}) planet orbiting a mid-late M dwarf (M≃ 0.2 {M}ȯ ) that lies {D}LS}≃ 1.0 {kpc} in the foreground of the microlensed Galactic-bar source star. The planet–host projected separation is {a}\\perp ≃ 1.0 {au}, i.e., well beyond the snow line. By measuring the source proper motion {{\\boldsymbol{μ }}}s from ongoing long-term OGLE imaging and combining this with the lens-source relative proper motion {{\\boldsymbol{μ }}}rel} derived from the microlensing solution, we show that the lens proper motion {{\\boldsymbol{μ }}}l={{\\boldsymbol{μ }}}rel}+{{\\boldsymbol{μ }}}s is consistent with the lens lying in the Galactic disk, although a bulge lens is not ruled out. We show that while the Spitzer and ground-based data are comparably well fitted by planetary (i.e., binary-lens (2L1S)) and binary-source (1L2S) models, the combination of Spitzer and ground-based data decisively favors the planetary model. This is a new channel to resolve the 2L1S/1L2S degeneracy, which can be difficult to break in some cases.

YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD STAR-FORMING REGION N206

International Nuclear Information System (INIS)

Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B.; Carlson, Lynn Redding; Whitney, B.; Babler, B.; Meade, M.; Indebetouw, R.; Hora, J. L.

2010-01-01

We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 μm and MIPS 24 μm), Infrared Survey Facility near-infrared survey (J, H, K s ), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 μm. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ∼14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ∼520 M sun . We calculate a current star formation rate of 0.27 x 10 -1 M sun yr -1 kpc -2 . The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

Expanding CME-flare relations to other stellar systems

Science.gov (United States)

Moschou, Sofia P.; Drake, Jeremy J.; Cohen, Ofer

2017-05-01

Stellar activity is one of the main parameters in exoplanet habitability studies. While the effects of UV to X-ray emission from extreme flares on exoplanets are beginning to be investigated, the impact of coronal mass ejections is currently highly speculative because CMEs and their properties cannot yet be directly observed on other stars. An extreme superflare was observed in X-rays on the Algol binary system on August 30 1997, emitting a total of energy 1.4x 10^{37} erg and making it a great candidate for studying the upper energy limits of stellar superflares in solar-type (GK) stars. A simultaneous increase and subsequent decline in absorption during the flare was also observed and interpretted as being caused by a CME. Here we investigate the dynamic properties of a CME that could explain such time-dependent absorption and appeal to trends revealed from solar flare and CME statistics as a guide. Using the ice-cream cone model that is extensively used in solar physics to describe the three-dimensional CME structure, in combination with the temporal profile of the hydrogen column density evolution, we are able to characterize the CME and estimate its kinetic energy and mass. We examine the mass, kinetic and flare X-ray fluence in the context of solar relations to examine the extent to which such relations can be extrapolated to much more extreme stellar events.

Recent advances in non-LTE stellar atmosphere models

Science.gov (United States)

Sander, Andreas A. C.

2017-11-01

In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

PLANETARY NEBULAE DETECTED IN THE SPITZER SPACE TELESCOPE GLIMPSE II LEGACY SURVEY

International Nuclear Information System (INIS)

Zhang Yong; Sun Kwok

2009-01-01

We report the result of a search for the infrared counterparts of 37 planetary nebulae (PNs) and PN candidates in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire II (GLIMPSE II) survey. The photometry and images of these PNs at 3.6, 4.5, 5.8, 8.0, and 24 μm, taken through the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS), are presented. Most of these nebulae are very red and compact in the IRAC bands, and are found to be bright and extended in the 24 μm band. The infrared morphology of these objects are compared with Hα images of the Macquarie-AAO-Strasbourg (MASH) and MASH II PNs. The implications for morphological difference in different wavelengths are discussed. The IRAC data allow us to differentiate between PNs and H II regions and be able to reject non-PNs from the optical catalog (e.g., PNG 352.1 - 00.0). Spectral energy distributions are constructed by combing the IRAC and MIPS data with existing near-, mid-, and far-IR photometry measurements. The anomalous colors of some objects allow us to infer the presence of aromatic emission bands. These multi-wavelength data provide useful insights into the nature of different nebular components contributing to the infrared emission of PNs.

Engineering aspects of compact stellarators

International Nuclear Information System (INIS)

Nelson, B.E.; Benson, R.D.; Brooks, A.

2003-01-01

Compact stellarators could combine the good confinement and high beta of a tokamak with the inherently steady state, disruption-free characteristics of a stellarator. Two U.S. compact stellarator facilities are now in the conceptual design phase: the National Compact Stellarator Experiment (NCSX) and the Quasi- Poloidal Stellarator (QPS). NCSX has a major radius of 1.4 m and a toroidal field up to 2 T. The primary feature of both NCSX and QPS is the set of modular coils that provide the basic magnetic configuration. These coils represent a major engineering challenge due to the complex shape, precise geometric accuracy, and high current density of the windings. The winding geometry is too complex for conventional hollow copper conductor construction. Instead, the modular coils will be wound with flexible, multi strand cable conductor that has been compacted to a 75% copper packing fraction. Inside the NCSX coil set and surrounding the plasma is a highly contoured vacuum vessel. The vessel consists of three identical, 120 deg. segments that are bolted together at double sealed joints. The QPS device has a major radius of 0.9 m, a toroidal field of 1 T, and an aspect ratio of only 2.7. Instead of an internal vacuum vessel, the QPS modular coils will operate in an external vacuum tank. (author)

The Stellar Imager (SI) Project: Resolving Stellar Surfaces, Interiors, and Magnetic Activity

Science.gov (United States)

Carpenter, Kenneth G.; Schrijver, K.; Karovska, M.

2007-01-01

The Stellar Imager (SI) is a UV/Optical. Space-Based Interferometer designed to enable 0.1 milli-arcsec (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. The science of SI focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. Its prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we discuss the science goals, technology needs, and baseline design of the SI mission.

Time-scales of stellar rotational variability and starspot diagnostics

Science.gov (United States)

Arkhypov, Oleksiy V.; Khodachenko, Maxim L.; Lammer, Helmut; Güdel, Manuel; Lüftinger, Teresa; Johnstone, Colin P.

2018-01-01

The difference in stability of starspot distribution on the global and hemispherical scales is studied in the rotational spot variability of 1998 main-sequence stars observed by Kepler mission. It is found that the largest patterns are much more stable than smaller ones for cool, slow rotators, whereas the difference is less pronounced for hotter stars and/or faster rotators. This distinction is interpreted in terms of two mechanisms: (1) the diffusive decay of long-living spots in activity complexes of stars with saturated magnetic dynamos, and (2) the spot emergence, which is modulated by gigantic turbulent flows in convection zones of stars with a weaker magnetism. This opens a way for investigation of stellar deep convection, which is yet inaccessible for asteroseismology. Moreover, a subdiffusion in stellar photospheres was revealed from observations for the first time. A diagnostic diagram was proposed that allows differentiation and selection of stars for more detailed studies of these phenomena.

Sensitive Spitzer Photometry of Supermassive Black Holes at the Final Stage of Adolescence

Science.gov (United States)

Shemmer, Ohad; Netzer, Hagai; Mor, Rivay; Trakhtenbrot, Benny

2011-05-01

We propose to obtain sensitive Spitzer snapshot observations of a unique sample of 35 Sloan Digital Sky Survey quasars at redshift 4.8 for which we obtained reliable, Mg II-based determinations of the supermassive black hole (SMBH) mass and normalized accretion rate (L/L_Edd). These quasars appear to mark the final stage of SMBH `adolescence' in the history of the Universe as their SMBHs are significantly less massive and their L/L_Edd values are significantly higher with respect to their counterparts at lower redshifts. Our observations will provide both 1) deep coverage of the fields around these quasars which will be utilized as crucial priors for our approved Herschel/SPIRE observations of these sources, and 2) coverage of the rest-frame optical SEDs of these fast accreting quasars. The results will maximize our ability to measure the star-formation rate in the host galaxies of these quasars using Herschel. We will thus be able to investigate correlations between SMBH growth and star-forming activity in the early Universe. The Spitzer photometry will also provide invaluable information about the shape of the rest-frame optical continuum in these quasars which will be used to search for extreme disk properties that may be signatures of the remarkably high accretion rates in these sources.

Random walks, Brownian motion, and interacting particle systems: a festschrift in honor of Frank Spitzer

National Research Council Canada - National Science Library

Durrett, Richard; Kesten, Harry; Spitzer, Frank

1991-01-01

..., made the transparency used in the printing process. STUDENTS OF FRANK SPITZERSTUDENTS OF FRANK SPITZER 1957 J. W. Lamperti, On the asymptotic behavior of recurrent and almostrecurrent events. 1964 W. W. Whitman, Some strong laws for random walks and Brownian motion. 1965 J. C. Mineka, The existence and uniqueness of positive solutions to the Wien...

Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

International Nuclear Information System (INIS)

Sewiło, M.; Carlson, L. R.; Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B.

2013-01-01

The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

Energy Technology Data Exchange (ETDEWEB)

Sewiło, M. [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Carlson, L. R. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B., E-mail: mmsewilo@pha.jhu.edu, E-mail: carlson@strw.leidenuniv.nl, E-mail: seale@stsci.edu, E-mail: meixner@stsci.edu, E-mail: kgordon@stsci.edu, E-mail: shiao@stsci.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); and others

2013-11-20

The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK {sub s}) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

A Search for Faint, Diffuse Halo Emission in Edge-On Galaxies with Spitzer/IRAC

Science.gov (United States)

Ashby, Matthew; Arendt, R. G.; Pipher, J. L.; Forrest, W. J.; Marengo, M.; Barmby, P.; Willner, S. P.; Stauffer, J. R.; Fazio, G. G.

2006-12-01

We present deep infrared mosaics of the nearby edge-on spiral galaxies NGC 891, 4244, 4565, and 5907. These data were acquired at 3.6, 4.5, 5.8, and 8.0 microns using the Infrared Array Camera aboard Spitzer as part of GTO program number 3. This effort is designed to detect the putative faint, diffuse emission from halos and thick disks of spiral galaxies in the near-mid infrared under the thermally stable, low-background conditions of space. These conditions in combination with the advantageous viewing angles presented by these well-known edge-on spirals provide arguably the best opportunity to characterize the halo/thick disk components of such galaxies in the infrared. In this contribution we describe our observations, data reduction techniques, corrections for artifacts in the data, and the modeling approach we applied to analyze this unique dataset. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

Estimating precise metallicity and stellar mass evolution of galaxies

Science.gov (United States)

Mosby, Gregory

2018-01-01

The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

YSOVAR II: Mapping YSO Inner Disk Structure in NGC 2264 with Simultaneous Spitzer and CoRoT Time Series Photometry

Science.gov (United States)

Stauffer, John; Morales-Calderon, Maria; Rebull, Luisa; Affer, Laura; Alencar, Sylvia; Allen, Lori; Barrado, David; Bouvier, Jerome; Calvet, Nuria; Carey, Sean; Carpenter, John; Ciardi, David; Covey, Kevin; D'Alessio, Paola; Espaillat, Catherine; Favata, Fabio; Flaccomio, Ettore; Forbrich, Jan; Furesz, Gabor; Hartman, Lee; Herbst, William; Hillenbrand, Lynne; Holtzman, Jon; Hora, Joe; Marchis, Franck; McCaughrean, Mark; Micela, Giusi; Mundt, Reinhard; Plavchan, Peter; Turner, Neal; Skrutzkie, Mike; Smith, Howard; Song, Inseok; Szentgyorgi, Andy; Terebey, Susan; Vrba, Fred; Wasserman, Lawrence; Watson, Alan; Whitney, Barbara; Winston, Elaine; Wood, Kenny

2011-05-01

We propose a simultaneous, continuous 30 day observation of the star forming region NGC2264 with Spitzer and CoRoT. NGC2264 is the only nearby, rich star-forming region which can be observed with CoRoT; it is by definition then the only nearby, rich star-forming region where a simultaneous Spitzer/CoRoT campaign is possible. Fortunately, the visibility windows for the two spacecraft overlap, allowing this program to be done in the Nov. 25, 2011 to Jan. 4, 2012 time period. For 10 days, we propose to map the majority of the cluster (a 35'x35' region) to a depth of 48 seconds per point, with each epoch taking 1.7 hours, allowing of order 12 epochs per day. For the other 20 days, we propose to obtaining staring-mode data for two positions in the cluster having a high density of cluster members. We also plan to propose for a variety of other ground and space-based data, most of which would also be simultaneous with the Spitzer and CoRoT observing. These data will allow us to address many astrophysical questions related to the structure and evolution of the disks of young stars and the interaction of those disks with the forming star. The data may also help inform models of planet formation since planets form and migrate through the pre-main sequence disks during the 0.5-5 Myr age range of stars in NGC2264. The data we collect will also provide an archive of the variability properties of young stars that is unmatched in its accuracy, sensitivity, cadence and duration and which therefore could inspire investigation of phenomena which we cannot now imagine. The CoRoT observations have been approved, contingent on approval of a simultaneous Spitzer observing program (this proposal).

Stellar winds

International Nuclear Information System (INIS)

Weymann, R.J.

1978-01-01

It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

Energy Technology Data Exchange (ETDEWEB)

Andrews, Brett H. [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A., E-mail: andrewsb@pitt.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

2017-02-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

International Nuclear Information System (INIS)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A.

2017-01-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Two-fluid limits on stellarator performance: Explanation of three stellarator puzzles and comparison to axisymmetric plasmas

International Nuclear Information System (INIS)

Sugiyama, L.E.; Strauss, H.R.; Park, W.; Fu, G.Y.; Breslau, J.A.; Chen, J.

2005-01-01

The basic two-fluid processes, those related to the nonlinearly self-consistent diamagnetic drifts of the electrons and ions, are shown to have fundamentally different effects on the steady state and beta limits of stellarator configurations, compared to MHD predictions. Nonlinear numerical simulation shows that the ideal MHD ballooning modes and the resistive MHD ballooning and interchange modes at relatively high mode numbers, that set the most severe theoretical limits on beta in stellarators with fixed boundary, are easily stabilized by two-fluid effects at realistic parameters, including finite Larmor radius effects related to the ion diamagnetic drift. Magnetic reconnection at low-order rational magnetic surfaces, on the other hand, is enhanced through the parallel component of the two-fluid electron pressure gradient in Ohm's law. The accelerated reconnection rates may impose the true intrinsic limit on beta in stellarators, as a 'soft' or confinement mediated limit in β e , due to steady confinement degradation in the presence of large magnetic islands. Study of the corresponding axisymmetric configurations shows that the helical component of the stellarator configuration provides an important amplifying factor for these effects. The two-fluid results may explain several previously puzzling experimental observations on stellarator behavior. (author)

Exploring the dust content of galactic winds with Herschel - II. Nearby dwarf galaxies

Science.gov (United States)

McCormick, Alexander; Veilleux, Sylvain; Meléndez, Marcio; Martin, Crystal L.; Bland-Hawthorn, Joss; Cecil, Gerald; Heitsch, Fabian; Müller, Thomas; Rupke, David S. N.; Engelbracht, Chad

2018-06-01

We present the results from an analysis of deep Herschel Space Observatory observations of six nearby dwarf galaxies known to host galactic-scale winds. The superior far-infrared sensitivity and angular resolution of Herschel have allowed detection of cold circumgalactic dust features beyond the stellar components of the host galaxies traced by Spitzer 4.5 μm images. Comparisons of these cold dust features with ancillary data reveal an imperfect spatial correlation with the ionized gas and warm dust wind components. We find that typically ˜10-20 per cent of the total dust mass in these galaxies resides outside of their stellar discs, but this fraction reaches ˜60 per cent in the case of NGC 1569. This galaxy also has the largest metallicity (O/H) deficit in our sample for its stellar mass. Overall, the small number of objects in our sample precludes drawing strong conclusions on the origin of the circumgalactic dust. We detect no statistically significant trends with star formation properties of the host galaxies, as might be expected if the dust were lifted above the disc by energy inputs from ongoing star formation activity. Although a case for dust entrained in a galactic wind is seen in NGC 1569, in all cases, we cannot rule out the possibility that some of the circumgalactic dust might be associated instead with gas accreted or removed from the disc by recent galaxy interaction events, or that it is part of the outer gas-rich portion of the disc that lies below the sensitivity limit of the Spitzer 4.5 μm data.

Archival Investigation of Outburst Sites and Progenitors of Extragalactic Intermediate-Luminosity Mid-IR Transients

Science.gov (United States)

Bond, Howard

2017-08-01

Our team is using Spitzer in a long-term search for extragalactic mid-infrared (MIR) variable stars and transients-the SPIRITS project (SPitzer InfraRed Intensive Transients Survey). In this first exploration of luminous astrophysical transients in the infrared, we have discovered a puzzling new class. We call them SPRITEs: eSPecially Red Intermediate-luminosity Transient Events. They have maximum MIR luminosities between supernovae and classical novae, but are not detected in the optical to deep limits. To date, we have discovered more than 50 SPRITEs in galaxies out to 17 Mpc. In this Archival Research proposal, we request support in order to investigate the pre-eruption sites in HST images of some 3 dozen SPRITEs discovered to date, and an additional 2 dozen that we are likely to find until the end of Spitzer observing in late 2018. Our aims are (1) characterize the pre-outburst environments at HST resolution in the visible and near-IR, to understand the stellar populations, stellar ages and masses, and interstellar medium at the outburst sites; (2) search for progenitors; (3) help prepare the way for a better understanding of the nature of extragalactic IR transients that will be investigated by JWST.

A CAUTIONARY TALE: MARVELS BROWN DWARF CANDIDATE REVEALS ITSELF TO BE A VERY LONG PERIOD, HIGHLY ECCENTRIC SPECTROSCOPIC STELLAR BINARY

Energy Technology Data Exchange (ETDEWEB)

Mack, Claude E. III; Stassun, Keivan G.; De Lee, Nathan [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Ge, Jian; Fleming, Scott W. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL, 32611-2055 (United States); Deshpande, Rohit; Mahadevan, Suvrath [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Wisniewski, John P. [Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 (United States); Gaudi, B. Scott; Eastman, Jason; Beatty, Thomas G. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Observatorio Nacional, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ 20921-400 (Brazil); Gonzalez Hernandez, Jonay I.; Femenia, Bruno; Mata Sanchez, Daniel [Instituto de Astrofisica de Canarias (IAC), E-38205 La Laguna, Tenerife (Spain); Ferreira, Leticia; Porto de Mello, Gustavo [Laboratorio Interinstitucional de e-Astronomia-LIneA, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ 20921-400 (Brazil); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Agol, Eric [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Bizyaev, Dmitry, E-mail: claude.e.mack@vanderbilt.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others

2013-05-15

We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial-velocity (RV) measurements (R {approx}< 30, 000), this particular stellar binary mimics a single-lined binary with an RV signal that would be induced by a brown dwarf companion (Msin i {approx} 50 M{sub Jup}) to a solar-type primary. At least three properties of this system allow it to masquerade as a single star with a very-low-mass companion: its large eccentricity (e {approx} 0.8), its relatively long period (P {approx} 238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight ({omega} {approx} 189 Degree-Sign ). As a result of these properties, for {approx}95% of the orbit the two sets of stellar spectral lines are completely blended, and the RV measurements based on centroiding on the apparently single-lined spectrum is very well fit by an orbit solution indicative of a brown dwarf companion on a more circular orbit (e {approx} 0.3). Only during the {approx}5% of the orbit near periastron passage does the true, double-lined nature and large RV amplitude of {approx}15 km s{sup -1} reveal itself. The discovery of this binary system is an important lesson for RV surveys searching for substellar companions; at a given resolution and observing cadence, a survey will be susceptible to these kinds of astrophysical false positives for a range of orbital parameters. Finally, for surveys like MARVELS that lack the resolution for a useful line bisector analysis, it is imperative to monitor the peak of the cross-correlation function for suspicious changes in width or shape, so that such false positives can be flagged during the candidate vetting process.

