STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

International Nuclear Information System (INIS)

Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

2012-01-01

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ( U -shapes ) in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (≤36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (∼11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (≥50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field

SHORT DISSIPATION TIMES OF PROTO-PLANETARY DISKS: AN ARTIFACT OF SELECTION EFFECTS?

International Nuclear Information System (INIS)

Pfalzner, Susanne; Steinhausen, Manuel; Menten, Karl

2014-01-01

The frequency of disks around young stars, a key parameter for understanding planet formation, is most readily determined in young stellar clusters where many relatively coeval stars are located in close proximity. Observational studies seem to show that the disk frequency decreases rapidly with cluster age with <10% of cluster stars retaining their disks for longer than 2-6 Myr. Given that at least half of all stars in the field seem to harbor one or more planets, this would imply extremely fast disk dispersal and rapid planet growth. Here we question the validity of this constraint by demonstrating that the short disk dissipation times inferred to date might have been heavily underestimated by selection effects. Critically, for ages >3 Myr only stars that originally populated the densest areas of very populous clusters, which are prone to disk erosion, are actually considered. This tiny sample may not be representative of the majority of stars. In fact, the higher disk fractions in co-moving groups indicate that it is likely that over 30% of all field stars retain their disks well beyond 10 Myr, leaving ample time for planet growth. Equally, our solar system, with a likely formation time >10 Myr, need no longer be an exception but in fact typical of planetary systems

THE PHOTOECCENTRIC EFFECT AND PROTO-HOT JUPITERS. II. KOI-1474.01, A CANDIDATE ECCENTRIC PLANET PERTURBED BY AN UNSEEN COMPANION

Energy Technology Data Exchange (ETDEWEB)

Dawson, Rebekah I.; Murray-Clay, Ruth A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, MS-10, Cambridge, MA 02138 (United States); Johnson, John Asher; Morton, Timothy D. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Fabrycky, Daniel C. [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, California 95064 (United States); Howard, Andrew W., E-mail: rdawson@cfa.harvard.edu [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822-1839 (United States)

2012-12-20

The exoplanets known as hot Jupiters-Jupiter-sized planets with periods of less than 10 days-likely are relics of dynamical processes that shape all planetary system architectures. Socrates et al. argued that high eccentricity migration (HEM) mechanisms proposed for situating these close-in planets should produce an observable population of highly eccentric proto-hot Jupiters that have not yet tidally circularized. HEM should also create failed-hot Jupiters, with periapses just beyond the influence of fast circularization. Using the technique we previously presented for measuring eccentricities from photometry (the ''photoeccentric effect''), we are distilling a collection of eccentric proto- and failed-hot Jupiters from the Kepler Objects of Interest (KOI). Here, we present the first, KOI-1474.01, which has a long orbital period (69.7340 days) and a large eccentricity e 0.81{sup +0.10}{sub -0.07}, skirting the proto-hot Jupiter boundary. Combining Kepler photometry, ground-based spectroscopy, and stellar evolution models, we characterize host KOI-1474 as a rapidly rotating F star. Statistical arguments reveal that the transiting candidate has a low false-positive probability of 3.1%. KOI-1474.01 also exhibits transit-timing variations of the order of an hour. We explore characteristics of the third-body perturber, which is possibly the ''smoking-gun'' cause of KOI-1474.01's large eccentricity. We use the host star's period, radius, and projected rotational velocity to measure the inclination of the stellar spin. Comparing KOI 1474.01's inclination, we find that its orbit is marginally consistent with being aligned with the stellar spin axis, although a reanalysis is warranted with future additional data. Finally, we discuss how the number and existence of proto-hot Jupiters will not only demonstrate that hot Jupiters migrate via HEM, but also shed light on the typical timescale for the mechanism.

Confronting Standard Models of Proto-planetary Disks with New Mid-infrared Sizes from the Keck Interferometer

Science.gov (United States)

Millan-Gabet, Rafael; Che, Xiao; Monnier, John D.; Sitko, Michael L.; Russell, Ray W.; Grady, Carol A.; Day, Amanda N.; Perry, R. B.; Harries, Tim J.; Aarnio, Alicia N.; Colavita, Mark M.; Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien

2016-08-01

We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.

CONFRONTING STANDARD MODELS OF PROTO-PLANETARY DISKS WITH NEW MID-INFRARED SIZES FROM THE KECK INTERFEROMETER

Energy Technology Data Exchange (ETDEWEB)

Millan-Gabet, Rafael [California Institute of Technology, NASA Exoplanet Science Institute, Pasadena, CA 91125 (United States); Che, Xiao; Monnier, John D.; Aarnio, Alicia N. [University of Michigan Astronomy Department, 1085 S. University Avenue 303B West Hall University of Michigan, Ann Arbor, MI 48109-1107 (United States); Sitko, Michael L.; Day, Amanda N. [Department of Physics, University of Cincinnati, Cincinnati OH 45221 (United States); Russell, Ray W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Perry, R. B. [NASA Langley Research Center, MS 160, Hampton, VA 23681 (United States); Harries, Tim J. [Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Colavita, Mark M. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien, E-mail: R.Millan-Gabet@caltech.edu [Keck Observatory, 65-1120 Mamalahoa Hwy, Kamuela, HI 96743 (United States)

2016-08-01

We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.

CONFRONTING STANDARD MODELS OF PROTO-PLANETARY DISKS WITH NEW MID-INFRARED SIZES FROM THE KECK INTERFEROMETER

International Nuclear Information System (INIS)

Millan-Gabet, Rafael; Che, Xiao; Monnier, John D.; Aarnio, Alicia N.; Sitko, Michael L.; Day, Amanda N.; Russell, Ray W.; Grady, Carol A.; Perry, R. B.; Harries, Tim J.; Colavita, Mark M.; Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien

2016-01-01

We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.

Stochastic 2-D galaxy disk evolution models. Resolved stellar populations in the galaxy M33

Science.gov (United States)

Mineikis, T.; Vansevičius, V.

We improved the stochastic 2-D galaxy disk models (Mineikis & Vansevičius 2014a) by introducing enriched gas outflows from galaxies and synthetic color-magnitude diagrams of stellar populations. To test the models, we use the HST/ACS stellar photometry data in four fields located along the major axis of the galaxy M33 (Williams et al. 2009) and demonstrate the potential of the models to derive 2-D star formation histories in the resolved disk galaxies.

A MULTIWAVELENGTH CHARACTERIZATION OF PROTO-BROWN-DWARF CANDIDATES IN SERPENS

Energy Technology Data Exchange (ETDEWEB)

Riaz, B.; Caselli, P. [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Vorobyov, E. [Institute of Astrophysics, University of Vienna, Vienna 1180 (Austria); Research Institute of Physics, Southern Federal University, Rostov-on-Don 344090 (Russian Federation); Harsono, D. [Universitt Heidelberg, Zentrum fr Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120, Heidelberg (Germany); Tikare, K. [IRAP, BP 44346-31028 Toulouse Cedex 4 (France); Gonzalez-Martin, O., E-mail: briaz@mpe.mpg.de [Instituto de Radioastronoma y Astrofsica (IRyA), UNAM, Antigua Carretera a Pátzcuaro # 8701, Col. Ex Hacienda San José de la Huerta, Morelia, Michoacán, C.P. 58089 (Mexico)

2016-11-10

We present results from a deep submillimeter survey in the Serpens Main and Serpens/G3–G6 clusters, conducted with the Submillimetre Common-User Bolometer Array (SCUBA-2) at the James Clerk Maxwell Telescope. We have combined near- and mid-infrared spectroscopy, Herschel PACS far-infrared photometry, submillimeter continuum, and molecular gas line observations, with the aim of conducting a detailed multiwavelength characterization of “proto-brown-dwarf” (proto-BD) candidates in Serpens. We have performed continuum and line radiative transfer modeling and have considered various classification schemes to understand the structure and the evolutionary stage of the system. We have identified four proto-BD candidates, of which the lowest-luminosity source has an L {sub bol} ∼ 0.05 L {sub ☉}. Two of these candidates show characteristics consistent with Stage 0/I systems, while the other two are Stage I-T/Class Flat systems with tenuous envelopes. Our work has also revealed a ∼20% fraction of misidentified Class 0/I/Flat sources that show characteristics consistent with Class II edge-on disk systems. We have set constraints on the mass of the central object using the measured bolometric luminosities and numerical simulations of stellar evolution. Considering the available gas+dust mass reservoir and the current mass of the central source, three of these candidates are likely to evolve into BDs.

Alma Survey of Circumstellar Disks in the Young Stellar Cluster IC 348

Science.gov (United States)

Ruíz-Rodríguez, D.; Cieza, L. A.; Williams, J. P.; Andrews, S. M.; Principe, D. A.; Caceres, C.; Canovas, H.; Casassus, S.; Schreiber, M. R.; Kastner, J. H.

2018-05-01

We present a 1.3 mm continuum survey of the young (2-3 Myr) stellar cluster IC 348, which lies at a distance of 310 pc, and is dominated by low-mass stars (M⋆ ˜ 0.1-0.6 M⊙). We observed 136 Class II sources (disks that are optically thick in the infrared) at 0.8″ (200 au) resolution with a 3σ sensitivity of ˜ 0.45 mJy (Mdust ˜ 1.3 M⊕). We detect 40 of the targets and construct a mm-continuum luminosity function. We compare the disk mass distribution in IC 348 to those of younger and older regions, taking into account the dependence on stellar mass. We find a clear evolution in disk masses from 1 to 5-10 Myr. The disk masses in IC 348 are significantly lower than those in Taurus (1-3 Myr) and Lupus (1-3 Myr), similar to those of Chamaleon I, (2-3 Myr) and σ Ori (3-5 Myr) and significantly higher than in Upper Scorpius (5-10 Myr). About 20 disks in our sample (˜5% of the cluster members) have estimated masses (dust + gas) >1 MJup and hence might be the precursors of giant planets in the cluster. Some of the most massive disks include transition objects with inner opacity holes based on their infrared SEDs. From a stacking analysis of the 96 non-detections, we find that these disks have a typical dust mass of just ≲ 0.4 M⊕, even though the vast majority of their infrared SEDs remain optically thick and show little signs of evolution. Such low-mass disks may be the precursors of the small rocky planets found by Kepler around M-type stars.

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.

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

and the molecules' abundances are similar to those found in other circumstellar disks. We furthermore detected C 2 H toward the objects and discuss this finding in the context of star formation. Finally, we have performed radiative transfer modeling of the K-band scattered light image varying a disk plus outflow two-dimensional density profile and the stellar properties. The model approximately reproduces extent and location of the dark lane, and the basic appearance of the outflow. We discuss our findings in the context of circumstellar disks across all mass regimes and conclude that our discovery is an ideal laboratory to study the early phases in the evolution of massive circumstellar disks surrounding young stellar objects.

Stellar Disk Truncations: HI Density and Dynamics

Science.gov (United States)

Trujillo, Ignacio; Bakos, Judit

2010-06-01

Using HI Nearby Galaxy Survey (THINGS) 21-cm observations of a sample of nearby (nearly face-on) galaxies we explore whether the stellar disk truncation phenomenon produces any signature either in the HI gas density and/or in the gas dynamics. Recent cosmological simulations suggest that the origin of the break on the surface brightness distribution is produced by the appearance of a warp at the truncation position. This warp should produce a flaring on the gas distribution increasing the velocity dispersion of the HI component beyond the break. We do not find, however, any evidence of this increase in the gas velocity dispersion profile.

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.

A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

International Nuclear Information System (INIS)

Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Jörg-Uwe; Müller, André; Bonnefoy, Mickaël; Henning, Thomas; Lacour, Sylvestre; Thebault, Philippe; Juhász, Attila; Sicilia-Aguilar, Aurora; Tuthill, Peter; Crida, Aurelien

2012-01-01

With the uniquely high contrast within 0.''1 (Δmag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 ± 5 mas (12.8 ± 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 ± 0.007, 0.012 ± 0.008, and 0.0086 ± 0.0011, respectively (3σ errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion with an estimated mass of ∼0.1-0.4 M ☉ . HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.

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.

The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

International Nuclear Information System (INIS)

Xiang, Mao-Sheng; Liu, Xiao-Wei; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Yuan, Hai-Bo; Rebassa-Mansergas, Alberto; Huo, Zhi-Ying

2015-01-01

Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

Energy Technology Data Exchange (ETDEWEB)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2015-03-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

International Nuclear Information System (INIS)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

2015-01-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

THE STRUCTURE AND STELLAR CONTENT OF THE OUTER DISKS OF GALAXIES: A NEW VIEW FROM THE Pan-STARRS1 MEDIUM DEEP SURVEY

Energy Technology Data Exchange (ETDEWEB)

Zheng, Zheng; Thilker, David A.; Heckman, Timothy M. [Department of Physics and Astronomy, Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218 (United States); Meurer, Gerhardt R. [International Center for Radio Astronomy Research, The University of Western Australia, M468, 35 StirlingHighway, Crawley, WA 6009 (Australia); Burgett, W. S.; Huber, M. E.; Kaiser, N.; Magnier, E. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Chambers, K. C.; Metcalfe, N. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Price, P. A. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2015-02-20

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r {sub 90}, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples of galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r {sub 90}. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic 'U' shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.

PROTO-PLANETARY DISK CHEMISTRY RECORDED BY D-RICH ORGANIC RADICALS IN CARBONACEOUS CHONDRITES

International Nuclear Information System (INIS)

Remusat, Laurent; Robert, Francois; Meibom, Anders; Mostefaoui, Smail; Delpoux, Olivier; Binet, Laurent; Gourier, Didier; Derenne, Sylvie

2009-01-01

Insoluble organic matter (IOM) in primitive carbonaceous meteorites has preserved its chemical composition and isotopic heterogeneity since the solar system formed ∼4.567 billion years ago. We have identified the carrier moieties of isotopically anomalous hydrogen in IOM isolated from the Orgueil carbonaceous chondrite. Data from high spatial resolution, quantitative isotopic NanoSIMS mapping of Orgueil IOM combined with data from electron paramagnetic resonance spectroscopy reveals that organic radicals hold all the deuterium excess (relative to the bulk IOM) in distinct, micrometer-sized, D-rich hotspots. Taken together with previous work, the results indicate that an isotopic exchange reaction took place between pre-existing organic compounds characterized by low D/H ratios and D-rich gaseous molecules, such as H 2 D + or HD 2 + . This exchange reaction most likely took place in the diffuse outer regions of the proto-planetary disk around the young Sun, offering a model that reconciles meteoritic and cometary isotopic compositions of organic molecules.

Proto-Planetary Disk Chemistry Recorded by D-Rich Organic Radicals in Carbonaceous Chondrites

Science.gov (United States)

Remusat, Laurent; Robert, François; Meibom, Anders; Mostefaoui, Smail; Delpoux, Olivier; Binet, Laurent; Gourier, Didier; Derenne, Sylvie

2009-06-01

Insoluble organic matter (IOM) in primitive carbonaceous meteorites has preserved its chemical composition and isotopic heterogeneity since the solar system formed ~4.567 billion years ago. We have identified the carrier moieties of isotopically anomalous hydrogen in IOM isolated from the Orgueil carbonaceous chondrite. Data from high spatial resolution, quantitative isotopic NanoSIMS mapping of Orgueil IOM combined with data from electron paramagnetic resonance spectroscopy reveals that organic radicals hold all the deuterium excess (relative to the bulk IOM) in distinct, micrometer-sized, D-rich hotspots. Taken together with previous work, the results indicate that an isotopic exchange reaction took place between pre-existing organic compounds characterized by low D/H ratios and D-rich gaseous molecules, such as H2D+ or HD2 +. This exchange reaction most likely took place in the diffuse outer regions of the proto-planetary disk around the young Sun, offering a model that reconciles meteoritic and cometary isotopic compositions of organic molecules.

PLANET FORMATION IN STELLAR BINARIES. I. PLANETESIMAL DYNAMICS IN MASSIVE PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Rafikov, Roman R.; Silsbee, Kedron

2015-01-01

About 20% of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of planetesimals in protoplanetary disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star, has been challenged recently, as the gravity of the protoplanetary disk was shown to play a crucial role in planetesimal dynamics. An added complication is the tendency of protoplanetary disks in binaries to become eccentric, giving rise to additional excitation of planetesimal eccentricity. Here, for the first time, we analytically explore the secular dynamics of planetesimals in binaries such as α Cen and γ Cep under the combined action of (1) gravity of the eccentric protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of planetesimal eccentricity e p in non-precessing disks (and in precessing disks in certain limits). We obtain the analytical form of the distribution of the relative velocities of planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push the sizes of planetesimals colliding with comparable objects at the highest speed to small values, ∼1 km. We also find that planetesimals in eccentric protoplanetary disks apsidally aligned with the binary orbit collide at lower relative velocities than in misaligned disks. Our results highlight the decisive role that disk gravity plays in planetesimal dynamics in binaries

Rotational stellar structures based on the Lagrangian variational principle

International Nuclear Information System (INIS)

Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

2017-01-01

A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc. (paper)

Rotational stellar structures based on the Lagrangian variational principle

Science.gov (United States)

Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

2017-06-01

A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc.

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.

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey. II. Disk Masses from ALMA Continuum Observations

Science.gov (United States)

Ward-Duong, K.; Patience, J.; Bulger, J.; van der Plas, G.; Ménard, F.; Pinte, C.; Jackson, A. P.; Bryden, G.; Turner, N. J.; Harvey, P.; Hales, A.; De Rosa, R. J.

2018-02-01

We report 885 μm ALMA continuum flux densities for 24 Taurus members spanning the stellar/substellar boundary with spectral types from M4 to M7.75. Of the 24 systems, 22 are detected at levels ranging from 1.0 to 55.7 mJy. The two nondetections are transition disks, though other transition disks in the sample are detected. Converting ALMA continuum measurements to masses using standard scaling laws and radiative transfer modeling yields dust mass estimates ranging from ∼0.3 to 20 M ⊕. The dust mass shows a declining trend with central object mass when combined with results from submillimeter surveys of more massive Taurus members. The substellar disks appear as part of a continuous sequence and not a distinct population. Compared to older Upper Sco members with similar masses across the substellar limit, the Taurus disks are brighter and more massive. Both Taurus and Upper Sco populations are consistent with an approximately linear relationship in M dust to M star, although derived power-law slopes depend strongly upon choices of stellar evolutionary model and dust temperature relation. The median disk around early-M stars in Taurus contains a comparable amount of mass in small solids as the average amount of heavy elements in Kepler planetary systems on short-period orbits around M-dwarf stars, with an order of magnitude spread in disk dust mass about the median value. Assuming a gas-to-dust ratio of 100:1, only a small number of low-mass stars and brown dwarfs have a total disk mass amenable to giant planet formation, consistent with the low frequency of giant planets orbiting M dwarfs.

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)

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.

PROTO-II: a short pulse water insulated accelerator

International Nuclear Information System (INIS)

Martin, T.H.; VanDevender, J.P.; Johnson, D.L.; McDaniel, D.H.; Aker, M.

1975-01-01

A new accelerator, designated Proto-II, is presently under construction at Sandia Laboratories. Proto-II will have a nominal output of 100 kJ into a two-sided diode at a voltage of 1.5 MV and a total current of over 6 MA for 24 ns. This accelerator will be utilized for electron beam fusion experiments and for pulsed power and developmental studies leading to a proposed further factor of five scale-up in power. The design of Proto-II is based upon recent water switching developments and represents a 10-fold extrapolation of those results. Initial testing of Proto-II is scheduled to begin in 1976. Proto-II power flow starts with eight Marx generators which charge 16 water-insulated storage capacitors. Eight triggered, 3 MV, SF 6 gas-insulated switches next transfer the energy through oil-water interfaces into the first stage of 16 parallel lines. Next, the 16 first stages transfer their energy into the pulse forming lines and fast switching sections.The energy is then delivered to two converging, back-to-back, disk-shaped transmission line. Two back-to-back diodes then form the electron beams which are focused onto a common anode

Low frequency RF heating of plasmas in a toroidal stellarator

International Nuclear Information System (INIS)

Golovato, S.N.

1977-01-01

Studies of transit-time magnetic pumping and Alfven wave heating have been done in the Proto-Cleo stellarator. Both plasma heating and plasma confinement have been investigated. A traveling wave was launched around the Proto-Cleo l = 2, 6 field period stellarator to attempt transit-time magnetic pumping of a pulsed electron beam moving along the magnetic field lines. An apparent loss of the beam was seen when the transit-time magnetic pumping was applied. A random walk diffusion of the beam electrons with a step size determined by the radial EXB drift due to the poloidal electric field agrees well with the experimental results. Alfven wave heating was applied to plasmas in the Proto-Cleo l = 3, 7 field period stellarator. Global excitation of Alfven waves was accomplished by exciting an electrostatically shielded helical winding corresponding to a q = 3 rational field line with a pulsed, high-power RF source. Theoretical analysis of this helical wave launcher predicted effective energy absorption in the Proto-Cleo gun-produced plasma

INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS

Energy Technology Data Exchange (ETDEWEB)

Bird, Jonathan C.; Kazantzidis, Stelios; Weinberg, David H. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Guedes, Javiera [Institute for Astronomy, ETH Zuerich, Wolgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland); Callegari, Simone [Anthropology Institute and Museum, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Mayer, Lucio [Institute for Theoretical Physics, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Madau, Piero [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

2013-08-10

We analyze the present day structure and assembly history of a high-resolution hydrodynamic simulation of the formation of a Milky-Way-(MW)-like disk galaxy, from the ''Eris'' simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. At z = 0, stars with t{sub form} < 2 Gyr mainly occupy the stellar spheroid, with the oldest (earliest forming) stars having more centrally concentrated profiles. The younger age cohorts populate disks of progressively longer radial scale lengths and shorter vertical scale heights. At a given radius, the vertical density profiles and velocity dispersions of stars vary smoothly as a function of age, and the superposition of old, vertically extended and young, vertically compact cohorts gives rise to a double-exponential profile like that observed in the MW. Turning to formation history, we find that the trends of spatial structure and kinematics with stellar age are largely imprinted at birth, or immediately thereafter. Stars that form during the active merger phase at z > 3 are quickly scattered into rounded, kinematically hot configurations. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms ''inside out'' in a radial sense and ''upside down'' in a vertical sense. Secular heating and radial migration influence the final state of each age cohort, but the changes they produce are small compared to the trends established at formation. The predicted correlations of stellar age with spatial and kinematic structure are in good qualitative agreement with the correlations observed for mono-abundance stellar populations in the MW.

On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

Science.gov (United States)

Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

2018-02-01

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

Dust in Proto-Planetary Disks: Properties and Evolution

OpenAIRE

Natta, A.; Testi, L.; Calvet, N.; Henning, Th.; Waters, R.; Wilner, D.

2006-01-01

We review the properties of dust in protoplanetary disks around optically visible pre-main sequence stars obtained with a variety of observational techniques, from measurements of scattered light at visual and infrared wavelengths to mid-infrared spectroscopy and millimeter interferometry. A general result is that grains in disks are on average much larger than in the diffuse interstellar medium (ISM). In many disks, there is evidence that a large mass of dust is in grains with millimeter and...

Evolution and Photoevaporation of Protoplanetary Disks in Clusters: The Role of Pre-stellar Core Properties

Science.gov (United States)

Xiao, Lin; Chang, Qiang

2018-01-01

We explore the effects of progenitor pre-stellar core properties on the evolution of disks with external photoevaporation in clusters. Since the strength of external photoevaporation is largely determined by the depth of the gravitational potential well of the disk, the external photoevaporation rate is the function of star mass and disk size. The properties of a core collapse set up the initial conditions of protoplanetary disks, so they influence the evolutions of star mass and disk size. Our calculations show that the core properties can dramatically influence the efficiency of external photoevaporation. For the core with low angular velocity, most core mass directly falls onto the central star or onto the disk near the star. External photoevaporation is suppressed even if external radiation from nearby massive stars are strong. In this case, the disk evolution in clusters is primarily driven by its own internal viscosity. However, if the core angular velocity is high, most core mass falls onto the disk far from the central star. External photoevaporation is so strong that the disk mass is severely evaporated. Finally, the star mass is very low and the disk lifetime is very short. Our calculations could interpret some observational features of disks in clusters, such as the diameter distribution of disks in the Trapezium cluster and the correlation between mass accretion rate and star mass. We suggest that the disk mass determined by (sub)millimeter wavelength observations may be underestimated.

EVOLUTION OF MASSIVE PROTOSTARS VIA DISK ACCRETION

International Nuclear Information System (INIS)

Hosokawa, Takashi; Omukai, Kazuyuki; Yorke, Harold W.

2010-01-01

Mass accretion onto (proto-)stars at high accretion rates M-dot * > 10 -4 M sun yr -1 is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk accretion. We consider a limiting case of 'cold' disk accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the accretion shock front. We examine how different accretion geometries affect the evolution of massive protostars. For cold disk accretion at 10 -3 M sun yr -1 , the radius of a protostar is initially small, R * ≅ a few R sun . After several solar masses have accreted, the protostar begins to bloat up and for M * ≅ 10 M sun the stellar radius attains its maximum of 30-400 R sun . The large radius ∼100 R sun is also a feature of spherically symmetric accretion at the same accreted mass and accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times, the protostar eventually begins to contract and reaches the zero-age main sequence (ZAMS) for M * ≅ 30 M sun , independent of the accretion geometry. For accretion rates exceeding several 10 -3 M sun yr -1 , the protostar never contracts to the ZAMS. The very large radius of several hundreds R sun results in the low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable H II regions.

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

On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

Science.gov (United States)

Windhorst, Rogier A.; Wyithe, Stuart; Alpaslan, Mehmet; Timmes, F. X.; Andrews, Stephen K.; Kim, Duho; Kelly, Patrick; Coe, Dan A.; Diego, Jose M.; Driver, Simon P.; Dijkstra, Mark

2018-06-01

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-IR surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z=7-17.We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z>7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions.We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be 10^4-10^5x, with rise times of hours and decline times of z~Economia y Competitividad of Spain Consolider Project CSD2010-00064.

THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS

International Nuclear Information System (INIS)

Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J.

2013-01-01

We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new ''snapshot'' λ = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L mm ), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3σ depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L mm and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L mm and the disk mass, M d , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of ∼25 mJy for 1 M ☉ hosts and a power-law scaling L mm ∝M * 1.5-2.0 . We suggest that a reasonable treatment of dust temperature in the conversion from L mm to M d favors an inherently linear M d ∝M * scaling, with a typical disk-to-star mass ratio of ∼0.2%-0.6%. The measured rms dispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of ∼40 on the inferred M d (or L mm ) at any given host mass. We argue that this relationship between M d and M * likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the

The Mass Dependence between Protoplanetary Disks and their Stellar Hosts

Science.gov (United States)

Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J.

2013-07-01

We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new "snapshot" λ = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L mm), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3σ depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L mm and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L mm and the disk mass, Md , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of ~25 mJy for 1 M ⊙ hosts and a power-law scaling L_mm ∝ M_{\\ast}^{1.5-2.0}. We suggest that a reasonable treatment of dust temperature in the conversion from L mm to Md favors an inherently linear Md vpropM * scaling, with a typical disk-to-star mass ratio of ~0.2%-0.6%. The measured rms dispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of ~40 on the inferred Md (or L mm) at any given host mass. We argue that this relationship between Md and M * likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet

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.

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.

Protoplanetary disks studied with 2-Dimensional imaging polarimetry

International Nuclear Information System (INIS)

Hajjar, R.; Bastien, P.

2000-01-01

Full text: This paper describes a method devised to determine density profiles of disks around Young Stellar Objects (YSOs), since this is crucial for the determination of the possible creation of planets based on theories of the proto solar nebula. It is based on the determination of the position of null polarization points in maps of YSOs as a function of wavelength. This information is interpreted in terms of variation in optical depth then converted to densities based on opacity tables for published grain models. This method has been used on a number of YSOs, namely HL Tau, the archetypal low mass T tauri protostar and showed a density profile compatible with previous models based on the spectral energy distribution of T Tauri stars. We will also explore the possibility of combining this method with millimeter and submillimeter data in order to better constraint grain models circumstellar matter distribution around YSOs

The Stability of Galaxy Disks

NARCIS (Netherlands)

Westfall, K. B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T. P. K.; Swaters, R. A.; Verheijen, M. A. W.; Seigar, M.S.; Treuthardt, P.