Oscillations in stellar atmospheres

International Nuclear Information System (INIS)

Costa, A.; Ringuelet, A.E.; Fontenla, J.M.

1989-01-01

Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized. 7 refs

The Spitzer survey of interstellar clouds in the gould belt. VI. The Auriga-California molecular cloud observed with IRAC and MIPS

International Nuclear Information System (INIS)

Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Miller, Jennifer F.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jørgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merín, Bruno; Terebey, Susan; Peterson, Dawn E.

2014-01-01

We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg 2 with IRAC and 10.47 deg 2 with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

The Spitzer survey of interstellar clouds in the gould belt. VI. The Auriga-California molecular cloud observed with IRAC and MIPS

Energy Technology Data Exchange (ETDEWEB)

Broekhoven-Fiene, Hannah; Matthews, Brenda C. [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6 (Canada); Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Gutermuth, Robert A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Huard, Tracy L.; Miller, Jennifer F. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Tothill, Nicholas F. H. [School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751 (Australia); Nutter, David [School of Physics and Astronomy, Cardiff University, Queen' s Buildings, The Parade, Cardiff CF24 3AA (United Kingdom); Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); DiFrancesco, James [National Research Council Herzberg Astronomy and Astrophysics, Victoria, BC, V9E 2E7 (Canada); Jørgensen, Jes K. [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-DK-2100 Copenhagen Ø. (Denmark); Allen, Lori E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Chapman, Nicholas L. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Dunham, Michael M. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Merín, Bruno [Herschel Science Centre, ESAC-ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Terebey, Susan [Department of Physics and Astronomy PS315, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Peterson, Dawn E. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); and others

2014-05-01

We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg{sup 2} with IRAC and 10.47 deg{sup 2} with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

Spitzer sage survey of the large magellanic cloud. II. Evolved stars and infrared color-magnitude diagrams

NARCIS (Netherlands)

Blum, R. D.; Mould, J. R.; Olsen, K. A.; Frogel, J. A.; Meixner, M.; Markwick-Kemper, F.; Indebetouw, R.; Whitney, B.; Meade, M.; Babler, B.; Churchwell, E. B.; Gordon, K.; Engelbracht, C.; For, B. -Q.; Misselt, K.; Vijh, U.; Leitherer, C.; Volk, K.; Points, S.; Reach, W.; Hora, J. L.; Bernard, J. -P.; Boulanger, F.; Bracker, S.; Cohen, M.; Fukui, Y.; Gallagher, J.; Gorjian, V.; Harris, J.; Kelly, D.; Kawamura, A.; Latter, W. B.; Madden, S.; Mizuno, A.; Mizuno, N.; Oey, M. S.; Onishi, T.; Paladini, R.; Panagia, N.; Perez-Gonzalez, P.; Shibai, H.; Sato, S.; Smith, L.; Staveley-Smith, L.; Tielens, A.G.G.M; Ueta, T.; Van Dyk, S.; Zaritsky, D.; Werner, M.J.

Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 mu m epoch 1 data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in

The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

Science.gov (United States)

Belkus, H.; van Bever, J.; Vanbeveren, D.

In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

THE SPITZER c2d SURVEY OF WEAK-LINE T TAURI STARS. III. THE TRANSITION FROM PRIMORDIAL DISKS TO DEBRIS DISKS

International Nuclear Information System (INIS)

Wahhaj, Zahed; Cieza, Lucas; Koerner, David W.; Case, April; Stapelfeldt, Karl R.; Chapman, Nicholas; Padgett, Deborah L.; Brooke, Tim; Keller, James R.; MerIn, Bruno; Evans, Neal J.; Harvey, Paul; Sargent, Anneila; Van Dishoeck, Ewine F.; Allen, Lori; Blake, Geoff; Mundy, Lee; Myers, Philip C.

2010-01-01

We present 3.6 to 70 μm Spitzer photometry of 154 weak-line T Tauri stars (WTTSs) in the Chamaeleon, Lupus, Ophiuchus, and Taurus star formation regions, all of which are within 200 pc of the Sun. For a comparative study, we also include 33 classical T Tauri stars which are located in the same star-forming regions. Spitzer sensitivities allow us to robustly detect the photosphere in the IRAC bands (3.6 to 8 μm) and the 24 μm MIPS band. In the 70 μm MIPS band, we are able to detect dust emission brighter than roughly 40 times the photosphere. These observations represent the most sensitive WTTSs survey in the mid- to far-infrared to date and reveal the frequency of outer disks (r = 3-50 AU) around WTTSs. The 70 μm photometry for half the c2d WTTSs sample (the on-cloud objects), which were not included in the earlier papers in this series, those of Padgett et al. and Cieza et al., are presented here for the first time. We find a disk frequency of 19% for on-cloud WTTSs, but just 5% for off-cloud WTTSs, similar to the value reported in the earlier works. WTTSs exhibit spectral energy distributions that are quite diverse, spanning the range from optically thick to optically thin disks. Most disks become more tenuous than L disk /L * = 2 x 10 -3 in 2 Myr and more tenuous than L disk /L * = 5 x 10 -4 in 4 Myr.

Stellar remnants

CERN Document Server

Kawaler, S D; Srinivasan, G

1997-01-01

This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

STEADY-STATE RELATIVISTIC STELLAR DYNAMICS AROUND A MASSIVE BLACK HOLE

Energy Technology Data Exchange (ETDEWEB)

Bar-Or, Ben; Alexander, Tal [Department of Particle Physics and Astrophysics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 (Israel)

2016-04-01

A massive black hole (MBH) consumes stars whose orbits evolve into the small phase-space volume of unstable orbits, the “loss cone,” which take them into the MBH, or close enough to interact strongly with it. The resulting phenomena, e.g., tidal heating and disruption, binary capture and hyper-velocity star ejection, gravitational wave (GW) emission by inspiraling compact remnants, or hydrodynamical interactions with an accretion disk, can produce observable signatures and thereby reveal the MBH, affect its mass and spin evolution, test strong gravity, and probe stars and gas near the MBH. These continuous stellar loss and resupply processes shape the central stellar distribution. We investigate relativistic stellar dynamics near the loss cone of a non-spinning MBH in steady state, analytically and by Monte Carlo simulations of the diffusion of the orbital parameters. These take into account Newtonian mass precession due to enclosed stellar mass, in-plane precession due to general relativity, dissipation by GW, uncorrelated two-body relaxation, correlated resonant relaxation (RR), and adiabatic invariance due to secular precession, using a rigorously derived description of correlated post-Newtonian dynamics in the diffusion limit. We argue that general maximal entropy considerations strongly constrain the orbital diffusion in steady state, irrespective of the relaxation mechanism. We identify the exact phase-space separatrix between plunges and inspirals, and predict their steady-state rates. We derive the dependence of the rates on the mass of the MBH, show that the contribution of RR in steady state is small, and discuss special cases where unquenched RR in restricted volumes of phase-space may affect the steady state substantially.

A Dream of a Mission: Stellar Imager and Seismic Probe

Science.gov (United States)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Fisher, Richard R. (Technical Monitor)

2000-01-01

The Stellar Imager and Seismic Probe (SISP) is a mission to understand the various effects of magnetic fields of stars, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best-possible forecasting of solar activity on times scales ranging up to decades, and an understanding of the impact of stellar magnetic activity on astrobiology and life in the Universe. The road to that goal will revolutionize our understanding of stars and stellar systems, the building blocks of the Universe. SISP will zoom in on what today - with few exceptions - we only know as point sources, revealing processes never before seen, thus providing a tool to astrophysics as fundamental as the microscope is to the study of life on Earth. SISP is an ultraviolet aperture-synthesis imager with 8-10 telescopes with meter-class apertures, and a central hub with focal-plane instrumentation that allows spectrophotometry in passbands as narrow as a few Angstroms up to hundreds of Angstroms. SISP will image stars and binaries with one hundred to one thousand resolution elements on their surface, and sound their interiors through asteroseismology to image internal structure, differential rotation, and large-scale circulations; this will provide accurate knowledge of stellar structure and evolution and complex transport processes, and will impact numerous branches of (astro)physics ranging from the Big Bang to the future of the Universe. Fitting naturally within the NASA long-term time line, SISP complements defined missions, and with them will show us entire other solar systems, from the central star to their orbiting planets.

The relation between stellar evolution and cosmology

International Nuclear Information System (INIS)

Tayler, R.J.

1984-01-01

Observations of star clusters combined with the theory of stellar evolution enable us to estimate the ages of stars while cosmological observations and theories give us a value for the age of the Universe. This is the most important interaction between cosmology and stellar evolution because it is clearly necessary that stars are younger than the Universe. Stellar evolution also plays an important role in relating the present chemical composition of the Universe to its original composition. The author restricts the review to a discussion of the relation between stellar evolution and the big bang cosmological theory because there is such a good qualitative agreement between the hot big bang theory and observations. (Auth.)

Science with Synthetic Stellar Surveys

Science.gov (United States)

Sanderson, Robyn Ellyn

2018-04-01

A new generation of observational projects is poised to revolutionize our understanding of the resolved stellar populations of Milky-Way-like galaxies at an unprecedented level of detail, ushering in an era of precision studies of galaxy formation. In the Milky Way itself, astrometric, spectroscopic and photometric surveys will measure three-dimensional positions and velocities and numerous chemical abundances for stars from the disk to the halo, as well as for many satellite dwarf galaxies. In the Local Group and beyond, HST, JWST and eventually WFIRST will deliver pristine views of resolved stars. The groundbreaking scale and dimensionality of this new view of resolved stellar populations in galaxies challenge us to develop new theoretical tools to robustly compare these surveys to simulated galaxies, in order to take full advantage of our new ability to make detailed predictions for stellar populations within a cosmological context. I will describe a framework for generating realistic synthetic star catalogs and mock surveys from state-of-the-art cosmological-hydrodynamical simulations, and present several early scientific results from, and predictions for, resolved stellar surveys of our Galaxy and its neighbors.

TEM turbulence optimisation in stellarators

Science.gov (United States)

Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.

2016-01-01

With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

International Nuclear Information System (INIS)

Christensen-Dalsgaard, Joergen; Carpenter, Kenneth G; Schrijver, Carolus J; Karovska, Margarita

2011-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

Science.gov (United States)

Christensen-Dalsgaard, Jørgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita; Si Team

2011-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a "Landmark/Discovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

Science.gov (United States)

Christensen-Dalsgaard, Jorgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2012-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

The Quasi-Toroidal Stellarator: An Innovative Confinement Experiment

International Nuclear Information System (INIS)

Knowlton, S. F.

2001-01-01

To develop a new class of stellarators that exhibit improved confinement compared to conventional stellarators. This approach generally makes use of a designed symmetry of the magnetic field strength along a particular coordinate axis in the toroidal geometry of the stellarator, and is referred to as quasi-symmetry

SPITZER SPECTROSCOPY OF CIRCUMSTELLAR DISKS IN THE 5 Myr OLD UPPER SCORPIUS OB ASSOCIATION

International Nuclear Information System (INIS)

Dahm, S. E.; Carpenter, John M.

2009-01-01

We present mid-infrared spectra between 5.2 and 38 μm for 26 disk-bearing members of the ∼5 Myr old Upper Scorpius OB association obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. We find clear evidence for changes in the spectral characteristics of dust emission between the early-type (B+A) and late-type (K+M) infrared excess stars. The early-type members exhibit featureless continuum excesses that become apparent redward of ∼8 μm. In contrast, 10 and 20 μm silicate features or polycyclic aromatic hydrocarbon emission are present in all but one of the late-type excess members of Upper Scorpius. The strength of silicate emission among late-type Upper Scorpius members is spectral-type dependent, with the most prominent features being associated with K5-M2-type stars. By fitting the spectral energy distributions (SED) of a representative sample of low-mass stars with accretion disk models, we find that the SEDs are consistent with models having inner disk radii ranging from ∼0.2 to 1.2 AU. Complementary high-resolution (R ∼ 33, 000) optical (λλ4800-9200) spectra for the Upper Scorpius excess stars were examined for signatures of gaseous accretion. Of the 35 infrared excess stars identified in Upper Scorpius, only seven (all late-type) exhibit definitive signatures of accretion. Mass-accretion rates for these stars were estimated to range from 10 -11 to 10 -8.9 M sun yr -1 . Compared to Class II sources in Taurus-Auriga, the disk population in Upper Scorpius exhibits reduced levels of near- and mid-infrared excess emission and an order of magnitude lower mass-accretion rates. These results suggest that the disk structure has changed significantly over the 2-4 Myr in age separating these two stellar populations. The ubiquity of depleted inner disks in the Upper Scorpius excess sample implies that such disks are a common evolutionary pathway that persists for some time.

When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

Energy Technology Data Exchange (ETDEWEB)

El-Badry, Kareem; Quataert, Eliot [Department of Astronomy, University of California, Berkeley, CA (United States); Wetzel, Andrew R.; Hopkins, Philip F. [TAPIR, California Institute of Technology, Pasadena, CA (United States); Geha, Marla [Department of Astronomy, Yale University, New Haven, CT (United States); Kereš, Dusan; Chan, T. K. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla (United States); Faucher-Giguère, Claude-André, E-mail: kelbadry@berkeley.edu [Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL (United States)

2017-02-01

In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

International Nuclear Information System (INIS)

El-Badry, Kareem; Quataert, Eliot; Wetzel, Andrew R.; Hopkins, Philip F.; Geha, Marla; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André

2017-01-01

In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

A Spectroscopic Study of Young Stellar Objects in the Serpens Cloud Core and NGC 1333

Science.gov (United States)

Winston, E.; Megeath, S. T.; Wolk, S. J.; Hernandez, J.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Covey, K.; Allen, L. E.; Spitzbart, B.; Peterson, D.; Myers, P.; Fazio, G. G.

2009-06-01

We present spectral observations of 130 young stellar objects (YSOs) in the Serpens Cloud Core and NGC 1333 embedded clusters. The observations consist of near-IR spectra in the H and K bands from SpeX on the IRTF and far-red spectra (6000-9000 Å) from Hectospec on the Multi-Mirror Telescope. These YSOs were identified in previous Spitzer and Chandra observations, and the evolutionary classes of the YSOs were determined from the Spitzer mid-IR photometry. With these spectra we search for corroborating evidence for the pre-main-sequence nature of the objects, study the properties of the detected emission lines as a function of evolutionary class, and obtain spectral types for the observed YSOs. The temperatures implied by the spectral types are combined with luminosities determined from the near-IR photometry to construct Hertzsprung-Russell (H-R) diagrams for the clusters. By comparing the positions of the YSOs in the H-R diagrams with the pre-main-sequence tracks of Baraffe (1998), we determine the ages of the embedded sources and study the relative ages of the YSOs with and without optically thick circumstellar disks. The apparent isochronal ages of the YSOs in both clusters range from less than 1 Myr to 10 Myr, with most objects below 3 Myr. The observed distributions of ages for the Class II and Class III objects are statistically indistinguishable. We examine the spatial distribution and extinction of the YSOs as a function of their isochronal ages. We find the sources dispersed and are not deeply embedded. Nonetheless, the sources with isochronal ages >3 Myr show all the characteristics of YSOs in their spectra, their IR spectral energy distributions, and their X-ray emission; we find no evidence that they are contaminating background giants or foreground dwarfs. However, we find no corresponding decrease in the fraction of sources with infrared excess with isochronal age; this suggests that the older isochronal ages may not measure the true age of the >3

On plasma radiative properties in stellar conditions

International Nuclear Information System (INIS)

Turck-Chieze, S.; Delahaye, F.; Gilles, D.; Loisel, G.; Piau, L.; Loisel, G.

2009-01-01

The knowledge of stellar evolution is evolving quickly thanks to an increased number of opportunities to scrutinize the stellar internal plasma properties by stellar seismology and by 1D and 3D simulations. These new tools help us to introduce the internal dynamical phenomena in stellar modeling. A proper inclusion of these processes supposes a real confidence in the microscopic physics used, partly checked by solar or stellar acoustic modes. In the present paper we first recall which fundamental physics has been recently verified by helioseismology. Then we recall that opacity is an important ingredient of the secular evolution of stars and we point out why it is necessary to measure absorption coefficients and degrees of ionization in the laboratory for some well identified astrophysical conditions. We examine two specific experimental conditions which are accessible to large laser facilities and are suitable to solve some interesting questions of the stellar community: are the solar internal radiative interactions properly estimated and what is the proper role of the opacity in the excitation of the non-radial modes in the envelop of the β Cepheids and the Be stars? At the end of the paper we point out the difficulties of the experimental approach that we need to overcome. (authors)

A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

Energy Technology Data Exchange (ETDEWEB)

Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Fallscheer, Cassandra [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 (Canada); Ginsburg, Adam [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-0389 (United States); Terebey, Susan [Department of Physics and Astronomy PS315, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Andre, Philippe; Koenyves, Vera [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d' Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Di Francesco, James; Matthews, Brenda C. [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Peterson, Dawn E., E-mail: pmh@astro.as.utexas.edu, E-mail: Cassandra.Fallscheer@nrc-cnrc.gc.ca, E-mail: adam.ginsburg@colorado.edu, E-mail: sterebe@calstatela.edu, E-mail: pandre@cea.fr, E-mail: vera.konyves@cea.fr, E-mail: tbourke@cfa.harvard.edu, E-mail: James.DiFrancesco@nrc-cnrc.gc.ca, E-mail: Brenda.Matthews@nrc-cnrc.gc.ca, E-mail: dpeterson@spacescience.org [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80303 (United States)

2013-02-20

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few Multiplication-Sign 10{sup 22} cm{sup -2} (N {sub H2}) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to {approx}10 K from values {approx}14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

International Nuclear Information System (INIS)

Harvey, Paul M.; Fallscheer, Cassandra; Ginsburg, Adam; Terebey, Susan; André, Philippe; Könyves, Vera; Bourke, Tyler L.; Di Francesco, James; Matthews, Brenda C.; Peterson, Dawn E.

2013-01-01

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 μm sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few × 10 22 cm –2 (N H2 ) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to ∼10 K from values ∼14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

Hydrodynamics and stellar winds an introduction

CERN Document Server

Maciel, Walter J

2014-01-01

Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

Stellarator Coil Design and Plasma Sensitivity

International Nuclear Information System (INIS)

Ku, Long-Poe; Boozer, Allen H.

2010-01-01

The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first devel oping a simple, direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sen- sitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, (3) choose the ratios of the magnitudes of the the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) that are either smoother or can be located much farther from the plasma boundary than those of the present design.

Review of stellarator research world wide

International Nuclear Information System (INIS)

Shonet, J.L.

1987-01-01

The world-wide effort in stellarators has evolved considerably during the past few years. Stellarator facilities are located in the Australia, Federal Republic of Germany, Japan, the Soviet Union, Spain, the United Kingdom and the United States. Dimensions of stellarators range from less than 20 centimeters in major radius to more than 2 meters, and magnetic field values between 0.2 Tesla to more than 3.0 Tesla. Stellarators are made in a variety of magnetic configurations with wide ranges of toroidal aspect ratios and methods of generating the stellarator magnetic surfaces. In particular, continuous helical coils, twisted modular coils, or twisted vacuum chambers all provide different means to generate nested toroidal magnetic surfaces without the need for currents flowing in the plasma. The goal of present day experiments is to accumulate a physics data base. This is being done by increasing electron and ion temperatures with non-ohmic heating, by transport and scaling studies considering neoclassical scaling, global scaling, effects of electric fields, the bootstrap current and magnetic islands. Higher betas are being attempted by designing suitable magnetic configurations, pellet injection and/or minimizing transport losses. Plasma-wall interactions and particle control are being examined by divertor, pumped-limiter and carbonization experiments

THE MID-INFRARED PERIOD-LUMINOSITY RELATIONS FOR THE SMALL MAGELLANIC CLOUD CEPHEIDS DERIVED FROM SPITZER ARCHIVAL DATA

International Nuclear Information System (INIS)

Ngeow, Chow-Choong; Kanbur, Shashi M.

2010-01-01

In this paper, we derive the Spitzer IRAC band period-luminosity (P-L) relations for the Small Magellanic Cloud (SMC) Cepheids, by matching the Spitzer archival SAGE-SMC data with the OGLE-III SMC Cepheids. We find that the 3.6 μm and 4.5 μm band P-L relations can be better described using two P-L relations with a break period at log(P) = 0.4: this is consistent with similar results at optical wavelengths for SMC P-L relations. The 5.8 μm and 8.0 μm band P-L relations do not extend to sufficiently short periods to enable a similar detection of a slope change at log(P) = 0.4. The slopes of the SMC P-L relations, for log(P) > 0.4, are consistent with their Large Magellanic Cloud counterparts that were derived from a similar data set. They are also in agreement with those obtained from a small sample of Galactic Cepheids with parallax measurements.

A new mechanical stellar wind feedback model for the Rosette Nebula

Science.gov (United States)

Wareing, C. J.; Pittard, J. M.; Wright, N. J.; Falle, S. A. E. G.

2018-04-01

The famous Rosette Nebula has an evacuated central cavity formed from the stellar winds ejected from the 2-6 Myr old codistant and comoving central star cluster NGC 2244. However, with upper age estimates of less than 110 000 yr, the central cavity is too young compared to NGC 2244 and existing models do not reproduce its properties. A new proper motion study herein using Gaia data reveals the ejection of the most massive star in the Rosette, HD 46223, from NGC 2244 occurred 1.73 (+0.34, -0.25) Myr (1σ uncertainty) in the past. Assuming this ejection was at the birth of the most massive stars in NGC 2244, including the dominant centrally positioned HD 46150, the age is set for the famous ionized region at more than 10 times that derived for the cavity. Here, we are able to reproduce the structure of the Rosette Nebula, through simulation of mechanical stellar feedback from a 40 M⊙ star in a thin sheet-like molecular cloud. We form the 135 000 M⊙ cloud from thermally unstable diffuse interstellar medium (ISM) under the influence of a realistic background magnetic field with thermal/magnetic pressure equilibrium. Properties derived from a snapshot of the simulation at 1.5 Myr, including cavity size, stellar age, magnetic field, and resulting inclination to the line of sight, match those derived from observations. An elegant explanation is thus provided for the stark contrast in age estimates based on realistic diffuse ISM properties, molecular cloud formation and stellar wind feedback.

Tracing dust in old stellar populations : the mid-infrared spectrum of globular cluster AGB stars

International Nuclear Information System (INIS)

Richter, H.

2010-01-01

Asymptotic Giant Branch (AGB) stars are considered to be the main stellar dust producers in the universe. Their dusty circumstellar shells leave fingerprints in the mid-infrared (MIR) spectra of AGB stars and in unresolved old stellar populations. Bressan et al. (2007) showed that co-added MIR-spectra of AGB stars of known luminosity, metallicity and age (like those found in the Galactic globular cluster NGC104) can be used to model the dust excess in early-type galaxies. This work aims to improve our understanding of the MIR-spectra of old stellar populations with respect to their metallicities by studying a large sample of AGB stars in Galactic globular clusters. A sample of AGB stars (taken from Lebzelter et al. 2006 and Sloan et al. 2010) is used to produce co-added MIR-spectra of globular cluster combinations for three metallicity groups. Each group consists of several globular clusters with similar age and metallicity. Combining the clusters leads to a higher number of AGB stars with available Spitzer spectra in each group. The low metallicity group (Z=0.0038) consists of five globular clusters with 18 AGB star spectra, the intermediate (Z=0.0058) and high (Z=0.01) metallicity groups both include three clusters with eight and seven available MIR-spectra, respectively. Stars within the 90% mass radius of each globular cluster are used to generate 2MASS Color- Magnitude diagrams (CMDs) of each cluster combination. Binning the stars in the CMDs with respect to their MK-values results in Luminosity Functions (LFs) for the cluster combinations. The LFs based on 2MASS data are compared to LFs obtained using theoretical isochrones from the Padova group (Bertelli et al. 2008, Marigo et al. 2008). Using the 2MASS LFs integrated MIR-spectra of the three globular cluster combinations are derived by weighting the existing spectra with the total number of AGB stars within each MK-bin of the LFs along the upper giant branch. This relies on the assumption that stars that

Exploring stellar evolution with gravitational-wave observations

Science.gov (United States)

Dvorkin, Irina; Uzan, Jean-Philippe; Vangioni, Elisabeth; Silk, Joseph

2018-05-01

Recent detections of gravitational waves from merging binary black holes opened new possibilities to study the evolution of massive stars and black hole formation. In particular, stellar evolution models may be constrained on the basis of the differences in the predicted distribution of black hole masses and redshifts. In this work we propose a framework that combines galaxy and stellar evolution models and use it to predict the detection rates of merging binary black holes for various stellar evolution models. We discuss the prospects of constraining the shape of the time delay distribution of merging binaries using just the observed distribution of chirp masses. Finally, we consider a generic model of primordial black hole formation and discuss the possibility of distinguishing it from stellar-origin black holes.

AKARI/IRC source catalogues and source counts for the IRAC Dark Field, ELAIS North and the AKARI Deep Field South

Science.gov (United States)

Davidge, H.; Serjeant, S.; Pearson, C.; Matsuhara, H.; Wada, T.; Dryer, B.; Barrufet, L.

2017-12-01

We present the first detailed analysis of three extragalactic fields (IRAC Dark Field, ELAIS-N1, ADF-S) observed by the infrared satellite, AKARI, using an optimized data analysis toolkit specifically for the processing of extragalactic point sources. The InfaRed Camera (IRC) on AKARI complements the Spitzer Space Telescope via its comprehensive coverage between 8-24 μm filling the gap between the Spitzer/IRAC and MIPS instruments. Source counts in the AKARI bands at 3.2, 4.1, 7, 11, 15 and 18 μm are presented. At near-infrared wavelengths, our source counts are consistent with counts made in other AKARI fields and in general with Spitzer/IRAC (except at 3.2 μm where our counts lie above). In the mid-infrared (11 - 18 μm), we find our counts are consistent with both previous surveys by AKARI and the Spitzer peak-up imaging survey with the InfraRed Spectrograph (IRS). Using our counts to constrain contemporary evolutionary models, we find that although the models and counts are in agreement at mid-infrared wavelengths there are inconsistencies at wavelengths shortward of 7 μm, suggesting either a problem with stellar subtraction or indicating the need for refinement of the stellar population models. We have also investigated the AKARI/IRC filters, and find an active galactic nucleus selection criteria out to z < 2 on the basis of AKARI 4.1, 11, 15 and 18 μm colours.

IRAC Imaging of LSB Galaxies

Science.gov (United States)

Schombert, James; McGaugh, Stacy; Lelli, Federico

2017-04-01

We propose a program to observe a large sample of Low Surface Brightness (LSB) galaxies. Large galaxy surveys conducted with Spitzer suffer from the unavoidable selection bias against LSB systems (e.g., the S4G survey). Even those programs thathave specifically targeted LSB galaxies have usually been restricted objects of intermediate surface brightness (between 22 and 23 B mag/ []). Our sample is selected to be of a more extreme LSB nature (with central surface brightness fainter than 23 Bmag/[]). Even warm, Spitzer is the ideal instrument to image these low contrast targets in the near infrared: our sample goes a considerable way towards remedying this hole in the Spitzer legacy archive, also increasing coverage in terms of stellar mass, gas mass, and SFR. The sample will be used to address the newly discovered radial acceleration relation (RAR) in disk galaxies. While issues involving the connection between baryons and dark matter have been known since the development of the global baryonic Tully-Fisher (bTF) relation, it is only in the last six months that the particle physics and theoretical communities have recognized and responded to the local coupling between dark and baryonic matter represented by the RAR. This important new correlation is effectively a new natural law for galaxies. Spitzer photometry has been at the forefront of resolving the stellar mass component in galaxies that make-up the RAR and is the primary reason for the discovery of this new kinematic law.

Spitzer Trigonometric Parallaxes of L, T, and Y Dwarfs: Complementing Gaia's Optically-selected Census of Nearby Stars

Science.gov (United States)

Kirkpatrick, J. Davy; Smart, Richard; Marocco, Federico; Martin, Emily; Faherty, Jacqueline; Tinney, Christopher; Cushing, Michael; Beichman, Charles; Gelino, Christopher; Schneider, Adam; Wright, Edward; Lowrance, Patrick; Ingalls, James

2018-05-01

We now find ourselves at a moment in history where a parallax-selected census of nearby objects from the hottest A stars to the coldest Y dwarfs is almost a reality. With the release of Gaia DR2 in April of this year, we will be able to extract a volume-limited sample of stars out to 20 pc down to a spectral type of L5. Extending the census to colder types is much more difficult but nonetheless possible and essential. Ground-based astrometric monitoring of some of these colder dwarfs can be done with deep infrared detections on moderate to large (4+ meter) telescopes, but given the amount of time needed, only a portion of the colder objects believed to lie within 20 pc has been monitored. Our prior Spitzer observations have already enabled direct distance measures for T6 through Y dwarfs, but many 20-pc objects with spectral types between L5 and T5.5 have still not been astrometrically monitored, leaving a hole in our knowledge of this important all-sky sample. Spitzer Cycle 14 observations of modest time expenditure can rectify this problem by providing parallaxes for the 150+ objects remaining. Analysis of the brown dwarfs targeted by Spitzer is particularly important because it will provide insight into the low-mass cutoff of star formation, the shape of the mass function as inferred from the observed temperature distribution, the binary fraction of near-equal mass doubles, and the prevalence of extremely young (low-gravity) and extremely old (low metallicity) objects within the sample - all of which can be used to test and further refine model predictions of the underlying mass function.

Wolf-Rayet stars in the central region of the Milky Way

Science.gov (United States)

Hamann, Wolf-Rainer; Graefener, Goetz; Oskinova, Lidia; Zinnecker, Hans

2004-09-01

We propose to take mid-IR spectra of two Wolf-Rayet stars in the inner part of our Galaxy, within 30pc projected distance from the central Black Hole. Massive stars dominate the central galactic region by their mass-loss and ionizing radiation. A quantitative analysis of this stellar inventory is essential for understanding the energy, momentum and mass budget, for instance with respect to the feeding of the central black hole. Our group developed a highly advanced model code for the expanding atmospheres of WR stars. Recently we extended the spectrum synthesis to IR wavelengths. These models will be applied for the analysis of the Spitzer IRS data. The proposed mid-IR observations will provide a wide spectral range with many lines which are needed to determine the stellar parameters, such as stellar luminosity, effective temperature, mass-loss rate and chemical composition. Near-IR spectra of the program stars are available and will augment the analysis. The capability of our code to reproduce the observed mid-IR spectrum of a WN star has been demonstrated. The two targets we selected are sufficiently isolated, while the Galactic center cluster is too crowded for the size of Spitzer's spectrograph slit. As estimated from the K-band spectra, one of the stars (WR102ka) is of very late subtype (WN9), while the other star (WR102c) has the early subtype WN6. Hence they represent different stages in the evolutionary sequence of massive stars, the late-WN just having entered the Wolf-Rayet phase and the early WN being further evolved. We expect that the parameters of massive stars in the inner galaxy differ from the usual Galactic population. One reason is that higher metallicity should lead to stronger mass-loss, which affects the stellar evolution. The Spitzer IRS, with its high sensitivity, provides a unique opportunity to study representative members of the stellar population in the vicinity of the Galactic center.

Comparative studies of stellarator and tokamak transport

Energy Technology Data Exchange (ETDEWEB)

Stroth, U; Burhenn, R; Geiger, J; Giannone, L.; Hartfuss, H J; Kuehner, G; Ledl, L; Simmet, E E; Walter, H [Max-Planck-Inst. fuer Plasmaphysik, IPP-Euratom Association, Garching (Germany); ECRH Team; W7-AS Team

1997-09-01

Transport properties in the W7-AS stellarator and in tokamaks are compared. The parameter dependences and the absolute values of the energy confinement time are similar. Indications are found that the density dependence, which is usually observed in stellarator confinement, can vanish above a critical density. The density dependence in stellarators seems to be similar to that in the linear ohmic confinement regime, which, in small tokamaks, extends to high density values, too. Because of the similarity in the gross confinement properties, transport in stellarators and tokamaks should not be dominated by the parameters which are very different in the two concepts, i.e. magnetic shear, major rational values of the rotational transform and plasma current. A difference in confinement is that there exists evidence for pinches in the particle and, possibly, energy transport channels in tokamaks whereas in stellarators no pinches have been observed, so far. In order to study the effect of plasma current and toroidal electric fields, stellarator discharges were carried out with an increasing amount of plasma current. From these experiments, no clear evidence of a connection of pinches with these parameters is found. The transient response in W7-AS plasmas can be described in terms of a non-local model. As in tokamaks, also cold pulse experiments in W7-AS indicate the importance of non-local transport. (author). 8 refs, 5 figs.

Direct Imaging of Stellar Surfaces: Results from the Stellar Imager (SI) Vision Mission Study

Science.gov (United States)

Carpenter, Kenneth; Schrijver, Carolus; Karovska, Margarita

2006-01-01

The Stellar Imager (SI) is a UV-Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified as a "Flagship and Landmark Discovery Mission'' in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory'' in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we will discuss the results of the SI Vision Mission Study, elaborating on the science goals of the SI Mission and a mission architecture that could meet those goals.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

Energy Technology Data Exchange (ETDEWEB)

Christensen-Dalsgaard, Joergen [Department of Physics and Astronomy, Aarhus University (Denmark); Carpenter, Kenneth G [Code 667 NASA-GSFC, Greenbelt, MD 20771 (United States); Schrijver, Carolus J [LMATC 3251 Hanover St., Bldg. 252, Palo Alto, CA 94304 (United States); Karovska, Margarita, E-mail: jcd@phys.au.d, E-mail: Kenneth.G.Carpenter@nasa.gov, E-mail: schryver@lmsal.com, E-mail: karovska@head.cfa.harvard.edu [60 Garden St., Cambridge, MA 02138 (United States)

2011-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

Geometric phase modulation for stellar interferometry

International Nuclear Information System (INIS)

Roy, M.; Boschung, B.; Tango, W.J.; Davis, J.

2002-01-01

Full text: In a long baseline optical interferometer, the fringe visibility is normally measured by modulation of the optical path difference between the two arms of the instruments. To obtain accurate measurements, the spectral bandwidth must be narrow, limiting the sensitivity of the technique. The application of geometric phase modulation technique to stellar interferometry has been proposed by Tango and Davis. Modulation of the geometric phase has the potential for improving the sensitivity of optical interferometers, and specially the Sydney University Stellar Interferometer (SUSI), by allowing broad band modulation of the light signals. This is because a modulator that changes the geometric phase of the signal is, in principle, achromatic. Another advantage of using such a phase modulator is that it can be placed in the common path traversed by the two orthogonally polarized beams emerging from the beam combiner in a stellar interferometer. Thus the optical components of the modulator do not have to be interferometric quality and could be relatively easily introduced into SUSI. We have investigated the proposed application in a laboratory-based experiment using a Mach-Zehnder interferometer with white-light source. This can be seen as a small model of an amplitude stellar interferometer where the light source takes the place of the distant star and two corner mirrors replaces the entrance pupils of the stellar interferometer

The Stellar Imager (SI)"Vision Mission"

Science.gov (United States)

Carpenter, Ken; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Karovska, M.; Allen, R.

2004-01-01

The Stellar Imager (SI) is a "Vision" mission in the Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar magnetic activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and thus baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (less than 20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution will make it an invaluable resource for many other areas of astrophysics, including studies of AGN s, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.

Near-infrared imaging survey of faint companions around young dwarfs in the Pleiades cluster

International Nuclear Information System (INIS)

Itoh, Yoichi; Funayama, Hitoshi; Hashiguchi, Toshio; Oasa, Yumiko; Hayashi, Masahiko; Fukagawa, Misato; Currie, Thayne

2011-01-01

We conducted a near-infrared imaging survey of 11 young dwarfs in the Pleiades cluster using the Subaru Telescope and the near-infrared coronagraph imager. We found ten faint point sources, with magnitudes as faint as 20 mag in the K-band, with around seven dwarfs. Comparison with the Spitzer archive images revealed that a pair of the faint sources around V 1171 Tau is very red in infrared wavelengths, which indicates very low-mass young stellar objects. However, the results of our follow-up proper motion measurements implied that the central star and the faint sources do not share common proper motions, suggesting that they are not physically associated.

Radiative otacity tables for 40 stellar mixtures

International Nuclear Information System (INIS)

Cox, A.N.; Tabor, J.E.

1976-01-01

Using improved methods, radiative opacities for 40 mixtures of elements are given for use in calculations of stellar structure, stellar evolution, and stellar pulsation. The major improvements over previous Los Alamos data are increased iron abundance in the composition, better allowance for the continuum depression for bound electrons, and corrections in some bound-electron energy levels. These opacities have already been widely used, and represent a relatively homogeneous set of data for stellar structures. Further improvements to include more bound-bound (line) transitions by a smearing technique and to include molecular absorptions are becoming available, and in a few years these tables, as well as all previous tables, will be outdated. At high densities the conduction of energy will dominate radiation flow, and this effect must be added separately

The First Simultaneous Microlensing Observations by Two Space Telescopes: Spitzer and Swift Reveal a Brown Dwarf in Event OGLE-2015-BLG-1319

Science.gov (United States)

Shvartzvald, Y.; Li, Z.; Udalski, A.; Gould, A.; Sumi, T.; Street, R. A.; Calchi Novati, S.; Hundertmark, M.; Bozza, V.; Beichman, C.;

On origin of stellar clusters

International Nuclear Information System (INIS)

Tovmasyan, G.M.