2014-01-01

We calculate the stellar surface mass density (Σ*) and two-component (gas+stars) disk stability (QRW) for 25 late-type galaxies from the DiskMass Survey. These calculations are based on fits of a dynamical model to our ionized-gas and stellar kinematic data performed using a Markov Chain Monte Carlo

Testing the Formation Mechanism of Sub-Stellar Objects in Lupus (A SOLA Team Study)

Science.gov (United States)

De Gregorio-Monsalvo, Itziar; Lopez, C.; Takahashi, S.; Santamaria-Miranda

2017-06-01

The international SOLA team (Soul of Lupus with ALMA) has identified a set of pre- and proto-stellar candidates in Lupus 1 and 3 of substellar nature using 1.1mm ASTE/AzTEC maps and our optical to submillimeter database. We have observed with ALMA the most promising pre- and proto-brown dwarfs candidates. Our aims are to provide insights on how substellar objects form and evolve, from the equivalent to the pre-stellar cores to the Class II stage in the low mass regime of star formation. Our sample comprises 33 pre-stellar objects, 7 Class 0 and I objects, and 22 Class II objects.

Studies of the magnetic configuration of an l=2 stellarator

International Nuclear Information System (INIS)

Fedyanin, O.I.

1975-05-01

The first part of this report describes a computational study of the effect of first and second order resonances on an l = 2 stellarator, taking as model the PROTO-CLEO experiment. The magnetic surfaces are computed in each case and the break up shown. The second part of the report deals with measurements made with an electron beam on the PROTO-CLEO l = 2 stellarator. The magnetic surfaces are measured by means of a movable probe which intercepts the beams. It is shown that the form of the surfaces, particularly near the separatrix, is sensitive to quite small perturbations of a resonant type. (author)

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.

Chemical evolution of the galactic disk

International Nuclear Information System (INIS)

Wyse, R.F.G.; Gilmore, G.

1987-01-01

The distribution of enriched material in the stars and gas of their Galaxy contains information pertaining to the chemical evolution of the Milky Way from its formation epoch to the present day, and provides general constraints on theories of galaxy formation. The separate stellar components of the Galaxy cannot readily be understood if treated in isolation, but a reasonably self-consistent model for Galactic chemical evolution may be found if one considers together the chemical properties of the extreme spheroid, thick disk and thin disk populations of the Galaxy. The three major stellar components of the Galaxy are characterized by their distinct spatial distributions, metallicity structure, and kinematics, with the newly-identified thick disk being approximately three times more massive than the classical metal-poor, non-rotating extreme spheroid. Stellar evolution in the thick disk straightforwardly provides the desired pre-enrichment for resolution of the thin disk G dwarf problem

A NEW STELLAR CHEMO-KINEMATIC RELATION REVEALS THE MERGER HISTORY OF THE MILKY WAY DISK

International Nuclear Information System (INIS)

Minchev, I.; Chiappini, C.; Steinmetz, M.; De Jong, R. S.; Scannapieco, C.; Martig, M.; Boeche, C.; Grebel, E. K.; Zwitter, T.; Wyse, R. F. G.; Binney, J. J.; Bland-Hawthorn, J.; Bienaymé, O.; Famaey, B.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Kordopatis, G.; Helmi, A.; Lee, Y. S.

2014-01-01

The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine, so a proxy like the abundance of α elements (e.g., Mg) with respect to iron, [α/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the Radial Velocity Experiment survey with high-quality chemical and kinematic information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first gigayear of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early universe, which have affected the outer parts of the disk more strongly, and the subsequent radial migration of stars with cooler kinematics from the inner disk. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disk merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events

A NEW STELLAR CHEMO-KINEMATIC RELATION REVEALS THE MERGER HISTORY OF THE MILKY WAY DISK

Energy Technology Data Exchange (ETDEWEB)

Minchev, I.; Chiappini, C.; Steinmetz, M.; De Jong, R. S.; Scannapieco, C. [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Martig, M. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia); Boeche, C.; Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Zwitter, T. [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia); Wyse, R. F. G. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Binney, J. J. [Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford OX1 3NP (United Kingdom); Bland-Hawthorn, J. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Bienaymé, O.; Famaey, B. [CNRS, Observatoire Astronomique, Université de Strasbourg, 11 rue de l' Université, F-67000 Strasbourg (France); Freeman, K. C. [Australian National University, Canberra, ACT 0200 (Australia); Gibson, B. K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilmore, G.; Kordopatis, G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Helmi, A. [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands); Lee, Y. S. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); and others

2014-01-20

The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine, so a proxy like the abundance of α elements (e.g., Mg) with respect to iron, [α/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the Radial Velocity Experiment survey with high-quality chemical and kinematic information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first gigayear of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early universe, which have affected the outer parts of the disk more strongly, and the subsequent radial migration of stars with cooler kinematics from the inner disk. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disk merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events.

Buoyancy limits on magnetic viscosity stress-law scalings in quasi stellar object accretion disk models

International Nuclear Information System (INIS)

Sakimoto, P.J.

1985-01-01

Quasi-Stellar Objects (QSOs) are apparently the excessively bright nuclei of distant galaxies. They are thought to be powered by accretion disks surrounding supermassive black holes: however, proof of this presumption is hampered by major uncertainties in the viscous stress necessary for accretion to occur. Models generally assume an and hoc stress law which scales the stress with the total pressure. Near the black hole, radiation pressure dominates gas pressure; scaling the stress with the radiation pressure results in disk models that are thermally unstable and optically thin. This dissertation shows that a radiation pressure scaling for the stress is not possible if the viscosity is due to turbulent magnetic Maxwell stresses. The argument is one of internal self-consistency. First, four model accretion disks that bound the reasonably expected ranges of viscous stress scalings and vertical structures are constructed. Magnetic flux tubes of various initial field strengths are then placed within these models, nd their buoyancy is modeled numerically. In disks using the radiation pressure stress law scaling, low opacities allow rapid heat flow into the flux tubes: the tubes are extremely buoyant, and magnetic fields strong enough to provide the required stress cannot be retained. If an alternative gas pressure scaling for the stress is assumed, then the disks are optically thick; flux tubes have corresponding lower buoyancy, and magnetic fields strong enough to provide the stress can be retained for dynamically significant time periods

FIRST DETECTION OF THERMAL RADIOJETS IN A SAMPLE OF PROTO-BROWN DWARF CANDIDATES

Energy Technology Data Exchange (ETDEWEB)

Morata, Oscar [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China); Palau, Aina; González, Ricardo F. [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090 Morelia, Michoacán, México (Mexico); Gregorio-Monsalvo, Itziar de [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Ribas, Álvaro [European Space Astronomy Centre (ESA), P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Perger, Manuel [Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB—Facultat de Ciències, Torre C5—parell 2, E-08193 Bellaterra, Catalunya (Spain); Bouy, Hervé; Barrado, David; Huélamo, Nuria; Morales-Calderón, María [Centro de Astrobiología, INTA-CSIC, Dpto.Astrofísica, ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Eiroa, Carlos [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Bayo, Amelia, E-mail: omorata@asiaa.sinica.edu.tw [Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); and others

2015-07-01

We observed with the Jansky Very Large Array at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf (BD) candidates in Taurus in a search for thermal radio jets driven by the most embedded BDs. We detected for the first time four thermal radio jets in proto-BD candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE, and Herschel to build the spectral energy distribution (SED) of the objects in our sample, which are similar to typical Class I SEDs of young stellar objects (YSOs). The four proto-BD candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some excess of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the “excess” centimeter emission, the intrinsic properties of proto-BDs are consistent with a continuation of those of very low-mass stars to a lower mass range. Overall, our study favors the formation of BDs as a scaled-down version of low-mass stars.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

Energy Technology Data Exchange (ETDEWEB)

Chiang, Eugene; Fung, Jeffrey, E-mail: echiang@astro.berkeley.edu, E-mail: jeffrey.fung@berkeley.edu [Department of Astronomy, University of California at Berkeley, Campbell Hall, Berkeley, CA 94720-3411 (United States)

2017-10-10

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

NEBULAR AND STELLAR DUST EXTINCTION ACROSS THE DISK OF EMISSION-LINE GALAXIES ON KILOPARSEC SCALES

Energy Technology Data Exchange (ETDEWEB)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam [University of California, Riverside, CA 92512 (United States); Nayyeri, Hooshang; Miller, Sarah [University of California, Irvine, CA 92697 (United States); Sobral, David, E-mail: shemm001@ucr.edu [Universidade de Lisboa, PT1349-018 Lisbon (Portugal)

2015-11-20

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this

ABSENCE OF SIGNIFICANT COOL DISKS IN YOUNG STELLAR OBJECTS EXHIBITING REPETITIVE OPTICAL OUTBURSTS

Energy Technology Data Exchange (ETDEWEB)

Liu, Hauyu Baobab; Hirano, Naomi; Takami, Michihiro; Dong, Ruobing [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Galván-Madrid, Roberto; Rodríguez, Luis F.; Carrasco-González, Carlos [Instituto de Radioastronomía y Astrofísica, UNAM, A.P. 3-72, Xangari, Morelia, 58089 (Mexico); Vorobyov, Eduard I. [Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180, Vienna (Austria); Kóspál, Ágnes [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, 1525 Budapest (Hungary); Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Henning, Thomas [Max-Planck-Institut für Astronomie Königstuhl, 17 D-69117 Heidelberg (Germany); Hashimoto, Jun [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 Japan (Japan); Hasegawa, Yasuhiro, E-mail: baobabyoo@gmail.com [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2016-01-10

We report Submillimeter Array 1.3 mm high angular resolution observations toward the four EXor-type outbursting young stellar objects VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses M{sub dust} in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with M{sub dust} ∼ 9 × 10{sup −4}M{sub ⊙}. V1118 Ori has a marginal detection equivalent to M{sub dust} ∼ 6 × 10{sup −5}M{sub ⊙}. V1143 Ori has a non-detection also equivalent to M{sub dust} < 6 × 10{sup −5}M{sub ⊙}. For the nearest source, VY Tau, we get a surprising non-detection that provides a stringent upper limit M{sub dust} < 6 × 10{sup −6}M{sub ⊙}. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short-duration, repetitive optical outbursts seen in some EXors may be limited to the small-scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor-type outbursts.

Deconstructing Disk Velocity Distribution Functions in the Disk-Mass Survey

NARCIS (Netherlands)

Westfall, K. B.; Bershady, M. A.; Verheijen, M. A. W.; Andersen, D. R.; Swaters, R. A.

2008-01-01

We analyze integral-field ionized gas and stellar line-of-sight kinematics in the context of determining the stellar velocity ellipsoid for spiral galaxies observed by the Disk-Mass Survey. Our new methodology enables us to measure, for the first time, a radial gradient in the ellipsoid ratio

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 galactic disk as a two-fluid system: Consequences for the critical stellar velocity dispersion and the formation of condensations in the gas

International Nuclear Information System (INIS)

Jog, C.J.; Solomon, P.M.

1984-01-01

We examine the consequences of treating a galactic disk as a two-fluid system for the stability of the entire disk and for the stability and form of the gas in the disk. We find that the existence of even a small fraction of the total disk surface density in a cold fluid (that is, the gas) makes it much harder to stabilize the entire two-fluid disk. (C/sub s/,min)/sub 2-f/, the critical stellar velocity dispersion for a two-fluid disk in an increasing function of μ/sub g//μ/sub s/, the gas fraction, and μ/sub t//kappa, where μ/sub g/, μ/sub s/, and μ/sub t/ are the gaseous, stellar, and total disk surface densities and kappa is the epicyclic frequency. In the Galaxy, we find that (C/sub s/,min)/sub 2-f/ as a function of R peaks when μ/sub t//kappa peaks-at galactocentric radii of Rapprox.5-7 kpc; two-fluid instabilities are most likely to occur in this region. This region is coincident with the peak in the molecular cloud distribution in the Galaxy. At the higher effective gas density resulting from the growth of a two-fluid instability, the gas may become unstble, even when originally the gas by itself is stable. The wavelength of a typical (induced) gas instability in the inner galaxy is approx.400 pc, and it contains approx.10 7 M/sub sun/ of interstellar matter; these instabilities may be identified with clusters of giant molecular clouds. We suggest that many of the spiral features seen in gas-rich spiral galaxies may be material arms or arm segments resulting from sheared two-fluid gravitational instabilities. The analysis presented here is applicable to any general disk galaxy consisting of stars and gas

The offset dependent behavior of narrow optical emission features in the Red Rectangle proto-planetary nebula

NARCIS (Netherlands)

Wehres, N.; Linnartz, H.; Van Winckel, H.; Tielens, A. G. G. M.

Context. The Red Rectangle proto-planetary nebula provides a unique laboratory to study the physical conditions and chemical processes in stellar outflows. Snapshots of the ongoing chemical evolution are obtained by monitoring spectra as function of the offset from the central star. Aims. The focus

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

Misaligned disks in the binary protostar IRS 43

DEFF Research Database (Denmark)

Brinch, Christian; Jørgensen, Jes Kristian; Hogerheijde, Michiel R.

2016-01-01

and position angle and also with respect to the binary orbital plane. Each stellar component has an associated circumstellar disk while the binary is surrounded by a circumbinary disk. Together with archival VLA measurements of the stellar positions over 25 years, and assuming a circular orbit, we use our...

Disk Detective: Discovery of New Circumstellar Disk Candidates Through Citizen Science

Science.gov (United States)

Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; Garcia, Luciano; Jung, Dawoon; Lintott, Chris;

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

Science.gov (United States)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

Identifying Likely Disk-hosting M dwarfs with Disk Detective

Science.gov (United States)

Silverberg, Steven; Wisniewski, John; Kuchner, Marc J.; Disk Detective Collaboration

2018-01-01

M dwarfs are critical targets for exoplanet searches. Debris disks often provide key information as to the formation and evolution of planetary systems around higher-mass stars, alongside the planet themselves. However, less than 300 M dwarf debris disks are known, despite M dwarfs making up 70% of the local neighborhood. The Disk Detective citizen science project has identified over 6000 new potential disk host stars from the AllWISE catalog over the past three years. Here, we present preliminary results of our search for new disk-hosting M dwarfs in the survey. Based on near-infrared color cuts and fitting stellar models to photometry, we have identified over 500 potential new M dwarf disk hosts, nearly doubling the known number of such systems. In this talk, we present our methodology, and outline our ongoing work to confirm systems as M dwarf disks.

The DiskMass Survey. VIII. On the Relationship between Disk Stability and Star Formation

NARCIS (Netherlands)

Westfall, Kyle B.; Andersen, David R.; Bershady, Matthew A.; Martinsson, Thomas P. K.; Swaters, Robert A.; Verheijen, Marc A. W.

2014-01-01

We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo & Wiegert (Q RW), incorporating stellar

The DiskMass Survey. II. Error Budget

Science.gov (United States)

Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

2010-06-01

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

RED FRACTION AMONG SATELLITE GALAXIES WITH DISK-LIKE LIGHT PROFILES: EVIDENCE FOR INFLOW IN THE H I DISK

International Nuclear Information System (INIS)

Hester, J. A.

2010-01-01

The relationships between color, characterized with respect to the g - r red sequence; stellar structure, as determined using the i-band Sersic index; and group membership are explored using the Sloan Digital Sky Survey (SDSS). The new results place novel constraints on theories of galaxy evolution, despite the strong correlation between color and stellar structure. Observed correlations are of three independent types-those based on stellar structure, on the color of disk-like galaxies, and on the color of elliptical galaxies. Of particular note, the fraction of galaxies residing on the red sequence measured among galaxies with disk-like light profiles is enhanced for satellite galaxies compared to central galaxies. This fraction increases with group mass. When these new results are considered, theoretical treatments of galaxy evolution that adopt a gas accretion model centered on the hot galactic halo cannot consistently account for all observations of disk galaxies. The hypothesis is advanced that inflow within the extended H I disk prolongs star formation in satellite galaxies. When combined with partial ram pressure stripping (RPS) of this disk, this new scenario is consistent with the observations. This is demonstrated by applying an analytical model of RPS of the extended H I disk to the SDSS groups. These results motivate incorporating more complex modes of gas accretion into models of galaxy evolution, including cold mode accretion, an improved treatment of gas dynamics within disks, and disk stripping.

The physics of relic neutrinos

International Nuclear Information System (INIS)

Dighe, A.; Pastor, S.; Smirnov, A.

1998-12-01

We report on the main results presented at the workshop on the Physics of Relic Neutrinos. The study of relic neutrinos involves a broad spectrum of problems in particle physics, astrophysics and cosmology. Features of baryogenesis and leptogenesis could be imprinted in the properties of the relic neutrino sea. Relic neutrinos played a crucial role in the big bang nucleosynthesis. Being the hot component of the dark matter, they have participated in the structure formation in the universe. Although the direct detection of the sea seems impossible at this stage, there could be various indirect manifestations of these neutrinos which would allow us to study the properties of the sea both in the past and at the present epoch. (author)

WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

International Nuclear Information System (INIS)

Perets, Hagai B.; Kenyon, Scott J.

2013-01-01

Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10 –5 -10 –3 M ☉ , with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ☉ . When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

Circumstellar disks around binary stars in Taurus

International Nuclear Information System (INIS)

Akeson, R. L.; Jensen, E. L. N.

2014-01-01

We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10 –4 M ☉ . We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F mm ∝M ∗ 1.5--2.0 to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

THE ODD OFFSET BETWEEN THE GALACTIC DISK AND ITS BAR IN NGC 3906

Energy Technology Data Exchange (ETDEWEB)

Swardt, Bonita de [South African Astronomical Observatory, Observatory, 7935 Cape Town (South Africa); Sheth, Kartik; Kim, Taehyun; Muñoz-Mateos, Juan-Carlos [National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Stephen Pardy; Elena D’ Onghia; Eric Wilcots [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States); Hinz, Joannah [MMTO, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Regan, Michael W. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Athanassoula, E.; Bosma, Albert [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Buta, Ronald J. [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Cisternas, Mauricio; Erroz-Ferrer, Santiago [Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Comerón, Sébastien [Division of Astronomy, Department of Physical Sciences, University of Oulu, Oulu, FI-90014 (Finland); Gadotti, Dimitri A. [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Paz, Armando Gil de [Departamento de Astrofísica, Universidad Complutense de Madrid, Madrid E-28040 (Spain); Jarrett, Thomas H. [Astronomy Department, University of Cape Town, Rondebosch 7701 (South Africa); Elmegreen, Bruce G. [IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY 10598 (United States); Ho, Luis C. [The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); and others

2015-07-20

We use mid-infrared 3.6 and 4.5 μm imaging of NGC 3906 from the Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G) to understand the nature of an unusual offset between its stellar bar and the photometric center of an otherwise regular, circular outer stellar disk. We measure an offset of ∼910 pc between the center of the stellar bar and photometric center of the stellar disk; the bar center coincides with the kinematic center of the disk determined from previous HI observations. Although the undisturbed shape of the disk suggests that NGC 3906 has not undergone a significant merger event in its recent history, the most plausible explanation for the observed offset is an interaction. Given the relatively isolated nature of NGC 3906 this interaction could be with dark matter substructure in the galaxy's halo or from a recent interaction with a fast moving neighbor that remains to be identified. Simulations aimed at reproducing the observed offset between the stellar bar/kinematic center of the system and the photometric center of the disk are necessary to confirm this hypothesis and constrain the interaction history of the galaxy.

SMSS J130522.47-293113.0: a high-latitude stellar X-ray source with pc-scale outflow relics?

Science.gov (United States)

Da Costa, G. S.; Soria, R.; Farrell, S. A.; Bayliss, D.; Bessell, M. S.; Vogt, F. P. A.; Zhou, G.; Points, S. D.; Beers, T. C.; López-Sánchez, Á. R.; Bannister, K. W.; Bell, M.; Hancock, P. J.; Burlon, D.; Gaensler, B. M.; Sadler, E. M.; Tingay, S.; Keller, S. C.; Schmidt, B. P.; Tisserand, P.

2018-06-01

We report the discovery of an unusual stellar system SMSS J130522.47-293113.0. The optical spectrum is dominated by a blue continuum together with emission lines of hydrogen, neutral, and ionized helium, and the N III, C III blend at ˜4640-4650 Å. The emission-line profiles vary in strength and position on time-scales as short as 1 d, while optical photometry reveals fluctuations of as much as ˜0.2 mag in g on time-scales as short as 10-15 min. The system is a weak X-ray source (f0.3-10 = (1.2 ± 0.1) × 10-13 ergs cm2 s-1 in the 0.3-10 keV band) but is not detected at radio wavelengths (3σ upper limit of 50 μJy at 5.5 GHz). The most intriguing property of the system, however, is the existence of two `blobs', a few arcsec in size, that are symmetrically located 3{^'.}8 (2.2 pc for our preferred system distance of ˜2 kpc) each side of the central object. The blobs are detected in optical and near-IR broad-band images but do not show any excess emission in H α images. We discuss the interpretation of the system, suggesting that the central object is most likely a nova-like CV, and that the blobs are relics of a pc-scale accretion-powered collimated outflow.

CIRCUMSTELLAR DEBRIS DISKS: DIAGNOSING THE UNSEEN PERTURBER

Energy Technology Data Exchange (ETDEWEB)

Nesvold, Erika R. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd., Washington, DC 20015 (United States); Naoz, Smadar; Vican, Laura [Department of Physics and Astronomy, UCLA, 475 Portola Plaza, Los Angeles, CA 90095 (United States); Farr, Will M. [School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT (United Kingdom)

2016-07-20

The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N -body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

International Nuclear Information System (INIS)

Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik

2016-01-01

Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R g , where R g  = 2GM/c 2 is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations

WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-02-20

Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

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.

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

Energy Technology Data Exchange (ETDEWEB)

Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Greenwood, Aaron; Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Henning, Thomas [Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany); Ménard, François [Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France); Dent, William R. F. [Department of Engineering, Atacama Large Millimeter/submillimeter Array (ALMA) Santiago Central Offices, Alonso de Córdova 3107, Vitacura, Casilla 763 0355, Santiago (Chile); II, Neal J. Evans, E-mail: equant@lpl.arizona.edu [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States)

2017-06-01

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

International Nuclear Information System (INIS)

Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria; Greenwood, Aaron; Kamp, Inga; Henning, Thomas; Ménard, François; Dent, William R. F.; II, Neal J. Evans

2017-01-01

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

Circumstellar disks around binary stars in Taurus

Energy Technology Data Exchange (ETDEWEB)

Akeson, R. L. [NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, CA 91125 (United States); Jensen, E. L. N. [Swarthmore College, Department of Physics and Astronomy, Swarthmore, PA 19081 (United States)

2014-03-20

We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup –4} M {sub ☉}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}∝M{sub ∗}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

Relics in galaxy clusters at high radio frequencies

Science.gov (United States)

Kierdorf, M.; Beck, R.; Hoeft, M.; Klein, U.; van Weeren, R. J.; Forman, W. R.; Jones, C.

2017-04-01

Aims: We investigated the magnetic properties of radio relics located at the peripheries of galaxy clusters at high radio frequencies, where the emission is expected to be free of Faraday depolarization. The degree of polarization is a measure of the magnetic field compression and, hence, the Mach number. Polarization observations can also be used to confirm relic candidates. Methods: We observed three radio relics in galaxy clusters and one radio relic candidate at 4.85 and 8.35 GHz in total emission and linearly polarized emission with the Effelsberg 100-m telescope. In addition, we observed one radio relic candidate in X-rays with the Chandra telescope. We derived maps of polarization angle, polarization degree, and Faraday rotation measures. Results: The radio spectra of the integrated emission below 8.35 GHz can be well fitted by single power laws for all four relics. The flat spectra (spectral indices of 0.9 and 1.0) for the so-called Sausage relic in cluster CIZA J2242+53 and the so-called Toothbrush relic in cluster 1RXS 06+42 indicate that models describing the origin of relics have to include effects beyond the assumptions of diffuse shock acceleration. The spectra of the radio relics in ZwCl 0008+52 and in Abell 1612 are steep, as expected from weak shocks (Mach number ≈2.4). Polarization observations of radio relics offer a method of measuring the strength and geometry of the shock front. We find polarization degrees of more than 50% in the two prominent Mpc-sized radio relics, the Sausage and the Toothbrush, which are among the highest percentages of linear polarization detected in any extragalactic radio source to date. This is remarkable because the large beam size of the Effelsberg single-dish telescope corresponds to linear extensions of about 300 kpc at 8.35 GHz at the distances of the relics. The high degree of polarization indicates that the magnetic field vectors are almost perfectly aligned along the relic structure, as expected for shock

DISCOVERY OF AN Hα EMITTING DISK AROUND THE SUPERMASSIVE BLACK HOLE OF M31

International Nuclear Information System (INIS)

Menezes, R. B.; Steiner, J. E.; Ricci, T. V.

2013-01-01

Due to its proximity, the mass of the supermassive black hole in the nucleus of the Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk which surrounds it. We report here the discovery of an eccentric Hα emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0 +0.8 –1.0 × 10 7 M ☉ for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1σ level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-σ relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Hα emitting disk. This result suggests that the stellar and the Hα emitting disks are intrinsically different from each other. A plausible explanation is that the Hα emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Hα emission is, at least partially, generated by stars.

MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

Energy Technology Data Exchange (ETDEWEB)

Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024 (United States)

2016-03-10

Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R{sub g}, where R{sub g} = 2GM/c{sup 2} is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.

ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

International Nuclear Information System (INIS)

Spalding, Christopher; Batygin, Konstantin; Adams, Fred C.

2014-01-01

Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function

Proto-planetary nebulae

International Nuclear Information System (INIS)

Zuckerman, B.

1978-01-01

A 'proto-planetary nebula' or a 'planetary nebula progenitor' is the term used to describe those objects that are losing mass at a rate >approximately 10 -5 Msolar masses/year (i.e. comparable to mass loss rates in planetary nebulae with ionized masses >approximately 0.2 Msolar masses) and which, it is believed, will become planetary nebulae themselves within 5 years. It is shown that most proto-planetary nebulae appear as very red objects although a few have been 'caught' near the middle of the Hertzsprung-Russell diagram. The precursors of these proto-planetaries are the general red giant population, more specifically probably Mira and semi-regular variables. (Auth.)end

The applicability of the viscous α-parameterization of gravitational instability in circumstellar disks

Science.gov (United States)

Vorobyov, E. I.

2010-01-01

We study numerically the applicability of the effective-viscosity approach for simulating the effect of gravitational instability (GI) in disks of young stellar objects with different disk-to-star mass ratios ξ . We adopt two α-parameterizations for the effective viscosity based on Lin and Pringle [Lin, D.N.C., Pringle, J.E., 1990. ApJ 358, 515] and Kratter et al. [Kratter, K.M., Matzner, Ch.D., Krumholz, M.R., 2008. ApJ 681, 375] and compare the resultant disk structure, disk and stellar masses, and mass accretion rates with those obtained directly from numerical simulations of self-gravitating disks around low-mass (M∗ ∼ 1.0M⊙) protostars. We find that the effective viscosity can, in principle, simulate the effect of GI in stellar systems with ξ≲ 0.2- 0.3 , thus corroborating a similar conclusion by Lodato and Rice [Lodato, G., Rice, W.K.M., 2004. MNRAS 351, 630] that was based on a different α-parameterization. In particular, the Kratter et al.'s α-parameterization has proven superior to that of Lin and Pringle's, because the success of the latter depends crucially on the proper choice of the α-parameter. However, the α-parameterization generally fails in stellar systems with ξ≳ 0.3 , particularly in the Classes 0 and I phases of stellar evolution, yielding too small stellar masses and too large disk-to-star mass ratios. In addition, the time-averaged mass accretion rates onto the star are underestimated in the early disk evolution and greatly overestimated in the late evolution. The failure of the α-parameterization in the case of large ξ is caused by a growing strength of low-order spiral modes in massive disks. Only in the late Class II phase, when the magnitude of spiral modes diminishes and the mode-to-mode interaction ensues, may the effective viscosity be used to simulate the effect of GI in stellar systems with ξ≳ 0.3 . A simple modification of the effective viscosity that takes into account disk fragmentation can somewhat improve

CLUSTER DYNAMICS LARGELY SHAPES PROTOPLANETARY DISK SIZES

Energy Technology Data Exchange (ETDEWEB)

Vincke, Kirsten; Pfalzner, Susanne, E-mail: kvincke@mpifr-bonn.mpg.de [Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

2016-09-01

To what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. This is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 Myr. In previous studies, the effect of the gas on the cluster dynamics has often been neglected; this is remedied here. Using the code NBody6++, we study the stellar dynamics in different developmental phases—embedded, expulsion, and expansion—including the gas, and quantify the effect of fly-bys on the disk size. We concentrate on massive clusters (M {sub cl} ≥ 10{sup 3}–6 ∗ 10{sup 4} M {sub Sun}), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. By contrast, disks in sparser clusters are initially less affected, but because these clusters expand more slowly, 13% of disks are truncated after gas expulsion. For ONC-like clusters, we find that disks larger than 500 au are usually affected by the environment, which corresponds to the observation that 200 au-sized disks are common. For NGC 6611-like clusters, disk sizes are cut-down on average to roughly 100 au. A testable hypothesis would be that the disks in the center of NGC 6611 should be on average ≈20 au and therefore considerably smaller than those in the ONC.