1977-01-01

The ratios of the gas component of the mass of young stellar clusters to their stellar mass are considered. They change by more than four orders from one cluster to another. The results are in direct contradiction with the hypothesis of formation of cluster stars from a preliminarily existing gas cloud by its condensation, and they favour the Ambartsumian hypothesis of the joint origin of stars and gas clouds from superdense protostellar matter

STELLAR POPULATIONS OF Lyα EMITTERS AT z ∼ 6-7: CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS FROM GALAXY BUILDING BLOCKS

International Nuclear Information System (INIS)

Ono, Yoshiaki; Shimasaku, Kazuhiro; Okamura, Sadanori; Masami Ouchi; Dunlop, James; Farrah, Duncan; McLure, Ross

2010-01-01

We investigate the stellar populations of Lyα emitters (LAEs) at z = 5.7 and 6.6 in a 0.65 deg 2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field, using deep images taken with the Subaru/Suprime-Cam, United Kingdom Infrared Telescope/Wide Field Infrared Camera, and Spitzer/Infrared Array Camera (IRAC). We produce stacked multiband images at each redshift from 165 (z = 5.7) and 91 (z = 6.6) IRAC-undetected objects to derive typical spectral energy distributions (SEDs) of z ∼ 6-7 LAEs for the first time. The stacked LAEs have as blue UV continua as the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) z-dropout galaxies of similar M UV , with a spectral slope β ∼ -3, but at the same time they have red UV-to-optical colors with detection in the 3.6 μm band. Using SED fitting we find that the stacked LAEs have low stellar masses of ∼(3-10) x 10 7 M sun , very young ages of ∼1-3 Myr, negligible dust extinction, and strong nebular emission from the ionized interstellar medium, although the z = 6.6 object is fitted similarly well with high-mass models without nebular emission; inclusion of nebular emission reproduces the red UV-to-optical colors while keeping the UV colors sufficiently blue. We infer that typical LAEs at z ∼ 6-7 are building blocks of galaxies seen at lower redshifts. We find a tentative decrease in the Lyα escape fraction from z = 5.7 to 6.6, which may imply an increase in the intergalactic medium neutral fraction. From the minimum contribution of nebular emission required to fit the observed SEDs, we place an upper limit on the escape fraction of ionizing photons of f ion esc ∼ 0.6 at z = 5.7 and ∼0.9 at z = 6.6. We also compare the stellar populations of our LAEs with those of stacked HST/WFC3 z-dropout galaxies.

The Relationship Between Infrared Dark Cloud and Stellar Properties

Science.gov (United States)

Calahan, Jenny; Hora, Joseph L.

2018-01-01

Massive stars are known to form within infrared dark clouds (IRDCs), but many details about how molecular clouds collapse and form stars remain poorly understood.We determine the relationship between the dark cloud mass and the population of young stellar objects (YSOs) associated with the cloud to shed light on the physical processes occurring within these star forming regions. We chose to use a sample of IRDCs and YSOs within the Cygnus-X region, a close-by giant star formation complex that has every stage of star formation represented. Using observations from IRAC, MIPS, PACS, and SPIRE on Spitzer and Herschel we identified a sample of 30,903 YSOs and 167 IRDCs. We derived the class of each YSO as well as the mass of YSO and IRDCs from the flux information. Using these parameters, as well as their locations in the cloud, we were sorted IRDC fragments into larger filaments and associate a set of YSOs with each IRDC. By measuring and comparing parameters such as YSO total mass, number of YSOs, Class 0, Class I, and Class II populations, distance from host filament, and filament mass we tested for correlations between the YSO and IRDC parameters. Using this treasure trove of information, we find that Class 0 and I objects are located more closely to their host IRDC than their Class II counterparts. We also find that high-density IRDCs are better environments for star formation than low-density IRDCs. However, we find no correlation between the total mass of the IRDC and the largest YSO mass in the IRDC, suggesting that IRDCs of any mass can have massive YSOs associated with them.The SAO REU program is funded by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant AST-1659473, and by the Smithsonian Institution.

Stellar populations in the Carina region. The Galactic plane at l = 291°

Science.gov (United States)

Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

2016-08-01

Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the

FINDING η CAR ANALOGS IN NEARBY GALAXIES USING SPITZER. I. CANDIDATE SELECTION

International Nuclear Information System (INIS)

Khan, Rubab; Stanek, K. Z.; Kochanek, C. S.

2013-01-01

The late-stage evolution of the most massive stars such as η Carinae is controlled by the effects of mass loss, which may be dominated by poorly understood eruptive mass ejections. Understanding this population is challenging because no true analogs of η Car have been clearly identified in the Milky Way or other galaxies. We utilize Spitzer IRAC images of seven nearby (∼ 10 5 L ☉ in the IRAC bands (3.6 to 8.0 μm) and are not known to be background sources. Based on our estimates for the expected number of background sources, we expect that follow-up observations will show that most of these candidates are not dust enshrouded massive stars, with an expectation of only 6 ± 6 surviving candidates. Since we would detect true analogs of η Car for roughly 200 years post-eruption, this implies that the rate of eruptions like η Car is less than the core-collapse supernova rate. It is possible, however, that every M > 40 M ☉ star undergoes such eruptions given our initial results. In Paper II we will characterize the candidates through further analysis and follow-up observations, and there is no barrier to increasing the galaxy sample by an order of magnitude. The primary limitation of the present search is that Spitzer's resolution limits us to the shorter wavelength IRAC bands. With the James Webb Space Telescope, such surveys can be carried out at the far more optimal wavelengths of 10-30 μm, allowing identification of η Car analogs for millennia rather than centuries post-eruption.

Theories for convection in stellar atmospheres

International Nuclear Information System (INIS)

Nordlund, Aa.

1976-02-01

A discussion of the fundamental differences between laboratory convection in a stellar atmosphere is presented. The shortcomings of laterally homogeneous model atmospheres are analysed, and the extent to which these shortcoming are avoided in the two-component representation is discussed. Finally a qualitative discussion on the scaling properties of stellar granulation is presented. (Auth.)

The Prospect for Detecting Stellar Coronal Mass Ejections

Science.gov (United States)

Osten, Rachel A.; Crosley, Michael Kevin

2018-06-01

The astrophysical study of mass loss, both steady-state and transient, on the cool half of the HR diagram has implications bothfor the star itself and the conditions created around the star that can be hospitable or inimical to supporting life. Recent results from exoplanet studies show that planets around M dwarfs are exceedingly common, which together with the commonality of M dwarfs in our galaxy make this the dominant mode of star and planet configurations. The closeness of the exoplanets to the parent M star motivate a comprehensive understanding of habitability for these systems. Radio observations provide the most clear signature of accelerated particles and shocks in stars arising as the result of MHD processes in the stellar outer atmosphere. Stellar coronal mass ejections have not been conclusively detected, despite the ubiquity with which their radiative counterparts in an eruptive event (stellar flares) have. I will review some of the different observational methods which have been used and possibly could be used in the future in the stellar case, emphasizing some of the difficulties inherent in such attempts. I will provide a framework for interpreting potential transient stellar mass loss in light of the properties of flares known to occur on magnetically active stars. This uses a physically motivated way to connect the properties of flares and coronal mass ejections and provides a testable hypothesis for observing or constraining transient stellar mass loss. I will describe recent results using radio observations to detect stellar coronal mass ejections, and what those results imply about transient stellar mass loss. I will provide some motivation for what could be learned in this topic from space-based low frequency radio experiments.

Hot electron transport modelling in fast ignition relevant targets with non-Spitzer resistivity

Energy Technology Data Exchange (ETDEWEB)

Chapman, D A; Hoarty, D J; Swatton, D J R [Plasma Physics Department, AWE, Aldermaston, Reading, Berkshire, RG7 4PR (United Kingdom); Hughes, S J, E-mail: david.chapman@awe.co.u [Computational Physics Group, AWE, Aldermaston, Reading, Berkshire, RG7 4PR (United Kingdom)

2010-08-01

The simple Lee-More model for electrical resistivity is implemented in the hybrid fast electron transport code THOR. The model is shown to reproduce experimental data across a wide range of temperatures using a small number of parameters. The effect of this model on the heating of simple Al targets by a short-pulse laser is studied and compared to the predictions of the classical Spitzer-Haerm resistivity. The model is then used in simulations of hot electron transport experiments using buried layer targets.

A COMPREHENSIVE SEARCH FOR STELLAR BOWSHOCK NEBULAE IN THE MILKY WAY: A CATALOG OF 709 MID-INFRARED SELECTED CANDIDATES

Energy Technology Data Exchange (ETDEWEB)

Kobulnicky, Henry A.; Chick, William T.; Schurhammer, Danielle P.; Andrews, Julian E.; Munari, Stephan A.; Olivier, Grace M.; Sorber, Rebecca L.; Wernke, Heather N.; Dale, Daniel A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY 82070 (United States); Povich, Matthew S.; Dixon, Don M. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States)

2016-12-01

We identify 709 arc-shaped mid-infrared nebula in 24 μ m Spitzer Space Telescope or 22 μ m Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 μ m or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0.°6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate “runaway” stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. We discuss a population of “in situ” bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μ m bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., “PEF bowshocks”). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.

Constraining Stellar Coronal Mass Ejections through Multi-wavelength Analysis of the Active M Dwarf EQ Peg

Science.gov (United States)

Crosley, M. K.; Osten, R. A.

2018-03-01

Stellar coronal mass ejections remain experimentally unconstrained, unlike their stellar flare counterparts, which are observed ubiquitously across the electromagnetic spectrum. Low-frequency radio bursts in the form of a type II burst offer the best means of identifying and constraining the rate and properties of stellar CMEs. CME properties can be further improved through the use of proposed solar-stellar scaling relations and multi-wavelength observations of CMEs through the use of type II bursts and the associated flares expected to occur alongside them. We report on 20 hr of observation of the nearby, magnetically active, and well-characterized M dwarf star EQ Peg. The observations are simultaneously observed with the Jansky Very Large Array at their P-band (230–470 MHz) and at the Apache Point observatory in the SDSS u‧ filter (λ = 3557 Å). Dynamic spectra of the P-band data, constructed to search for signals in the frequency-time domains, did not reveal evidence of drifting radio bursts that could be ascribed to type II bursts. Given the sensitivity of our observations, we are able to place limits on the brightness temperature and source size of any bursts that may have occurred. Using solar scaling rations on four observed stellar flares, we predict CME parameters. Given the constraints on coronal density and photospheric field strength, our models suggest that the observed flares would have been insufficient to produce detectable type II bursts at our observed frequencies. We consider the implications of these results, and other recent findings, on stellar mass loss.

Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events

Science.gov (United States)

Novati, S. Calchi; Gould, A.; Udalski, A.; Menzies, J. W.; Bond, I. A.; Shvartzvald, Y.; Street, R. A.; Hundertmark, M.; Beichman, C. A.; Barry, R. K.

2015-01-01

We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was approximately 1 Astronomical Unit west of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle, it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations yielded only one planet, this is not yet possible in practice. However, it will become possible as larger samples are accumulated.

Collisionless microinstabilities in stellarators. II. Numerical simulations

International Nuclear Information System (INIS)

Proll, J. H. E.; Xanthopoulos, P.; Helander, P.

2013-01-01

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations

Indicators of Mass in Spherical Stellar Atmospheres

Science.gov (United States)

Lester, John B.; Dinshaw, Rayomond; Neilson, Hilding R.

2013-04-01

Mass is the most important stellar parameter, but it is not directly observable for a single star. Spherical model stellar atmospheres are explicitly characterized by their luminosity ( L⋆), mass ( M⋆), and radius ( R⋆), and observations can now determine directly L⋆ and R⋆. We computed spherical model atmospheres for red giants and for red supergiants holding L⋆ and R⋆ constant at characteristic values for each type of star but varying M⋆, and we searched the predicted flux spectra and surface-brightness distributions for features that changed with mass. For both stellar classes we found similar signatures of the stars’ mass in both the surface-brightness distribution and the flux spectrum. The spectral features have been use previously to determine log 10(g), and now that the luminosity and radius of a non-binary red giant or red supergiant can be observed, spherical model stellar atmospheres can be used to determine a star’s mass from currently achievable spectroscopy. The surface-brightness variations of mass are slightly smaller than can be resolved by current stellar imaging, but they offer the advantage of being less sensitive to the detailed chemical composition of the atmosphere.

Evolution of rotating stellar clusters at the stage of inelastic collisions

International Nuclear Information System (INIS)

Romanova, M.M.

1985-01-01

The dynamics of a gas-stellar disk in a dense stellar cluster of small ellipticity (epsilon or approximately 0.2-0.3. Possible existence of a thin stellar disk in a dense stellar cluster is analysed. With epsilon in the above range, collisions between cluster and disk stars are shown to have no effect on the evolution of the disk up to the instability time, provided that the ratio of disk stellar mass to the cluster stellar mass > or approximately 0.04

Superbanana orbits in stellarator geometries

International Nuclear Information System (INIS)

Derr, J.A.; Shohet, J.L.

1979-04-01

The presence of superbanana orbit types localized to either the interior or the exterior of stellarators and torsatrons is numerically investigated for 3.5 MeV alpha particles. The absence of the interior superbanana in both geometries is found to be due to non-conservation of the action. Exterior superbananas are found in the stellarator only, as a consequence of the existence of closed helical magnetic wells. No superbananas of either type are found in the torsatron

Stellar Parameters for Trappist-1

Science.gov (United States)

Van Grootel, Valérie; Fernandes, Catarina S.; Gillon, Michael; Jehin, Emmanuel; Manfroid, Jean; Scuflaire, Richard; Burgasser, Adam J.; Barkaoui, Khalid; Benkhaldoun, Zouhair; Burdanov, Artem; Delrez, Laetitia; Demory, Brice-Olivier; de Wit, Julien; Queloz, Didier; Triaud, Amaury H. M. J.

2018-01-01

TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of {L}* =(5.22+/- 0.19)× {10}-4 {L}ȯ , which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are {M}* =0.089+/- 0.006 {M}ȯ , {R}* =0.121+/- 0.003 {R}ȯ , and {T}{eff} = 2516 ± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.

Spitzer/IRAC observations of the variability of Sgr A* and the object G2 at 4.5 μm

Energy Technology Data Exchange (ETDEWEB)

Hora, J. L.; Ashby, M. L. N.; Fazio, G. G.; Smith, H. A.; Willner, S. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Witzel, G.; Becklin, E. E.; Ghez, A.; Meyer, L.; Morris, M. R. [University of California, Los Angeles, CA 90095 (United States); Carey, S.; Ingalls, J. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)

2014-10-01

We present the first detection from the Spitzer Space Telescope of 4.5 μm variability from Sgr A*, the emitting source associated with the Milky Way's central black hole. The >23 hr continuous light curve was obtained with the Infrared Array Camera (IRAC) instrument in 2013 December. The result characterizes the variability of Sgr A* prior to the closest approach of the tidally deformed G2 object, a putative infalling gas cloud that orbits close to Sgr A*. The high stellar density at the location of Sgr A* produces a background of ∼250 mJy at 4.5 μm in each pixel with a large pixel-to-pixel gradient, but the light curve for the highly variable Sgr A* source was successfully measured by modeling and removing the variations due to pointing wobble. The observed flux densities range from the noise level of ∼0.7 mJy rms in a 6.4 s measurement to ≳10 mJy. Emission was seen above the noise level ∼34% of the time. The light-curve characteristics, including the flux density distribution and structure function, are consistent with those previously derived at shorter infrared wavelengths. We see no evidence in the light curve for activity attributable to the G2 interaction at the observing epoch, ∼100 days before the expected G2 periapsis passage. The IRAC light curve is more than a factor of two longer than any previous infrared observation, improving constraints on the timescale of the break in the power spectral distribution of Sgr A* flux densities. The data favor the longer of the two previously published values for the timescale.

ESTIMATION OF DISTANCES TO STARS WITH STELLAR PARAMETERS FROM LAMOST

Energy Technology Data Exchange (ETDEWEB)

Carlin, Jeffrey L.; Newberg, Heidi Jo [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Liu, Chao; Deng, Licai; Li, Guangwei; Luo, A-Li; Wu, Yue; Yang, Ming; Zhang, Haotong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Beers, Timothy C. [Department of Physics and JINA: Joint Institute for Nuclear Astrophysics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Chen, Li; Hou, Jinliang; Smith, Martin C. [Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030 (China); Guhathakurta, Puragra [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Hou, Yonghui [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China); Lépine, Sébastien [Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Zheng, Zheng, E-mail: jeffreylcarlin@gmail.com [Department of Physics and Astronomy, University of Utah, UT 84112 (United States)

2015-07-15

We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

Constraining stellar physics from red-giant stars in binaries – stellar rotation, mixing processes and stellar activity

Directory of Open Access Journals (Sweden)

Beck P. G.

2017-01-01

Full Text Available The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

Plea for stellarator funding raps tokamaks

International Nuclear Information System (INIS)

Blake, M.

1992-01-01

The funding crunch in magnetic confinement fusion development has moved the editor of a largely technical publication to speak out on a policy issue. James A. Rome, who edits Stellarator News from the Fusion Energy Division at Oak Ridge National Laboratory, wrote an editorial that appeared on the front page of the May 1992 issue. It was titled open-quotes The US Stellarator Program: A Time for Renewal,close quotes and while it focused chiefly on that subject (and lamented the lack of funding for the operation of the existing ATF stellarator at Oak Ridge), it also cited some of the problems inherent in the mainline MCF approach--the tokamak--and stated that if the money can be found for further tokamak design upgrades, it should also be found for stellarators. Rome wrote, open-quotes There is growing recognition in the US, and elsewhere, that the conventional tokamak does not extrapolate to a commercially competitive energy source except with very high field coils ( 1000 MWe).close quotes He pointed up open-quotes the difficulty of simultaneously satisfying conflicting tokamak requirements for efficient current drive, high bootstrap-current fraction, complete avoidance of disruptions, adequate beta limits, and edge-plasma properties compatible with improved (H-mode) confinement and acceptable erosion of divertor plates.close quotes He then called for support for the stellarator as open-quotes the only concept that has performance comparable to that achieved in tokamaks without the plasma-current-related limitations listed above.close quotes

ON THE ORIGIN OF STELLAR MASSES

International Nuclear Information System (INIS)

Krumholz, Mark R.

2011-01-01

It has been a longstanding problem to determine, as far as possible, the characteristic masses of stars in terms of fundamental constants; the almost complete invariance of this mass as a function of the star-forming environment suggests that this should be possible. Here I provide such a calculation. The typical stellar mass is set by the characteristic fragment mass in a star-forming cloud, which depends on the cloud's density and temperature structure. Except in the very early universe, the latter is determined mainly by the radiation released as matter falls onto seed protostars. The energy yield from this process is ultimately set by the properties of deuterium burning in protostellar cores, which determines the stars' radii. I show that it is possible to combine these considerations to compute a characteristic stellar mass almost entirely in terms of fundamental constants, with an extremely weak residual dependence on the interstellar pressure and metallicity. This result not only explains the invariance of stellar masses, it resolves a second mystery: why fragmentation of a cold, low-density interstellar cloud, a process with no obvious dependence on the properties of nuclear reactions, happens to select a stellar mass scale such that stellar cores can ignite hydrogen. Finally, the weak residual dependence on the interstellar pressure and metallicity may explain recent observational hints of a smaller characteristic mass in the high-pressure, high-metallicity cores of giant elliptical galaxies.

Status of stellarator research

International Nuclear Information System (INIS)

Wobig, H.

1985-01-01

In recent years main activities in stellarator research were focussed on production and investigation of currentless plasmas. Several heating methods have been applied: electron cyclotron heating, ion cyclotron heating and neutral beam injection. The parameters achieved in HELIOTRON E and W VII-A are: antin 20 m 3 , Tsub(i) <= 1 keV. The confinement is improved as compared with ohmically heated discharges. By ECRH (P = 200 kW) it is possible to heat electrons up to 1.4 keV, confinement in this regime is dominated already by trapped particle effects. Toroidal currents up to 2 kA - either bootstrap currents or externally driven currents - were observed. High β-values (antiβ = 2%) have been obtained in HELIOTRON E, in this regime already pressure driven MHD-modes were observed. Future experiments (ATF-1 and W VII-AS) will extend the parameter regime to temperatures of several keV. These experiments will give important information about critical problems of the stellarator line (β-limit, neoclassical confinement impurity transport). A few reactor studies of stellarators exist, attention is mainly concentrated on technical problems of the modular coil system

THE LAST GASP OF GAS GIANT PLANET FORMATION: A SPITZER STUDY OF THE 5 Myr OLD CLUSTER NGC 2362

International Nuclear Information System (INIS)

Currie, Thayne; Lada, Charles J.; Robitaille, Thomas P.; Irwin, Jonathan; Kenyon, Scott J.; Plavchan, Peter

2009-01-01

Expanding upon the Infrared Array Camera (IRAC) survey from Dahm and Hillenbrand, we describe Spitzer IRAC and Multiband Imaging Photometer for Spitzer observations of the populous, 5 Myr old open cluster NGC 2362. We analyze the mid-IR colors of cluster members and compared their spectral energy distributions (SEDs) to star+circumstellar disk models to constrain the disk morphologies and evolutionary states. Early/intermediate-type confirmed/candidate cluster members either have photospheric mid-IR emission or weak, optically thin IR excess emission at λ ≥ 24 μm consistent with debris disks. Few late-type, solar/subsolar-mass stars have primordial disks. The disk population around late-type stars is dominated by disks with inner holes (canonical 'transition disks') and 'homologously depleted' disks. Both types of disks represent an intermediate stage between primordial disks and debris disks. Thus, in agreement with previous results, we find that multiple paths for the primordial-to-debris disk transition exist. Because these 'evolved primordial disks' greatly outnumber primordial disks, our results undermine standard arguments in favor of a ∼ 5 yr timescale for the transition based on data from Taurus-Auriga. Because the typical transition timescale is far longer than 10 5 yr, these data also appear to rule out standard ultraviolet photoevaporation scenarios as the primary mechanism to explain the transition. Combining our data with other Spitzer surveys, we investigate the evolution of debris disks around high/intermediate-mass stars and investigate timescales for giant planet formation. Consistent with Currie et al., the luminosity of 24 μm emission in debris disks due to planet formation peaks at ∼10-20 Myr. If the gas and dust in disks evolve on similar timescales, the formation timescale for gas giant planets surrounding early-type, high/intermediate-mass (∼>1.4 M sun ) stars is likely 1-5 Myr. Most solar/subsolar-mass stars detected by Spitzer

THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

NARCIS (Netherlands)

Pascucci, I.; Apai, D.; Luhman, K.; Henning, Th.; Bouwman, J.; Meyer, M. R.; Lahuis, F.; Natta, A.

2009-01-01

Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks

Detached dust shell around Wolf-Rayet star WR60-6 in the young stellar cluster VVV CL036

Energy Technology Data Exchange (ETDEWEB)

Borissova, J.; Amigo, P.; Kurtev, R. [Departamento de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030 (Chile); Kumar, M. S. N. [Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Chené, A.-N. [Gemini Observatory, Northern Operations Center, 670 North A' ohoku Place Hilo, HI 96720 (United States); Minniti, D., E-mail: jura.borissova@uv.cl [Pontificia Universidad Católica de Chile, Facultad de Física, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

2014-01-01

The discovery of a detached dust shell around the Wolf-Rayet (WR) star WR60-6 in the young stellar cluster VVV CL036 is reported. This shell is uncovered through the Spitzer-MIPS 24 μm image, where it appears brightest, and it is invisible at shorter wavelengths. Using new APEX observations and other data available from the literature, we have estimated some of the shell parameters: the inner and outer radii of 0.15 and 0.90 pc, respectively; the overall systemic velocity of the molecular {sup 12}CO(3 → 2) emission of –45.7 ± 2.3 km s{sup –1}; an expansion velocity of the gas of 16.3 ± 1 km s{sup –1}; the dust temperature and opacity of 122 ± 12 K and 1.04, respectively; and an age of 2.8 × 10{sup 4} yr. The WR star displays some cyclic variability. The mass computed for the WR60-6 nebula indicates that the material was probably ejected during its previous stages of evolution. In addition, we have identified a bright spot very close to the shell, which can be associated with the Midcourse Space Experiment source G312.13+00.20.

Solar and stellar oscillations

International Nuclear Information System (INIS)

Fossat, E.

1981-01-01

We try to explain in simple words what a stellar oscillation is, what kind of restoring forces and excitation mechanisms can be responsible for its occurence, what kind of questions the theoretician asks to the observer and what kind of tools the latter is using to look for the answers. A selected review of the most striking results obtained in the last few years in solar seismology and the present status of their consequences on solar models is presented. A brief discussion on the expected extension towards stellar seismology will end the paper. A selected bibliography on theory as well as observations and recent papers is also included. (orig.)

EVIDENCE FOR DELAYED MASSIVE STAR FORMATION IN THE M17 PROTO-OB ASSOCIATION

International Nuclear Information System (INIS)

Povich, Matthew S.; Whitney, Barbara A.

2010-01-01

Through analysis of archival images and photometry from the Spitzer GLIMPSE and MIPSGAL surveys combined with Two Micron All Sky Survey and MSX data, we have identified 488 candidate young stellar objects (YSOs) in the giant molecular cloud M17 SWex, which extends ∼50 pc southwest from the prominent Galactic H II region M17. Our sample includes >200 YSOs with masses >3 M sun that will become B-type stars on the main sequence. Extrapolating over the stellar initial mass function (IMF), we find that M17 SWex contains >1.3 x 10 4 young stars, representing a proto-OB association. The YSO mass function is significantly steeper than the Salpeter IMF, and early O stars are conspicuously absent from M17 SWex. Assuming M17 SWex will form an OB association with a Salpeter IMF, these results reveal the combined effects of (1) more rapid circumstellar disk evolution in more massive YSOs and (2) delayed onset of massive star formation.

OBSERVATIONAL 5-20 μm INTERSTELLAR EXTINCTION CURVES TOWARD STAR-FORMING REGIONS DERIVED FROM SPITZER IRS SPECTRA

International Nuclear Information System (INIS)

McClure, M.

2009-01-01

Using Spitzer Infrared Spectrograph observations of G0-M4 III stars behind dark clouds, I construct 5-20 μm empirical extinction curves for 0.3 ≤ A K V between ∼3 and 50. For A K K > 1, the curve exhibits lower contrast between the silicate and absorption continuum, develops ice absorption, and lies closer to the Weingartner and Draine R V = 5.5 Case B curve, a result which is consistent with that of Flaherty et al. and Chiar et al. Recently, work using Spitzer Infrared Array Camera data by Chapman et al. independently reaches a similar conclusion that the shape of the extinction curve changes as a function of increasing A K . By calculating the optical depths of the 9.7 μm silicate and 6.0, 6.8, and 15.2 μm ice features, I determine that a process involving ice is responsible for the changing shape of the extinction curve and speculate that this process is a coagulation of ice-mantled grains rather than ice-mantled grains alone.

Featured Image: A Molecular Cloud Outside Our Galaxy

Science.gov (United States)

Kohler, Susanna

2018-06-01

What do molecular clouds look like outside of our own galaxy? See for yourself in the images above and below of N55, a molecular cloud located in the Large Magellanic Cloud (LMC). In a recent study led by Naslim Neelamkodan (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), a team of scientists explore N55 to determine how its cloud properties differ from clouds within the Milky Way. The image above reveals the distribution of infrared-emitting gas and dust observed in three bands by the Spitzer Space Telescope. Overplotted in cyan are observations from the Atacama Submillimeter Telescope Experiment tracing the clumpy, warm molecular gas. Below, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the sub-parsec-scale molecular clumps in greater detail, showing the correlation of massive clumps with Spitzer-identified young stellar objects (crosses). The study presented here indicates that this cloud in the LMC is the site of massive star formation, with properties similar to equivalent clouds in the Milky Way. To learn more about the authors findings, check out the article linked below.CitationNaslim N. et al 2018 ApJ 853 175. doi:10.3847/1538-4357/aaa5b0

Stellar CCD Photometry: New Approach, Principles and Application

Science.gov (United States)

El-Bassuny Alawy, A.

A new approach is proposed and developed to handle pre-processed CCD frames in order to identify stellar images and derive their relevant parameters. It relies on: 1) Identifying stellar images and assigning approximate positions of their centres using an artificial intelligence technique, (Knowledge Based System), 2) Accurate determination of the centre co-ordinates applying an elementary statistical concept and 3) Estimating the image peak intensity as a stellar magnitude measure employing simple numerical analysis approach. The method has been coded for personal computer users. A CCD frame of the star cluster M67 was adopted as a test case. The results obtained are discussed in comparison with the DAOPHOTII ones and the corresponding published data. Exact coincidence has been found between both results except in very few cases. These exceptions have been discussed in the light of the basis of both methods and the cluster plates. It has been realised that the method suggested represents a very simple, extremely fast, high precision method of stellar CCD photometry. Moreover, it is more capable than DAOPHOTII of handling blended and distorted stellar images. These characteristics show the usefulness of the present method in some astronomical applications, such as auto-focusing and auto-guiding, beside the main purpose, viz. stellar photometry.

Disruption of circumstellar discs by large-scale stellar magnetic fields

Science.gov (United States)

ud-Doula, Asif; Owocki, Stanley P.; Kee, Nathaniel Dylan

2018-05-01

Spectropolarimetric surveys reveal that 8-10% of OBA stars harbor large-scale magnetic fields, but thus far no such fields have been detected in any classical Be stars. Motivated by this, we present here MHD simulations for how a pre-existing Keplerian disc - like that inferred to form from decretion of material from rapidly rotating Be stars - can be disrupted by a rotation-aligned stellar dipole field. For characteristic stellar and disc parameters of a near-critically rotating B2e star, we find that a polar surface field strength of just 10 G can significantly disrupt the disc, while a field of 100 G, near the observational upper limit inferred for most Be stars, completely destroys the disc over just a few days. Our parameter study shows that the efficacy of this magnetic disruption of a disc scales with the characteristic plasma beta (defined as the ratio between thermal and magnetic pressure) in the disc, but is surprisingly insensitive to other variations, e.g. in stellar rotation speed, or the mass loss rate of the star's radiatively driven wind. The disc disruption seen here for even a modest field strength suggests that the presumed formation of such Be discs by decretion of material from the star would likely be strongly inhibited by such fields; this provides an attractive explanation for why no large-scale fields are detected from such Be stars.

Spitzer Observations of Comet 9P/Tempel 1 During Deep Impact : Water and Dust Production and Spatial Distribution

Science.gov (United States)

Gicquel, Adeline; Bockelée-Morvan, D.; Kelley, M. S.; Woodward, C. E.

2009-09-01

The Deep Impact (DI) spacecraft encountered comet 9P/Tempel 1 on July 4th, 2005 (rh = 1.506 AU). Spectral maps covering 20'' x 67'' (1.85''/pixel) were acquired with the IRS instrument on the Spitzer Space Telescope (ΔSpitzer = 0.72 AU) at different times around the Deep Impact event: twice before impact (TI-41.3hrs and TI-22.9hrs) and twelve times after impact (between TI+0.67hrs and TI+1027hrs). These IRS observations (Lisse et al 2006, Sciences 313, 635) were taken from the Spitzer data archive. We present the interpretation of 5.2-7.6 µm spectra obtained in the second order of the short-wavelength module (SL2). To reduce the contribution of artifacts in the spectra, 5x5 pixel extraction apertures (9.25''x9.25'') were used. On the first stage we studied the water ν2 vibrational band emission at 6.4µm, which is present in most spectra. The water production rate before impact is deduced ( 4.25e27 molecules/sec). In order to study both the amount and origin of the water molecules released after impact, we used extractions centered on the nucleus and along the length of the slit. We analyzed the spatial distribution of water and its time evolution with a time-dependent model which describes the evolution of the water cloud after impact. The underlying continuum in the spectra provides information on the evolution and color temperature of the dust ejecta. The dust mass and dust/gas ratio in the ejecta cloud are derived and compared with other values published in the literature.

Planets, stars and stellar systems

CERN Document Server

Bond, Howard; McLean, Ian; Barstow, Martin; Gilmore, Gerard; Keel, William; French, Linda

2013-01-01

This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in...

The Stellar IMF from Isothermal MHD Turbulence

Science.gov (United States)

Haugbølle, Troels; Padoan, Paolo; Nordlund, Åke

2018-02-01

We address the turbulent fragmentation scenario for the origin of the stellar initial mass function (IMF), using a large set of numerical simulations of randomly driven supersonic MHD turbulence. The turbulent fragmentation model successfully predicts the main features of the observed stellar IMF assuming an isothermal equation of state without any stellar feedback. As a test of the model, we focus on the case of a magnetized isothermal gas, neglecting stellar feedback, while pursuing a large dynamic range in both space and timescales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 pc region within a typical Galactic molecular cloud, with a mass of 3000 M ⊙ and an rms velocity 10 times the isothermal sound speed and 5 times the average Alfvén velocity, in agreement with observations. We achieve a maximum resolution of 50 au and a maximum duration of star formation of 4.0 Myr, forming up to a thousand sink particles whose mass distribution closely matches the observed stellar IMF. A large set of medium-size simulations is used to test the sink particle algorithm, while larger simulations are used to test the numerical convergence of the IMF and the dependence of the IMF turnover on physical parameters predicted by the turbulent fragmentation model. We find a clear trend toward numerical convergence and strong support for the model predictions, including the initial time evolution of the IMF. We conclude that the physics of isothermal MHD turbulence is sufficient to explain the origin of the IMF.

Direct UV/Optical Imaging of Stellar Surfaces: The Stellar Imager (SI) Vision Mission

Science.gov (United States)

Carpenter, Kenneth G.; Lyon, Richard G.; Schrijver, Carolus; Karovska, Margarita; Mozurkewich, David

2007-01-01

The Stellar Imager (SI) is a UV/optical, space-based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living with a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in thc Universe. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap. We discuss herein the science goals of the SI Mission, a mission architecture that could meet those goals, and the technologies needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

Probing Large-scale Coherence between Spitzer IR and Chandra X-Ray Source-subtracted Cosmic Backgrounds

Energy Technology Data Exchange (ETDEWEB)

Cappelluti, N.; Urry, M. [Yale Center for Astronomy and Astrophysics, P.O. Box 208120, New Haven, CT 06520 (United States); Arendt, R. [University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States); Kashlinsky, A. [Observational Cosmology Laboratory, NASA Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Li, Y.; Hasinger, G. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Helgason, K. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Natarajan, P. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); Finoguenov, A. [Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, D-85741, Garching bei München (Germany)

2017-09-20

We present new measurements of the large-scale clustering component of the cross-power spectra of the source-subtracted Spitzer -IRAC cosmic infrared background and Chandra -ACIS cosmic X-ray background surface brightness fluctuations Our investigation uses data from the Chandra Deep Field South, Hubble Deep Field North, Extended Groth Strip/AEGIS field, and UDS/SXDF surveys, comprising 1160 Spitzer hours and ∼12 Ms of Chandra data collected over a total area of 0.3 deg{sup 2}. We report the first (>5 σ ) detection of a cross-power signal on large angular scales >20″ between [0.5–2] keV and the 3.6 and 4.5 μ m bands, at ∼5 σ and 6.3 σ significance, respectively. The correlation with harder X-ray bands is marginally significant. Comparing the new observations with existing models for the contribution of the known unmasked source population at z < 7, we find an excess of about an order of magnitude at 5 σ confidence. We discuss possible interpretations for the origin of this excess in terms of the contribution from accreting early black holes (BHs), including both direct collapse BHs and primordial BHs, as well as from scattering in the interstellar medium and intra-halo light.

Stellar Spectral Classification with Locality Preserving Projections ...

Indian Academy of Sciences (India)

With the help of computer tools and algorithms, automatic stellar spectral classification has become an area of current interest. The process of stellar spectral classification mainly includes two steps: dimension reduction and classification. As a popular dimensionality reduction technique, Principal Component Analysis (PCA) ...

Inferring probabilistic stellar rotation periods using Gaussian processes

Science.gov (United States)

Angus, Ruth; Morton, Timothy; Aigrain, Suzanne; Foreman-Mackey, Daniel; Rajpaul, Vinesh

2018-02-01

Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online.

Teetering Stars: Resonant Excitation of Stellar Obliquities by Hot and Warm Jupiters with External Companions

Science.gov (United States)

Anderson, Kassandra; Lai, Dong

2018-04-01

Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have been extensively probed in recent years thanks to Rossiter-McLaughlin observations. Such obliquities may reveal clues about hot Jupiter dynamical and migration histories. Common explanations for generating stellar obliquities include high-eccentricity migration, or primordial disk misalignment. This talk investigates another mechanism for producing stellar spin-orbit misalignments in systems hosting a close-in giant planet with an external, inclined planetary companion. Spin-orbit misalignment may be excited due to a secular resonance, occurring when the precession rate of the stellar spin axis (due to the inner orbit) becomes comparable to the precession rate of the inner orbital axis (due to the outer companion). Due to the spin-down of the host star via magnetic braking, this resonance may be achieved at some point during the star's main sequence lifetime for a wide range of giant planet masses and orbital architectures. We focus on both hot Jupiters (with orbital periods less than ten days) and warm Jupiters (with orbital periods around tens of days), and identify the outer perburber properties needed to generate substantial obliquities via resonant excitation, in terms of mass, separation, and inclination. For hot Jupiters, the stellar spin axis is strongly coupled to the orbital axis, and resonant excitation of obliquity requires a close perturber, located within 1-2 AU. For warm Jupiters, the spin and orbital axes are more weakly coupled, and the resonance may be achieved for more distant perturbers (at several to tens of AU). Resonant excitation of the stellar obliquity is accompanied by a decrease in the planets' mutual orbital inclination, and can thus erase high mutual inclinations in two-planet systems. Since many warm Jupiters are known to have outer planetary companions at several AU or beyond, stellar obliquities in warm Jupiter systems may be common, regardless of the

Ultraviolet photometry of stellar populations in galaxies

International Nuclear Information System (INIS)

Deharveng, J.M.

1981-01-01

The UV flux of stellar populations, which is essentially emitted by young stars, conveys information on the process of star formation and its recent history. However, the evaluation of the flux arising from the young stellar component may be difficult. In the case of late type galaxies it is hampered by the extinction and the effect of scattered stellar radiation. In the case of early type galaxies, the star formation, if any, has to be disentangled from the contribution of hot evolved stars and of a possible 'active' phenomenon. A review of observations and results relevant two cases is presented [fr

Equilibrium 𝛽-limits in classical stellarators

Science.gov (United States)

Loizu, J.; Hudson, S. R.; Nührenberg, C.; Geiger, J.; Helander, P.