A DWARF TRANSITIONAL PROTOPLANETARY DISK AROUND XZ TAU B

Energy Technology Data Exchange (ETDEWEB)

Osorio, Mayra; Macías, Enrique; Anglada, Guillem; Gómez, José F. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Carrasco-González, Carlos; Galván-Madrid, Roberto; Zapata, Luis; Rodríguez, Luis F. [Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Calvet, Nuria [Department of Astronomy, University of Michigan, 825 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Nagel, Erick [Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Gto 36240 (Mexico); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC)-Institut de Ciències del Cosmos (UB)/IEEC, Martí i Franquès 1, E-08028 Barcelona (Spain); Zhu, Zhaohuan, E-mail: osorio@iaa.es [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2016-07-01

We report the discovery of a dwarf protoplanetary disk around the star XZ Tau B that shows all the features of a classical transitional disk but on a much smaller scale. The disk has been imaged with the Atacama Large Millimeter/submillimeter Array (ALMA), revealing that its dust emission has a quite small radius of ∼3.4 au and presents a central cavity of ∼1.3 au in radius that we attribute to clearing by a compact system of orbiting (proto)planets. Given the very small radii involved, evolution is expected to be much faster in this disk (observable changes in a few months) than in classical disks (observable changes requiring decades) and easy to monitor with observations in the near future. From our modeling we estimate that the mass of the disk is large enough to form a compact planetary system.

Stellar dynamics and galactic evolution

International Nuclear Information System (INIS)

Gilmore, G.; Kuijken, K.; Wyse, R.F.G.

1989-01-01

Solar neighbourhood observations have the unique capability of providing detailed study of the consequences of the early evolution of the Galaxy. Important examples of this capability include determination of the distribution of luminous and unseen mass in the Galaxy, and deduction of the rate of star formation and chemical evolution in the proto-Galaxy. We describe a new method to determine the distribution of mass in the Galactic disk. We reinvestigate determinations of the local volume mass density (the Oort limit) and show there to be serious internal inconsistencies in the available data. The most likely value for the local volume mass density, based on old stars and with kinematic models consistent with the age structure of the local disk is ∼ 0.1 solar mass pc -3 , though this value is still poorly determined. Thus, there is no significant evidence for any missing mass associated with the Galactic disk. We also reinvestigate observational data on the chemical abundances and kinematics of old stars in the Galaxy. The (Intermediate Population II) thick disk stars are most likely as old as the globular clusters, and kinematically distinct from the old disk. This favours models of thick disk origin involving a discrete disruptive event, such as the accretion of a satellite of the Galaxy early in the evolution of the Galactic disk. (author)

Transport of gas from disk to halo in starforming galaxies

Directory of Open Access Journals (Sweden)

Shevchenko Mikhail G.

2017-12-01

Full Text Available Using 3-D gas dynamic simulations, we study the supernova (SNe driven transport of gas from the galactic disk. We assume that SNe are distributed randomly and uniformly in the galactic plane and we consider sufficiently high volume SNe rates that are typical for starforming galaxies: νSN = (0.3 − 3 × 10−11 pc−3 yr−1. We found that under such conditions, a major part of gas locked initially in the galactic disk is transported up to ∼ 1 − 5 stellar scale heights within several millions years. As expected gas transport is more efficient in the case of a thinner stellar disk. An decrease/increase of SN rate in the galactic disk with the same stellar scale height leads to an enlarging/shortening of time scale for gas transport. Independent of SN rate, the major fraction of the swept up gas is in the cold phase (T 106 K is elevated to larger heights than cold gas.

The AMBRE project: The thick thin disk and thin thick disk of the Milky Way

Science.gov (United States)

Hayden, M. R.; Recio-Blanco, A.; de Laverny, P.; Mikolaitis, S.; Worley, C. C.

2017-11-01

We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPS survey. These stars have accurate astrometric information from Gaia DR1, providing reliable age estimates with relative uncertainties of ±1 or 2 Gyr and allowing precise orbital determinations. The sample is split based on chemistry into a low-[Mg/Fe] sequence, which are often identified as thin disk stellar populations, and high-[Mg/Fe] sequence, which are often associated with thick disk stellar populations. We find that the high-[Mg/Fe] chemical sequence has extended star formation for several Gyr and is coeval with the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- and high-[Mg/Fe] sequences were forming stars at the same time. We find that the high-[Mg/Fe] stellar populations are only vertically extended for the oldest, most-metal poor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion for the low- and high-[Mg/Fe] sequences, the high-[Mg/Fe] sequence has lower vertical velocity dispersion than the low-[Mg/Fe] sequence for stars of similar age. This means that identifying either group as thin or thick disk based on chemistry is misleading. The stars belonging to the high-[Mg/Fe] sequence have perigalacticons that originate in the inner disk, while the perigalacticons of stars on the low-[Mg/Fe] sequence are generally around the solar neighborhood. From the orbital properties of the stars, the high-[Mg/Fe] and low-[Mg/Fe] sequences are most likely a reflection of the chemical enrichment history of the inner and outer disk populations, respectively; radial mixing causes both populations to be observed in situ at the solar position. Based on these results, we emphasize that it is important to be clear in defining what populations are being referenced when using the terms thin and thick disk, and that ideally the term thick disk should be reserved for purely geometric definitions to avoid confusion and be consistent with definitions in external

The Disk Mass Project: breaking the disk-halo degeneracy

NARCIS (Netherlands)

Verheijen, Marc A. W.; Bershady, Matthew A.; Swaters, Rob A.; Andersen, David R.; Westfall, Kyle B.; DE JONG, R. S.

2007-01-01

Little is known about the content and distribution of dark matter in spiral galaxies. To break the degeneracy in galaxy rotation curve decompositions, which allows a wide range of dark matter halo density profiles, an independent measure of the mass surface density of stellar disks is needed. Here,

TESTING THE HYPOTHESIS THAT METHANOL MASER RINGS TRACE CIRCUMSTELLAR DISKS: HIGH-RESOLUTION NEAR-INFRARED AND MID-INFRARED IMAGING

International Nuclear Information System (INIS)

De Buizer, James M.; Bartkiewicz, Anna; Szymczak, Marian

2012-01-01

Milliarcsecond very long baseline interferometry maps of regions containing 6.7 GHz methanol maser emission have lead to the recent discovery of ring-like distributions of maser spots and the plausible hypothesis that they may be tracing circumstellar disks around forming high-mass stars. We aimed to test this hypothesis by imaging these regions in the near- and mid-infrared at high spatial resolution and compare the observed emission to the expected infrared morphologies as inferred from the geometries of the maser rings. In the near-infrared we used the Gemini North adaptive optics system of ALTAIR/NIRI, while in the mid-infrared we used the combination of the Gemini South instrument T-ReCS and super-resolution techniques. Resultant images had a resolution of ∼150 mas in both the near-infrared and mid-infrared. We discuss the expected distribution of circumstellar material around young and massive accreting (proto)stars and what infrared emission geometries would be expected for the different maser ring orientations under the assumption that the masers are coming from within circumstellar disks. Based upon the observed infrared emission geometries for the four targets in our sample and the results of spectral energy distribution modeling of the massive young stellar objects associated with the maser rings, we do not find compelling evidence in support of the hypothesis that methanol masers rings reside in circumstellar disks.

Relic gravitational waves and cosmology

International Nuclear Information System (INIS)

Grishchuk, Leonid P

2005-01-01

The paper begins with a brief recollection of interactions of the author with Ya B Zeldovich in the context of the study of relic gravitational waves. The principles and early results on the quantum-mechanical generation of cosmological perturbations are then summarized. The expected amplitudes of relic gravitational waves differ in various frequency windows, and therefore the techniques and prospects of their detection are distinct. One section of the paper describes the present state of efforts in direct detection of relic gravitational waves. Another section is devoted to indirect detection via the anisotropy and polarization measurements of the cosmic microwave background (CMB) radiation. It is emphasized throughout the paper that the inference about the existence and expected amount of relic gravitational waves is based on a solid theoretical foundation and the best available cosmological observations. It is also explained in great detail what went wrong with the so-called 'inflationary gravitational waves', whose amount is predicted by inflationary theorists to be negligibly small, thus depriving them of any observational significance. (reviews of topical problems)

Herschel/SPIRE observations of the dusty disk of NGC 4244

NARCIS (Netherlands)

Holwerda, B. W.; Bianchi, S.; Boker, T.; Radburn-Smith, D.; de Jong, R. S.; Baes, M.; van der Kruit, P. C.; Xilouris, M.; Gordon, K. D.; Dalcanton, J. J.

We present Herschel/SPIRE images at 250, 350, and 500 mu m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the

Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced?

Science.gov (United States)

Zanazzi, J. J.; Lai, Dong

2018-04-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary disks, and inclined binary companions may tilt the stellar spin axis with respect to the disk's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disk evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disk photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disk-binary systems. We take into account planet-disk interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disk via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with "cold" Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

DISCOVERY OF AN H{alpha} EMITTING DISK AROUND THE SUPERMASSIVE BLACK HOLE OF M31

Energy Technology Data Exchange (ETDEWEB)

Menezes, R. B.; Steiner, J. E.; Ricci, T. V., E-mail: robertobm@astro.iag.usp.br [Instituto de Astronomia Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP CEP 05508-090 (Brazil)

2013-01-10

Due to its proximity, the mass of the supermassive black hole in the nucleus of the Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk which surrounds it. We report here the discovery of an eccentric H{alpha} emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 7} M{sub Sun} for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1{sigma} level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-{sigma} relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the H{alpha} emitting disk. This result suggests that the stellar and the H{alpha} emitting disks are intrinsically different from each other. A plausible explanation is that the H{alpha} emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the H{alpha} emission is, at least partially, generated by stars.

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.

Evolution of accretion disks in tidal disruption events

Energy Technology Data Exchange (ETDEWEB)

Shen, Rong-Feng [Current address: Racah Institute of Physics, Hebrew University of Jerusalem, Israel. (Israel); Matzner, Christopher D., E-mail: rf.shen@mail.huji.ac.il, E-mail: matzner@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, M5S 3H4 (Canada)

2014-04-01

During a stellar tidal disruption event (TDE), an accretion disk forms as stellar debris returns to the disruption site and circularizes. Rather than being confined within the circularizing radius, the disk can spread to larger radii to conserve angular momentum. A spreading disk is a source of matter for re-accretion at rates that may exceed the later stellar fallback rate, although a disk wind can suppress its contribution to the central black hole accretion rate. A spreading disk is detectible through a break in the central accretion rate history or, at longer wavelengths, by its own emission. We model the evolution of TDE disk size and accretion rate by accounting for the time-dependent fallback rate, for the influence of wind losses in the early advective stage, and for the possibility of thermal instability for accretion rates intermediate between the advection-dominated and gas-pressure-dominated states. The model provides a dynamic basis for modeling TDE light curves. All or part of a young TDE disk will precess as a solid body because of the Lense-Thirring effect, and precession may manifest itself as a quasi-periodic modulation of the light curve. The precession period increases with time. Applying our results to the jetted TDE candidate Swift J1644+57, whose X-ray light curve shows numerous quasi-periodic dips, we argue that the data best fit a scenario in which a main-sequence star was fully disrupted by an intermediate mass black hole on an orbit significantly inclined from the black hole equator, with the apparent jet shutoff at t = 500 days corresponding to a disk transition from the advective state to the gas-pressure-dominated state.

THE EVOLUTION OF PROTOPLANETARY DISKS IN THE ARCHES CLUSTER

International Nuclear Information System (INIS)

Olczak, C.; Kaczmarek, T.; Pfalzner, S.; Harfst, S.; Portegies Zwart, S.

2012-01-01

Most stars form in a cluster environment. These stars are initially surrounded by disks from which potentially planetary systems form. Of all cluster environments, starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favor rapid destruction of circumstellar disks via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field, we investigate the effect of stellar encounters on circumstellar disks in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic center, only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one-third of the circumstellar disks in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a weaker second pair of tidal tails that is overpopulated by disk-poor stars. Two predictions arise from our study. (1) If not destroyed by photoevaporation protoplanetary disks of massive late B- and early O-type stars represent the most likely hosts of planet formation in starburst clusters. (2) Multi-epoch K- and L-band photometry of the Arches cluster would provide the kinematically selected membership sample required to detect the additional pair of disk-poor tidal tails.

EMBEDDED PROTOSTELLAR DISKS AROUND (SUB-)SOLAR STARS. II. DISK MASSES, SIZES, DENSITIES, TEMPERATURES, AND THE PLANET FORMATION PERSPECTIVE

International Nuclear Information System (INIS)

Vorobyov, Eduard I.

2011-01-01

We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun , M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun , M mdn d,CI = 0.15 M sun , respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun . Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

From Disks to Planets: The Making of Planets and Their Early Atmospheres. An Introduction

Science.gov (United States)

Lammer, Helmut; Blanc, Michel

2018-03-01

This paper is an introduction to volume 56 of the Space Science Series of ISSI, "From disks to planets—the making of planets and their proto-atmospheres", a key subject in our quest for the origins and evolutionary paths of planets, and for the causes of their diversity. Indeed, as exoplanet discoveries progressively accumulated and their characterization made spectacular progress, it became evident that the diversity of observed exoplanets can in no way be reduced to the two classes of planets that we are used to identify in the solar system, namely terrestrial planets and gas or ice giants: the exoplanet reality is just much broader. This fact is no doubt the result of the exceptional diversity of the evolutionary paths linking planetary systems as a whole as well as individual exoplanets and their proto-atmospheres to their parent circumstellar disks: this diversity and its causes are exactly what this paper explores. For each of the main phases of the formation and evolution of planetary systems and of individual planets, we summarize what we believe we understand and what are the important open questions needing further in-depth examination, and offer some suggestions on ways towards solutions. We start with the formation mechanisms of circumstellar disks, with their gas and disk components in which chemical composition plays a very important role in planet formation. We summarize how dust accretion within the disk generates planet cores, while gas accretion on these cores can lead to the diversity of their fluid envelopes. The temporal evolution of the parent disk itself, and its final dissipation, put strong constraints on how and how far planetary formation can proceed. The radiation output of the central star also plays an important role in this whole story. This early phase of planet evolution, from disk formation to dissipation, is characterized by a co-evolution of the disk and its daughter planets. During this co-evolution, planets and their

From circumstellar disks to planetary systems: observation and modeling of protoplanetary disks

OpenAIRE

Macías Quevedo, Enrique

2016-01-01

The existence of exoplanetary systems was first predicted after the discovery of accretion disks around young stars. Nowadays, with nearly 3500 exoplanets discovered, and almost 5000 more candidates identified by the Kepler space mission, planetary systems are now known to be ubiquitous around low-mass stars. The formation of these systems takes place during the stellar formation itself, from the dust and gas orbiting around the star in the protoplanetary disks. However, the process that lead...

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.

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.

Inside ProtoDune

CERN Multimedia

Brice, Maximilien

2017-01-01

The protoDUNE experimental program is designed to test and validate the technologies and design that will be applied to the construction of the DUNE Far Detector at the Sanford Underground Research Facility (SURF). The protoDUNE detectors will be run in a dedicated beam line at the CERN SPS accelerator complex. The rate and volume of data produced by these detectors will be substantial and will require extensive system design and integration effort. As of Fall 2015, "protoDUNE" is the official name for the two apparatuses to be used in CERN beam test: single-phase and dual-phase LArTPC detectors. Each received a formal CERN experiment designation: NP02 for the dual-phase detector. NP04 for single-phase detector.

Formation of globular cluster candidates in merging proto-galaxies at high redshift: a view from the FIRE cosmological simulations

Science.gov (United States)

Kim, Ji-hoon; Ma, Xiangcheng; Grudić, Michael Y.; Hopkins, Philip F.; Hayward, Christopher C.; Wetzel, Andrew; Faucher-Giguère, Claude-André; Kereš, Dušan; Garrison-Kimmel, Shea; Murray, Norman

2018-03-01

Using a state-of-the-art cosmological simulation of merging proto-galaxies at high redshift from the FIRE project, with explicit treatments of star formation and stellar feedback in the interstellar medium, we investigate the formation of star clusters and examine one of the formation hypotheses of present-day metal-poor globular clusters. We find that frequent mergers in high-redshift proto-galaxies could provide a fertile environment to produce long-lasting bound star clusters. The violent merger event disturbs the gravitational potential and pushes a large gas mass of ≳ 105-6 M⊙ collectively to high density, at which point it rapidly turns into stars before stellar feedback can stop star formation. The high dynamic range of the reported simulation is critical in realizing such dense star-forming clouds with a small dynamical time-scale, tff ≲ 3 Myr, shorter than most stellar feedback time-scales. Our simulation then allows us to trace how clusters could become virialized and tightly bound to survive for up to ˜420 Myr till the end of the simulation. Because the cluster's tightly bound core was formed in one short burst, and the nearby older stars originally grouped with the cluster tend to be preferentially removed, at the end of the simulation the cluster has a small age spread.

Research on Splicing Method of Digital Relic Fragment Model

Science.gov (United States)

Yan, X.; Hu, Y.; Hou, M.

2018-04-01

In the course of archaeological excavation, a large number of pieces of cultural relics were unearthed, and the restoration of these fragments was done manually by traditional arts and crafts experts. In this process, cultural relics experts often try to splice the existing cultural relics, and then use adhesive to stick together the fragments of correct location, which will cause irreversible secondary damage to cultural relics. In order to minimize such damage, the surveyors combine 3D laser scanning with computer technology, and use the method of establishing digital cultural relics fragments model to make virtual splicing of cultural relics. The 3D software on the common market can basically achieve the model translation and rotation, using this two functions can be achieved manually splicing between models, mosaic records after the completion of the specific location of each piece of fragments, so as to effectively reduce the damage to the relics had tried splicing process.

Stellar Angular Momentum Distributions and Preferential Radial Migration

Science.gov (United States)

Wyse, Rosemary; Daniel, Kathryne J.

2018-04-01

I will present some results from our recent investigations into the efficiency of radial migration in stellar disks of differing angular momentum distributions, within a given adopted 2D spiral disk potential. We apply to our models an analytic criterion that determines whether or not individual stars are in orbits that could lead to radial migration around the corotation resonance. We couch our results in terms of the local stellar velocity dispersion and find that the fraction of stars that could migrate radially decreases as the velocity dispersion increases. I will discuss implications and comparisons with the results of other approaches.

Chemical constraints on the formation of the Galactic thick disk

Directory of Open Access Journals (Sweden)

Feltzing S.

2012-02-01

Full Text Available We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R = 45000 to 110 000 and high signal-to-noise (S/N ≈ 150 to 300. The main findings include: (1 at a given metallicity, the thick disk abundance trends are more α-enhanced than those of the thin disk; (2 the metal-rich limit of the thick disk reaches at least solar metallicities; (3 the metal-poor limit of the thin disk is around [Fe/H] ≈−0.8; (4 the thick disk shows an age-metallicity gradient; (5 the thin disk does not show an age-metallicity gradient; (6 the most metal-rich thick disk stars at [Fe/H] ≈ 0 are significantly older than the most metal-poor thin disk stars at [Fe/H] ≈−0.7; (7 based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8 age criteria appears to produce thin and thick disk stellar samples with less contamination.

Spectral energy distributions of T Tauri stars - disk flaring and limits on accretion

International Nuclear Information System (INIS)

Kenyon, S.J.; Hartmann, L.

1987-01-01

The Adams et al. (1987) conclusion that much of the IR excess emission in the spectral energy distribution of T Tauri stars arises from reprocessing of stellar radiation by a dusty circumstellar disk is presently supported by analyses conducted in light of various models of these stars' spectra. A low mass reprocessing disk can, however, produce these spectra as well as a massive accretion disk. The detection of possible boundary layer radiation in the optical and near-UV regions poses the strongest limits on accretion rates. Disk accretion in the T Tauri phase does not significantly modify stellar evolution. 85 references

NGC 1277: A MASSIVE COMPACT RELIC GALAXY IN THE NEARBY UNIVERSE

Energy Technology Data Exchange (ETDEWEB)

Trujillo, Ignacio; Vazdekis, Alexandre [Instituto de Astrofísica de Canarias, c/Vía Láctea s/n, E-38205-La Laguna, Tenerife (Spain); Ferré-Mateu, Anna [Subaru Telescope, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Balcells, Marc [Isaac Newton Group of Telescopes, E-38700 Santa Cruz de La Palma, Canary Islands (Spain); Sánchez-Blázquez, Patricia, E-mail: trujillo@iac.es [Departamento de Física Teórica, Universidad Autónoma de Madrid, E-28049, Cantoblanco, Madrid (Spain)

2014-01-10

As early as 10 Gyr ago, galaxies with more than 10{sup 11} M {sub ☉} of stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (≲0.1%) may have survived untouched until today. Searches for such relic galaxies, useful windows to explore the early universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high redshift (M {sub *} ≳ 10{sup 11} M {sub ☉}; R{sub e} ≲ 1.5 kpc) have been found in the local universe, but their stars are far too young for the galaxy to be a relic galaxy. This paper explores the first case of a nearby galaxy, NGC 1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfills many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H] = 0.20 ± 0.04 with a smooth decline toward the outer regions) and α-enriched ([α/Fe] = 0.4 ± 0.1). This suggests a very short formation time scale for the bulk of the stars in this galaxy. This object also rotates very fast (V {sub rot} ∼ 300 km s{sup –1}) and has a large central velocity dispersion (σ > 300 km s{sup –1}). NGC 1277 allows the exploration in full detail of properties such as the structure, internal dynamics, metallicity, and initial mass function as they were at ∼10-12 Gyr ago when the first massive galaxies were built.

Observational Corollaries of Proto-AGN: Understanding Formation of Supermassive Black Hole Seeds

Science.gov (United States)

Shlosman, Isaac

2016-10-01

Formation of supermassive black holes (SMBHs) is still an enigma. Recent detections of high-z quasars which harbor massive SMBHs provide a challenge to models of structure buildup in the universe. Main alternatives for the formation of SMBH seeds are (1) remnants of Population III stars, and (2) a direct baryonic collapse within dark matter (DM) halos of 10^8 Mo -- first halos whose virial temperature exceeds 10^4 K, and which can lead to the formation of proto-AGN -- luminous pre-SMBH objects. Potentially, this can involve both high-z objects as well as low-z dwarf galaxies in voids. We focus on the direct collapse in 10^8 Mo halos which circumvents the pitfalls of Pop III remnants. The collapse can proceed via a radiation pressure-supported quasistar -- with a modified blackbody continuum. Such a configuration requires a very efficient angular momentum transfer. Or, it can form a thick, differentially rotating, self-gravitating disk, which is associated with an X-ray-infrared continuum and Seyfert-level luminosity, anisotropic emission, massive bi-conical outflows, and will be a powerful source of the Ly-alpha emission. We propose to perform radiative transfer in the continuum and hydrogen lines (e.g., Lyman and Balmer), using our models of proto-AGN, and do it on-the-fly -- concurrently with the collapse. We shall test the path to quasistellar and disky proto-AGN, produce first synthetic spectra of proto-AGN, and address the issue of feasibility of their detection by the JWST. Finally, we shall develop the strategy of searching for these objects at high- and low-z, based on the specific features in the spectra and associated variability.

Circumstellar and circumplanetary disks

Science.gov (United States)

Chiang, Eugene

2000-11-01

This thesis studies disks in three astrophysical contexts: (1)protoplanetary disks; (2)the Edgeworth-Kuiper Belt; and (3)planetary rings. We derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 μm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on. We present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, Σ(surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2 M⊕ and 1 × 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU. We propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self- gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1)velocity dispersions are enhanced by resonant satellite perturbations, and (2)the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with

Characterizing Debris Disks in the Late Stages of Planet Formation

Science.gov (United States)

White, Jacob

2018-01-01

The planet formation process shapes the morphology and grain size distribution of circumstellar disks, encoding the formation history of a given system. Remnants of planet formation, such as comets and asteroids, collisionally evolve and can replenish the dust and small solids that would otherwise be cleared on short timescales. These grains are observed through reprocessed starlight at submm to cm wavelengths.The spectrum of the mm/cm emission reveals details of the grain population. However, one confounding parameter in studying these grains around stars is the stars themselves. The emission from stars in the mm/cm is nontrivial and generally not well-constrained. I will present examples of debris systems (HD 141569 and Fomalhaut) studied by ALMA and the VLA, in which unconstrained stellar emission may be contributing to the observed flux densities. Such contamination in turn biases the inferred emission from the disk and the corresponding dust properties. In some cases, the behavior of the observed A/B stars can exhibit an emission profile that has similarities to that of the Sun's mm/cm emission, although the same processes are not thought to necessarily occur in the atmospheres of massive stars.To address the uncertainty in stellar emission at mm/cm wavelengths, we present ongoing radio observations (JCMT, SMA, VLA) of Sirius A, which is a bright, nearby star with no known debris. We seek to use this system to set an observationally determined standard for stellar atmosphere modeling and debris disk studies around A stars, as well as to take the first step toward characterizing potential intrinsic uncertainty in stellar emission at these wavelengths. This talk will highlight the effort to characterize stellar atmospheres through a project known as MESAS (Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths) which is imperative to the success of current and future debris disk studies.

Application of 3d Model of Cultural Relics in Virtual Restoration

Science.gov (United States)

Zhao, S.; Hou, M.; Hu, Y.; Zhao, Q.

2018-04-01

In the traditional cultural relics splicing process, in order to identify the correct spatial location of the cultural relics debris, experts need to manually splice the existing debris. The repeated contact between debris can easily cause secondary damage to the cultural relics. In this paper, the application process of 3D model of cultural relic in virtual restoration is put forward, and the relevant processes and ideas are verified with the example of Terracotta Warriors data. Through the combination of traditional cultural relics restoration methods and computer virtual reality technology, virtual restoration of high-precision 3D models of cultural relics can provide a scientific reference for virtual restoration, avoiding the secondary damage to the cultural relics caused by improper restoration. The efficiency and safety of the preservation and restoration of cultural relics have been improved.

APPLICATION OF 3D MODEL OF CULTURAL RELICS IN VIRTUAL RESTORATION

Directory of Open Access Journals (Sweden)

S. Zhao

2018-04-01

Full Text Available In the traditional cultural relics splicing process, in order to identify the correct spatial location of the cultural relics debris, experts need to manually splice the existing debris. The repeated contact between debris can easily cause secondary damage to the cultural relics. In this paper, the application process of 3D model of cultural relic in virtual restoration is put forward, and the relevant processes and ideas are verified with the example of Terracotta Warriors data. Through the combination of traditional cultural relics restoration methods and computer virtual reality technology, virtual restoration of high-precision 3D models of cultural relics can provide a scientific reference for virtual restoration, avoiding the secondary damage to the cultural relics caused by improper restoration. The efficiency and safety of the preservation and restoration of cultural relics have been improved.

THE DISK IMAGING SURVEY OF CHEMISTRY WITH SMA. I. TAURUS PROTOPLANETARY DISK DATA

International Nuclear Information System (INIS)

Oeberg, Karin I.; Qi Chunhua; Andrews, Sean M.; Espaillat, Catherine; Van Kempen, Tim A.; Wilner, David J.; Fogel, Jeffrey K. J.; Bergin, Edwin A.; Pascucci, Ilaria

2010-01-01

Chemistry plays an important role in the structure and evolution of protoplanetary disks, with implications for the composition of comets and planets. This is the first of a series of papers based on data from DISCS, a Submillimeter Array survey of the chemical composition of protoplanetary disks. The six Taurus sources in the program (DM Tau, AA Tau, LkCa 15, GM Aur, CQ Tau, and MWC 480) range in stellar spectral type from M1 to A4 and offer an opportunity to test the effects of stellar luminosity on the disk chemistry. The disks were observed in 10 different lines at ∼3'' resolution and an rms of ∼100 mJy beam -1 at ∼0.5 km s -1 . The four brightest lines are CO 2-1, HCO + 3-2, CN 2 33/4/2 - 1 22/3/1 , and HCN 3-2, and these are detected toward all sources (except for HCN toward CQ Tau). The weaker lines of CN 2 22 -1 11 , DCO + 3-2, N 2 H + 3-2, H 2 CO 3 03 -2 02 , and 4 14 -3 13 are detected toward two to three disks each, and DCN 3-2 only toward LkCa 15. CH 3 OH 4 21 -3 1 2 and c-C 3 H 2 are not detected. There is no obvious difference between the T Tauri and Herbig Ae sources with regard to CN and HCN intensities. In contrast, DCO + , DCN, N 2 H + , and H 2 CO are detected only toward the T Tauri stars, suggesting that the disks around Herbig Ae stars lack cold regions for long enough timescales to allow for efficient deuterium chemistry, CO freeze-out, and grain chemistry.

PLANETESIMAL DISK MICROLENSING

International Nuclear Information System (INIS)

Heng, Kevin; Keeton, Charles R.

2009-01-01

Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

THE MASS-INDEPENDENCE OF SPECIFIC STAR FORMATION RATES IN GALACTIC DISKS

Energy Technology Data Exchange (ETDEWEB)

Abramson, Louis E.; Gladders, Michael D. [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Kelson, Daniel D.; Dressler, Alan; Oemler, Augustus Jr. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Poggianti, Bianca [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Vulcani, Benedetta, E-mail: labramson@uchicago.edu [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8582 (Japan)

2014-04-20

The slope of the star formation rate/stellar mass relation (the SFR {sup M}ain Sequence{sup ;} SFR-M {sub *}) is not quite unity: specific star formation rates (SFR/M {sub *}) are weakly but significantly anti-correlated with M {sub *}. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions—portions of a galaxy not forming stars—with M {sub *}. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFR{sub disk} ≡ SFR/M {sub *,} {sub disk}) reduces the M {sub *} dependence of SF efficiency by ∼0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log sSFR{sub disk}-log M {sub *} to have a slope β{sub disk} in [ – 0.20, 0.00] ± 0.02 (depending on the SFR estimator and Main Sequence definition) for star-forming galaxies with M {sub *} ≥ 10{sup 10} M {sub ☉} and bulge mass-fractions B/T ≲ 0.6, generally consistent with a pure-disk control sample (β{sub control} = –0.05 ± 0.04). That (SFR/M {sub *,} {sub disk}) is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any SFR-M {sub *} relation, including manifestations of ''mass quenching'' (bulge growth), factors shaping the star-forming stellar mass function (uniform dlog M {sub *}/dt for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in SFR(M {sub *}, t)). Our results emphasize the need to treat galaxies as composite systems—not integrated masses—in observational and theoretical work.

The disk wind in the rapidly spinning stellar-mass black hole 4U 1630-472 observed with NuSTAR

DEFF Research Database (Denmark)

King, Ashley L.; Walton, Dominic J.; Miller, Jon M.

2014-01-01

We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630-472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we...... find evidence for a rapidly spinning black hole, (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also...

SED Modeling of 20 Massive Young Stellar Objects

Science.gov (United States)

Tanti, Kamal Kumar

In this paper, we present the spectral energy distributions (SEDs) modeling of twenty massive young stellar objects (MYSOs) and subsequently estimated different physical and structural/geometrical parameters for each of the twenty central YSO outflow candidates, along with their associated circumstellar disks and infalling envelopes. The SEDs for each of the MYSOs been reconstructed by using 2MASS, MSX, IRAS, IRAC & MIPS, SCUBA, WISE, SPIRE and IRAM data, with the help of a SED Fitting Tool, that uses a grid of 2D radiative transfer models. Using the detailed analysis of SEDs and subsequent estimation of physical and geometrical parameters for the central YSO sources along with its circumstellar disks and envelopes, the cumulative distribution of the stellar, disk and envelope parameters can be analyzed. This leads to a better understanding of massive star formation processes in their respective star forming regions in different molecular clouds.

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

Energy Technology Data Exchange (ETDEWEB)

Carrasco-González, Carlos; Rodríguez, Luis F.; Galván-Madrid, Roberto [Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México (Mexico); Henning, Thomas; Linz, Hendrik; Birnstiel, Til; Boekel, Roy van; Klahr, Hubert [Max-Planck-Institut für Astronomie Heidelberg, Königstuhl 17, D-69117 Heidelberg (Germany); Chandler, Claire J.; Pérez, Laura [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801-0387 (United States); Anglada, Guillem; Macias, Enrique; Osorio, Mayra [Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, E-18080 Granada (Spain); Flock, Mario [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Menten, Karl [Jansky Fellow of the National Radio Astronomy Observatory (United States); Testi, Leonardo [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC-IEEC) and Institut de Ciències del Cosmos (UB-IEEC), Martí i Franquès 1, E-08028 Barcelona (Spain); Zhu, Zhaohuan, E-mail: c.carrasco@crya.unam.mx, E-mail: l.rodriguez@crya.unam.mx, E-mail: r.galvan@crya.unam.mx, E-mail: henning@mpia.de, E-mail: linz@mpia.de [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2016-04-10

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk–planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of (1–3) × 10{sup −3} M {sub ⊙}, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

International Nuclear Information System (INIS)

Carrasco-González, Carlos; Rodríguez, Luis F.; Galván-Madrid, Roberto; Henning, Thomas; Linz, Hendrik; Birnstiel, Til; Boekel, Roy van; Klahr, Hubert; Chandler, Claire J.; Pérez, Laura; Anglada, Guillem; Macias, Enrique; Osorio, Mayra; Flock, Mario; Menten, Karl; Testi, Leonardo; Torrelles, José M.; Zhu, Zhaohuan

2016-01-01

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk–planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of (1–3) × 10 −3 M ⊙ , depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings

Compact objects and accretion disks

NARCIS (Netherlands)

Blandford, Roger; Agol, Eric; Broderick, Avery; Heyl, Jeremy; Koopmans, Leon; Lee, Hee-Won

2002-01-01

Recent developments in the spectropolarimetric study of compact objects, specifically black holes (stellar and massive) and neutron stars are reviewed. The lectures are organized around five topics: disks, jets, outflows, neutron stars and black holes. They emphasize physical mechanisms and are

ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii

Science.gov (United States)

Ansdell, M.; Williams, J. P.; Trapman, L.; van Terwisga, S. E.; Facchini, S.; Manara, C. F.; van der Marel, N.; Miotello, A.; Tazzari, M.; Hogerheijde, M.; Guidi, G.; Testi, L.; van Dishoeck, E. F.

2018-05-01

We present Atacama Large Millimeter/Sub-Millimeter Array (ALMA) Band 6 observations of a complete sample of protoplanetary disks in the young (∼1–3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12CO, 13CO, and C18O J = 2–1 lines. The spatial resolution is ∼0.″25 with a medium 3σ continuum sensitivity of 0.30 mJy, corresponding to M dust ∼ 0.2 M ⊕. We apply Keplerian masking to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 μm continuum observations, we also calculate the millimeter spectral index, α mm, for 70 Lupus disks; we find an anticorrelation between α mm and millimeter flux for low-mass disks (M dust ≲ 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.

The two young star disks in the central parsec of the Galaxy: properties, dynamics, and formation

International Nuclear Information System (INIS)

Paumard, T; Genzel, R; Martins, F; Nayakshin, S; Beloborodov, A M; Levin, Y; Trippe, S; Eisenhauer, F; Ott, T; Gillessen, S; Abuter, R; Cuadra, J; Alexander, T; Sternberg, A

2006-01-01

We report the definite spectroscopic identification of ≅ 40 OB supergiants, giants and main sequence stars in the central parsec of the Galaxy. Detection of their absorption lines have become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral Held spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium and nitrogen rich. Almost all of the ≅80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick ((|/R) ≅ 0.14) rotating disks. These stellar disks have fairly sharp inner edges (R ≅ 1'') and surface density profiles that scale as R -2 . We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the clockwise system appear to be on almost circular orbits, whereas most of those in the 'counter-clockwise' disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics we propose that IRS 13E is an extremely dense cluster (ρ core ∼> 3 x 10 8 M o-dot pc -3 ), which has formed in the counter-clockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of ≅ 6±2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to ≅ 1.5 x 10 4 M o-dot . Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the clockwise disk and highly plausible for the counter-clockwise system

The Disk Mass Project

NARCIS (Netherlands)

Verheijen, Marc A. W.; Bershady, Matthew A.; Swaters, Rob A.; Andersen, David R.; Westfall, Kyle B.; de Jong, Roelof Sybe

2007-01-01

Little is known about the content and distribution of dark matter in spiral galaxies. To break the degeneracy in galaxy rotation curve decompositions, which allows a wide range of dark matter halo density profiles, an independent measure of the mass surface density of stellar disks is needed. Here,

The SOLA Team: A Star Formation Project To Study the Soul of Lupus with ALMA

Science.gov (United States)

De Gregorio-Monsalvo, Itziar; Saito, M.; Rodon, J.; Takahashi, S.

2017-06-01

The SOLA team is a multi-national and multi-wavelength collaboration composed by scientists with technical expertise in ALMA and in infrared and optical techniques. The aim of the team is to establish a low-mass star formation scenario based on the Lupus molecular clouds. In this talk I will present our unique catalog of pre-stellar and proto-stellar cores toward Lupus molecular clouds, the results on our latest studies in protoplanetary disks, as well as our ALMA Cycle 3 data aiming at testing the formation mechanism of sub-stellar objects in Lupus molecular clouds.

Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon

Science.gov (United States)

Schiller, Martin; Bizzarro, Martin; Fernandes, Vera Assis

2018-03-01

Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth–Moon system. Using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-Solar-System objects predominantly reflects spatial heterogeneity. Here we use the isotopic composition of the refractory element calcium to show that the nucleosynthetic variability in the inner Solar System primarily reflects a rapid change in the mass-independent calcium isotope composition of protoplanetary disk solids associated with early mass accretion to the proto-Sun. We measure the mass-independent 48Ca/44Ca ratios of samples originating from the parent bodies of ureilite and angrite meteorites, as well as from Vesta, Mars and Earth, and find that they are positively correlated with the masses of their parent asteroids and planets, which are a proxy of their accretion timescales. This correlation implies a secular evolution of the bulk calcium isotope composition of the protoplanetary disk in the terrestrial planet-forming region. Individual chondrules from ordinary chondrites formed within one million years of the collapse of the proto-Sun reveal the full range of inner-Solar-System mass-independent 48Ca/44Ca ratios, indicating a rapid change in the composition of the material of the protoplanetary disk. We infer that this secular evolution reflects admixing of pristine outer-Solar-System material into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The identical calcium isotope composition of Earth

Disk accretion onto magnetic T Tauri stars

International Nuclear Information System (INIS)

Koenigl, A.

1991-01-01

The dynamical and radiative consequences of disk accretion onto magnetic T Tauri stars (TTS) are examined using the Ghosh and Lamb model. It is shown that a prolonged disk accretion phase is compatible with the low rotation rates measured in these stars if they possess a kilogauss strength field that disrupts the disk at a distance of a few stellar radii from the center. It is estimated that a steady state in which the net torque exerted on the star is zero can be attained on a time scale that is shorter than the age of the youngest visible TTS. Although the disk does not develop an ordinary shear boundary layer in this case, one can account for the observed UV excess and Balmer emission in terms of the shocks that form at the bottom of the high-latitude magnetic accretion columns on the stellar surface. This picture also provides a natural explanation of some of the puzzling variability properties of stars like DF Tau and RY Lup. YY Ori stars are interpreted as magnetic TTS in which the observer's line of sight is roughly parallel to an accretion column. 37 refs

THE INFLUENCE OF RADIAL STELLAR MIGRATION ON THE CHEMICAL EVOLUTION OF THE MILKY WAY

Energy Technology Data Exchange (ETDEWEB)

Wang Yue; Zhao Gang, E-mail: gzhao@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2013-05-20

Stellar migration is an important dynamical process in the Galactic disk. Here we model radial stellar migration in the Galactic disk with an analytical method, then add it to a detailed Galactic chemical evolution model to study the influence of radial stellar migration on the chemical evolution of the Milky Way, especially for the abundance gradients. We found that the radial stellar migration in the Galactic disk can make the profile of the G-dwarf metallicity distribution of the solar neighborhood taller and narrower, and thus it becomes another solution to the ''G-dwarf problem''. It can also scatter the age-metallicity relation. However, after migration, the abundance distributions along the Galactic radius do not change much; namely, the abundance gradients would not be flattened by the radial stellar migration, which is different from the predictions of many theoretical works. However, it can flatten the radial gradients of the mean chemical abundance of stars, and older stars possess flatter abundance gradients than younger stars. The most significant effect of radial stellar migration on the chemical abundance is that at a certain position it scatters the abundance of stars from a relatively concentrated value to a range.

A CHARA ARRAY SURVEY OF CIRCUMSTELLAR DISKS AROUND NEARBY Be-TYPE STARS

International Nuclear Information System (INIS)

Touhami, Y.; Gies, D. R.; McAlister, H. A.; Matson, R.

2013-01-01

We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30-331 m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good (u, v) coverage, we used a four-parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk's major axis. For the other targets with relatively limited (u, v) coverage, we constrained the axial ratio, inclination angle, and/or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions (SEDs) to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity Hα emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.

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.

INSIGHTS ON THE STELLAR MASS-METALLICITY RELATION FROM THE CALIFA SURVEY

Energy Technology Data Exchange (ETDEWEB)

González Delgado, R. M.; García-Benito, R.; Pérez, E.; Cortijo-Ferrero, C.; López Fernández, R.; Sánchez, S. F. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Cid Fernandes, R.; De Amorim, A. L.; Lacerda, E. A. D.; Vale Asari, N. [Departamento de Física, Universidade Federal de Santa Catarina, P.O. Box 476, 88040-900 Florianópolis, SC (Brazil); Alves, J. [University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Bland-Hawthorn, J. [Sydney Institute for Astronomy, The University of Sydney, NSW 2006 (Australia); Galbany, L. [Millennium Institute of Astrophysics and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Gallazzi, A. [INAF—Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Husemann, B. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching b. München (Germany); Bekeraite, S. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Jungwiert, B. [Astronomical Institute of the Academy of Sciences of the Czech Republic, v.v.i., Bocni II 1401, 14131 Prague (Czech Republic); López-Sánchez, A. R. [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); De Lorenzo-Cáceres, A. [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS (United Kingdom); Marino, R. A. [CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de Madrid, Avda. Complutense s/n, E-28040 Madrid (Spain); Collaboration: CALIFA collaboration920; and others

2014-08-10

We use spatially and temporally resolved maps of stellar population properties of 300 galaxies from the CALIFA integral field survey to investigate how the stellar metallicity (Z {sub *}) relates to the total stellar mass (M {sub *}) and the local mass surface density (μ{sub *}) in both spheroidal- and disk-dominated galaxies. The galaxies are shown to follow a clear stellar mass-metallicity relation (MZR) over the whole 10{sup 9}-10{sup 12} M {sub ☉} range. This relation is steeper than the one derived from nebular abundances, which is similar to the flatter stellar MZR derived when we consider only young stars. We also find a strong relation between the local values of μ{sub *} and Z {sub *} (the μZR), betraying the influence of local factors in determining Z {sub *}. This shows that both local (μ{sub *}-driven) and global (M {sub *}-driven) processes are important in determining metallicity in galaxies. We find that the overall balance between local and global effects varies with the location within a galaxy. In disks, μ{sub *} regulates Z {sub *}, producing a strong μZR whose amplitude is modulated by M {sub *}. In spheroids it is M {sub *} that dominates the physics of star formation and chemical enrichment, with μ{sub *} playing a minor, secondary role. These findings agree with our previous analysis of the star formation histories of CALIFA galaxies, which showed that mean stellar ages are mainly governed by surface density in galaxy disks and by total mass in spheroids.

Exploration and implementation of ontology-based cultural relic knowledge map integration platform

Science.gov (United States)

Yang, Weiqiang; Dong, Yiqiang

2018-05-01

To help designers to better carry out creative design and improve the ability of searching traditional cultural relic information, the ontology-based knowledge map construction method was explored and an integrated platform for cultural relic knowledge map was developed. First of all, the construction method of the ontology of cultural relics was put forward, and the construction of the knowledge map of cultural relics was completed based on the constructed cultural relic otology. Then, a personalized semantic retrieval framework for creative design was proposed. Finally, the integrated platform of the knowledge map of cultural relics was designed and realized. The platform was divided into two parts. One was the foreground display system, which was used for designers to search and browse cultural relics. The other was the background management system, which was for cultural experts to manage cultural relics' knowledge. The research results showed that the platform designed could improve the retrieval ability of cultural relic information. To sum up, the platform can provide a good support for the designer's creative design.

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.

DETECTIONS OF TRANS-NEPTUNIAN ICE IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

McClure, M. K.; Calvet, N.; Bergin, E.; Cleeves, L. I. [Department of Astronomy, The University of Michigan, 500 Church Street, 830 Dennison Bldg., Ann Arbor, MI 48109 (United States); Espaillat, C. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); D' Alessio, P. [Centro de Radioastronomía y Astrofísica, Universidad NacionalAUtónoma de México, 58089 Morelia, Michoacán (Mexico); Watson, D. M. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Manoj, P. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Sargent, B., E-mail: melisma@umich.edu, E-mail: ncalvet@umich.edu, E-mail: ebergin@umich.edu, E-mail: cleeves@umich.edu, E-mail: cce@bu.edu, E-mail: p.dalessio@crya.unam.mx, E-mail: dmw@pas.rochester.edu, E-mail: manoj.puravankara@tifr.res.in, E-mail: baspci@rit.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2015-02-01

We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30 AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location (1) colder than its crystallization temperature and (2) where it should have been re-amorphized in ∼1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 μm may probe the location of the water ice snowline in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.

Ludwik Fleck on proto-ideas in medicine

DEFF Research Database (Denmark)

Brorson, S

2000-01-01

and his nominalist view on medical taxonomy. Finally, I discuss four philosophical problems implied by Fleck's concept of proto-ideas: (a) the problem of combining two conflicting perspectives on the history of science (b) the problem of accounting for the notion of 'continuity' within a nonrealist theory......'Proto-idea' was a central concept in the thinking of the Polish microbiologist and philosopher of science Ludwik Fleck (1896-1961). Based on studies of the origin of the modern concept of syphilis, Fleck claimed that many established scientific facts are best understood as interpretations...... of prescientific, somewhat hazy 'proto-ideas' in the framework of a certain 'thought-style'. As an example, Fleck saw the modern knowledge of infection as an interpretation of the ancient proto-idea of diseases as caused by minute 'animalcules'. However, the epistemological aspects of the concept of proto-ideas...

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.

Mottled Protoplanetary Disk Ionization by Magnetically Channeled T Tauri Star Energetic Particles

Science.gov (United States)

Fraschetti, F.; Drake, J. J.; Cohen, O.; Garraffo, C.

2018-02-01

The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought to be due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares, or traveling shock waves, and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesized along the individual particle trajectories. We have investigated the energy range [0.1–10] GeV, consistent with expectations from Chandra X-ray observations of large flares on T Tauri stars and recent indications by the Herschel Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding a dominance of energetic particles over X-rays in the ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area, except within narrow regions where particles are channeled onto the disk by the strongly tangled and turbulent magnetic field. The radial thickness of such regions is 5 stellar radii close to the star and broadens with increasing radial distance. This likely continues out to large distances from the star (10 au or greater), where particles can be copiously advected and diffused by the turbulent wind.

STELLAR, GAS, AND DARK MATTER CONTENT OF BARRED GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Cervantes Sodi, Bernardo, E-mail: b.cervantes@crya.unam.mx [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Campus Morelia, A.P. 3-72, C.P. 58089 Michoacán, México (Mexico)

2017-01-20

We select a sample of galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) where galaxies are classified, through visual inspection, as hosting strong bars, weak bars, or as unbarred galaxies, and make use of H i mass and kinematic information from the Arecibo Legacy Fast ALFA survey catalog, to study the stellar, atomic gas, and dark matter content of barred disk galaxies. We find, in agreement with previous studies, that the bar fraction increases with increasing stellar mass. A similar trend is found with total baryonic mass, although the dependence is not as strong as with stellar mass, due to the contribution of gas. The bar fraction shows a decrease with increasing gas mass fraction. This anticorrelation between the likelihood of a galaxy hosting a bar with the gas richness of the galaxy results from the inhibiting effect the gas has in the formation of bars. We also find that for massive galaxies with stellar masses larger than 10{sup 10} M {sub ⊙}, at fixed stellar mass, the bar fraction decreases with increasing global halo mass (i.e., halo mass measured up to a radius of the order of the H i disk extent).

Characterizing the X-ray Radiation Field in the Earth-like Planet Forming ExoSystem HD 113766

Science.gov (United States)

Lisse, Carey

2010-09-01

We propose a 100 ksec ACIS-S observation of the 12 Myr old system HD 113766, the site of on-going terrestrial planet formation (Lisse et al. 2008), in order to determine the spectrum of x-ray radiation in the fledgling system, its origin in the stellar coronae and proto-planetary disk, and its potential impact on the nascent planet.

PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

International Nuclear Information System (INIS)

Mohanty, Subhanjoy; Mortlock, Daniel; Greaves, Jane; Pascucci, Ilaria; Apai, Daniel; Scholz, Aleks; Thompson, Mark; Lodato, Giuseppe; Looper, Dagny

2013-01-01

We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ∼100 AU for intermediate-mass stars, solar types, and VLMS, and ∼20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ∼ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly

SCRMS: An RFID and Sensor Web-Enabled Smart Cultural Relics Management System.

Science.gov (United States)

Xiao, Changjiang; Chen, Nengcheng; Li, Dandan; Lv, You; Gong, Jianya

2016-12-30

Cultural relics represent national or even global resources of inestimable value. How to efficiently manage and preserve these cultural relics is a vitally important issue. To achieve this goal, this study proposed, designed, and implemented an RFID and Sensor Web-enabled smart cultural relics management system (SCRMS). In this system, active photovoltaic subtle energy-powered Radio Frequency Identification (RFID) is used for long-range contactless identification and lifecycle management of cultural relics during their storage and circulation. In addition, different types of ambient sensors are integrated with the RFID tags and deployed around cultural relics to monitor their environmental parameters, helping to ensure that they remain in good condition. An Android-based smart mobile application, as middleware, is used in collaboration with RFID readers to collect information and provide convenient management for the circulation of cultural relics. Moreover, multiple sensing techniques are taken advantage of simultaneously for preservation of cultural relics. The proposed system was successfully applied to a museum in the Yongding District, Fujian Province, China, demonstrating its feasibility and advantages for smart and efficient management and preservation of cultural relics.

AGES OF 70 DWARFS OF THREE POPULATIONS IN THE SOLAR NEIGHBORHOOD: CONSIDERING O AND C ABUNDANCES IN STELLAR MODELS

Energy Technology Data Exchange (ETDEWEB)

Ge, Z. S.; Bi, S. L.; Liu, K.; Wu, Y. Q. [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Chen, Y. Q.; Zhao, J. K. [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Li, T. D. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Ferguson, J. W. [Department of Physics, Wichita State University, Wichita, KS 67260-0032 (United States)

2016-12-20

Oxygen and carbon are important elements in stellar populations. Their behavior refers to the formation history of the stellar populations. C and O abundances would also obviously influence stellar opacities and the overall metal abundance Z . With observed high-quality spectroscopic properties, we construct stellar models with C and O elements to give more accurate ages for 70 metal-poor dwarfs, which have been determined to be high- α halo, low- α halo, and thick-disk stars. Our results show that high- α halo stars are somewhat older than low- α halo stars by around 2.0 Gyr. The thick-disk population has an age range in between the two halo populations. The age distribution profiles indicate that high- α halo and low- α halo stars match the in situ accretion simulation by Zolotov et al., and the thick-disk stars might be formed in a relatively quiescent and long-lasting process. We also note that stellar ages are very sensitive to O abundance, since the ages clearly increase with increasing [O/Fe] values. Additionally, we obtain several stars with peculiar ages, including 2 young thick-disk stars and 12 stars older than the universe age.

Stochastic backgrounds of relic gravitons: a theoretical appraisal

CERN Document Server

Giovannini, Massimo

2010-01-01

Stochastic backgrounds or relic gravitons, if ever detected, will constitute a prima facie evidence of physical processes taking place during the earliest stages of the evolution of the plasma. The essentials of the stochastic backgrounds of relic gravitons are hereby introduced and reviewed. The pivotal observables customarily employed to infer the properties of the relic gravitons are discussed both in the framework of the $\\Lambda$CDM paradigm as well as in neighboring contexts. The complementarity between experiments measuring the polarization of the Cosmic Microwave Background (such as, for instance, WMAP, Capmap, Quad, Cbi, just to mention a few) and wide band interferometers (e.g. Virgo, Ligo, Geo, Tama) is emphasized. While the analysis of the microwave sky strongly constrains the low-frequency tail of the relic graviton spectrum, wide-band detectors are sensitive to much higher frequencies where the spectral energy density depends chiefly upon the (poorly known) rate of post-inflationary expansion.

A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars within 30 pc

Energy Technology Data Exchange (ETDEWEB)

Hinkel, Natalie R.; Somers, Garrett [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Mamajek, Eric E. [Jet Propulsion Laboratory, California Institute of Technology, M/S 321-100, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Turnbull, Margaret C. [Global Science Institute, P.O. Box 252, Antigo, WI 54409 (United States); Osby, Ella; Shkolnik, Evgenya L.; Desch, Steven J. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Smith, Graeme H. [University of California Observatories and Department of Astronomy and Astrophysics, University of California, Santa Cruz CA 95064 (United States); Klimasewski, Alexis, E-mail: natalie.hinkel@gmail.com [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States)

2017-10-10

Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet’s mass and radius demand accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (<30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca ii H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT , XMM, and Chandra . We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate that CATSUP will be useful for discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk versus thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.

A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars within 30 pc

International Nuclear Information System (INIS)

Hinkel, Natalie R.; Somers, Garrett; Mamajek, Eric E.; Turnbull, Margaret C.; Osby, Ella; Shkolnik, Evgenya L.; Desch, Steven J.; Smith, Graeme H.; Klimasewski, Alexis

2017-01-01

Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet’s mass and radius demand accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (<30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca ii H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT , XMM, and Chandra . We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate that CATSUP will be useful for discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk versus thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.

OT1_ipascucc_1: Understanding the Origin of Transition Disks via Disk Mass Measurements

Science.gov (United States)

Pascucci, I.

2010-07-01

Transition disks are a distinguished group of few Myr-old systems caught in the phase of dispersing their inner dust disk. Three different processes have been proposed to explain this inside-out clearing: grain growth, photoevaporation driven by the central star, and dynamical clearing by a forming giant planet. Which of these processes lead to a transition disk? Distinguishing between them requires the combined knowledge of stellar accretion rates and disk masses. We propose here to use 43.8 hours of PACS spectroscopy to detect the [OI] 63 micron emission line from a sample of 21 well-known transition disks with measured mass accretion rates. We will use this line, in combination with ancillary CO millimeter lines, to measure their gas disk mass. Because gas dominates the mass of protoplanetary disks our approach and choice of lines will enable us to trace the bulk of the disk mass that resides beyond tens of AU from young stars. Our program will quadruple the number of transition disks currently observed with Herschel in this setting and for which disk masses can be measured. We will then place the transition and the ~100 classical/non-transition disks of similar age (from the Herschel KP "Gas in Protoplanetary Systems") in the mass accretion rate-disk mass diagram with two main goals: 1) reveal which gaps have been created by grain growth, photoevaporation, or giant planet formation and 2) from the statistics, determine the main disk dispersal mechanism leading to a transition disk.