2017-12-01

A numerical investigation is carried out to understand the equilibrium -limit in a classical stellarator. The stepped-pressure equilibrium code (Hudson et al., Phys. Plasmas, vol. 19 (11), 2012) is used in order to assess whether or not magnetic islands and stochastic field-lines can emerge at high . Two modes of operation are considered: a zero-net-current stellarator and a fixed-iota stellarator. Despite the fact that relaxation is allowed (Taylor, Rev. Mod. Phys., vol. 58 (3), 1986, pp. 741-763), the former is shown to maintain good flux surfaces up to the equilibrium -limit predicted by ideal-magnetohydrodynamics (MHD), above which a separatrix forms. The latter, which has no ideal equilibrium -limit, is shown to develop regions of magnetic islands and chaos at sufficiently high , thereby providing a `non-ideal -limit'. Perhaps surprisingly, however, the value of at which the Shafranov shift of the axis reaches a fraction of the minor radius follows in all cases the scaling laws predicted by ideal-MHD. We compare our results to the High-Beta-Stellarator theory of Freidberg (Ideal MHD, 2014, Cambridge University Press) and derive a new prediction for the non-ideal equilibrium -limit above which chaos emerges.

The Stellar Imager (SI) Mission Concept

Science.gov (United States)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Lyon, Richard G.; Mundy, Lee G.; Allen, Ronald J.; Armstrong, Thomas; Danchi, William C.; Karovska, Margarita; Marzouk, Joe; Mazzuca, Lisa M.;

Improving 1D Stellar Models with 3D Atmospheres

Science.gov (United States)

Rørsted Mosumgaard, Jakob; Silva Aguirre, Víctor; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

2017-10-01

Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature - also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

Confinement and heating in modular and continuous coil stellarators

International Nuclear Information System (INIS)

Anderson, D.T.; Anderson, F.S.B.; Bonomo, R.L.

1983-01-01

Major efforts on the Proto-Cleo stellarator have focused on ICRH of a net current-free plasma, measurements of plasma secondary currents, RF heating by externally induced magnetic reconnection through the formation and destruction of an internal separatrix, and RF current drive experiments. Efforts on the Proto-Cleo torsatron have focused on electron heat conduction. A modular stellarator has been designed and is under fabrication at the University of Wisconsin. The Interchangeable Module Stellarator (IMS) is designed to approximate closely the magnetic properties of the existing Proto-Cleo stellarator as much as possible. Monte-Carlo transport calculations have been made in flux coordinates using model fields patterned after magnetic fields in Proto-Cleo and IMS. Plasma simulation techniques using a 2.5-dimensional particle-in-cell method have been utilized in a numerical search for the bootstrap current. A current is found which is proportional to temperature and density gradients but is independent of poloidal field. The behaviour of charged particles moving in a stellarator under the influence of a steady magnetic field is analysed in terms of the Hamiltonian of the moving particle and the technique of repeated canonical transformations to identify possible adiabatic invariants and drift motions. An improved theory of collisionless particle motion in stellarators has been developed for a family of stellarator configurations. The broad range of configurations encompassed by this family permits an understanding of the differences in numerically observed transport coefficients. Two procedures have been developed to calculate the bootstrap current in non-axisymmetric stellarators. In fully toroidal stellarators the flows and consequent bootstrap current are reduced from their axisymmetric values by a factor of order l slash-l/m in the Pfirsch-Schlueter regime. (author)

Constraints on stellar evolution from pulsations

International Nuclear Information System (INIS)

Cox, A.N.

1984-01-01

Consideration of the many types of intrinsic variable stars, that is, those that pulsate, reveals that perhaps a dozen classes can indicate some constraints that affect the results of stellar evolution calculations, or some interpretations of observations. Many of these constraints are not very strong or may not even be well defined yet. The author discusses the case for six classes: classical Cepheids with their measured Wesselink radii, the observed surface effective temperatures of the known eleven double-mode Cepheids, the pulsation periods and measured surface effective temperatures of three R CrB variables, the delta Scuti variable VZ Cnc with a very large ratio of its two observed periods, the nonradial oscillations of the Sun, and the period ratios of the newly discovered double-mode RR Lyrae variables. (Auth.)

The Stellar-Dynamical Oeuvre James Binney

Indian Academy of Sciences (India)

tribpo

of the eigenvalues of M. The variation of the stellar density from point to point .... of Σ,(ΔΕ)2 , where ∆ Ε is the change in energy that a star suffers during a binary ... could use these results to calculate the relaxation time in a stellar system if he .... the region of enhanced density that tails behind it like a wake behind a ship. By.

Two novel compact toroidal concepts with Stellarator features

International Nuclear Information System (INIS)

Moroz, P.E.

1997-07-01

Two novel compact toroidal concepts are presented. One is the Stellarator-Spheromak (SSP) and another is the Extreme-Low-Aspect-Ratio Stellarator (ELARS). An SSP device represents a hybrid between a spherical stellarator (SS) and a spheromak. This configuration retains the main advantages of spheromaks ans has a potential for improving the spheromak concept regarding its main problems. The MHD equilibrium in an SSP with very high β of the confined plasma is demonstrated. Another concept, ELARS, represents an extreme limit of the SS approach, and considers devices with stellarator features and aspect ratios A ∼ 1. We have succeeded in finding ELARS configurations with extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and good particle transport characteristics

Evaluating Stellarator Divertor Designs with EMC3

Science.gov (United States)

Bader, Aaron; Anderson, D. T.; Feng, Y.; Hegna, C. C.; Talmadge, J. N.

2013-10-01

In this paper various improvements of stellarator divertor design are explored. Next step stellarator devices require innovative divertor solutions to handle heat flux loads and impurity control. One avenue is to enhance magnetic flux expansion near strike points, somewhat akin to the X-Divertor concept in Tokamaks. The effect of judiciously placed external coils on flux deposition is calculated for configurations based on the HSX stellarator. In addition, we attempt to optimize divertor plate location to facilitate the external coil placement. Alternate areas of focus involve altering edge island size to elucidate the driving physics in the edge. The 3-D nature of stellarators complicates design and necessitates analysis of new divertor structures with appropriate simulation tools. We evaluate the various configurations with the coupled codes EMC3-EIRENE, allowing us to benchmark configurations based on target heat flux, impurity behavior, radiated power, and transitions to high recycling and detached regimes. Work supported by DOE-SC0006103.

Robust Modeling of Stellar Triples in PHOEBE

Science.gov (United States)

Conroy, Kyle E.; Prsa, Andrej; Horvat, Martin; Stassun, Keivan G.

2017-01-01

The number of known mutually-eclipsing stellar triple and multiple systems has increased greatly during the Kepler era. These systems provide significant opportunities to both determine fundamental stellar parameters of benchmark systems to unprecedented precision as well as to study the dynamical interaction and formation mechanisms of stellar and planetary systems. Modeling these systems to their full potential, however, has not been feasible until recently. Most existing available codes are restricted to the two-body binary case and those that do provide N-body support for more components make sacrifices in precision by assuming no stellar surface distortion. We have completely redesigned and rewritten the PHOEBE binary modeling code to incorporate support for triple and higher-order systems while also robustly modeling data with Kepler precision. Here we present our approach, demonstrate several test cases based on real data, and discuss the current status of PHOEBE's support for modeling these types of systems. PHOEBE is funded in part by NSF grant #1517474.

Alpha centauri unveiling the secrets of our nearest stellar neighbor

CERN Document Server

Beech, Martin

2015-01-01

As our closest stellar companion and composed of two Sun-like stars and a third small dwarf star, Alpha Centauri is an ideal testing ground of astrophysical models and has played a central role in the history and development of modern astronomy—from the first guesses at stellar distances to understanding how our own star, the Sun, might have evolved. It is also the host of the nearest known exoplanet, an ultra-hot, Earth-like planet recently discovered. Just 4.4 light years away Alpha Centauri is also the most obvious target for humanity’s first directed interstellar space probe. Such a mission could reveal the small-scale structure of a new planetary system and also represent the first step in what must surely be humanity’s greatest future adventure—exploration of the Milky Way Galaxy itself. For all of its closeness, α Centauri continues to tantalize astronomers with many unresolved mysteries, such as how did it form, how many planets does it contain and where are they, and how might we view its ex...

REPEATABILITY AND ACCURACY OF EXOPLANET ECLIPSE DEPTHS MEASURED WITH POST-CRYOGENIC SPITZER

Energy Technology Data Exchange (ETDEWEB)

Ingalls, James G.; Krick, J. E.; Carey, S. J.; Stauffer, John R.; Lowrance, Patrick J.; Grillmair, Carl J.; Capak, Peter; Glaccum, William; Laine, Seppo; Surace, Jason; Storrie-Lombardi, Lisa [Spitzer Science Center, California Institute of Technology, 1200 E California Boulevard, Mail Code 314-6, Pasadena, CA 91125 (United States); Buzasi, Derek [Department of Chemistry and Physics, Florida Gulf Coast University, Fort Myers, FL 33965 (United States); Deming, Drake [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Diamond-Lowe, Hannah; Stevenson, Kevin B. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S Ellis Avenue, Chicago, IL 60637 (United States); Evans, Thomas M. [School of Physics, University of Exeter, EX4 4QL Exeter (United Kingdom); Morello, G. [Department of Physics and Astronomy, University College London, Gower Street, WC1 E6BT (United Kingdom); Wong, Ian, E-mail: ingalls@ipac.caltech.edu [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)

2016-08-01

We examine the repeatability, reliability, and accuracy of differential exoplanet eclipse depth measurements made using the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope during the post-cryogenic mission. We have re-analyzed an existing 4.5 μ m data set, consisting of 10 observations of the XO-3b system during secondary eclipse, using seven different techniques for removing correlated noise. We find that, on average, for a given technique, the eclipse depth estimate is repeatable from epoch to epoch to within 156 parts per million (ppm). Most techniques derive eclipse depths that do not vary by more than a factor 3 of the photon noise limit. All methods but one accurately assess their own errors: for these methods, the individual measurement uncertainties are comparable to the scatter in eclipse depths over the 10 epoch sample. To assess the accuracy of the techniques as well as to clarify the difference between instrumental and other sources of measurement error, we have also analyzed a simulated data set of 10 visits to XO-3b, for which the eclipse depth is known. We find that three of the methods (BLISS mapping, Pixel Level Decorrelation, and Independent Component Analysis) obtain results that are within three times the photon limit of the true eclipse depth. When averaged over the 10 epoch ensemble,  5 out of 7 techniques come within 60 ppm of the true value. Spitzer exoplanet data, if obtained following current best practices and reduced using methods such as those described here, can measure repeatable and accurate single eclipse depths, with close to photon-limited results.

Stellar signatures of AGN-jet-triggered star formation

International Nuclear Information System (INIS)

Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

2014-01-01

To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

Energy Technology Data Exchange (ETDEWEB)

Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Muirhead, Philip S. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Lopez-Morales, Mercedes [Institut de Ciencies de L' Espai (CSIC-IEEC), E-08193 Bellaterra (Spain); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States); Rojas-Ayala, Barbara [Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); and others

2012-10-01

We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally

Color-size Relations of Disc Galaxies with Similar Stellar Masses

Science.gov (United States)

Fu, W.; Chang, R. X.; Shen, S. Y.; Zhang, B.

2011-01-01

To investigate the correlations between colors and sizes of disc galaxies with similar stellar masses, a sample of 7959 local face-on disc galaxies is collected from the main galaxy sample of the Seventh Data Release of Sloan Digital Sky Survey (SDSS DR7). Our results show that, under the condition that the stellar masses of disc galaxies are similar, the relation between u-r and size is weak, while g-r, r-i and r-z colors decrease with disk size. This means that the color-size relations of disc galaxies with similar stellar masses do exist, i.e., the more extended disc galaxies with similar stellar masses tend to have bluer colors. An artificial sample is constructed to confirm that this correlation is not driven by the color-stellar mass relations and size-stellar mass relation of disc galaxies. Our results suggest that the mass distribution of disk galaxies may have an important influence on their stellar formation history, i.e., the galaxies with more extended mass distribution evolve more slowly.

Helical post stellarator. Part 1: Vacuum configuration

International Nuclear Information System (INIS)

Moroz, P.E.

1997-08-01

Results on a novel type of stellarator configuration, the Helical Post Stellarator (HPS), are presented. This configuration is different significantly from all previously known stellarators due to its unique geometrical characteristics and unique physical properties. Among those are: the magnetic field has only one toroidal period (M = 1), the plasma has an extremely low aspect ratio, A ∼ 1, and the variation of the magnetic field, B, along field lines features a helical ripple on the inside of the torus. Among the main advantages of a HPS for a fusion program are extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and improved particle transport characteristics

Radio Telescopes Reveal Youngest Stellar Corpse

Science.gov (United States)

2004-06-01

Astronomers using a global combination of radio telescopes to study a stellar explosion some 30 million light-years from Earth have likely discovered either the youngest black hole or the youngest neutron star known in the Universe. Their discovery also marks the first time that a black hole or neutron star has been found associated with a supernova that has been seen to explode since the invention of the telescope nearly 400 years ago. M51 An artist's impression of Supernova 1986J. The newly discovered nebula around the black hole or neutron star in the center is shown in blue, and is in the center of the expanding, fragmented shell of material thrown off in the supernova explosion, which is shown in red. CREDIT: Norbert Bartel and Michael F. Bietenholz, York University; Artist: G. Arguner (Click on image for larger version) Image Files Artist's Conception (above image, 836K) Galaxy and Supernova (47K) A VLA image (left) of the galaxy NGC 891, showing the bright supernova explosion below the galaxy's center. At right, a closer view of the supernova, made with a global array of radio telescopes. CREDIT: Miguel A. Perez-Torres, Antxon Alberdi and Lucas Lara, Instituto de Astrofisica de Andalucia - CSIC, Spain, Jon Marcaide and Jose C. Guirado, Universidad de Valencia, Spain Franco Mantovani, IRA-CNR, Italy, Eduardo Ros, MPIfR, Germany, and Kurt W. Weiler, Naval Research Laboratory, USA Multi-Frequency Closeup View (201K) Blue and white area shows the nebula surrounding the black hole or neutron star lurking in the center of the supernova. This nebula is apparent at a higher radio frequency (15 GHz). The red and also the contours show the distorted, expanding shell of material thrown off in the supernova explosion. This shell is seen at a lower radio frequency (5 GHz). CREDIT: Michael F. Bietenholz and Norbert Bartel, York University, Michael Rupen, NRAO, NRAO/AUI/NSF A supernova is the explosion of a massive star after it exhausts its supply of nuclear fuel and

The WEGA Stellarator: Results and Prospects

International Nuclear Information System (INIS)

Otte, M.; Andruczyk, D.; Koenig, R.; Laqua, H. P.; Lischtschenko, O.; Marsen, S.; Schacht, J.; Podoba, Y. Y.; Wagner, F.; Warr, G. B.; Holzhauer, E.; Howard, J.; Krupnik, L.; Zhezhera, A.; Urban, J.; Preinhalter, J.

2008-01-01

In this article an overview is given on results from magnetic flux surface measurements, applied ECR heating scenarios for 2.45 GHz and 28 GHz, fluctuation and transport studies and plasma edge biasing experiments performed in the WEGA stellarator. Examples for the development of new diagnostics and the machine control system are given that will be used at Wendelstein 7-X stellarator, which is currently under construction in Greifswald

Progress in modular-stellarator fusion-power-reactor conceptual designs

International Nuclear Information System (INIS)

Sviatoslavsky, I.N.; Van Sciver, S.W.; Kulcinski, G.L.

1982-01-01

Recent encouraging experimental results on stellarators/torsatrons/heliotrons (S/T/H) have revived interest in these concepts as possible fusion power reactors. The use of modular coils to generate the stellarator topology has added impetus to this renewed interest. Studies of the modular coil approach to stellarators by UW-Madison and Los Alamos National Laboratory are summarized in this paper

The galaxy population of Abell 1367: the stellar mass-metallicity relation

Science.gov (United States)

Mouhcine, M.; Kriwattanawong, W.; James, P. A.

2011-04-01

Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

A New Measurement of the Stellar Mass Density at z~5: Implications for the Sources of Cosmic Reionization

Science.gov (United States)

Stark, D. P.; Bunker, A. J.; Ellis, R. S.; Eyles, L. P.; Lacy, M.

2007-04-01

We present a new measurement of the integrated stellar mass per comoving volume at redshift 5 determined via spectral energy fitting drawn from a sample of 214 photometrically selected galaxies with z'850LPmasses for various subsamples for which reliable and unconfused Spitzer IRAC detections are available. A spectroscopic sample of 14 of the most luminous sources with z=4.92 provides a firm lower limit to the stellar mass density of 1×106 Msolar Mpc-3. Several galaxies in this subsample have masses of order 1011 Msolar, implying that significant earlier activity occurred in massive systems. We then consider a larger sample whose photometric redshifts in the publicly available GOODS-MUSIC catalog lie in the range 4.4MUSIC photometric redshifts, we check the accuracy of their photometry and explore the possibility of contamination by low-z galaxies and low-mass stars. After excising probable stellar contaminants and using the z'850LP-J color to exclude any remaining foreground red galaxies, we conclude that 196 sources are likely to be at z~=5. The implied mass density from the unconfused IRAC fraction of this sample, scaled to the total available, is 6×106 Msolar Mpc-3. We discuss the uncertainties, as well as the likelihood that we have underestimated the true mass density. By including fainter and quiescent sources, the total integrated density could be as high as 1×107 Msolar Mpc-3. Even accounting for 25% cosmic variance within a single GOODS field, such a high mass density only 1.2 Gyr after the big bang has interesting consequences for the implied past average star formation during the period when cosmic reionization is now thought to have taken place. Using the currently available (but highly uncertain) rate of decline in the star formation history over 5mass at z~=5 if we admit significant dust extinction at early times or extend the luminosity function to very faint limits. An interesting consequence of the latter possibility is an abundant population

A Spitzer five-band analysis of the Jupiter-sized planet TrES-1

Energy Technology Data Exchange (ETDEWEB)

Cubillos, Patricio; Harrington, Joseph; Foster, Andrew S. D.; Lust, Nate B.; Hardy, Ryan A.; Bowman, M. Oliver [Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Madhusudhan, Nikku, E-mail: pcubillos@fulbrightmail.org [Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511 (United States)

2014-12-10

With an equilibrium temperature of 1200 K, TrES-1 is one of the coolest hot Jupiters observed by Spitzer. It was also the first planet discovered by any transit survey and one of the first exoplanets from which thermal emission was directly observed. We analyzed all Spitzer eclipse and transit data for TrES-1 and obtained its eclipse depths and brightness temperatures in the 3.6 μm (0.083% ± 0.024%, 1270 ± 110 K), 4.5 μm (0.094% ± 0.024%, 1126 ± 90 K), 5.8 μm (0.162% ± 0.042%, 1205 ± 130 K), 8.0 μm (0.213% ± 0.042%, 1190 ± 130 K), and 16 μm (0.33% ± 0.12%, 1270 ± 310 K) bands. The eclipse depths can be explained, within 1σ errors, by a standard atmospheric model with solar abundance composition in chemical equilibrium, with or without a thermal inversion. The combined analysis of the transit, eclipse, and radial-velocity ephemerides gives an eccentricity of e=0.033{sub −0.031}{sup +0.015}, consistent with a circular orbit. Since TrES-1's eclipses have low signal-to-noise ratios, we implemented optimal photometry and differential-evolution Markov Chain Monte Carlo (MCMC) algorithms in our Photometry for Orbits, Eclipses, and Transits pipeline. Benefits include higher photometric precision and ∼10 times faster MCMC convergence, with better exploration of the phase space and no manual parameter tuning.