PROTOPLANETARY DISK HEATING AND EVOLUTION DRIVEN BY SPIRAL DENSITY WAVES

Energy Technology Data Exchange (ETDEWEB)

Rafikov, Roman R., E-mail: rrr@ias.edu [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)

2016-11-10

Scattered light imaging of protoplanetary disks often reveals prominent spiral arms, likely excited by massive planets or stellar companions. Assuming that these arms are density waves, evolving into spiral shocks, we assess their effect on the thermodynamics, accretion, and global evolution of the disk. We derive analytical expressions for the direct (irreversible) heating, angular momentum transport, and mass accretion rate induced by disk shocks of arbitrary amplitude. These processes are very sensitive to the shock strength. We show that waves of moderate strength (density jump at the shock ΔΣ/Σ ∼ 1) result in negligible disk heating (contributing at the ∼1% level to the energy budget) in passive, irradiated protoplanetary disks on ∼100 au scales, but become important within several au. However, shock heating is a significant (or even dominant) energy source in disks of cataclysmic variables, stellar X-ray binaries, and supermassive black hole binaries, heated mainly by viscous dissipation. Mass accretion induced by the spiral shocks is comparable to (or exceeds) the mass inflow due to viscous stresses. Protoplanetary disks featuring prominent global spirals must be evolving rapidly, in ≲0.5 Myr at ∼100 au. A direct upper limit on the evolution timescale can be established by measuring the gravitational torque due to the spiral arms from the imaging data. We find that, regardless of their origin, global spiral waves must be important agents of the protoplanetary disk evolution. They may serve as an effective mechanism of disk dispersal and could be related to the phenomenon of transitional disks.

PROTOPLANETARY DISK HEATING AND EVOLUTION DRIVEN BY SPIRAL DENSITY WAVES

International Nuclear Information System (INIS)

Rafikov, Roman R.

2016-01-01

Scattered light imaging of protoplanetary disks often reveals prominent spiral arms, likely excited by massive planets or stellar companions. Assuming that these arms are density waves, evolving into spiral shocks, we assess their effect on the thermodynamics, accretion, and global evolution of the disk. We derive analytical expressions for the direct (irreversible) heating, angular momentum transport, and mass accretion rate induced by disk shocks of arbitrary amplitude. These processes are very sensitive to the shock strength. We show that waves of moderate strength (density jump at the shock ΔΣ/Σ ∼ 1) result in negligible disk heating (contributing at the ∼1% level to the energy budget) in passive, irradiated protoplanetary disks on ∼100 au scales, but become important within several au. However, shock heating is a significant (or even dominant) energy source in disks of cataclysmic variables, stellar X-ray binaries, and supermassive black hole binaries, heated mainly by viscous dissipation. Mass accretion induced by the spiral shocks is comparable to (or exceeds) the mass inflow due to viscous stresses. Protoplanetary disks featuring prominent global spirals must be evolving rapidly, in ≲0.5 Myr at ∼100 au. A direct upper limit on the evolution timescale can be established by measuring the gravitational torque due to the spiral arms from the imaging data. We find that, regardless of their origin, global spiral waves must be important agents of the protoplanetary disk evolution. They may serve as an effective mechanism of disk dispersal and could be related to the phenomenon of transitional disks.

THE DISK POPULATION OF THE TAURUS STAR-FORMING REGION

International Nuclear Information System (INIS)

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

2010-01-01

We have analyzed nearly all images of the Taurus star-forming region at 3.6, 4.5, 5.8, 8.0, and 24 μm that were obtained during the cryogenic mission of the Spitzer Space Telescope (46 deg 2 ) and have measured photometry for all known members of the region that are within these data, corresponding to 348 sources, or 99% of the known stellar population. By combining these measurements with previous observations with the Spitzer Infrared Spectrograph and other facilities, we have classified the members of Taurus according to whether they show evidence of circumstellar disks and envelopes (classes I, II, and III). Through these classifications, we find that the disk fraction in Taurus, N(II)/N(II+III), is ∼75% for solar-mass stars and declines to ∼45% for low-mass stars and brown dwarfs (0.01-0.3 M sun ). This dependence on stellar mass is similar to that measured for Chamaeleon I, although the disk fraction in Taurus is slightly higher overall, probably because of its younger age (1 Myr versus 2-3 Myr). In comparison, the disk fraction for solar-mass stars is much lower (∼20%) in IC 348 and σ Ori, which are denser than Taurus and Chamaeleon I and are roughly coeval with the latter. These data indicate that disk lifetimes for solar-mass stars are longer in star-forming regions that have lower stellar densities. Through an analysis of multiple epochs of Spitzer photometry that are available for ∼200 Taurus members, we find that stars with disks exhibit significantly greater mid-infrared (mid-IR) variability than diskless stars, which agrees with the results of similar variability measurements for a smaller sample of stars in Chamaeleon I. The variability fraction for stars with disks is higher in Taurus than in Chamaeleon I, indicating that the IR variability of disks decreases with age. Finally, we have used our data in Taurus to refine the observational criteria for primordial, evolved, and transitional disks. The ratio of the number of evolved and

Wobbling The Galactic Disk with Bombardment of Satellite Galaxies

Science.gov (United States)

D'Onghia, Elena

We propose to assess the effect of impacts of large visible satellite galaxies on a disk, as well as the relevance of the continuing bombardment of the Galactic disk by dark matter clumps as predicted by the current cosmological framework that can wobble the disk, heating it and eventually exciting ragged spiral structures. In particular, we make detailed predictions for observable features such as spiral arms, rings and their associated stars in galactic disks and relate them to the physical processes that drive their formation and evolution in our Milky Way galaxy and nearby spirals. To do this, we will combine analytic methods and numerical simulations that allow us to calculate observables, which we will compare to present and forthcoming observations. Our methodology utilizes a combination of state of the art hydrodynamic simulations of galaxy evolution and multi- wavelength radiative transfer simulations. Our primary goals are: (1) To identify the physical processes that are responsible for spiral structure formation observed in our Milky Way and nearby disk galaxies, from the flocculent to grand- designed spiral galaxies and to provide observable signatures to be compared with data on nearby galaxies combining maps of 24 micron emission (Spitzer) and cold gas, CO (Heracles) and HI (THINGS). (2) To explore different morphologies of spiral galaxies: from the multi-armed galaxies to the Milky Way sized galaxies with few arms. (3) For a Milky Way disk we will assess the effect of impacts of substructures passing through the disk to origin the asymmetry in the number density of stars recently discovered from SDSS and SEGUE data and confirmed from RAVE data. We will also investigate the disk heating in the vertical plane due to the formation of vertical oscillations that are produced by the impact and migration of stars in the disk as consequence of the heating as compared to the classical stellar migration mechanism. (4) We will measure the spiral pattern speed

Isotopic Dichotomy among Meteorites and Its Bearing on the Protoplanetary Disk

Science.gov (United States)

Scott, Edward R. D.; Krot, Alexander N.; Sanders, Ian S.

2018-02-01

Whole rock Δ17O and nucleosynthetic isotopic variations for chromium, titanium, nickel, and molybdenum in meteorites define two isotopically distinct populations: carbonaceous chondrites (CCs) and some achondrites, pallasites, and irons in one and all other chondrites and differentiated meteorites in the other. Since differentiated bodies accreted 1–3 Myr before the chondrites, the isotopic dichotomy cannot be attributed to temporal variations in the disk. Instead, the two populations were most likely separated in space, plausibly by proto-Jupiter. Formation of CCs outside Jupiter could account for their characteristic chemical and isotopic composition. The abundance of refractory inclusions in CCs can be explained if they were ejected by disk winds from near the Sun to the disk periphery where they spiraled inward due to gas drag. Once proto-Jupiter reached 10–20 M ⊕, its external pressure bump could have prevented millimeter- and centimeter-sized particles from reaching the inner disk. This scenario would account for the enrichment in CCs of refractory inclusions, refractory elements, and water. Chondrules in CCs show wide ranges in Δ17O as they formed in the presence of abundant 16O-rich refractory grains and 16O-poor ice particles. Chondrules in other chondrites (ordinary, E, R, and K groups) show relatively uniform, near-zero Δ17O values as refractory inclusions and ice were much less abundant in the inner solar system. The two populations were plausibly mixed together by the Grand Tack when Jupiter and Saturn migrated inward emptying and then repopulating the asteroid belt with roughly equal masses of planetesimals from inside and outside Jupiter’s orbit (S- and C-type asteroids).

A combined N-body and hydrodynamic code for modeling disk galaxies

International Nuclear Information System (INIS)

Schroeder, M.C.

1989-01-01

A combined N-body and hydrodynamic computer code for the modeling of two dimensional galaxies is described. The N-body portion of the code is used to calculate the motion of the particle component of a galaxy, while the hydrodynamics portion of the code is used to follow the motion and evolution of the fluid component. A complete description of the numerical methods used for each portion of the code is given. Additionally, the proof tests of the separate and combined portions of the code are presented and discussed. Finally, a discussion of the topics researched with the code and results obtained is presented. These include: the measurement of stellar relaxation times in disk galaxy simulations; the effects of two-armed spiral perturbations on stable axisymmetric disks; the effects of the inclusion of an instellar medium (ISM) on the stability of disk galaxies; and the effect of the inclusion of stellar evolution on disk galaxy simulations

SCRMS: An RFID and Sensor Web-Enabled Smart Cultural Relics Management System

Directory of Open Access Journals (Sweden)

Changjiang Xiao

2016-12-01

Full Text Available Cultural relics represent national or even global resources of inestimable value. How to efficiently manage and preserve these cultural relics is a vitally important issue. To achieve this goal, this study proposed, designed, and implemented an RFID and Sensor Web–enabled smart cultural relics management system (SCRMS. In this system, active photovoltaic subtle energy-powered Radio Frequency Identification (RFID is used for long-range contactless identification and lifecycle management of cultural relics during their storage and circulation. In addition, different types of ambient sensors are integrated with the RFID tags and deployed around cultural relics to monitor their environmental parameters, helping to ensure that they remain in good condition. An Android-based smart mobile application, as middleware, is used in collaboration with RFID readers to collect information and provide convenient management for the circulation of cultural relics. Moreover, multiple sensing techniques are taken advantage of simultaneously for preservation of cultural relics. The proposed system was successfully applied to a museum in the Yongding District, Fujian Province, China, demonstrating its feasibility and advantages for smart and efficient management and preservation of cultural relics.

Cosmic-Ray Propagation in Turbulent Spiral Magnetic Fields Associated with Young Stellar Objects

Science.gov (United States)

Fatuzzo, Marco; Adams, Fred C.

2018-04-01

External cosmic rays impinging upon circumstellar disks associated with young stellar objects provide an important source of ionization, and, as such, play an important role in disk evolution and planet formation. However, these incoming cosmic rays are affected by a variety of physical processes internal to stellar/disk systems, including modulation by turbulent magnetic fields. Globally, these fields naturally provide both a funneling effect, where cosmic rays from larger volumes are focused into the disk region, and a magnetic mirroring effect, where cosmic rays are repelled due to the increasing field strength. This paper considers cosmic-ray propagation in the presence of a turbulent spiral magnetic field, analogous to that produced by the solar wind. The interaction of this wind with the interstellar medium defines a transition radius, analogous to the heliopause, which provides the outer boundary to this problem. We construct a new coordinate system where one coordinate follows the spiral magnetic field lines and consider magnetic perturbations to the field in the perpendicular directions. The presence of magnetic turbulence replaces the mirroring points with a distribution of values and moves the mean location outward. Our results thus help quantify the degree to which cosmic-ray fluxes are reduced in circumstellar disks by the presence of magnetic field structures that are shaped by stellar winds. The new coordinate system constructed herein should also be useful in other astronomical applications.

Relic abundance of WIMPs in non-standard cosmological scenarios

Energy Technology Data Exchange (ETDEWEB)

Yimingniyazi, W.

2007-08-06

In this thesis we study the relic density n{sub {chi}} of non--relativistic long--lived or stable particles {chi} in various non--standard cosmological scenarios. First, we discuss the relic density in the non--standard cosmological scenario in which the temperature is too low for the particles {chi} to achieve full chemical equilibrium. We also investigated the case where {chi} particles are non--thermally produced from the decay of heavier particles in addition to the usual thermal production. In low temperature scenario, we calculate the relic abundance starting from arbitrary initial temperatures T{sub 0} of the radiation--dominated epoch and derive approximate solutions for the temperature dependence of the relic density which can accurately reproduces numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the {chi} number density. However, we can contrive a semi-analytic formula which gives the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures. We also derive the lower bound on the initial temperature T{sub 0}, assuming that the relic particle accounts for the dark matter energy density in the universe. The observed cold dark matter abundance constrains the initial temperature T{sub 0} {>=}m{sub {chi}}/23, where m{sub {chi}} is the mass of {chi}. Second, we discuss the {chi} density in the scenario where the the Hubble parameter is modified. Even in this case, an approximate formula similar to the standard one is found to be capable of predicting the final relic abundance correctly. Choosing the {chi} annihilation cross section such that the observed cold dark matter abundance is reproduced in standard cosmology, we constrain possible modifications of the expansion rate at T {proportional_to}m{sub {chi}}/20, well before Big Bang Nucleosynthesis. (orig.)

Relic abundance of WIMPs in non-standard cosmological scenarios

International Nuclear Information System (INIS)

Yimingniyazi, W.

2007-01-01

In this thesis we study the relic density n χ of non--relativistic long--lived or stable particles χ in various non--standard cosmological scenarios. First, we discuss the relic density in the non--standard cosmological scenario in which the temperature is too low for the particles χ to achieve full chemical equilibrium. We also investigated the case where χ particles are non--thermally produced from the decay of heavier particles in addition to the usual thermal production. In low temperature scenario, we calculate the relic abundance starting from arbitrary initial temperatures T 0 of the radiation--dominated epoch and derive approximate solutions for the temperature dependence of the relic density which can accurately reproduces numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the χ number density. However, we can contrive a semi-analytic formula which gives the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures. We also derive the lower bound on the initial temperature T 0 , assuming that the relic particle accounts for the dark matter energy density in the universe. The observed cold dark matter abundance constrains the initial temperature T 0 ≥m χ /23, where m χ is the mass of χ. Second, we discuss the χ density in the scenario where the the Hubble parameter is modified. Even in this case, an approximate formula similar to the standard one is found to be capable of predicting the final relic abundance correctly. Choosing the χ annihilation cross section such that the observed cold dark matter abundance is reproduced in standard cosmology, we constrain possible modifications of the expansion rate at T ∝m χ /20, well before Big Bang Nucleosynthesis. (orig.)

IMAGING DISCOVERY OF THE DEBRIS DISK AROUND HIP 79977

Energy Technology Data Exchange (ETDEWEB)

Thalmann, C.; Dominik, C. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam, Amsterdam (Netherlands); Janson, M.; Brandt, T. D.; Knapp, G. R. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Buenzli, E. [Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ (United States); Wisniewski, J. P. [H.L. Dodge Department of Physics and Astronomy, University of Oklahoma, OK (United States); Carson, J. [Department of Physics and Astronomy, College of Charleston, Charleston, SC (United States); McElwain, M. W. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Currie, T. [Department of Astronomy and Astrophysics, University of Toronto, Toronto (Canada); Moro-Martin, A. [Department of Astrophysics, CAB-CSIC/INTA, Madrid (Spain); Usuda, T.; Egner, S.; Golota, T.; Guyon, O. [Subaru Telescope, Hilo, HI (United States); Abe, L. [Laboratoire Hippolyte Fizeau, Nice (France); Brandner, W.; Feldt, M. [Max Planck Institute for Astronomy, Heidelberg (Germany); Goto, M. [Universitaetssternwerte Muenchen, Ludwig-Maximilians-Universitaet, Munich (Germany); Hashimoto, J., E-mail: thalmann@uva.nl [National Astronomical Observatory of Japan, Tokyo (Japan); and others

2013-02-01

We present Subaru/HiCIAO H-band high-contrast images of the debris disk around HIP 79977, whose presence was recently inferred from an infrared excess. Our images resolve the disk for the first time, allowing characterization of its shape, size, and dust grain properties. We use angular differential imaging (ADI) to reveal the disk geometry in unpolarized light out to a radius of {approx}2'', as well as polarized differential imaging to measure the degree of scattering polarization out to {approx}1.''5. In order to strike a favorable balance between suppression of the stellar halo and conservation of disk flux, we explore the application of principal component analysis to both ADI and reference star subtraction. This allows accurate forward modeling of the effects of data reduction on simulated disk images, and thus direct comparison with the imaged disk. The resulting best-fit values and well-fitting intervals for the model parameters are a surface brightness power-law slope of S{sub out} = -3.2[ - 3.6, -2.9], an inclination of i = 84 Degree-Sign [81 Degree-Sign , 86 Degree-Sign ], a high Henyey-Greenstein forward-scattering parameter of g = 0.45[0.35, 0.60], and a non-significant disk-star offset of u = 3.0[ - 1.5, 7.5] AU = 24[ - 13, 61] mas along the line of nodes. Furthermore, the tangential linear polarization along the disk rises from {approx}10% at 0.''5 to {approx}45% at 1.''5. These measurements paint a consistent picture of a disk of dust grains produced by collisional cascades and blown out to larger radii by stellar radiation pressure.

Star formation rates and abundance gradients in disk galaxies

International Nuclear Information System (INIS)

Wyse, R.F.G.; Silk, J.

1989-01-01

Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies. 67 refs

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

Dynamical Evolution of the Debris Disk after a Satellite Catastrophic Disruption around Saturn

International Nuclear Information System (INIS)

Hyodo, Ryuki; Charnoz, Sébastien

2017-01-01

The hypothesis of the recent origin of Saturn’s rings and its midsized moons is actively debated. It was suggested that a proto-Rhea and a proto-Dione might have collided recently, giving birth to the modern system of midsized moons. It has also been suggested that the rapid viscous spreading of the debris may have implanted mass inside Saturn’s Roche limit, giving birth to its modern ring system. However, this scenario has only been investigated in a very simplified way for the moment. This paper investigates it in detail to assess its plausibility by using N -body simulations and analytical arguments. When the debris disk is dominated by its largest remnant, N -body simulations show that the system quickly reaccretes into a single satellite without significant spreading. On the other hand, if the disk is composed of small particles, analytical arguments suggest that the disk experiences dynamical evolutions in three steps. The disk starts significantly excited after the impact and collisional damping dominates over the viscous spreading. After the system flattens, the system can become gravitationally unstable when particles are smaller than ∼100 m. However, the particles grow faster than spreading. Then, the system becomes gravitationally stable again and accretion continues at a slower pace, but spreading is inhibited. Therefore, the debris is expected to reaccrete into several large bodies. In conclusion, our results show that such a scenario may not form today’s ring system. In contrast, our results suggest that today’s midsized moons are likely reaccreted from such a catastrophic event.

Dynamical Evolution of the Debris Disk after a Satellite Catastrophic Disruption around Saturn

Energy Technology Data Exchange (ETDEWEB)

Hyodo, Ryuki [Earth-Life Science Institute/Tokyo Institute of Technology, 2-12-1 Tokyo (Japan); Charnoz, Sébastien [Institut de Physique du Globe, 75005 Paris (France)

2017-07-01

The hypothesis of the recent origin of Saturn’s rings and its midsized moons is actively debated. It was suggested that a proto-Rhea and a proto-Dione might have collided recently, giving birth to the modern system of midsized moons. It has also been suggested that the rapid viscous spreading of the debris may have implanted mass inside Saturn’s Roche limit, giving birth to its modern ring system. However, this scenario has only been investigated in a very simplified way for the moment. This paper investigates it in detail to assess its plausibility by using N -body simulations and analytical arguments. When the debris disk is dominated by its largest remnant, N -body simulations show that the system quickly reaccretes into a single satellite without significant spreading. On the other hand, if the disk is composed of small particles, analytical arguments suggest that the disk experiences dynamical evolutions in three steps. The disk starts significantly excited after the impact and collisional damping dominates over the viscous spreading. After the system flattens, the system can become gravitationally unstable when particles are smaller than ∼100 m. However, the particles grow faster than spreading. Then, the system becomes gravitationally stable again and accretion continues at a slower pace, but spreading is inhibited. Therefore, the debris is expected to reaccrete into several large bodies. In conclusion, our results show that such a scenario may not form today’s ring system. In contrast, our results suggest that today’s midsized moons are likely reaccreted from such a catastrophic event.

EFFECT OF A STELLAR COMPANION ON THE MODELING OF HD 142527 INFRARED SED

OpenAIRE

Erick Nagel

2014-01-01

The discovery of a companion of the Herbig Ae/Be star HD 142527 motivates the study of the effect that it produces on the SED. The main change on the system configuration is the formation of a gap in the disk. Due to this change, a wall (outer edge of the gap), which is frontally illuminated by stellar radiation is formed. We present a model for the SED, considering all the components: a disk with two gaps (one produced by the stellar companion and the other by potential planets), three walls...

Twin radio relics in the nearby low-mass galaxy cluster Abell 168

Science.gov (United States)

Dwarakanath, K. S.; Parekh, V.; Kale, R.; George, L. T.

2018-06-01

We report the discovery of twin radio relics in the outskirts of the low-mass merging galaxy cluster Abell 168 (redshift=0.045). One of the relics is elongated with a linear extent ˜800 kpc and projected width of ˜80 kpc and is located ˜900 kpc towards the north of the cluster centre, oriented roughly perpendicular to the major axis of the X-ray emission. The second relic is ring-shaped with a size ˜220 kpc and is located near the inner edge of the elongated relic at a distance of ˜600 kpc from the cluster centre. These radio sources were imaged at 323 and 608 MHz with the Giant Meterwave Radio Telescope and at 1520 MHz with the Karl G. Jansky Very Large Array (VLA). The elongated relic was detected at all frequencies, with a radio power of 1.38 ± 0.14 × 1023 W Hz-1 at 1.4 GHz and a power law in the frequency range 70-1500 MHz (S ∝ να, α = -1.1 ± 0.04). This radio power is in good agreement with that expected from the known empirical relation between the radio powers of relics and host cluster masses. This is the lowest mass (M500 = 1.24 × 1014 M⊙) cluster in which relics due to merger shocks are detected. The ring-shaped relic has a steeper spectral index (α) of -1.74 ± 0.29 in the frequency range 100-600 MHz. We propose this relic to be an old plasma, revived due to adiabatic compression by the outgoing shock that produced the elongated relic.

SPATIALLY RESOLVED STAR FORMATION HISTORY ALONG THE DISK OF M82 USING MULTI-BAND PHOTOMETRIC DATA

International Nuclear Information System (INIS)

Rodriguez-Merino, L. H.; Rosa-Gonzalez, D.; Mayya, Y. D.

2011-01-01

We present results on the star formation history and extinction in the disk of M82 over spatial scales of 10'' (∼180 pc). Multi-band photometric data covering the far-ultraviolet to the near-infrared bands were fitted to a grid of synthetic spectral energy distributions. We obtained distribution functions of age and extinction for each of the 117 apertures analyzed, taking into account observational errors through Monte Carlo simulations. These distribution functions were fitted with Gaussian functions to obtain the mean ages and extinctions together with their errors. The zones analyzed include the high surface brightness complexes defined by O'Connell and Mangano. We found that these complexes share the same star formation history and extinction as the field stellar populations in the disk. There is an indication that the stellar populations are marginally older at the outer disk (450 Myr at ∼3 kpc) as compared to the inner disk (100 Myr at 0.5 kpc). For the nuclear region (radius less than 500 pc), we obtained an age of less than 10 Myr. The results obtained in this work are consistent with the idea that the 0.5-3 kpc part of the disk of M82 formed around 90% of the stellar mass in a star-forming episode that started around 450 Myr ago and lasted for about 350 Myr. We found that field stars are the major contributors to the flux over the spatial scales analyzed in this study, with the stellar cluster contribution being 7% in the nucleus and 0.7% in the disk.

Island universes structure and evolution of disk galaxies

CERN Document Server

DE JONG, R. S

2007-01-01

This book contains an up-to-date review of the structure and evolution of disk galaxies from both the observational and theoretical point of view. The book is the proceedings of the "Island Universes" conference held at the island of Terschelling, The Netherlands in July 2005, which attracted about 130 experts and students in the field. The conference was organized as a tribute to Dr. Piet C. van der Kruit for receiving the honorary Jacobus C. Kapteyn Professorship in Astronomy. The eight topical themes discussed at the meeting are reflected in these proceedings: 1) Properties of Stellar Disks, 2) Kinematics and Dynamics of Disk Galaxies, 3) Bars, Spiral Structure, and Secular Evolution in Disk Galaxies, 4) The Outskirts and Environment of Disk Galaxies, 5) Interstellar Matter, 6) (Evolution of) Star Formation in Galactic Disks, 7) Disk Galaxies through Cosmic Time, and 8) Formation Models of Disk Galaxies. These proceedings are concluded with a conference summary reflecting on the most significant recent pro...

The atomic and molecular content of disks around very low-mass stars and brown dwarfs

Energy Technology Data Exchange (ETDEWEB)

Pascucci, I. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Herczeg, G. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Carr, J. S. [Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States); Bruderer, S., E-mail: pascucci@lpl.arizona.edu [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany)

2013-12-20

There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne{sup +}, H{sub 2}, CO{sub 2}, and tentative detections of H{sub 2}O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (≥5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H{sub 2} S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C{sub 2}H{sub 2}/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H{sub 2}O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H{sub 2}O lines trace warm ≥600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs.

The effect of radial migration on galactic disks

International Nuclear Information System (INIS)

Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

2014-01-01

We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (∼40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

Proto-cooperation

DEFF Research Database (Denmark)

Herbert-Read, James E; Romanczuk, Pawel; Krause, Stefan

2016-01-01

beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realized through the facilitative effects of individuals' hunting actions without spatial coordination of attacks. Such 'proto-cooperation' may be the pre...

THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404

International Nuclear Information System (INIS)

Williams, Benjamin F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Stilp, Adrienne; Dolphin, Andrew; Seth, Anil C.; Weisz, Daniel; Skillman, Evan

2010-01-01

We present HST/WFPC2 observations across the disk of the nearby isolated dwarf S0 galaxy NGC 404, which hosts an extended gas disk. The locations of our fields contain a roughly equal mixture of bulge and disk stars. All of our resolved stellar photometry reaches m F814W = 26 (M F814W = -1.4), which covers 2.5 mag of the red giant branch and main-sequence stars with ages F814W = 27.2 (M F814W = -0.2), sufficient to resolve the red clump and main-sequence stars with ages 10 Gyr) population. Detailed modeling of the color-magnitude diagram suggests that ∼70% of the stellar mass in the NGC 404 disk formed by z ∼ 2 (10 Gyr ago) and at least ∼90% formed prior to z ∼ 1 (8 Gyr ago). These results indicate that the stellar populations of the NGC 404 disk are on average significantly older than those of other nearby disk galaxies, suggesting that early- and late-type disks may have different long-term evolutionary histories, not simply differences in their recent star formation rates. Comparisons of the spatial distribution of the young stellar mass and FUV emission in Galaxy Evolution Explorer images show that the brightest FUV regions contain the youngest stars, but that some young stars (<160 Myr) lie outside of these regions. FUV luminosity appears to be strongly affected by both age and stellar mass within individual regions. Finally, we use our measurements to infer the relationship between the star formation rate and the gas density of the disk at previous epochs. We find that most of the history of the NGC 404 disk is consistent with star formation that has decreased with the gas density according to the Schmidt law. However, ∼ 0.5-1 Gyr ago, the star formation rate was unusually low for the inferred gas density, consistent with the possibility that there was a gas accretion event that reignited star formation ∼0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an extended gas disk.

Accretion disks in active galactic nuclei

International Nuclear Information System (INIS)

Shields, G.A.

1989-01-01

Active galactic nuclei (AGN) have taunted astrophysicists for a quarter century. How do these objects produce huge luminosities---in some cases, far outshining our galaxy---from a region perhaps no larger than the solar system? Accretion onto supermassive black holes has been widely considered the best buy in theories of AGN. Much work has gone into accretion disk theory, searches for black holes in galactic nuclei, and observational tests. These efforts have not proved the disk model, but there is progress. Evidence for black holes in the nuclei of nearby galaxies is provided by observations of stellar velocities, and radiation from the disk's hot surface may be observed in the ultraviolet (UV) and neighboring spectral bands. In the review, the author describe some of the recent work on accretion disks in AGN, with an emphasis on points of contact between theory and observation

The Stability of Galaxy Disks

Science.gov (United States)

Westfall, K. B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T. P. K.; Swaters, R. A.; Verheijen, M. A. W.