Disk Heating, Galactoseismology, and the Formation of Stellar Halos

Directory of Open Access Journals (Sweden)

Kathryn V. Johnston

2017-08-01

Full Text Available Deep photometric surveys of the Milky Way have revealed diffuse structures encircling our Galaxy far beyond the “classical” limits of the stellar disk. This paper reviews results from our own and other observational programs, which together suggest that, despite their extreme positions, the stars in these structures were formed in our Galactic disk. Mounting evidence from recent observations and simulations implies kinematic connections between several of these distinct structures. This suggests the existence of collective disk oscillations that can plausibly be traced all the way to asymmetries seen in the stellar velocity distribution around the Sun. There are multiple interesting implications of these findings: they promise new perspectives on the process of disk heating; they provide direct evidence for a stellar halo formation mechanism in addition to the accretion and disruption of satellite galaxies; and, they motivate searches of current and near-future surveys to trace these oscillations across the Galaxy. Such maps could be used as dynamical diagnostics in the emerging field of “Galactoseismology”, which promises to model the history of interactions between the Milky Way and its entourage of satellites, as well examine the density of our dark matter halo. As sensitivity to very low surface brightness features around external galaxies increases, many more examples of such disk oscillations will likely be identified. Statistical samples of such features not only encode detailed information about interaction rates and mergers, but also about long sought-after dark matter halo densities and shapes. Models for the Milky Way’s own Galactoseismic history will therefore serve as a critical foundation for studying the weak dynamical interactions of galaxies across the universe.

A COMPARISON OF STELLAR ELEMENTAL ABUNDANCE TECHNIQUES AND MEASUREMENTS

Energy Technology Data Exchange (ETDEWEB)

Hinkel, Natalie R.; Young, Patrick A.; Pagano, Michael D.; Desch, Steven J.; Anbar, Ariel D. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Adibekyan, Vardan; Mena, Elisa Delgado; Sousa, Sergio G.; Santos, Nuno C. [Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto (Portugal); Blanco-Cuaresma, Sergi [Observatoire de Genève, Université de Genève, CH-1290 Versoix (Switzerland); Carlberg, Joleen K. [NASA Goddard Space Flight Center, Code 667, Greenbelt MD 20771 (United States); Liu, Fan [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Nordlander, Thomas; Korn, Andreas; Gruyters, Pieter; Heiter, Ulrike [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Jofré, Paula [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Soubiran, Caroline, E-mail: natalie.hinkel@gmail.com [CNRS/Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France)

2016-09-01

Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond the quoted error for the same elements within the same stars. The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and the United States) to calculate 10 element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD 361, HD 10700, HD 121504, and HD 202206). Each group produced measurements for each star using (1) their own autonomous techniques, (2) standardized stellar parameters, (3) a standardized line list, and (4) both standardized parameters and a line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies the homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise.

The stellar metallicity gradients in galaxy discs in a cosmological scenario

Science.gov (United States)

Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

2016-08-01

Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside

Models of hot stellar systems

International Nuclear Information System (INIS)

Van Albada, T.S.

1986-01-01

Elliptical galaxies consist almost entirely of stars. Sites of recent star formation are rare, and most stars are believed to be several billion years old, perhaps as old as the Universe itself (--10/sup 10/ yrs). Stellar motions in ellipticals show a modest amount of circulation about the center of the system, but most support against the force of gravity is provided by random motions; for this reason ellipticals are called 'hot' stellar systems. Spiral galaxies usually also contain an appreciable amount of gas (--10%, mainly atomic hydrogen) and new stars are continually being formed out of this gas, especially in the spiral arms. In contrast to ellipticals, support against gravity in spiral galaxies comes almost entirely from rotation; random motions of the stars with respect to rotation are small. Consequently, spiral galaxies are called 'cold' stellar systems. Other than in hot systems, in cold systems the collective response of stars to variations in the force field is an essential part of the dynamics. The present overview is limited to mathematical models of hot systems. Computational methods are also discussed

CCFpams: Atmospheric stellar parameters from cross-correlation functions

Science.gov (United States)

Malavolta, Luca; Lovis, Christophe; Pepe, Francesco; Sneden, Christopher; Udry, Stephane

2017-07-01

CCFpams allows the measurement of stellar temperature, metallicity and gravity within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, the technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. Literature stellar parameters of high signal-to-noise (SNR) and high-resolution HARPS spectra of FGK Main Sequence stars are used to calibrate the stellar parameters as a function of CCF areas.

Correcting Estimates of the Occurrence Rate of Earth-like Exoplanets for Stellar Multiplicity

Science.gov (United States)

Cantor, Elliot; Dressing, Courtney D.; Ciardi, David R.; Christiansen, Jessie

2018-06-01

One of the most prominent questions in the exoplanet field has been determining the true occurrence rate of potentially habitable Earth-like planets. NASA’s Kepler mission has been instrumental in answering this question by searching for transiting exoplanets, but follow-up observations of Kepler target stars are needed to determine whether or not the surveyed Kepler targets are in multi-star systems. While many researchers have searched for companions to Kepler planet host stars, few studies have investigated the larger target sample. Regardless of physical association, the presence of nearby stellar companions biases our measurements of a system’s planetary parameters and reduces our sensitivity to small planets. Assuming that all Kepler target stars are single (as is done in many occurrence rate calculations) would overestimate our search completeness and result in an underestimate of the frequency of potentially habitable Earth-like planets. We aim to correct for this bias by characterizing the set of targets for which Kepler could have detected Earth-like planets. We are using adaptive optics (AO) imaging to reveal potential stellar companions and near-infrared spectroscopy to refine stellar parameters for a subset of the Kepler targets that are most amenable to the detection of Earth-like planets. We will then derive correction factors to correct for the biases in the larger set of target stars and determine the true frequency of systems with Earth-like planets. Due to the prevalence of stellar multiples, we expect to calculate an occurrence rate for Earth-like exoplanets that is higher than current figures.

LUT REVEALS AN ALGOL-TYPE ECLIPSING BINARY WITH THREE ADDITIONAL STELLAR COMPANIONS IN A MULTIPLE SYSTEM

Energy Technology Data Exchange (ETDEWEB)

Zhu, L.-Y.; Zhou, X.; Qian, S.-B.; Li, L.-J.; Liao, W.-P.; Tian, X.-M.; Wang, Z.-H. [Yunnan Observatories, Chinese Academy of Sciences (CAS), P.O. Box 110, 650011 Kunming (China); Hu, J.-Y., E-mail: zhuly@ynao.ac.cn [National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing (China)

2016-04-15

A complete light curve of the neglected eclipsing binary Algol V548 Cygni in the UV band was obtained with the Lunar-based Ultraviolet Telescope in 2014 May. Photometric solutions are obtained using the Wilson–Devinney method. It is found that solutions with and without third light are quite different. The mass ratio without third light is determined to be q = 0.307, while that derived with third light is q = 0.606. It is shown that V548 Cygni is a semi-detached binary where the secondary component is filling the critical Roche lobe. An analysis of all available eclipse times suggests that there are three cyclic variations in the O–C diagram that are interpreted by the light travel-time effect via the presence of three additional stellar companions. This is in agreement with the presence of a large quantity of third light in the system. The masses of these companions are estimated as m sin i′ ∼ 1.09, 0.20, and 0.52 M{sub ⊙}. They are orbiting the central binary with orbital periods of about 5.5, 23.3, and 69.9 years, i.e., in 1:4:12 resonance orbit. Their orbital separations are about 4.5, 13.2, and 26.4 au, respectively. Our photometric solutions suggest that they contribute about 32.4% to the total light of the multiple system. No obvious long-term changes in the orbital period were found, indicating that the contributions of the mass transfer and the mass loss due to magnetic braking to the period variations are comparable. The detection of three possible additional stellar components orbiting a typical Algol in a multiple system make V548 Cygni a very interesting binary to study in the future.

Stellarator physics

International Nuclear Information System (INIS)

1990-07-01

This document consists of the proceedings of the Seventh International Workshop on Stellarators, held in Oak Ridge, Tennessee, USA, 10-14 April, 1989. The document consists of a summary of presentations, an overview of experimental results, and papers presented at the workshop on transport, impurities and divertors, diagnostics, ECH confinement experiments, equilibrium and stability studies, RF heating, confinement, magnetic configurations, and new experiments. Refs, figs and tabs

THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

Energy Technology Data Exchange (ETDEWEB)

Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

2017-01-20

We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

ACCELERATED FITTING OF STELLAR SPECTRA

Energy Technology Data Exchange (ETDEWEB)

Ting, Yuan-Sen; Conroy, Charlie [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Rix, Hans-Walter [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)

2016-07-20

Stellar spectra are often modeled and fitted by interpolating within a rectilinear grid of synthetic spectra to derive the stars’ labels: stellar parameters and elemental abundances. However, the number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of labels separately can introduce unknown systematics and do not produce correct error covariances in the derived labels. In this paper we present a new approach—Convex Hull Adaptive Tessellation (chat)—which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock data sets demonstrate that chat can reduce the number of required synthetic model calculations by three orders of magnitude in an eight-dimensional label space. The reduction will be even larger for higher dimensional label spaces. In chat the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in the label space an approximate synthetic spectrum can be generated through linear expansion using a set of “gradient spectra” that represent flux derivatives at every wavelength point with respect to all labels. These techniques provide new opportunities to fit the full stellar spectra from large surveys with 15–30 labels simultaneously.

Stellar-to-halo mass relation of cluster galaxies

International Nuclear Information System (INIS)

Niemiec, Anna; Jullo, Eric; Limousin, Marceau; Giocoli, Carlo

2017-01-01

In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.

Deriving stellar parameters with the SME software package

Science.gov (United States)

Piskunov, N.

2017-09-01

Photometry and spectroscopy are complementary tools for deriving accurate stellar parameters. Here I present one of the popular packages for stellar spectroscopy called SME with the emphasis on the latest developments and error assessment for the derived parameters.

Teaching stellar interferometry with polymer optical fibers

Science.gov (United States)

Illarramendi, M. A.; Arregui, L.; Zubia, J.; Hueso, R.; Sanchez-Lavega, A.

2017-08-01

In this manuscript we show the design of a simple experiment that reproduces the operation of the Michelson stellar interferometer by using step-index polymer optical fibers. The emission of stellar sources, single or binary stars, has been simulated by the laser light emerging from the output surface of the 2 meter-long polymer optical fiber. This light has an emission pattern that is similar to the emission pattern of stellar sources - circular, uniform, spatially incoherent, and quasi-monochromatic. Light coming from the fiber end faces passes through two identical pinholes located on a lid covering the objective of a small telescope, thus producing interference. Interference fringes have been acquired using a camera that is coupled to a telescope. The experiments have been carried out both outdoors in the daytime and indoors. By measuring the fringe visibilities, we have determined the size of our artificial stellar sources and the distance between them, when placing them at distances of 54 m from the telescope in the indoor measurements and of 75 m in the outdoor ones.

Stellar axion models

Energy Technology Data Exchange (ETDEWEB)

Nowakowski, Daniel; Kuster, Markus; Meister, Claudia V.; Fuelbert, Florian; Hoffmann, Dieter H.H. [TU Darmstadt (Germany). Institut fuer Kernphysik; Weiss, Achim [Max-Planck-Institut fuer Astrophysik, Garching (Germany)

2010-07-01

An axion helioscope is typically operated to observe the sun as an axion source. Additional pointings at celestial sources, e.g. stars in other galaxies, result in possible detections of axions from distant galactic objects. For the observation of supplementary axion sources we therefore calculate the thereotical axion flux from distant stars by extending axionic flux models for the axion Primakoff effect in the sun to other main sequence stars. The main sequence star models used for our calculations are based on full stellar structure calculations. To deduce the effective axion flux of stellar objects incident on the Earth the All-Sky catalogue was used to obtain the spectral class and distance of the stars treated. Our calculations of the axion flux in the galactic plane show that for a zero age main sequence star an maximum axion flux of {phi}{sub a}=303.43 cm{sup -2}s{sup -1} could be expected. Furthermore we present estimates of axion fluxes from time-evolved stars.

The fluctuation theory of the stellar mass loss

International Nuclear Information System (INIS)

Andriesse, C.D.

1981-01-01

The idea that fluctuations in the mass flow are as significant as the very existence of the flow has led to the development of a fluctuation theory of the stellar mass loss. A general theory for fluctuations in non-equilibrium systems - and such are stellar atmospheres - was developed long ago. In developing the general theory to a specific stellar theory, however, the arguments have not come up in their logical order. The present sketch of this theory improves on that order and is offered as a framework for further study. (Auth.)

SPITZER MAPPING OF MOLECULAR HYDROGEN PURE ROTATIONAL LINES IN NGC 1333: A DETAILED STUDY OF FEEDBACK IN STAR FORMATION

International Nuclear Information System (INIS)

Maret, Sebastien; Bergin, Edwin A.; Neufeld, David A.; Sonnentrucker, Paule; Yuan Yuan; Green, Joel D.; Watson, Dan M.; Harwit, Martin O.; Kristensen, Lars E.; Melnick, Gary J.; Tolls, Volker; Werner, Michael W.; Willacy, Karen

2009-01-01

We present mid-infrared spectral maps of the NGC 1333 star-forming region, obtained with the infrared spectrometer on board the Spitzer Space Telescope. Eight pure H 2 rotational lines, from S(0) to S(7), are detected and mapped. The H 2 emission appears to be associated with the warm gas shocked by the multiple outflows present in the region. A comparison between the observed intensities and the predictions of detailed shock models indicates that the emission arises in both slow (12-24 km s -1 ) and fast (36-53 km s -1 ) C-type shocks with an initial ortho-to-para ratio (opr) ∼ 2 opr exhibits a large degree of spatial variations. In the postshocked gas, it is usually about 2, i.e., close to the equilibrium value (∼3). However, around at least two outflows, we observe a region with a much lower (∼0.5) opr. This region probably corresponds to gas which has been heated up recently by the passage of a shock front, but whose ortho-to-para has not reached equilibrium yet. This, together with the low initial opr needed to reproduce the observed emission, provide strong evidence that H 2 is mostly in para form in cold molecular clouds. The H 2 lines are found to contribute to 25%-50% of the total outflow luminosity, and thus can be used to ascertain the importance of star formation feedback on the natal cloud. From these lines, we determine the outflow mass loss rate and, indirectly, the stellar infall rate, the outflow momentum and the kinetic energy injected into the cloud over the embedded phase. The latter is found to exceed the binding energy of individual cores, suggesting that outflows could be the main mechanism for core disruption.

Stellar Relics from the Early Galaxy T. Sivarani

Indian Academy of Sciences (India)

metal-poor stars is used to study the chemical history of the galaxy. Apart from this,. 5 .... They fit a color-magnitude diagram in order to trace different stellar population and derived a ... distinctly different stellar population with a different origin.

Spitzer Observations of a 24 μm Shadow: Bok Globule CB 190

Science.gov (United States)

Stutz, Amelia M.; Bieging, John H.; Rieke, George H.; Shirley, Yancy L.; Balog, Zoltan; Gordon, Karl D.; Green, Elizabeth M.; Keene, Jocelyn; Kelly, Brandon C.; Rubin, Mark; Werner, Michael W.

2007-08-01

We present Spitzer observations of the dark globule CB 190 (LDN 771). We observe a roughly circular 24 μm shadow with a 70" radius. The extinction profile of this shadow matches the profile derived from 2MASS photometry at the outer edges of the globule and reaches a maximum of ~32 visual magnitudes at the center. The corresponding mass of CB 190 is ~10 Msolar. Our 12CO and 13CO J=2-1 data over a 10'×10' region centered on the shadow show a temperature ~10 K. The thermal continuum indicates a similar temperature for the dust. The molecular data also show evidence of freezeout onto dust grains. We estimate a distance to CB 190 of 400 pc using the spectroscopic parallax of a star associated with the globule. Bonnor-Ebert fits to the density profile, in conjunction with this distance, yield ξmax=7.2, indicating that CB 190 may be unstable. The high temperature (56 K) of the best-fit Bonnor-Ebert model is in contradiction with the CO and thermal continuum data, leading to the conclusion that the thermal pressure is not enough to prevent free-fall collapse. We also find that the turbulence in the cloud is inadequate to support it. However, the cloud may be supported by the magnetic field, if this field is at the average level for dark globules. Since the magnetic field will eventually leak out through ambipolar diffusion, it is likely that CB 190 is collapsing or in a late precollapse stage. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.

Alien Sunset (Artist Concept)

Science.gov (United States)

2007-01-01

Our solitary sunsets here on Earth might not be all that common in the grand scheme of things. New observations from NASA's Spitzer Space Telescope have revealed that mature planetary systems -- dusty disks of asteroids, comets and possibly planets -- are more frequent around close-knit twin, or binary, stars than single stars like our sun. That means sunsets like the one portrayed in this artist's photo concept, and more famously in the movie 'Star Wars,' might be quite commonplace in the universe. Binary and multiple-star systems are about twice as abundant as single-star systems in our galaxy, and, in theory, other galaxies. In a typical binary system, two stars of roughly similar masses twirl around each other like pair-figure skaters. In some systems, the two stars are very far apart and barely interact with each other. In other cases, the stellar twins are intricately linked, whipping around each other quickly due to the force of gravity. Astronomers have discovered dozens of planets that orbit around a single member of a very wide stellar duo. Sunsets from these worlds would look like our own, and the second sun would just look like a bright star in the night sky. But do planets exist in the tighter systems, where two suns would dip below a planet's horizon one by one? Unveiling planets in these systems is tricky, so astronomers used Spitzer to look for disks of swirling planetary debris instead. These disks are made of asteroids, comets and possibly planets. The rocky material in them bangs together and kicks up dust that Spitzer's infrared eyes can see. Our own solar system is swaddled in a similar type of disk. Surprisingly, Spitzer found more debris disks around the tightest binaries it studied (about 20 stars) than in a comparable sample of single stars. About 60 percent of the tight binaries had disks, while the single stars only had about 20 percent. These snug binary systems are as close or closer than just three times the distance between Earth and

Development of code PRETOR for stellarator simulation

International Nuclear Information System (INIS)

Dies, J.; Fontanet, J.; Fontdecaba, J.M.; Castejon, F.; Alejandre, C.

1998-01-01

The Department de Fisica i Enginyeria Nuclear (DFEN) of the UPC has some experience in the development of the transport code PRETOR. This code has been validated with shots of DIII-D, JET and TFTR, it has also been used in the simulation of operational scenarios of ITER fast burnt termination. Recently, the association EURATOM-CIEMAT has started the operation of the TJ-II stellarator. Due to the need of validating the results given by others transport codes applied to stellarators and because all of them made some approximations, as a averaging magnitudes in each magnetic surface, it was thought suitable to adapt the PRETOR code to devices without axial symmetry, like stellarators, which is very suitable for the specific needs of the study of TJ-II. Several modifications are required in PRETOR; the main concerns to the models of: magnetic equilibrium, geometry and transport of energy and particles. In order to solve the complex magnetic equilibrium geometry the powerful numerical code VMEC has been used. This code gives the magnetic surface shape as a Fourier series in terms of the harmonics (m,n). Most of the geometric magnitudes are also obtained from the VMEC results file. The energy and particle transport models will be replaced by other phenomenological models that are better adapted to stellarator simulation. Using the proposed models, it is pretended to reproduce experimental data available from present stellarators, given especial attention to the TJ-II of the association EURATOM-CIEMAT. (Author)

Stellar Wakes from Dark Matter Subhalos.