2014-03-01

We calculate the stellar surface mass density (Σ*) and two-component (gas+stars) disk stability (QRW) for 25 late-type galaxies from the DiskMass Survey. These calculations are based on fits of a dynamical model to our ionized-gas and stellar kinematic data performed using a Markov Chain Monte Carlo sampling of the Bayesian posterior. Marginalizing over all galaxies, we find a median value of QRW = 2.0±0.9 at 1.5 scale lengths. We also find that QRW is anti-correlated with the star-formation rate surface density (Σ*), which can be predicted using a closed set of empirical scaling relations. Finally, we find that the star-formation efficiency (Σ*/Σg) is correlated with Σ* and weakly anti-correlated with QRW. The former is consistent with an equilibrium prediction of Σ*/Σg ∝ Σ*1/2. Despite its order-of-magnitude range, we find no correlation of Σ*/ΣgΣ*1/2 with any other physical quantity derived by our study.

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

Local protoplanetary disk ionisation by T Tauri star energetic particles

Science.gov (United States)

Fraschetti, F.; Drake, J.; Cohen, O.; Garraffo, C.

2017-10-01

The evolution of protoplanetary disks is believed to be driven largely by viscosity. The ionization of the disk that gives rise to viscosity is caused by X-rays from the central star or by energetic particles released by shock waves travelling into the circumstellar medium. We have performed test-particle numerical simulations of GeV-scale protons traversing a realistic magnetised wind of a young solar mass star with a superposed small-scale turbulence. The large-scale field is generated via an MHD model of a T Tauri wind, whereas the isotropic (Kolmogorov power spectrum) turbulent component is synthesised along the particles' trajectories. We have combined Chandra observations of T Tauri flares with solar flare scaling for describing the energetic particle spectrum. In contrast with previous models, we find that the disk ionization is dominated by X-rays except within narrow regions where the energetic particles are channelled onto the disk by the strongly tangled and turbulent field lines; the radial thickness of such regions broadens with the distance from the central star (5 stellar radii or more). In those regions, the disk ionization due to energetic particles can locally dominate the stellar X-rays, arguably, out to large distances (10, 100 AU) from the star.

Young Stellar Objects from Soft to Hard X-rays

Science.gov (United States)

Güdel, Manuel

2009-05-01

Magnetically active stars are the sites of efficient particle acceleration and plasma heating, processes that have been studied in detail in the solar corona. Investigation of such processes in young stellar objects is much more challenging due to various absorption processes. There is, however, evidence for violent magnetic energy release in very young stellar objects. The impact on young stellar environments (e.g., circumstellar disk heating and ionization, operation of chemical networks, photoevaporation) may be substantial. Hard X-ray devices like those carried on Simbol-X will establish a basis for detailed studies of these processes.

The Emergence of a Proto-institution

DEFF Research Database (Denmark)

Boxenbaum, Eva

2004-01-01

of inter-organizational networks, and actors embedded in multiple fields. The making of the proto-institution is intentional, yet the institutional building blocks and the apparent interests of actors are institutionally embedded. The results from this micro-dynamic analysis suggest revisions to current...... conceptualizations of institutional change processes. Keywords: Institutional change, proto-institution, cognition, institutional entrepreneurship, innovation, collaborative networks....

On the universal stellar law

Science.gov (United States)

Krot, Alexander

In this work, we consider a statistical theory of gravitating spheroidal bodies to derive and develop the universal stellar law for extrasolar systems. Previously, the statistical theory for a cosmogonic body forming (so-called spheroidal body)has been proposed [1-3]. This theory starts from the conception for forming a spheroidal body inside a gas-dust protoplanetary nebula; it permits us to derive the form of distribution functions, mass density, gravitational potentials and strengths both for immovable and rotating spheroidal bodies as well as to find the distribution function of specific angular momentum[1-3]. If we start from the conception for forming a spheroidal body as a protostar (in particular, proto-Sun) inside a prestellar (presolar) nebula then the derived distribution functions of particle (as well as the mass density of an immovable spheroidal body) characterizes the first stage of evolution: from a prestellar molecular cloud (the presolar nebula) to the forming core of protostar (the proto-Sun) together with its shell as a stellar nebula (the solar nebula). This work derives the equation of state of an ideal stellar substance based on conception of gravitating spheroidal body. Using this equation, we obtain the universal stellar law (USL) for the planetary systems connecting temperature, size and mass of each of stars. This work also considers the Solar corona in the connection with USL. Then it is accounting under calculation of the ratio of temperature of the Solar corona to effective temperature of the Sun’ surfaceand modification of USL. To test justice of the modified USLfor different types of stars, the temperature of stellar corona is estimated. The prediction of parameters of stars is carrying out by means of the modified USL,as well as the Hertzsprung-Russell’s dependence [5-7]is derivedby means of USL directly. This paper also shows that knowledge of some characteristics for multi-planet extrasolar systems refines own parameters of

Solar and Stellar X-ray Cycles

Science.gov (United States)

Martens, P. C. H.; SADE Team

2004-05-01

Stern et al. have shown that Yohkoh-SXT full disk X-ray irradiance shows an 11 year cycle with an max/min amplitude ratio of a factor 30. Similar cyclic X-ray variation in Sun-like stars observed by ROSAT and its predecessors is observed in only a few cases and limited to a factor two or three. We will show, by means of detailed bandpass comparisons, that this discrepancy cannot be ascribed to the differences in energy response between SXT and the stellar soft X-ray detectors. Is the Sun exceptional? After centuries of geocentric and heliocentric worldviews we find this a difficult proposition to entertain. But perhaps the Sun is a member of a small class of late-type stars with large amplitudes in their X-ray cycles. The stellar X-ray observations listed in the HEASARC catalog are too sparse to verify this hypothesis. To resolve these and related questions we have proposed a small low-cost stellar X-ray spectroscopic imager originally called SADE to obtain regular time series from late and early-type stars and accretion disks. This instrument is complimentary to the much more advanced Chandra and XMM-Newton observatories, and allows them to focus on those sources that require their full spatial and spectral resolution. We will describe the basic design and spectroscopic capability of SADE and show it meets the mission requirements.

Research in nuclear astrophysics: stellar collapse and supernovae. Progress report and renewal proposal

International Nuclear Information System (INIS)

Lattimer, J.M.; Yahil, A.

1982-01-01

The interaction between nuclear theory and the problem of stellar collapse and supernovae is examined. Experimentally determined nuclear parameters (compressibility, symmetry energies, level densities) are being used to determine a finite temperature equation of state. Detailed studies of shock propagation, neutrino transport and electron capture in stellar collapse are continued. The long-term evolution of collapsed stars (hot proto-neutron stars) is extended to find characteristic signatures of the neutrino spectrum, important for the experiments that can detect extraterrestrial neutrinos. A novel, conservative hydrodynamical code is used to alleviate the requirement of using artificial viscosity to follow shocks. This is coupled with a new, fast numerical scheme for the equation of state

Optical veiling, disk accretion, and the evolution of T Tauri stars

International Nuclear Information System (INIS)

Hartmann, L.W.; Kenyon, S.J.

1990-01-01

High-resolution spectra of 31 K7-M1 T Tauri stars (TTs) in the Taurus-Auriga molecular cloud demonstrate that most of these objects exhibit substantial excess emission at 5200 A. Extrapolations of these data consistent with low-resolution spectrophotometry indicate that the extra emission is comparable to the stellar luminosity in many cases. If this continuum emission arises in the boundary layers of accreting disks, more than about 30 percent of all TTs may be accreting material at a rate which is sufficiently rapid to alter their evolution from standard Hayashi tracks. It is estimated that roughly 10 percent of the final stellar mass is accreted in the TT phase. This amount of material is comparable to the minimum gravitationally unstable disk mass estimated by Larson and it is speculated that the TT phase represents the final stages of disk accretion driven by gravitational instabilities. 40 refs

The diskmass survey. VIII. On the relationship between disk stability and star formation

Energy Technology Data Exchange (ETDEWEB)

Westfall, Kyle B.; Verheijen, Marc A. W. [Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen (Netherlands); Andersen, David R. [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Bershady, Matthew A. [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States); Martinsson, Thomas P. K. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Swaters, Robert A., E-mail: westfall@astro.rug.nl [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

2014-04-10

We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo and Wiegert (Q {sub RW}), incorporating stellar kinematic data for the first time, and the star-formation rate estimated from 21 cm continuum emission. We determine the stability level of each disk probabilistically using a Bayesian analysis of our data and a simple dynamical model. Our method incorporates the shape of the stellar velocity ellipsoid (SVE) and yields robust SVE measurements for over 90% of our sample. Averaging over this subsample, we find a meridional shape of σ{sub z}/σ{sub R}=0.51{sub −0.25}{sup +0.36} for the SVE and, at 1.5 disk scale lengths, a stability parameter of Q {sub RW} = 2.0 ± 0.9. We also find that the disk-averaged star-formation-rate surface density ( Σ-dot {sub e,∗}) is correlated with the disk-averaged gas and stellar mass surface densities (Σ {sub e,} {sub g} and Σ {sub e,} {sub *}) and anti-correlated with Q {sub RW}. We show that an anti-correlation between Σ-dot {sub e,∗} and Q {sub RW} can be predicted using empirical scaling relations, such that this outcome is consistent with well-established statistical properties of star-forming galaxies. Interestingly, Σ-dot {sub e,∗} is not correlated with the gas-only or star-only Toomre parameters, demonstrating the merit of calculating a multi-component stability parameter when comparing to star-formation activity. Finally, our results are consistent with the Ostriker et al. model of self-regulated star-formation, which predicts Σ-dot {sub e,∗}/Σ{sub e,g}∝Σ{sub e,∗}{sup 1/2}. Based on this and other theoretical expectations, we discuss the possibility of a physical link between disk stability level and star-formation rate in light of our empirical results.

Calibrated Tully-fisher Relations For Improved Photometric Estimates Of Disk Rotation Velocities

Science.gov (United States)

Reyes, Reinabelle; Mandelbaum, R.; Gunn, J. E.; Pizagno, J.

2011-01-01

We present calibrated scaling relations (also referred to as Tully-Fisher relations or TFRs) between rotation velocity and photometric quantities-- absolute magnitude, stellar mass, and synthetic magnitude (a linear combination of absolute magnitude and color)-- of disk galaxies at z 0.1. First, we selected a parent disk sample of 170,000 galaxies from SDSS DR7, with redshifts between 0.02 and 0.10 and r band absolute magnitudes between -18.0 and -22.5. Then, we constructed a child disk sample of 189 galaxies that span the parameter space-- in absolute magnitude, color, and disk size-- covered by the parent sample, and for which we have obtained kinematic data. Long-slit spectroscopy were obtained from the Dual Imaging Spectrograph (DIS) at the Apache Point Observatory 3.5 m for 99 galaxies, and from Pizagno et al. (2007) for 95 galaxies (five have repeat observations). We find the best photometric estimator of disk rotation velocity to be a synthetic magnitude with a color correction that is consistent with the Bell et al. (2003) color-based stellar mass ratio. The improved rotation velocity estimates have a wide range of scientific applications, and in particular, in combination with weak lensing measurements, they enable us to constrain the ratio of optical-to-virial velocity in disk galaxies.

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 DISK-WIND-JET CONNECTION IN THE BLACK HOLE H 1743-322

Energy Technology Data Exchange (ETDEWEB)

Miller, J. M.; King, A. L. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Raymond, J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Fabian, A. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom); Reynolds, C. S. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Kallman, T. R. [Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Cackett, E. M. [Department of Physics and Astronomy, Wayne State University, 666 West Hancock Street, Detroit, MI 48201 (United States); Van der Klis, M. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam, Science Park 904, 1098-XH, Amsterdam (Netherlands); Steeghs, D. T. H., E-mail: jonmm@umich.edu [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

2012-11-01

X-ray disk winds are detected in spectrally soft, disk-dominated phases of stellar-mass black hole outbursts. In contrast, compact, steady, relativistic jets are detected in spectrally hard states that are dominated by non-thermal X-ray emission. Although these distinctive outflows appear to be almost mutually exclusive, it is possible that a disk wind persists in hard states but cannot be detected via X-ray absorption lines owing to very high ionization. Here, we present an analysis of a deep, 60 ks Chandra/HETGS observation of the black hole candidate H 1743-322 in the low/hard state. The spectrum shows no evidence of a disk wind, with tight limits, and within the range of ionizing flux levels that were measured in prior Chandra observations wherein a wind was clearly detected. In H 1743-322, at least, disk winds are actually diminished in the low/hard state, and disk winds and jets are likely state dependent and anti-correlated. These results suggest that although the launching radii of winds and jets may differ by orders of magnitude, they may both be tied to a fundamental property of the inner accretion flow, such as the mass accretion rate and/or the magnetic field topology of the disk. We discuss these results in the context of disk winds and jets in other stellar-mass black holes, and possible launching mechanisms for black hole outflows.

Pre-main-sequence disk accretion in Z Canis Majoris

International Nuclear Information System (INIS)

Hartmann, L.; Kenyon, S.J.; Hewett, R.; Edwards, S.; Strom, K.M.; Strom, S.E.; Stauffer, J.R.

1989-01-01

It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion. 41 references

Pre-main-sequence disk accretion in Z Canis Majoris

Science.gov (United States)

Hartmann, L.; Kenyon, S. J.; Hewett, R.; Edwards, S.; Strom, K. M.; Strom, S. E.; Stauffer, J. R.

1989-01-01

It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

Science.gov (United States)

Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

2015-10-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

A FUNDAMENTAL PLANE OF SPIRAL STRUCTURE IN DISK GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Davis, Benjamin L.; Kennefick, Daniel; Kennefick, Julia; Shields, Douglas W. [Arkansas Center for Space and Planetary Sciences, University of Arkansas, 346 1/2 North Arkansas Avenue, Fayetteville, AR 72701 (United States); Westfall, Kyle B. [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, NL-9700 AV Groningen (Netherlands); Flatman, Russell [School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332 (United States); Hartley, Matthew T. [Department of Physics, University of Arkansas, 226 Physics Building, 835 West Dickson Street, Fayetteville, AR 72701 (United States); Berrier, Joel C. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 (United States); Martinsson, Thomas P. K. [Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Swaters, Rob A., E-mail: bld002@email.uark.edu [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

2015-03-20

Spiral structure is the most distinctive feature of disk galaxies and yet debate persists about which theory of spiral structure is correct. Many versions of the density wave theory demand that the pitch angle be uniquely determined by the distribution of mass in the bulge and disk of the galaxy. We present evidence that the tangent of the pitch angle of logarithmic spiral arms in disk galaxies correlates strongly with the density of neutral atomic hydrogen in the disk and with the central stellar bulge mass of the galaxy. These three quantities, when plotted against each other, form a planar relationship that we argue should be fundamental to our understanding of spiral structure in disk galaxies. We further argue that any successful theory of spiral structure must be able to explain this relationship.

IMAGING THE DISK AND JET OF THE CLASSICAL T TAURI STAR AA TAU

International Nuclear Information System (INIS)

Cox, Andrew W.; Grady, Carol A.; Hammel, Heidi B.; Hornbeck, Jeremy; Russell, Ray W.; Sitko, Michael L.; Woodgate, Bruce E.

2013-01-01

Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light. We measure the outer disk radius, 1.''15 ± 0.''10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21'' from the star in data from 2005. The measured outer disk inclination, 71° ± 1°, is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.

Self-interacting dark matter constraints in a thick dark disk scenario

Science.gov (United States)

Vattis, Kyriakos; Koushiappas, Savvas M.

2018-05-01

A thick dark matter disk is predicted in cold dark matter simulations as the outcome of the interaction between accreted satellites and the stellar disk in Milky Way-sized halos. We study the effects of a self-interacting thick dark disk on the energetic neutrino flux from the Sun. We find that for particle masses between 100 GeV and 1 TeV and dark matter annihilation to τ+τ-, either the self-interaction may not be strong enough to solve the small-scale structure motivation or a dark disk cannot be present in the Milky Way.

The Dark Energy Survey: Prospects for resolved stellar populations

Energy Technology Data Exchange (ETDEWEB)

Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

2011-05-06

Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 10⁸ stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

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...

Time-Dependent Variations of Accretion Disk

Directory of Open Access Journals (Sweden)

Hye-Weon Na

1987-06-01

Full Text Available In dward nova we assume the primary star as a white dwarf and the secondary as the late type star which filled Roche lobe. Mass flow from the secondary star leads to the formation of thin accretion disk around the white dwarf. We use the α parameter as viscosity to maintain the disk form and propose that the outburst in dwarf nova cause the steep increase of source term. With these assumptions we solve the basic equations of stellar structure using Newton-Raphson method. We show the physical parameters like temperature, density, pressure, opacity, surface density, height and flux to the radius of disk. Changing the value of α, we compare several parameters when mass flow rate is constant with those of when luminosity of disk is brightest. At the same time, we obtain time-dependent variations of luminosity and mass of disk. We propose the suitable range of α is 0.15-0.18 to the difference of luminosity. We compare several parameters of disk with those of the normal late type stars which have the same molecular weight of disk is lower. Maybe the outburst in dwarf nova is due to the variation of the α value instead of increment of mass flow from the secondary star.

The 0.5-2.22 micrometer Scattered Light Spectrum of the Disk around TW Hya: Detection of a Partially Filled Disk Gap at 80 AU*

Science.gov (United States)

Debes, John H.; Jang-Condell, Hannah; Weinberger, Alycia J.; Roberge, Aki; Schneider, Glenn

2013-01-01

We present a 0.5-2.2 micrometer scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances greater than 40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at approximately 80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady a-disk with an ad hoc gap structure. The thermal properties of the disk are selfconsistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 solar mass.

A Zoo of Radio Relics: Cluster Cores to Filaments Ruta Kale1,2 ...

Indian Academy of Sciences (India)

Abstract. Radio relics in galaxy clusters can be electrons accelerated at cluster merger shocks or adiabatically compressed fossil radio cocoons or dying radio galaxies. The spectral evolution of radio relics is affected by the surrounding thermal plasma. We present a low frequency study of three radio relics representing ...

Imprint of accretion disk-induced migration on gravitational waves from extreme mass ratio inspirals.

Science.gov (United States)

Yunes, Nicolás; Kocsis, Bence; Loeb, Abraham; Haiman, Zoltán

2011-10-21

We study the effects of a thin gaseous accretion disk on the inspiral of a stellar-mass black hole into a supermassive black hole. We construct a phenomenological angular momentum transport equation that reproduces known disk effects. Disk torques modify the gravitational wave phase evolution to detectable levels with LISA for reasonable disk parameters. The Fourier transform of disk-modified waveforms acquires a correction with a different frequency trend than post-Newtonian vacuum terms. Such inspirals could be used to detect accretion disks with LISA and to probe their physical parameters. © 2011 American Physical Society

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.

Magnesium isotopes in giants in the Milky Way inner disk and bulge: First results with 3D stellar atmospheres.

Science.gov (United States)

Thygesen, Anders; Sbordone, Luca; Christlieb, Norbert; Asplund, Martin

2015-01-01

The Milky Way bulge is one of the most poorly understood components of our galaxy and its formation history is still a matter of debate (early collapse vs. disk instability). All knowledge of its chemical evolution history has been so far derived by measuring elemental abundances: no isotopic mixtures have been measured so far in the Bulge. While quite challenging, isotopic measurements can be accomplished with present instruments in bulge stars for a few elements, Magnesium being one of them.Of the three stable Mg isotopes, the most common one, 24Mg, is mainly produced by α capture in SN II, while the other two, 25Mg and 26Mg, can be produced efficiently in massive AGB stars, through the 22Ne(α, n)25Mg(n, γ)26Mg reactions as well as the Mg-Al chain. Moreover, SN II production of 25Mg and 26Mg increases with increasing progenitor metallicity, so in older stellar populations, where only the signature of metal-poor SNe is to be expected, one should not see a significant 25Mg or 26Mg fraction. However, if larger 25Mg/24Mg and 26Mg/24Mg ratios are observed, relative to what is produced in SNe, this is a clear sign of an AGB contribution. As such, Mg isotopic ratios are a very useful probe of AGB pollution onset and chemical enrichment timescale in a stellar population.Here, we present the first ever measurements of Mg isotopes in 7 red giant stars in the Milky Way bulge and inner disk, including two stars in the bulge globular cluster NGC6522. The isotopic abundances have been derived from high resolution, high signal-to-noise VLT-UVES spectra using both standard 1D atmospheric models as well as state-of-the-art 3D hydrodynamical models and spectrosynthesis. The use of 3D atmospheric models impacts the derived ratios and this work represents the first derivation of Mg isotopes using full 3D spectrosynthesis. These results yield new constraints on the proposed formation scenarios of the Milky Way bulge.

PHOTO-REVERBERATION MAPPING OF A PROTOPLANETARY ACCRETION DISK AROUND A T TAURI STAR

Energy Technology Data Exchange (ETDEWEB)

Meng, Huan Y. A.; Plavchan, Peter; Ciardi, David [Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, 770 S. Wilson Ave., Pasadena, CA 91125 (United States); Rieke, George H. [Lunar and Planetary Laboratory and Department of Planetary Sciences, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721 (United States); Cody, Ann Marie [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Güth, Tina [Department of Physics, New Mexico Institute of Mining and Technology, 801 Leroy Pl., Socorro, NM 87801 (United States); Stauffer, John; Carey, Sean; Rebull, Luisa M. [Infrared Science Archive and Spitzer Science Center, Infrared Processing and Analysis Center, California Institute of Technology, MC 314-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Covey, Kevin [Department of Physics and Astronomy, MS-9164, Western Washington University, 516 High St., Bellingham, WA 98225 (United States); Duran-Rojas, Maria C. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 106, 22800, Ensenada, Baja California, México (Mexico); Gutermuth, Robert A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Morales-Calderón, María, E-mail: hyameng@lpl.arizona.edu [Centro de Astrobiología, Departamento de Astrofísica, INTA-CSIC, P.O. Box 78, E-28691, ESAC Campus, Villanueva de la Cañada, Madrid (Spain); and others

2016-05-20

Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner “wall” at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the ρ Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 μ m) and K (2.2 μ m) bands were synchronized while the 4.5 μ m emission lagged by 74.5 ± 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at ∼1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.

Metallicity Distribution of Disk Stars and the Formation History of the Milky Way

Science.gov (United States)

Toyouchi, Daisuke; Chiba, Masashi

2018-03-01

We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, reaccretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters that are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in the APOGEE survey. We succeeded to obtain the best set of model parameters that well reproduces the observed radial dependences of the mean, standard deviation, skewness, and kurtosis of the MDFs for the disk stars. We analyze the basic properties of our model results in detail to gain new insights into the important baryonic processes in the formation history of the MW. One of the remarkable findings is that outflowing gas, containing many heavy elements, preferentially reaccretes onto the outer disk parts, and this recycling process of metal-enriched gas is a key ingredient for reproducing the observed narrower MDFs at larger radii. Moreover, important implications for the radial dependence of gas infall and the influence of radial migration on the MDFs are also inferred from our model calculation. Thus, the MDF of disk stars is a useful clue for studying the formation history of the MW.

THE DISK-WIND-JET CONNECTION IN THE BLACK HOLE H 1743–322

International Nuclear Information System (INIS)

Miller, J. M.; King, A. L.; Raymond, J.; Fabian, A. C.; Reynolds, C. S.; Kallman, T. R.; Cackett, E. M.; Van der Klis, M.; Steeghs, D. T. H.

2012-01-01

X-ray disk winds are detected in spectrally soft, disk-dominated phases of stellar-mass black hole outbursts. In contrast, compact, steady, relativistic jets are detected in spectrally hard states that are dominated by non-thermal X-ray emission. Although these distinctive outflows appear to be almost mutually exclusive, it is possible that a disk wind persists in hard states but cannot be detected via X-ray absorption lines owing to very high ionization. Here, we present an analysis of a deep, 60 ks Chandra/HETGS observation of the black hole candidate H 1743–322 in the low/hard state. The spectrum shows no evidence of a disk wind, with tight limits, and within the range of ionizing flux levels that were measured in prior Chandra observations wherein a wind was clearly detected. In H 1743–322, at least, disk winds are actually diminished in the low/hard state, and disk winds and jets are likely state dependent and anti-correlated. These results suggest that although the launching radii of winds and jets may differ by orders of magnitude, they may both be tied to a fundamental property of the inner accretion flow, such as the mass accretion rate and/or the magnetic field topology of the disk. We discuss these results in the context of disk winds and jets in other stellar-mass black holes, and possible launching mechanisms for black hole outflows.

Photo-reverberation Mapping of a Protoplanetary Accretion Disk around a T Tauri Star

Science.gov (United States)

Meng, Huan Y. A.; Plavchan, Peter; Rieke, George H.; Cody, Ann Marie; Güth, Tina; Stauffer, John; Covey, Kevin; Carey, Sean; Ciardi, David; Duran-Rojas, Maria C.; Gutermuth, Robert A.; Morales-Calderón, María; Rebull, Luisa M.; Watson, Alan M.

2016-05-01

Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner “wall” at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the ρ Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 μm) and K (2.2 μm) bands were synchronized while the 4.5 μm emission lagged by 74.5 ± 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at ˜1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.

Supernova relic electron neutrinos and anti-neutrinos in future large-scale observatories

International Nuclear Information System (INIS)

Volpe, C.; Welzel, J.

2007-01-01

We investigate the signal from supernova relic neutrinos in future large scale observatories, such as MEMPHYS (UNO, Hyper-K), LENA and GLACIER, at present under study. We discuss that complementary information might be gained from the observation of supernova relic electron antineutrinos and neutrinos using the scattering on protons on one hand, and on nuclei such as oxygen, carbon or argon on the other hand. When determining the relic neutrino fluxes we also include, for the first time, the coupling of the neutrino magnetic moment to magnetic fields within the core collapse supernova. We present numerical results on both the relic ν e and ν-bar e fluxes and on the number of events for ν e + C 12 , ν e + O 16 , ν e + Ar 40 and ν-bar e + p for various oscillation scenarios. The observation of supernova relic neutrinos might provide us with unique information on core-collapse supernova explosions, on the star formation history and on neutrino properties, that still remain unknown. (authors)

THE 0.5-2.22 μm SCATTERED LIGHT SPECTRUM OF THE DISK AROUND TW Hya: DETECTION OF A PARTIALLY FILLED DISK GAP AT 80 AU

International Nuclear Information System (INIS)

Debes, John H.; Jang-Condell, Hannah; Weinberger, Alycia J.; Roberge, Aki; Schneider, Glenn

2013-01-01

We present a 0.5-2.2 μm scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances >40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at ∼80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady α-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 M ⊕ .

Gradients of stellar population properties and evolution clues in a nearby galaxy M101

Energy Technology Data Exchange (ETDEWEB)

Lin, Lin; Kong, Xu; Lin, Xuanbin; Mao, Yewei; Cheng, Fuzhen [Center for Astrophysics, University of Science and Technology of China, Hefei 230026 (China); Zou, Hu; Jiang, Zhaoji; Zhou, Xu, E-mail: linlin@mail.ustc.edu.cn, E-mail: xkong@ustc.edu.cn, E-mail: zouhu@nao.cas.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2013-06-01

Multiband photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of the nearby Scd-type galaxy M101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-A {sub FUV} relation, found to depend on a second parameter of birth rate b (ratio of present- and past-averaged star formation rates), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an 'inside-out' disk growth scenario. Two distinct disk regions with different gradients of age and color are discovered, similar to another late-type galaxy, NGC 628. The metallicity gradient of the stellar content is flatter than that of H II regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower compared with galaxies of similar and earlier morphological type. We note that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar which is relatively young, metal-rich, and contains much dust.

Physical properties of dusty protoplanetary disks in Lupus: evidence for viscous evolution?

Science.gov (United States)

Tazzari, M.; Testi, L.; Natta, A.; Ansdell, M.; Carpenter, J.; Guidi, G.; Hogerheijde, M.; Manara, C. F.; Miotello, A.; van der Marel, N.; van Dishoeck, E. F.; Williams, J. P.

2017-10-01

Context. The formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in protoplanetary disks. Thanks to the improvements in resolution and sensitivity provided by ALMA, measurements of the surface density of mm-sized grains are now possible on large samples of disks. Such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation. Aims: We aim to analyze spatially resolved observations of 36 protoplanetary disks in the Lupus star forming complex from our ALMA survey at 890 μm, aiming to determine physical properties such as the dust surface density, the disk mass and size, and to provide a constraint on the temperature profile. Methods: We fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 μm emission by solving the energy balance at each disk radius. Results: For 22 out of 36 protoplanetary disks we derive robust estimates of their physical properties. The sample covers stellar masses between 0.1 and 2 M⊙, and we find no trend in the relationship between the average disk temperatures and the stellar parameters. We find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the Lupus disks. Comparing these results with observations at similar angular resolution of Taurus-Auriga and Ophiuchus disks found in literature and scaling them to the same distance, we observe that the Lupus disks are generally fainter and larger at a high level of statistical significance. Considering the 1-2 Myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass-size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out.

The number density of a charged relic

Energy Technology Data Exchange (ETDEWEB)

Berger, C.F. [Massachusetts Institute of Technology, Cambridge, MA (United States). Center for Theoretical Physics]|[California Univ., Santa Barbara, CA (United States). Kavli Inst. for Theoretical Physics; Covi, L. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kraml, S. [CNRS/IN2P3, Grenoble (France). Lab. de Physique Subatomique et de Cosmologie; Palorini, F. [Lyon Univ., UCBL, CNRS/IN2P3, Villeurbanne (France). IPN de Lyon

2008-07-15

We investigate scenarios in which a charged, long-lived scalar particle decouples from the primordial plasma in the Early Universe. We compute the number density at time of freeze-out considering both the cases of abelian and non-abelian interactions and including the effect of Sommerfeld enhancement at low initial velocity. We also discuss as extreme case the maximal cross section that fulfils the unitarity bound. We then compare these number densities to the exotic nuclei searches for stable relics and to the BBN bounds on unstable relics and draw conclusions for the cases of a stau or stop NLSP in supersymmetric models with a gravitino or axino LSP. (orig.)

The number density of a charged relic

International Nuclear Information System (INIS)

Berger, C.F.; Kraml, S.; Palorini, F.

2008-07-01

We investigate scenarios in which a charged, long-lived scalar particle decouples from the primordial plasma in the Early Universe. We compute the number density at time of freeze-out considering both the cases of abelian and non-abelian interactions and including the effect of Sommerfeld enhancement at low initial velocity. We also discuss as extreme case the maximal cross section that fulfils the unitarity bound. We then compare these number densities to the exotic nuclei searches for stable relics and to the BBN bounds on unstable relics and draw conclusions for the cases of a stau or stop NLSP in supersymmetric models with a gravitino or axino LSP. (orig.)

Radio observations of the double-relic galaxy cluster Abell 1240

Science.gov (United States)

Hoang, D. N.; Shimwell, T. W.; van Weeren, R. J.; Intema, H. T.; Röttgering, H. J. A.; Andrade-Santos, F.; Akamatsu, H.; Bonafede, A.; Brunetti, G.; Dawson, W. A.; Golovich, N.; Best, P. N.; Botteon, A.; Brüggen, M.; Cassano, R.; de Gasperin, F.; Hoeft, M.; Stroe, A.; White, G. J.

2018-05-01

We present LOFAR 120 - 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 - 629 MHz and VLA 2 - 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M=2.4 and 2.3 for the northern and southern shocks, respectively. For M≲ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (>10 per cent) particle acceleration efficiency required. However, for M≳ 4 shocks the required efficiency is ≳ 1% and ≳ 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥53 ± 3° and ≥39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (˜1.8 Mpc) our upper limit on the power is P1.4GHz = (1.4 ± 0.6) × 1023 W Hz-1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.

The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

Science.gov (United States)

King, Ashley L.; Walton, Dominic J.; Miller, Jon M.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fabian, Andy C.; Furst, Felix; Hailey, Charles J.;

An Account of Translation of Relics: the Writings of Alonso de Cartagena

Directory of Open Access Journals (Sweden)

Luis Fernández Gallardo

2018-01-01

Full Text Available The narratives of translation of relics is a genre of devotional literature that didn´t develop extensively in Medieval Castile. But Alonso de Cartagena contributed to it remarkably. In 1453, during a pastoral visit, he decided to move the relics of St. Juliana to a more honorable place. He wrote an account of these facts that adjusts strictly to the features of the genre. This vernacular text contains an exposition about the cult of saints and their relics, which has an intense Thomist inspiration: it sets theological questions with precision and clarity. The provisions on the decoration of the chapel of the relics offer an interesting testimony of the debate on religious image which is then developed in Castile.

a Review of Digital Watermarking and Copyright Control Technology for Cultural Relics

Science.gov (United States)

Liu, H.; Hou, M.; Hu, Y.

2018-04-01

With the rapid growth of the application and sharing of the 3-D model data in the protection of cultural relics, the problem of Shared security and copyright control of the three-dimensional model of cultural relics is becoming increasingly prominent. Followed by a digital watermarking copyright control has become the frontier technology of 3-D model security protection of cultural relics and effective means, related technology research and application in recent years also got further development. 3-D model based on cultural relics digital watermarking and copyright control technology, introduces the research background and demand, its unique characteristics were described, and its development and application of the algorithm are discussed, and the prospects of the future development trend and some problems and the solution.

Radiological data acquisition, investigation and evaluation of mining relics

International Nuclear Information System (INIS)

1992-01-01

Within the scope of a Federal Project, the environmental radioactivity and the radon concentration in buildings caused by mining relics in the new Federal Lands of Germany are investigated. In the first phase of the project, about 8000 relics of former mining were identified by analysing existing documents, categorised, and recorded in a special data bank. Thereby, 'areas of suspicion' of 1500 km 2 spaciously defined in the beginning could be reduced to 'areas of investigation' of 250 km 2 now to be examined in close coordination with the land and district authorities by a programme gradually adapted to the radiological significance of the relics. Experience with site-specific measuring programmes have already been gained through three pilot projects at typical sites of former mining activities. Recommendations of the German Radiation Protection Commission serve for the evaluation of the results. By the measuring programme for radon in buildings of mining and geological predestined regions more than 25000 buildings of 210 communities have been investigated. The results confirm the expected prevailing influence of the geologic underground on the radon concentration. Extreme values are observed where direct connections additionally exist to mining relics in the ground. (orig./HP) With 11 figs. in annex [de

MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED

International Nuclear Information System (INIS)

Martig, Marie; Bournaud, Frederic; Teyssier, Romain; Dekel, Avishai

2009-01-01

We point out a natural mechanism for quenching of star formation in early-type galaxies (ETGs). It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an ETG red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, active galactic nucleus feedback, virial shock heating, and gravitational heating are limited to massive halos, MQ can explain the appearance of red ETGs also in halos less massive than ∼10 12 M sun . The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.

Systematic problems with using dark matter simulations to model stellar halos

International Nuclear Information System (INIS)

Bailin, Jeremy; Bell, Eric F.; Valluri, Monica; Stinson, Greg S.; Debattista, Victor P.; Couchman, H. M. P.; Wadsley, James

2014-01-01

The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be 'painted' onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the 'painting' simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude.

EVIDENCE FOR DYNAMICAL CHANGES IN A TRANSITIONAL PROTOPLANETARY DISK WITH MID-INFRARED VARIABILITY

International Nuclear Information System (INIS)

Muzerolle, James; Flaherty, Kevin; Balog, Zoltan; Smith, Paul S.; Rieke, George H.; Furlan, Elise; Allen, Lori; Muench, August; Calvet, Nuria; D'Alessio, Paola; Megeath, S. Thomas; Sherry, William H.

2009-01-01

We present multi-epoch Spitzer Space Telescope observations of the transitional disk LRLL 31 in the 2-3 Myr old star-forming region IC 348. Our measurements show remarkable mid-infrared variability on timescales as short as one week. The infrared continuum emission exhibits systematic wavelength-dependent changes that suggest corresponding dynamical changes in the inner disk structure and variable shadowing of outer disk material. We propose several possible sources for the structural changes, including a variable accretion rate or a stellar or planetary companion embedded in the disk. Our results indicate that variability studies in the infrared can provide important new constraints on protoplanetary disk behavior.

Models of disk chemical evolution focusing the pure dynamical radial mixing

Directory of Open Access Journals (Sweden)

Re Fiorentin P.

2012-02-01

Full Text Available We performed N-body simulations to study the dynamical evolution of a stellar disk inside a Dark Matter (DM halo. Our results evidence how a standard -radially decreasing- metallicity gradient produces a negative vϕ vs. [Fe/H] correlation, similar to that shown by the thin disk stars, while an inverse radial gradient generates a positive rotation-metallicity correlation, as that observed in the old thick population.

Supernova relic electron neutrinos and anti-neutrinos in future large-scale observatories

Energy Technology Data Exchange (ETDEWEB)

Volpe, C.; Welzel, J. [Institut de Physique Nuclueaire, 91 - Orsay (France)

2007-07-01

We investigate the signal from supernova relic neutrinos in future large scale observatories, such as MEMPHYS (UNO, Hyper-K), LENA and GLACIER, at present under study. We discuss that complementary information might be gained from the observation of supernova relic electron antineutrinos and neutrinos using the scattering on protons on one hand, and on nuclei such as oxygen, carbon or argon on the other hand. When determining the relic neutrino fluxes we also include, for the first time, the coupling of the neutrino magnetic moment to magnetic fields within the core collapse supernova. We present numerical results on both the relic {nu}{sub e} and {nu}-bar{sub e} fluxes and on the number of events for {nu}{sub e} + C{sup 12}, {nu}{sub e} + O{sup 16}, {nu}{sub e} + Ar{sup 40} and {nu}-bar{sub e} + p for various oscillation scenarios. The observation of supernova relic neutrinos might provide us with unique information on core-collapse supernova explosions, on the star formation history and on neutrino properties, that still remain unknown. (authors)

The formation of stellar black holes

Science.gov (United States)

Mirabel, Félix

2017-08-01

It is believed that stellar black holes (BHs) can be formed in two different ways: Either a massive star collapses directly into a BH without a supernova (SN) explosion, or an explosion occurs in a proto-neutron star, but the energy is too low to completely unbind the stellar envelope, and a large fraction of it falls back onto the short-lived neutron star (NS), leading to the delayed formation of a BH. Theoretical models set progenitor masses for BH formation by implosion, namely, by complete or almost complete collapse, but observational evidences have been elusive. Here are reviewed the observational insights on BHs formed by implosion without large natal kicks from: (1) the kinematics in three dimensions of space of five Galactic BH X-ray binaries (BH-XRBs), (2) the diversity of optical and infrared observations of massive stars that collapse in the dark, with no luminous SN explosions, possibly leading to the formation of BHs, and (3) the sources of gravitational waves (GWs) produced by mergers of stellar BHs so far detected with LIGO. Multiple indications of BH formation without ejection of a significant amount of matter and with no natal kicks obtained from these different areas of observational astrophysics, and the recent observational confirmation of the expected dependence of BH formation on metallicity and redshift, are qualitatively consistent with the high merger rates of binary black holes (BBHs) inferred from the first detections with LIGO.

A-type Stellar Abundances: A Corollary to Herschel Observations of Debris Disks

Science.gov (United States)

Draper, Zachary H.; Matthews, Brenda; Venn, Kim; Lambert, David; Kennedy, Grant; Sitnova, Tatyana

2018-04-01

In order to assess the relationship between metallicity and exoplanetary systems, we compare the abundances of AF-type main-sequence stars with debris disk properties assessed using Herschel observations of an unbiased survey of nearby stars. Hot stars are not as commonly observed, given their unique constraints in data reduction, lack of metal lines, and “astrophysical noise” from rotation speed. Here, we address that deficiency using new and archival spectra of 83 AF-type stars. We measure the abundances of a few species in addition to Fe in order to classify the stars with Ap/Am or Lambda Boo signatures. Lambda Boo stars have a chemical signature of solar-abundant volatile species and sub-solar refractory abundances that is hypothesized to be altered by the pollution of volatiles. Overall, we see no correlation between debris disks and metallicity, primarily because the sample size is cut significantly when using only reliable fits to the spectroscopic data. The abundance measured from the Mg II 4481 blend is a useful diagnostic because it can be reliably measured at large v·sin(i) and is found to be lower around stars with bright debris disks. We find that Lambda Boo stars have brighter debris disks compared to a bias-free sample of AF stars. The trend with disk brightness and Mg abundances suggests pollution effects can be significant and used as a marker for the stability of planetary systems. We explore trends with other species, such as with the C/O ratios, but are significantly limited by the low number of reliable detections.

An ALMA continuum survey of circumstellar disks in the upper Scorpius OB association

Energy Technology Data Exchange (ETDEWEB)

Carpenter, John M.; Ricci, Luca; Isella, Andrea [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States)

2014-05-20

We present ALMA 880 μm continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M {sub ☉}) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 μm dust continuum at ≥3σ with inferred dust masses between 0.3 and 52 M {sub ⊕}. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ≈ 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around ∼1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3σ. For stellar masses between 0.49 M {sub ☉} and 1.6 M {sub ☉}, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Δlog M {sub dust} = 0.44 ± 0.26.

Vacuum birefringence and the x-ray polarization from black-hole accretion disks

Science.gov (United States)

Caiazzo, Ilaria; Heyl, Jeremy

2018-04-01

In the next decade, x-ray polarimetry will open a new window on the high-energy Universe, as several missions that include an x-ray polarimeter are currently under development. Observations of the polarization of x rays coming from the accretion disks of stellar-mass and supermassive black holes are among the new polarimeters' major objectives. In this paper, we show that these observations can be affected by the quantum electrodynamic (QED) effect of vacuum birefringence: after an x-ray photon is emitted from the accretion disk, its polarization changes as the photon travels through the accretion disk's magnetosphere, as a result of the vacuum becoming birefringent in the presence of a magnetic field. We show that this effect can be important for black holes in the energy band of the upcoming polarimeters and has to be taken into account in a complete model of the x-ray polarization that we expect to detect from black-hole accretion disks, both for stellar mass and for supermassive black holes. We find that, for a chaotic magnetic field in the disk, QED can significantly decrease the linear polarization fraction of edge-on photons, depending on the spin of the hole and on the strength of the magnetic field. This effect can provide, for the first time, a direct way to probe the magnetic field strength close to the innermost stable orbit of black-hole accretion disks and to study the role of magnetic fields in astrophysical accretion in general.

A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

International Nuclear Information System (INIS)

Lee, Eve J.; Chiang, Eugene

2016-01-01

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

A Primer on Unifying Debris Disk Morphologies

Science.gov (United States)

Lee, Eve J.; Chiang, Eugene

2016-08-01

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

A PRIMER ON UNIFYING DEBRIS DISK MORPHOLOGIES

Energy Technology Data Exchange (ETDEWEB)

Lee, Eve J.; Chiang, Eugene, E-mail: evelee@berkeley.edu, E-mail: echiang@astro.berkeley.edu [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720-3411 (United States)

2016-08-20

A “minimum model” for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: “rings,” “needles,” “ships-and-wakes,” “bars,” and “moths (a.k.a. fans),” depending on the viewing geometry. Moths can also sport “double wings.” We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.

THE DiskMass SURVEY. III. STELLAR KINEMATICS VIA CROSS-CORRELATION

International Nuclear Information System (INIS)

Westfall, Kyle B.; Bershady, Matthew A.; Verheijen, Marc A. W.

2011-01-01

We describe a new cross-correlation (CC) approach used by our survey to derive stellar kinematics from galaxy-continuum spectroscopy. This approach adopts the formal error analysis derived by Statler, but properly handles spectral masks. Thus, we address the primary concerns regarding application of the CC method to censored data, while maintaining its primary advantage by consolidating kinematic and template-mismatch information toward different regions of the CC function. We identify a systematic error in the nominal CC method of approximately 10% in velocity dispersion incurred by a mistreatment of detector-censored data, which is eliminated by our new method. We derive our approach from first principles, and we use Monte Carlo simulations to demonstrate its efficacy. An identical set of Monte Carlo simulations performed using the well-established penalized-pixel-fitting code of Cappellari and Emsellem compares favorably with the results from our newly implemented software. Finally, we provide a practical demonstration of this software by extracting stellar kinematics from SparsePak spectra of UGC 6918.

CN rings in full protoplanetary disks around young stars as probes of disk structure

Science.gov (United States)

Cazzoletti, P.; van Dishoeck, E. F.; Visser, R.; Facchini, S.; Bruderer, S.

2018-01-01

Aims: Bright ring-like structure emission of the CN molecule has been observed in protoplanetary disks. We investigate whether such structures are due to the morphology of the disk itself or if they are instead an intrinsic feature of CN emission. With the intention of using CN as a diagnostic, we also address to which physical and chemical parameters CN is most sensitive. Methods: A set of disk models were run for different stellar spectra, masses, and physical structures via the 2D thermochemical code DALI. An updated chemical network that accounts for the most relevant CN reactions was adopted. Results: Ring-shaped emission is found to be a common feature of all adopted models; the highest abundance is found in the upper outer regions of the disk, and the column density peaks at 30-100 AU for T Tauri stars with standard accretion rates. Higher mass disks generally show brighter CN. Higher UV fields, such as those appropriate for T Tauri stars with high accretion rates or for Herbig Ae stars or for higher disk flaring, generally result in brighter and larger rings. These trends are due to the main formation paths of CN, which all start with vibrationally excited H_2^* molecules, that are produced through far ultraviolet (FUV) pumping of H2. The model results compare well with observed disk-integrated CN fluxes and the observed location of the CN ring for the TW Hya disk. Conclusions: CN rings are produced naturally in protoplanetary disks and do not require a specific underlying disk structure such as a dust cavity or gap. The strong link between FUV flux and CN emission can provide critical information regarding the vertical structure of the disk and the distribution of dust grains which affects the UV penetration, and could help to break some degeneracies in the SED fitting. In contrast with C2H or c-C3H2, the CN flux is not very sensitive to carbon and oxygen depletion.

REMOVING BIASES IN RESOLVED STELLAR MASS MAPS OF GALAXY DISKS THROUGH SUCCESSIVE BAYESIAN MARGINALIZATION

Energy Technology Data Exchange (ETDEWEB)

Martínez-García, Eric E. [Cerrada del Rey 40-A, Chimalcoyoc Tlalpan, Ciudad de México, C.P. 14630, México (Mexico); González-Lópezlira, Rosa A.; Bruzual A, Gustavo [Instituto de Radioastronomía y Astrofísica, UNAM, Campus Morelia, Michoacán, C.P. 58089, México (Mexico); Magris C, Gladis, E-mail: martinezgarciaeric@gmail.com [Centro de Investigaciones de Astronomía, Apartado Postal 264, Mérida 5101-A (Venezuela, Bolivarian Republic of)

2017-01-20

Stellar masses of galaxies are frequently obtained by fitting stellar population synthesis models to galaxy photometry or spectra. The state of the art method resolves spatial structures within a galaxy to assess the total stellar mass content. In comparison to unresolved studies, resolved methods yield, on average, higher fractions of stellar mass for galaxies. In this work we improve the current method in order to mitigate a bias related to the resolved spatial distribution derived for the mass. The bias consists in an apparent filamentary mass distribution and a spatial coincidence between mass structures and dust lanes near spiral arms. The improved method is based on iterative Bayesian marginalization, through a new algorithm we have named Bayesian Successive Priors (BSP). We have applied BSP to M51 and to a pilot sample of 90 spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. By quantitatively comparing both methods, we find that the average fraction of stellar mass missed by unresolved studies is only half what previously thought. In contrast with the previous method, the output BSP mass maps bear a better resemblance to near-infrared images.

Modeling Protoplanetary Disks to Characterize the Evolution of their Structure

Science.gov (United States)

Allen, Magdelena; van der Marel, Nienke; Williams, Jonathan

2018-01-01

Stars form from gravitationally collapsing clouds of gas and dust. Most young stars retain a protoplanetary disk for a few million years. This disk’s dust reemits stellar flux in the infrared, producing a spectral energy distribution (SED) observable by Spitzer and other telescopes. To understand the inner clearing of dust cavities and evolution in the SED, we used the Chiang & Goldreich two-layer approximation. We first wrote a python script based on refinements by Dullemond that includes a hot, puffed inner rim, shadowed mid region, flaring outer disk, and a variable inner cavity. This was then coupled with a Markov Chain Monte Carlo procedure to fit the observed SEDs of disks in the star forming Lupus region. The fitting procedure recovers physical characteristics of the disk including temperature, size, mass, and surface density. We compare the characteristics of circumstellar disks without holes and more evolved transition disks with cleared inner regions.

Cosmic relics from the big bang

International Nuclear Information System (INIS)

Hall, L.J.

1988-12-01

A brief introduction to the big bang picture of the early universe is given. Dark matter is discussed; particularly its implications for elementary particle physics. A classification scheme for dark matter relics is given. 21 refs., 11 figs., 1 tab

Cosmic relics from the big bang

Energy Technology Data Exchange (ETDEWEB)

Hall, L.J.

1988-12-01

A brief introduction to the big bang picture of the early universe is given. Dark matter is discussed; particularly its implications for elementary particle physics. A classification scheme for dark matter relics is given. 21 refs., 11 figs., 1 tab.

ProtoMD: A prototyping toolkit for multiscale molecular dynamics

Science.gov (United States)

Somogyi, Endre; Mansour, Andrew Abi; Ortoleva, Peter J.

2016-05-01

ProtoMD is a toolkit that facilitates the development of algorithms for multiscale molecular dynamics (MD) simulations. It is designed for multiscale methods which capture the dynamic transfer of information across multiple spatial scales, such as the atomic to the mesoscopic scale, via coevolving microscopic and coarse-grained (CG) variables. ProtoMD can be also be used to calibrate parameters needed in traditional CG-MD methods. The toolkit integrates 'GROMACS wrapper' to initiate MD simulations, and 'MDAnalysis' to analyze and manipulate trajectory files. It facilitates experimentation with a spectrum of coarse-grained variables, prototyping rare events (such as chemical reactions), or simulating nanocharacterization experiments such as terahertz spectroscopy, AFM, nanopore, and time-of-flight mass spectroscopy. ProtoMD is written in python and is freely available under the GNU General Public License from github.com/CTCNano/proto_md.

Another shock for the Bullet cluster, and the source of seed electrons for radio relics

Science.gov (United States)

Shimwell, Timothy W.; Markevitch, Maxim; Brown, Shea; Feretti, Luigina; Gaensler, B. M.; Johnston-Hollitt, M.; Lage, Craig; Srinivasan, Raghav

2015-05-01

With Australia Telescope Compact Array observations, we detect a highly elongated Mpc-scale diffuse radio source on the eastern periphery of the Bullet cluster 1E 0657-55.8, which we argue has the positional, spectral and polarimetric characteristics of a radio relic. This powerful relic (2.3 ± 0.1 × 1025 W Hz-1) consists of a bright northern bulb and a faint linear tail. The bulb emits 94 per cent of the observed radio flux and has the highest surface brightness of any known relic. Exactly coincident with the linear tail, we find a sharp X-ray surface brightness edge in the deep Chandra image of the cluster - a signature of a shock front in the hot intracluster medium (ICM), located on the opposite side of the cluster to the famous bow shock. This new example of an X-ray shock coincident with a relic further supports the hypothesis that shocks in the outer regions of clusters can form relics via diffusive shock (re-)acceleration. Intriguingly, our new relic suggests that seed electrons for reacceleration are coming from a local remnant of a radio galaxy, which we are lucky to catch before its complete disruption. If this scenario, in which a relic forms when a shock crosses a well-defined region of the ICM polluted with aged relativistic plasma - as opposed to the usual assumption that seeds are uniformly mixed in the ICM - is also the case for other relics, this may explain a number of peculiar properties of peripheral relics.

Analysis on the environment of cultural relic as tourist attraction--take Yungang Grottoes as an example

Science.gov (United States)

Xiangdong, Zhu; Jie, Bai

2018-03-01

Cultural relic resources are precious non-renewable resources and an important cornerstone for the development of cultural relic tourism. With the rapid development of tourism industry, the native environment of cultural relics is being squeezed constantly. Meanwhile, under the economic interests, cultural relic’s protection and heritage tourism contradictions continue to intensify. The present era which the architectural style is convergence, cultural relics protection is simplistic, restore historical sites blindly and other. In the historical process of economic development and the acceleration of new-type urbanization, the heritage industry faces the dual tasks and development challenges. As cultural relic protection workers, investigation of the utilization of cultural relic’s tourist attractions, investigation and analysis of the Yungang Grottoes, indicating cultural relics as a tourist attraction, not only to strengthen the protection of ontology, also should attach importance to the coordinated development of the protection of cultural relics and the utilization of tourism.

Proto-2 seduces America

CERN Multimedia

2002-01-01

Proto-2, an ALICE detector prototype, overcame its prototype status to become a real part of the STAR experiment at the US Brookhaven National Laboratory. After more than two years across the ocean, it has just arrived back at CERN.

Relic gravitons and viscous cosmologies

International Nuclear Information System (INIS)

Cataldo, Mauricio; Mella, Patricio

2006-01-01

Previously it was shown that there exists a class of viscous cosmological models which violate the dominant energy condition for a limited amount of time after which they are smoothly connected to the ordinary radiation era (which preserves the dominant energy conditions). This violation of the dominant energy condition at an early cosmological epoch may influence the slopes of energy spectra of relic gravitons that might be of experimental relevance. However, the bulk viscosity coefficient of these cosmologies became negative during the ordinary radiation era, and then the entropy of the sources driving the geometry decreases with time. We show that in the presence of viscous sources with a linear barotropic equation of state p=γρ we get viscous cosmological models with positive bulk viscous stress during all their evolution, and hence the matter entropy increases with the expansion time. In other words, in the framework of viscous cosmologies, there exist isotropic models compatible with the standard second law of thermodynamics which also may influence the slopes of energy spectra of relic gravitons

Bright Localized Near-Infrared Emission at 1-4 AU in the AB Aurigae Disk Revealed by IOTA Closure Phases

Science.gov (United States)

Millan-Gabet, R.; Monnier, J. D.; Berger, J.-P.; Traub, W. A.; Schloerb, F. P.; Pedretti, E.; Benisty, M.; Carleton, N. P.; Haguenauer, P.; Kern, P.; Labeye, P.; Lacasse, M. G.; Malbet, F.; Perraut, K.; Pearlman, M.; Thureau, N.

2006-07-01

We report on the detection of localized off-center emission at 1-4 AU in the circumstellar environment of the young stellar object AB Aurigae. We used closure-phase measurements in the near-infrared that were made at the long-baseline interferometer IOTA, the first obtained on a young stellar object using this technique. When probing sub-AU scales, all closure phases are close to zero degrees, as expected given the previously determined size of the AB Aurigae inner-dust disk. However, a clear closure-phase signal of -3.5d +/- 0.5d is detected on one triangle containing relatively short baselines, requiring a high degree of non-point symmetry from emission at larger (AU-sized) scales in the disk. We have not identified any alternative explanation for these closure-phase results, and we demonstrate that a ``disk hot spot'' model can fit our data. We speculate that such detected asymmetric near-infrared emission might arise as a result of localized viscous heating due to a gravitational instability in the AB Aurigae disk, or to the presence of a close stellar companion or accreting substellar object.

EXTINCTION IN STAR-FORMING DISK GALAXIES FROM INCLINATION-DEPENDENT COMPOSITE SPECTRA

International Nuclear Information System (INIS)

Yip, Ching-Wa; Szalay, Alex S.; Wyse, Rosemary F. G.; Budavari, Tamas; Dobos, Laszlo; Csabai, Istvan

2010-01-01

Extinction in galaxies affects their observed properties. In scenarios describing the distribution of dust and stars in individual disk galaxies, the amplitude of the extinction can be modulated by the inclination of the galaxies. In this work, we investigate the inclination dependency in composite spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data Release 5. In a volume-limited sample within a redshift range 0.065-0.075 and a r-band Petrosian absolute magnitude range -19.5 to -22 mag which exhibits a flat distribution of inclination, the inclined relative to face-on extinction in the stellar continuum is found empirically to increase with inclination in the g, r, and i bands. Within the central 0.5 intrinsic half-light radius of the galaxies, the g-band relative extinction in the stellar continuum for the highly inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with previous studies. The extinction curve of the disk galaxies is given in the rest-frame wavelengths 3700-8000 A, identified with major optical emission and absorption lines in diagnostics. The Balmer decrement, Hα/Hβ, remains constant with inclination, suggesting a different kind of dust configuration and/or reddening mechanism in the H II region from that in the stellar continuum. One factor is shown to be the presence of spatially non-uniform interstellar extinction, presumably caused by clumped dust in the vicinity of the H II region.