Science.gov (United States)

Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R; Wu, Chih-Liang

2018-05-25

We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ∼10^{7}  M_{⊙} or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

Stellar Wakes from Dark Matter Subhalos

Science.gov (United States)

Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R.; Wu, Chih-Liang

2018-05-01

We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ˜107 M⊙ or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

Imaging Young Stellar Objects with VLTi/PIONIER

Science.gov (United States)

Kluska, J.; Malbet, F.; Berger, J.-P.; Benisty, M.; Lazareff, B.; Le Bouquin, J.-B.; Baron, F.; Dominik, C.; Isella, A.; Juhasz, A.; Kraus, S.; Lachaume, R.; Ménard, F.; Millan-Gabet, R.; Monnier, J.; Pinte, C.; Soulez, F.; Tallon, M.; Thi, W.-F.; Thiébaut, É.; Zins, G.

2014-04-01

Optical interferometry imaging is designed to help us to reveal complex astronomical sources without a prior model. Among these complex objects are the young stars and their environments, which have a typical morphology with a point-like source, surrounded by circumstellar material with unknown morphology. To image them, we have developed a numerical method that removes completely the stellar point source and reconstructs the rest of the image, using the differences in the spectral behavior between the star and its circumstellar material. We aim to reveal the first Astronomical Units of these objects where many physical phenomena could interplay: the dust sublimation causing a puffed-up inner rim, a dusty halo, a dusty wind or an inner gaseous component. To investigate more deeply these regions, we carried out the first Large Program survey of HAeBe stars with two main goals: statistics on the geometry of these objects at the first astronomical unit scale and imaging their very close environment. The images reveal the environment, which is not polluted by the star and allows us to derive the best fit for the flux ratio and the spectral slope. We present the first images from this survey and the application of the imaging method on other astronomical objects.

Diagnostics Plan for the National Compact Stellarator Experiment

International Nuclear Information System (INIS)

D. Johnson; T. Brown; H. Neilson; G. Schilling; H. Takahashi; M. Zarnstorff; M. Cole; E. Lazarus; and M. Fenstermacher

2002-01-01

The National Compact Stellarator Experiment (NCSX) is a stellarator-tokamak hybrid seeking to combine the good confinement, high beta and moderate aspect ratio of the tokamak with the quasi-steady-state operation and good stability properties of the stellarator. A preliminary list of measurement requirements, intended to satisfy the needs of the phased research plan, provides the basis for a full complement of plasma diagnostics. It is important to consider this full set, even at this early stage, to assess the adequacy of the stellarator design for diagnostic port access. The 3-D nature of the plasma is a measurement challenge, as is the necessity for high spatial resolution to assess the quality of magnetic surfaces. Other diagnostic requirements include the need for re-entrant views that penetrate the cryostat, for a convenient e-beam probe for field line mapping, and for a diagnostic neutral beam for active spectroscopy

LOCAL BENCHMARKS FOR THE EVOLUTION OF MAJOR-MERGER GALAXIES-SPITZER OBSERVATIONS OF A K-BAND SELECTED SAMPLE

International Nuclear Information System (INIS)

Xu, C. Kevin; Cheng Yiwen; Lu Nanyao; Mazzarella, Joseph M.; Cutri, Roc; Domingue, Donovan; Huang Jiasheng; Gao Yu; Sun, W.-H.; Surace, Jason

2010-01-01

We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from cross-matches between the Two Micron All Sky Survey and Sloan Digital Sky Survey Data Release 3. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed spiral-spiral (S+S) and spiral-elliptical (S+E) pairs in a parent sample that is complete for primaries brighter than K = 12.5 mag, projected separations of 5 h -1 kpc ≤ s ≤ 20 h -1 kpc, and mass ratios ≤2.5. The Spitzer data, consisting of images in seven bands (3.6, 4.5, 5.8, 8, 24, 70, 160 μm), show very diversified IR emission properties. Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR = SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with M ∼> 10 10.5 M sun show significant enhancement. Relatively low-mass (M ∼ 10 10 M sun ) spirals in S+S pairs have about the same SFR/M compared to their counterparts in the control sample, while those with 10 11 M sun have on average a ∼3 times higher SFR/M than single spirals. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the H olmberg effect ) . There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP KPAIR =2.54 x 10 -4 (M sun yr -1 Mpc -3 ).

VizieR Online Data Catalog: IR-bright MSX sources in the SMC with Spitzer/IRS (Kraemer+, 2017)

Science.gov (United States)

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.; Jones, O. C.; Egan, M. P.

2017-07-01

Our original set of infrared spectra of MSX SMC sources was obtained in Spitzer Cycle 1 (Program ID 3277, P.I. M. Egan). This program included 35 targets from the MSX SMC catalog. 24 targets were discussed in previous papers; this paper examines the remaining 11 sources in the sample. We also selected 4 objects in the MSX SMC catalog with similar photometric characteristics in an effort to uncover additional sources with crystalline dust. We observed these targets in Spitzer Cycle 3 (Program ID 30355, P.I. J. Houck). See tables 1 and 2 for observation data and basic properties of the targets. Table 3 lists 20 additional MSX SMC sources that were observed by other Spitzer IRS programs. Overall, 59 MSX SMC sources were observed with the IRS. The spectra were observed using the low-resolution modules of the IRS, Short-Low (SL) and Long-Low (LL), which provided spectra in the 5-14 and 14-37um ranges, respectively, at a resolution between ~60 and 120. For 10 evolved stars with oxygen-rich dust in our Cycle 1 program, we obtained spectra from 0.45 to 1.03um with the Double-Beam Spectrograph at the 2.3m telescope of the Australian National University at Siding Spring Observatory. A 0.45-0.89um spectrum for one of the stars in program 30355 was also observed. These spectra have a resolution of 10Å. Tables 5-7: catalog based on the 243 sources detected in the MSX survey of the SMC, updated with positions and photometry from more recent space-based missions and ground-based surveys. See the Appendix section for more details. The SMC catalog from MSX consists of the 243 sources in the main MSX catalog (Egan+ 2003, see V/114) that lie within the region 7°

STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

International Nuclear Information System (INIS)

Béky, Bence; Kocsis, Bence

2013-01-01

Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10 6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ∼10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

The Tucana/Horologium, Columba, AB Doradus, and Argus Associations: New Members and Dusty Debris Disks

Science.gov (United States)

Zuckerman, B.; Rhee, Joseph H.; Song, Inseok; Bessell, M. S.

2011-05-01

We propose 35 star systems within ~70 pc of Earth as newly identified members of nearby young stellar kinematic groups; these identifications include the first A- and late-B-type members of the AB Doradus moving group and field Argus Association. All but one of the 35 systems contain a bright solar- or earlier-type star that should make an excellent target for the next generation of adaptive optics (AO) imaging systems on large telescopes. AO imaging has revealed four massive planets in orbit around the λ Boo star HR 8799. Initially, the planets were of uncertain mass due in large part to the uncertain age of the star. We find that HR 8799 is a likely member of the ~30 Myr old Columba Association, implying planet masses ~6 times that of Jupiter. We consider Spitzer Space Telescope MIPS photometry of stars in the ~30 Myr old Tucana/Horologium and Columba Associations, the ~40 Myr old field Argus Association, and the ~70 Myr old AB Doradus moving group. The percentage of stars in these young stellar groups that display excess emission above the stellar photosphere at 24 and 70 μm wavelengths—indicative of the presence of a dusty debris disk—is compared with corresponding percentages for members of 11 open clusters and stellar associations with ages between 8 and 750 Myr, thus elucidating the decay of debris disks with time.

IPHAS A-TYPE STARS WITH MID-INFRARED EXCESSES IN SPITZER SURVEYS

International Nuclear Information System (INIS)

Hales, Antonio S.; Barlow, Michael J.; Drew, Janet E.; Unruh, Yvonne C.; Greimel, Robert; Irwin, Michael J.; Gonzalez-Solares, Eduardo

2009-01-01

We have identified 17 A-type stars in the Galactic Plane that have mid-infrared (mid-IR) excesses at 8 μm. From observed colors in the (r' - Hα) - (r' - i') plane, we first identified 23,050 early A-type main-sequence (MS) star candidates in the Isaac Newton Photometric H-Alpha Survey (IPHAS) point source database that are located in Spitzer Galactic Legacy Mid-Plane Survey Extraordinaire Galactic plane fields. Imposing the requirement that they be detected in all seven Two Micron All Sky Survey and Infrared Astronomical Satellite bands led to a sample of 2692 candidate A-type stars with fully sampled 0.6 to 8 μm spectral energy distributions (SEDs). Optical classification spectra of 18 of the IPHAS candidate A-type MS stars showed that all but one could be well fitted using MS A-type templates, with the other being an A-type supergiant. Out of the 2692 A-type candidates 17 (0.6%) were found to have 8 μm excesses above the expected photospheric values. Taking into account non-A-Type contamination estimates, the 8 μm excess fraction is adjusted to ∼0.7%. The distances to these sources range from 0.7 to 2.5 kpc. Only 10 out of the 17 excess stars had been covered by Spitzer MIPSGAL survey fields, of which five had detectable excesses at 24 μm. For sources with excesses detected in at least two mid-IR wavelength bands, blackbody fits to the excess SEDs yielded temperatures ranging from 270 to 650 K, and bolometric luminosity ratios L IR /L * from 2.2 x 10 -3 - 1.9 x 10 -2 , with a mean value of 7.9 x 10 -3 (these bolometric luminosities are lower limits as cold dust is not detectable by this survey). Both the presence of mid-IR excesses and the derived bolometric luminosity ratios are consistent with many of these systems being in the planet-building transition phase between the early protoplanetary disk phase and the later debris disk phase.

SPITZER AS A MICROLENS PARALLAX SATELLITE: MASS MEASUREMENT FOR THE OGLE-2014-BLG-0124L PLANET AND ITS HOST STAR

Energy Technology Data Exchange (ETDEWEB)

Udalski, A.; Skowron, J.; Kozłowski, S.; Poleski, R.; Pietrukowicz, P.; Pietrzyński, G.; Szymański, M. K.; Mróz, P.; Soszyński, I.; Ulaczyk, K.; Wyrzykowski, Ł. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Yee, J. C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Gould, A.; Zhu, W.; Pogge, R. W. [Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Carey, S. [Spitzer Science Center, MS 220-6, California Institute of Technology, Pasadena, CA (United States); Han, C. [Department of Physics, Chungbuk National University, Cheongju 371-763 (Korea, Republic of); Calchi Novati, S. [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)

2015-02-01

We combine Spitzer and ground-based observations to measure the microlens parallax vector π{sub E}, and thus the mass and distance of OGLE-2014-BLG-0124L, making it the first microlensing planetary system with a space-based parallax measurement. The planet and star have masses of m ∼ 0.5 M {sub jup} and M ∼ 0.7 M {sub ☉} and are separated by a ∼ 3.1 AU in projection. The main source of uncertainty in all of these numbers (approximately 30%, 30%, and 20%) is the relatively poor measurement of the Einstein radius θ{sub E}, rather than uncertainty in π{sub E}, which is measured with 2.5% precision. This compares to 22% based on OGLE data alone, implying that the Spitzer data provide not only a substantial improvement in the precision of the π{sub E} measurement, but also the first independent test of a ground-based π{sub E} measurement.

Is the Mercier criterion relevant to stellarator stability?

International Nuclear Information System (INIS)

Carreras, B.A.; Lynch, V.E.; Ichiguchi, K.; Wakatani, M.; Tatsuno, T.

2001-01-01

Local flattening of the pressure profile at the resonant surfaces may significantly change the stellarator stability properties. This flattening may be an intrinsic consequence of the three-dimensional nature of the equilibrium and may invalidate the local stability criteria often used in stellarator design. (author)

Close stellar encounters in globular clusters

International Nuclear Information System (INIS)

Bailyn, C.D.

1989-01-01

Stellar encounters are expected to produce a variety of interesting objects in the cores of globular clusters, either through the formation of binaries by tidal capture, or direct collisions. Here, I describe several attempts to observe the products of stellar encounters. In particular, the use of color maps has demonstrated the existence of a color gradient in the core of M15, which seems to be caused by a population of faint blue objects concentrated towards the cluster center. (author)

Compact Starburst Galaxies with Fast Outflows: Spatially Resolved Stellar Mass Profiles

Science.gov (United States)

Gottlieb, Sophia; Diamond-Stanic, Aleksandar; Lipscomb, Charles; Ohene, Senyo; Rines, Josh; Moustakas, John; Sell, Paul; Tremonti, Christy; Coil, Alison; Rudnick, Gregory; Hickox, Ryan C.; Geach, James; Kepley, Amanda

2018-01-01

Powerful galactic winds driven by stellar feedback and black hole accretion are thought to play an important role in regulating star formation in galaxies. In particular, strong stellar feedback from supernovae, stellar winds, radiation pressure, and cosmic rays is required by simulations of star-forming galaxies to prevent the vast majority of baryons from cooling and collapsing to form stars. However, it remains unclear whether these stellar processes play a significant role in expelling gas and shutting down star formation in massive progenitors of quiescent galaxies. What are the limits of stellar feedback? We present multi-band photometry with HST/WFC3 (F475W, F814W, F160W) for a dozen compact starburst galaxies at z~0.6 with half-light radii that suggest incredibly large central escape velocities. These massive galaxies are driving fast (>1000 km/s) outflows that have been previously attributed to stellar feedback associated with the compact (r~100 pc) starburst. But how compact is the stellar mass? In the context of the stellar feedback hypothesis, it is unclear whether these fast outflows are being driven at velocities comparable to the escape velocity of an incredibly dense stellar system (as predicted by some models of radiation-pressure winds) or at velocities that exceed the central escape velocity by large factor. Our spatially resolved measurements with HST show that the stellar mass is more extended than the light, and this requires that the physical mechanism responsible for driving the winds must be able to launch gas at velocities that are factors of 5-10 beyond the central escape velocity.

TRACING THE EVOLUTION OF HIGH-REDSHIFT GALAXIES USING STELLAR ABUNDANCES

Energy Technology Data Exchange (ETDEWEB)

Crosby, Brian D.; O’Shea, Brian W. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Beers, Timothy C. [Department of Physics and JINA—Center for the Evolution of the Elements, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Tumlinson, Jason, E-mail: crosby.bd@gmail.com [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2016-03-20

This paper presents the first results from a model for chemical evolution that can be applied to N-body cosmological simulations and quantitatively compared to measured stellar abundances from large astronomical surveys. This model convolves the chemical yield sets from a range of stellar nucleosynthesis calculations (including asymptotic giant branch stars, Type Ia and II supernovae, and stellar wind models) with a user-specified stellar initial mass function (IMF) and metallicity to calculate the time-dependent chemical evolution model for a “simple stellar population” (SSP) of uniform metallicity and formation time. These SSP models are combined with a semianalytic model for galaxy formation and evolution that uses merger trees from N-body cosmological simulations to track several α- and iron-peak elements for the stellar and multiphase interstellar medium components of several thousand galaxies in the early (z ≥ 6) universe. The simulated galaxy population is then quantitatively compared to two complementary data sets of abundances in the Milky Way stellar halo and is capable of reproducing many of the observed abundance trends. The observed abundance ratio distributions are best reproduced with a Chabrier IMF, a chemically enriched star formation efficiency of 0.2, and a redshift of reionization of 7. Many abundances are qualitatively well matched by our model, but our model consistently overpredicts the carbon-enhanced fraction of stars at low metallicities, likely owing to incomplete coverage of Population III stellar yields and supernova models and the lack of dust as a component of our model.

The low-luminosity stellar mass function

International Nuclear Information System (INIS)

Kroupa, Pavel; Tout, C.A.; Gilmore, Gerard

1990-01-01

The stellar mass function for low-mass stars is constrained using the stellar luminosity function and the slope of the mass-luminosity relation. We investigate the range of mass functions for stars with absolute visual magnitude fainter than M V ≅ +5 which are consistent with both the local luminosity function and the rather poorly determined mass-absolute visual magnitude relation. Points of inflexion in the mass-luminosity relation exist because of the effects of H - , H 2 and of other molecules on the opacity and equation of state. The first two of these correspond to absolute magnitudes M V ≅ +7 and M V ≅ +12, respectively, at which structure is evident in the stellar luminosity function (a flattening and a maximum, respectively). Combining the mass-luminosity relation which shows these inflexion points with a peaked luminosity function, we test smooth mass functions in the mass range 0.9-0.1 the solar mass. (author)

TEM-turbulence in stellarators and its optimization

Science.gov (United States)

Proll, Josefine H. E.; Helander, Per; Lazerson, Samuel; Mynick, Harry; Xanthopoulos, Pavlos

2014-10-01

Quasi-isodynamic stellarators, which are especially optimized for neoclassical transport, have been shown to be resilient towards trapped-electrons modes (TEMs) in large regions of parameter space. In these configurations, all particles have average ``good curvature.'' It was shown analytically that, thanks to this property, particles that bounce faster than the mode in question draw energy from it near marginal stability, so that the ordinary density-gradient-driven TEM has to be stable in the electrostatic and collisionless limit.This has been confirmed in linear flux-tube simulations that were performed with the GENE code. Several magnetic field configurations were compared and it was found that the growth rates of the TEMs drop with increasing degree of quasi-isodynamicity. These findings can be used to optimize stellarators with respect to TEM turbulence by reducing the fraction of trapped particles with bounce averaged ``bad curvature.'' An appropriate proxy function has therefore been designed to be implemented in STELLOPT, a stellarator optimization tool that can now be used to further explore the configuration space of neoclassically optimized stellarators with the aim to extract designs with improved turbulent transport. This work was facilitated by the Max-Planck/Princeton Center for Plasma Physics.

Unusual Slowly Rotating Brown Dwarfs Discovered through Precision Spitzer Photometry

Science.gov (United States)

Heinze, Aren; Metchev, S.

2014-01-01

Many brown dwarfs exhibit low-amplitude rotationally modulated variability due to photospheric inhomogeneities caused by condensate clouds in their atmospheres. The Spitzer Space Telescope 'Weather on Other Worlds' (WoW) project has monitored 44 brown dwarfs at unprecedented photometric precision from space. We present one of several important new results from WoW: the discovery of brown dwarfs with unexpectedly slow rotation periods. While most brown dwarfs have periods of 2-12 hours, we have identified two with well-constrained periods of 13±1 and >20 hours, respectively, and 2 others that show more tentative evidence of longer than 20-hour periods. By serving as almost non-rotating standards, these objects will allow more accurate calibration of spectroscopic measurements of brown dwarfs' projected rotational velocities. The existence of such slowly-rotating objects also constrains models of brown dwarf formation and angular momentum evolution.

Wimps and stellar structure

International Nuclear Information System (INIS)

Bouquet, A.; Salati, P.

1988-01-01

We present the results of an analytic approximation to compute the effects of WIMPs on stellar structures in a self-consistent way. We examine in particular the case of the Sun and of horizontal branch stars

Interaction effects on galaxy pairs with Gemini/GMOS- III: stellar population synthesis