Spiral density waves in M81. I. Stellar spiral density waves

International Nuclear Information System (INIS)

Feng, Chien-Chang; Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Taam, Ronald E.

2014-01-01

Aside from the grand-design stellar spirals appearing in the disk of M81, a pair of stellar spiral arms situated well inside the bright bulge of M81 has been recently discovered by Kendall et al. The seemingly unrelated pairs of spirals pose a challenge to the theory of spiral density waves. To address this problem, we have constructed a three-component model for M81, including the contributions from a stellar disk, a bulge, and a dark matter halo subject to observational constraints. Given this basic state for M81, a modal approach is applied to search for the discrete unstable spiral modes that may provide an understanding for the existence of both spiral arms. It is found that the apparently separated inner and outer spirals can be interpreted as a single trailing spiral mode. In particular, these spirals share the same pattern speed 25.5 km s –1 kpc –1 with a corotation radius of 9.03 kpc. In addition to the good agreement between the calculated and the observed spiral pattern, the variation of the spiral amplitude can also be naturally reproduced.

SS Cygni: The accretion disk in eruption and at minimum light

International Nuclear Information System (INIS)

Kiplinger, A.L.

1979-01-01

Absolute spectrophotometric observations of the dwarf nova SS Cygni have been obtained at maximum light, during the subsequent decline, and at minimum light. In order to provide a critical test of accretion disk theory, a model for a steady-state α-model accretion disk has been constructed which utilizes a grid of stellar energy distributions to synthesize the disk flux. Physical parameters for the accretion disk at maximum light are set by estimates of the intrinsic luminosity of the system that result from a desynthesis of a composite minimum light energy distribution. At maximum light, agreements between observational and theoretical continuum slopes and the Balmer jump are remarkably good. The model fails, however, during the eruption decline and at minimum light. It appears that the physical character of an accretion disk at minimum light must radiacally differ from the disk observed at maximum light

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.

RADIAL DISTRIBUTION OF STARS, GAS, AND DUST IN SINGS GALAXIES. III. MODELING THE EVOLUTION OF THE STELLAR COMPONENT IN GALAXY DISKS

International Nuclear Information System (INIS)

Munoz-Mateos, J. C.; Boissier, S.; Gil de Paz, A.; Zamorano, J.; Gallego, J.; Kennicutt, R. C. Jr; Moustakas, J.; Prantzos, N.

2011-01-01

We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey. We make use of ultraviolet (UV), optical, and near-infrared radial profiles, corrected for internal extinction using the total-infrared to UV ratio, to probe the emission of stellar populations of different ages as a function of galactocentric distance. We fit these radial profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward evolutionary models successfully reproduce the multi-wavelength profiles of our galaxies, except for the UV profiles of some early-type disks for which the models seem to retain too much gas. From the model fitting we infer the maximum circular velocity of the rotation curve V C and the dimensionless spin parameter λ. The values of V C are in good agreement with the velocities measured in H I rotation curves. Even though our sample is not volume limited, the resulting distribution of λ is close to the lognormal function obtained in cosmological N-body simulations, peaking at λ ∼ 0.03 regardless of the total halo mass. We do not find any evident trend between λ and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale lengths as they become more massive. The radial scale length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc Gyr -1 , although the same cannot be said of a volume-limited sample. In relative terms, the scale length has grown by 20%-25% since z = 1 and, unlike the former figure, we argue that this relative growth rate can be indeed representative of a complete galaxy sample.

Radial Distribution of Stars, Gas, and Dust in SINGS Galaxies. III. Modeling the Evolution of the Stellar Component in Galaxy Disks

Science.gov (United States)

Muñoz-Mateos, J. C.; Boissier, S.; Gil de Paz, A.; Zamorano, J.; Kennicutt, R. C., Jr.; Moustakas, J.; Prantzos, N.; Gallego, J.

2011-04-01

We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey. We make use of ultraviolet (UV), optical, and near-infrared radial profiles, corrected for internal extinction using the total-infrared to UV ratio, to probe the emission of stellar populations of different ages as a function of galactocentric distance. We fit these radial profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward evolutionary models successfully reproduce the multi-wavelength profiles of our galaxies, except for the UV profiles of some early-type disks for which the models seem to retain too much gas. From the model fitting we infer the maximum circular velocity of the rotation curve V C and the dimensionless spin parameter λ. The values of V C are in good agreement with the velocities measured in H I rotation curves. Even though our sample is not volume limited, the resulting distribution of λ is close to the lognormal function obtained in cosmological N-body simulations, peaking at λ ~ 0.03 regardless of the total halo mass. We do not find any evident trend between λ and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale lengths as they become more massive. The radial scale length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc Gyr-1, although the same cannot be said of a volume-limited sample. In relative terms, the scale length has grown by 20%-25% since z = 1 and, unlike the former figure, we argue that this relative growth rate can be indeed representative of a complete galaxy sample.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

International Nuclear Information System (INIS)

Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

2012-01-01

We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

WATER ICE AT THE SURFACE OF THE HD 100546 DISK

International Nuclear Information System (INIS)

Honda, M.; Kudo, T.; Terada, H.; Takato, N.; Takatsuki, S.; Nakamoto, T.; Inoue, A. K.; Fukagawa, M.; Tamura, M.

2016-01-01

We made near-infrared multicolor imaging observations of a disk around Herbig Be star HD 100546 using Gemini/NICI. K (2.2 μm), H 2 O ice (3.06 μm), and L′ (3.8 μm) disk images were obtained and we found a 3.1 μm absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on Oka et al., including the water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by both the disk models with and without the photodesorption effect within the measurement accuracy, but the model with photodesorption effects is slightly more favored, implying that the UV photons play an important role in the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement to the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models

WATER ICE AT THE SURFACE OF THE HD 100546 DISK

Energy Technology Data Exchange (ETDEWEB)

Honda, M. [Department of Physics, Kurume University School of Medicine, 67 Asahi-machi, Kurume, Fukuoka, 830-0011 (Japan); Kudo, T.; Terada, H.; Takato, N. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, Hawaii 96720 (United States); Takatsuki, S.; Nakamoto, T. [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Inoue, A. K. [College of General Education, Osaka Sangyo University, Daito, Osaka 574-8530 (Japan); Fukagawa, M.; Tamura, M. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2016-04-10

We made near-infrared multicolor imaging observations of a disk around Herbig Be star HD 100546 using Gemini/NICI. K (2.2 μm), H{sub 2}O ice (3.06 μm), and L′ (3.8 μm) disk images were obtained and we found a 3.1 μm absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on Oka et al., including the water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by both the disk models with and without the photodesorption effect within the measurement accuracy, but the model with photodesorption effects is slightly more favored, implying that the UV photons play an important role in the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement to the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models.

Relating the baryon asymmetry to the thermal relic dark matter density

International Nuclear Information System (INIS)

McDonald, John

2011-01-01

We present a generic framework, baryomorphosis, which modifies the baryon asymmetry to be naturally of the order of a typical thermal relic weakly interacting massive particle (WIMP) density. We consider a simple scalar-based model to show how this is possible. This model introduces a sector in which a large initial baryon asymmetry is injected into particles ('annihilons'), φ B , φ-circumflex B , of mass ∼100 GeV-1 TeV. φ B φ-circumflex B annihilations convert the initial φ B , φ-circumflex B asymmetry to a final asymmetry with a thermal relic WIMP-like density. This subsequently decays to a conventional baryon asymmetry whose magnitude is naturally related to the density of thermal relic WIMP dark matter. In this way the two coincidences of baryons and dark matter, i.e. why their densities are similar to each other and why they are both similar to a WIMP thermal relic density (the 'WIMP miracle'), may be understood. The model may be tested by the production of annihilons at colliders.

Measuring a Truncated Disk in Aquila X-1

Science.gov (United States)

King, Ashley L.; Tomsick, John A.; Miller, Jon M.; Chenevez, Jerome; Barret, Didier; Boggs, Steven E.; Chakrabarty, Deepto; Christensen, Finn E.; Craig, William W.; Feurst, Felix;

SEARCHING FOR PLANETS IN HOLEY DEBRIS DISKS WITH THE APODIZING PHASE PLATE

International Nuclear Information System (INIS)

Meshkat, Tiffany; Kenworthy, Matthew A.; Bailey, Vanessa P.; Su, Kate Y. L.; Hinz, Philip M.; Smith, Paul S.; Mamajek, Eric E.

2015-01-01

We present our first results from a high-contrast imaging search for planetary mass companions around stars with gapped debris disks, as inferred from the stars' bright infrared excesses. For the six considered stars, we model the disks' unresolved infrared spectral energy distributions in order to derive the temperature and location of the disk components. With VLT/NaCo Apodizing Phase Plate coronagraphic L'-band imaging, we search for planetary mass companions that may be sculpting the disks. We detect neither disks nor companions in this sample, confirmed by comparing plausible point sources with archival data. In order to calculate our mass sensitivity limit, we revisit the stellar age estimates. One target, HD 17848, at 540 ± 100 Myr old is significantly older than previously estimated. We then discuss our high-contrast imaging results with respect to the disk properties

SEARCHING FOR PLANETS IN HOLEY DEBRIS DISKS WITH THE APODIZING PHASE PLATE

Energy Technology Data Exchange (ETDEWEB)

Meshkat, Tiffany; Kenworthy, Matthew A. [Sterrewacht Leiden, P.O. Box 9513, Niels Bohrweg 2, 2300 RA Leiden (Netherlands); Bailey, Vanessa P.; Su, Kate Y. L.; Hinz, Philip M.; Smith, Paul S. [Steward Observatory, Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States)

2015-02-10

We present our first results from a high-contrast imaging search for planetary mass companions around stars with gapped debris disks, as inferred from the stars' bright infrared excesses. For the six considered stars, we model the disks' unresolved infrared spectral energy distributions in order to derive the temperature and location of the disk components. With VLT/NaCo Apodizing Phase Plate coronagraphic L'-band imaging, we search for planetary mass companions that may be sculpting the disks. We detect neither disks nor companions in this sample, confirmed by comparing plausible point sources with archival data. In order to calculate our mass sensitivity limit, we revisit the stellar age estimates. One target, HD 17848, at 540 ± 100 Myr old is significantly older than previously estimated. We then discuss our high-contrast imaging results with respect to the disk properties.

Dynamical behaviour of gaseous halo in a disk galaxy

International Nuclear Information System (INIS)

Ikeuchi, S.; Habe, A.

1981-01-01

Assuming that the gas in the halo of a disk galaxy is supplied from the disk as a hot gas, the authors have studied its dynamical and thermal behaviour by means of a time dependent, two-dimensional hydrodynamic code. They suppose the following boundary conditions at the disk. (i) The hot gas with the temperature Tsub(d) and the density nsub(d) is uniform at r=4-12 kpc in the disk and it is time independent. (ii) This hot gas rotates with the stellar disk in the same velocity. (iii) This hot gas can escape freely from the disk to the halo. These conditions will be verified if the filling factor of hot gas is so large as f=0.5-0.8, as proposed by McKee and Ostriker (1977). The gas motion in the halo has been studied for wider ranges of gas temperature and its density at the disk than previously studied. At the same time, the authors have clarified the observability of various types of gaseous haloes and discuss the roles of gaseous halo on the evolution of galaxies. (Auth.)

THE STABILITY OF LOW SURFACE BRIGHTNESS DISKS BASED ON MULTI-WAVELENGTH MODELING

International Nuclear Information System (INIS)

MacLachlan, J. M.; Wood, K.; Matthews, L. D.; Gallagher, J. S.

2011-01-01

To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multi-wavelength photometry to construct spectral energy distributions for three low-mass, edge-on LSB galaxies (V rot = 88-105 km s -1 ). We use Monte Carlo radiation transfer codes that include the effects of transiently heated small grains and polycyclic aromatic hydrocarbon molecules to model and interpret the data. We find that, unlike the high surface brightness galaxies previously modeled, the dust disks appear to have scale heights equal to or exceeding their stellar scale heights. This result supports the findings of previous studies that low-mass disk galaxies have dust scale heights comparable to their stellar scale heights and suggests that the cold ISM of low-mass, LSB disk galaxies may be stable against fragmentation and gravitational collapse. This may help to explain the lack of observed dust lanes in edge-on LSB galaxies and their low current star formation rates. Dust masses are found in the range (1.16-2.38) x 10 6 M sun , corresponding to face-on (edge-on), V-band, optical depths 0.034 ∼ face ∼ eq ∼< 1.99).

The Growth of the Disk Galaxy UGC8802

Science.gov (United States)

Chang, R. X.; Shen, S. Y.; Hou, J. L.

2012-07-01

The disk galaxy UGC8802 has high neutral gas content and a flat profile of star formation rate compared to other disk galaxies with similar stellar mass. It also shows a steep metallicity gradient. We construct a chemical evolution model to explore its growth history by assuming its disk grows gradually from continuous gas infall, which is shaped by a free parameter—the infall-peak time. By adopting the recently observed molecular surface density related star formation law, we show that a late infall-peak time can naturally explain the observed high neutral gas content, while an inside-out disk formation scenario can fairly reproduce the steep oxygen abundance gradient. Our results show that most of the observed features of UGC8802 can be well reproduced by simply "turning the knob" on gas inflow with one single parameter, which implies that the observed properties of gas-rich galaxies could also be modeled in a similar way.

Imprints of relic gravitational waves in cosmic microwave background radiation

International Nuclear Information System (INIS)

Baskaran, D.; Grishchuk, L. P.; Polnarev, A. G.

2006-01-01

A strong variable gravitational field of the very early Universe inevitably generates relic gravitational waves by amplifying their zero-point quantum oscillations. We begin our discussion by contrasting the concepts of relic gravitational waves and inflationary 'tensor modes'. We explain and summarize the properties of relic gravitational waves that are needed to derive their effects on cosmic microwave background (CMB) temperature and polarization anisotropies. The radiation field is characterized by four invariants I, V, E, B. We reduce the radiative transfer equations to a single integral equation of Voltairre type and solve it analytically and numerically. We formulate the correlation functions C l XX ' for X, X ' =T, E, B and derive their amplitudes, shapes and oscillatory features. Although all of our main conclusions are supported by exact numerical calculations, we obtain them, in effect, analytically by developing and using accurate approximations. We show that the TE correlation at lower l's must be negative (i.e. an anticorrelation), if it is caused by gravitational waves, and positive if it is caused by density perturbations. This difference in TE correlation may be a signature more valuable observationally than the lack or presence of the BB correlation, since the TE signal is about 100 times stronger than the expected BB signal. We discuss the detection by WMAP of the TE anticorrelation at l≅30 and show that such an anticorrelation is possible only in the presence of a significant amount of relic gravitational waves (within the framework of all other common assumptions). We propose models containing considerable amounts of relic gravitational waves that are consistent with the measured TT, TE and EE correlations

Variable H13CO+ Emission in the IM Lup Disk: X-Ray Driven Time-dependent Chemistry?

Science.gov (United States)

Cleeves, L. Ilsedore; Bergin, Edwin A.; Öberg, Karin I.; Andrews, Sean; Wilner, David; Loomis, Ryan

2017-07-01

We report the first detection of a substantial brightening event in an isotopologue of a key molecular ion, HCO+, within a protoplanetary disk of a T Tauri star. The H13CO+ J=3-2 rotational transition was observed three times toward IM Lup between 2014 July and 2015 May with the Atacama Large Millimeter/submillimeter Array. The first two observations show similar spectrally integrated line and continuum fluxes, while the third observation shows a doubling in the disk-integrated J=3-2 line flux compared to the continuum, which does not change between the three epochs. We explore models of an X-ray active star irradiating the disk via stellar flares, and find that the optically thin H13CO+ emission variation can potentially be explained via X-ray-driven chemistry temporarily enhancing the HCO+ abundance in the upper layers of the disk atmosphere during large or prolonged flaring events. If the HCO+ enhancement is indeed caused by an X-ray flare, future observations should be able to spatially resolve these events and potentially enable us to watch the chemical aftermath of the high-energy stellar radiation propagating across the face of protoplanetary disks, providing a new pathway to explore ionization physics and chemistry, including electron density, in disks.

Gravitational Instabilities in Circumstellar Disks

Science.gov (United States)

Kratter, Kaitlin; Lodato, Giuseppe

2016-09-01

Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES

International Nuclear Information System (INIS)

Fujita, Yutaka; Takizawa, Motokazu; Yamazaki, Ryo; Akamatsu, Hiroki; Ohno, Hiroshi

2015-01-01

Radio relics are synchrotron emission found on the periphery of galaxy clusters. From the position and the morphology, it is often believed that the relics are generated by cosmic-ray (CR) electrons accelerated at shocks through a diffusive shock acceleration (DSA) mechanism. However, some radio relics have harder spectra than the prediction of the standard DSA model. One example is observed in the cluster 1RXS J0603.3+4214, which is often called the “Toothbrush Cluster.” Interestingly, the position of the relic is shifted from that of a possible shock. In this study, we show that these discrepancies in the spectrum and the position can be solved if turbulent (re)acceleration is very effective behind the shock. This means that for some relics turbulent reacceleration may be the main mechanism to produce high-energy electrons, contrary to the common belief that it is the DSA. Moreover, we show that for efficient reacceleration, the effective mean free path of the electrons has to be much smaller than their Coulomb mean free path. We also study the merging cluster 1E 0657−56, or the “Bullet Cluster,” in which a radio relic has not been found at the position of the prominent shock ahead of the bullet. We indicate that a possible relic at the shock is obscured by the observed large radio halo that is generated by strong turbulence behind the shock. We propose a simple explanation of the morphological differences of radio emission among the Toothbrush, the Bullet, and the Sausage (CIZA J2242.8+5301) Clusters

Thermal relic dark matter beyond the unitarity limit

Energy Technology Data Exchange (ETDEWEB)

Harigaya, Keisuke [Berkeley Center for Theoretical Physics, Department of Physics, University of California,Berkeley, CA 94720 (United States); Theoretical Physics Group, Lawrence Berkeley National Laboratory,Berkeley, CA 94720 (United States); Ibe, Masahiro [Kavli IPMU (WPI), UTIAS, The University of Tokyo,Kashiwa, Chiba 277-8583 (Japan); ICRR, The University of Tokyo,Kashiwa, Chiba 277-8582 (Japan); Kaneta, Kunio [Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS),Daejeon 34051 (Korea, Republic of); Nakano, Wakutaka; Suzuki, Motoo [Kavli IPMU (WPI), UTIAS, The University of Tokyo,Kashiwa, Chiba 277-8583 (Japan); ICRR, The University of Tokyo,Kashiwa, Chiba 277-8582 (Japan)

2016-08-25

We discuss a simple model of thermal relic dark matter whose mass can be much larger than the so-called unitarity limit on the mass of point-like particle dark matter. The model consists of new strong dynamics with one flavor of fermions in the fundamental representation which is much heavier than the dynamical scale of the new strong dynamics. Dark matter is identified with the lightest baryonic hadron of the new dynamics. The baryonic hadrons annihilate into the mesonic hadrons of the new strong dynamics when they have large radii. Resultantly, thermal relic dark matter with a mass in the PeV range is possible.

Dark matter relic abundance and light sterile neutrinos

Energy Technology Data Exchange (ETDEWEB)

Tang, Yi-Lei [Center for High Energy Physics,Peking University, Beijing 100871 (China); Zhu, Shou-hua [Center for High Energy Physics,Peking University, Beijing 100871 (China); Institute of Theoretical Physics & State Key Laboratory of Nuclear Physics and Technology,Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter,Beijing 100871 (China)

2017-01-09

In this paper, we calculate the relic abundance of the dark matter particles when they can annihilate into sterile neutrinos with the mass ≲100 GeV in a simple model. Unlike the usual standard calculations, the sterile neutrino may fall out of the thermal equilibrium with the thermal bath before the dark matter freezes out. In such a case, if the Yukawa coupling y{sub N} between the Higgs and the sterile neutrino is small, this process gives rise to a larger Ω{sub DM}h{sup 2} so we need a larger coupling between the dark matter and the sterile neutrino for a correct relic abundance.

SOLAR STELLAR AND SUBSTELLAR ENVIRONMENT. I. LOCATION IN THE GALAXY AND CATALOGUES

OpenAIRE

Захожай, В. А.; Харьковский национальный университет им. В.Н.Каразина; Бабенко, М. А.; Херсонский государственный университет

2016-01-01

Structure of the solar neighborhoods (ten parsecs space, Local stellar system andthe Gould Belt), their place in the Galaxy and the distance from its center are analyzed. For the region within 10 pcfrom the Sun, except the stellar component, the contents of extrasolar planets and protoplanetary disks are presented.The catalogues of closest to Sun stars and substars that are compiled based on the results of ground-based and cosmic(HIPPARCOS) missions in the optical and infrared wavelengths ran...

RELICS: A Candidate Galaxy Arc at z~10 and Other Brightly Lensed z>6 Galaxies

Science.gov (United States)

Salmon, Brett; Coe, Dan; Bradley, Larry; Bradac, Marusa; Huang, Kuang-Han; Oesch, Pascal; Brammer, Gabriel; Stark, Daniel P.; Sharon, Keren; Trenti, Michele; Avila, Roberto J.; Ogaz, Sara; Acebron, Ana; Andrade-Santos, Felipe; Carrasco, Daniela; Cerny, Catherine; Cibirka, Nathália; Dawson, William; Frye, Brenda; Hoag, Austin; Jones, Christine; Mainali, Ramesh; Ouchi, Masami; Paterno-Mahler, Rachel; Rodney, Steven; Umetsu, Keiichi; Zitrin, Adi; RELICS

2018-01-01

Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here some of the most brightly lensed z>6 galaxy candidates known from the Reionization Lensing Cluster Survey (RELICS) and the discovery of a particularly fortuitous z~10 galaxy candidate which has been arced by the effects of strong gravitational lensing. The z~10 candidate has a lensed H-band magnitude of 25.8 AB mag and a high lensing magnification (~4-7). The inferred upper limits on the stellar mass (log [M_star /M_Sun]=9.5) and star formation rate (log [SFR/(M_Sun/yr)]=1.5) indicate that this candidate is a typical star-forming galaxy on the z>6 SFR-M_star relation. We rule out the only low-z solution as unphysical based on the required stellar mass, dust attenuation, size, and [OIII] EW needed for a z~2 SED to match the data. Finally, we reconstruct the source-plane image and estimate the candidate's physical size at z~10, finding a half-light radius of r_e 9 candidates. While the James Webb Space Telescope will detect z>10 with ease, this rare candidate offers the potential for unprecedented spatial resolution less than 500 Myr after the Big Bang.

SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION

International Nuclear Information System (INIS)

Perez-Becker, Daniel; Chiang, Eugene

2011-01-01

Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by small condensates, ranging from ∼0.01 μm sized grains to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Here we show that ionization by stellar far-ultraviolet (FUV) radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. The FUV-ionized layer, of thickness 0.01-0.1 g cm -2 , behaves in the ideal magnetohydrodynamic limit and can accrete at observationally significant rates at radii ∼> 1-10 AU. Surface layer accretion driven by FUV ionization can reproduce the trend of increasing accretion rate with increasing hole size seen in transitional disks. At radii ∼<1-10 AU, FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance, and unless turbulent mixing of plasma can thicken the MRI-active layer, an additional means of transport is needed. In the case of transitional disks, it could be provided by planets.

DEEP MIPS OBSERVATIONS OF THE IC 348 NEBULA: CONSTRAINTS ON THE EVOLUTIONARY STATE OF ANEMIC CIRCUMSTELLAR DISKS AND THE PRIMORDIAL-TO-DEBRIS DISK TRANSITION

International Nuclear Information System (INIS)

Currie, Thayne; Kenyon, Scott J.

2009-01-01

We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M sun at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 σ level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is ∼15%-35% for stars plausibly more massive than 0.5 M sun . The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

Low inductance diode design on the Proto II accelerator for imploding plasma loads

International Nuclear Information System (INIS)

Hsing, W.W.; Coats, R.; McDaniel, D.H.; Spielman, R.B.

1985-01-01

A new water transmission line convolute, single piece insulator, and double disk feed has been designed and tested on the .125 ohm, 10 TW Proto II accelerator. The water transmission lines have a 5 cm gap to eliminate any water arcing. A two-dimensional magnetic field code was used to calculate the convolute inductance. The authors used an acrylic insulator as well as a single piece, laminated polycarbonate insulator. They have been successfully tested at over 90% of the Shipman criteria for classical insulator breakdown, although the laminations in the polycarbonate insulator failed after a few shots. The anode and cathode each have two pieces and are held together mechanically. The vacuum MITL tapers to a 3 mm minimum gap. The total inductance is 8.4 nH for gas puff loads and 7.8 nH for imploding foil loads

The 'relics of Joan of Arc'

DEFF Research Database (Denmark)

Charlier, P.; Poupon, J.; Eb, A.

2010-01-01

Archaeological remains can provide concrete cases, making it possible to develop, refine or validate medico-legal techniques. In the case of the so-called 'Joan of Arc's relics' (a group of bone and archaeological remains known as the 'Bottle of Chinon'), 14 specialists analysed the samples such ...

Debris Disk Studies with the ngVLA

Science.gov (United States)

Wilner, David; Matthews, Brenda; Matra, Luca; Kennedy, Grant; Wyatt, Mark; Greaves, Jane

2018-01-01

We discuss the potential for the ngVLA to advance understanding of debris disks around main-sequence stars. Since the dust-producing planetesimals that replenish these disks through collisions persist only in stable regions like belts and resonances, their locations and physical properties encode essential information about the formation of exoplanetary systems and their dynamical evolution. Observations at long millimeter wavelengths can play a special role because the large grains that dominate the emission are faithful tracers of the dust-producing planetesimals, unlike small grains seen at shorter wavelengths that are rapidly redistributed by stellar radiation and winds. Sensitive observations of debris disks with the ngVLA can (1) reveal structures resulting from otherwise inaccessible planets on wide orbits, (2) test collisional models using spectral slopes to constrain mm/cm grain size distributions, and (3) for select sources, probe the water content of exocomets using the 21 cm HI line.

OPTICAL PROPERTIES OF THE ULTRALUMINOUS X-RAY SOURCE HOLMBERG IX X-1 AND ITS STELLAR ENVIRONMENT

International Nuclear Information System (INIS)

Grise, F.; Kaaret, P.; Pakull, M. W.; Motch, C.

2011-01-01

Holmberg IX X-1 is an archetypal ultraluminous X-ray source (ULX). Here we study the properties of the optical counterpart and of its stellar environment using optical data from SUBARU/Faint Object Camera and Spectrograph, GEMINI/GMOS-N and Hubble Space Telescope (HST)/Advanced Camera for Surveys, as well as simultaneous Chandra X-ray data. The V ∼ 22.6 spectroscopically identified optical counterpart is part of a loose cluster with an age ∼ sun . The counterpart is more luminous than the other stars of the association, suggesting a non-negligible optical contribution from the accretion disk. An observed UV excess also points to non-stellar light similar to X-ray active low-mass X-ray binaries. A broad He II λ4686 emission line identified in the optical spectrum of the ULX further suggests optical light from X-ray reprocessing in the accretion disk. Using stellar evolutionary tracks, we have constrained the mass of the counterpart to be ∼> 10 M sun , even if the accretion disk contributes significantly to the optical luminosity. Comparison of the photometric properties of the counterpart with binary models show that the donor may be more massive, ∼> 25 M sun , with the ULX system likely undergoing case AB mass transfer. Finally, the counterpart exhibits photometric variability of 0.14 mag between two HST observations separated by 50 days which could be due to ellipsoidal variations and/or disk reprocessing of variable X-ray emission.

RADIALLY MAGNETIZED PROTOPLANETARY DISK: VERTICAL PROFILE

International Nuclear Information System (INIS)

Russo, Matthew; Thompson, Christopher

2015-01-01

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field B r ∼ (10 −4 –10 −2 )(r/ AU) −2 G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ∼1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10 −8 M ⊙ yr −1 are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper

The age of the galactic disk

International Nuclear Information System (INIS)

Sandage, A.

1988-07-01

The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc

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.

THE CIRCUMSTELLAR DISK OF THE Be STAR o AQUARII AS CONSTRAINED BY SIMULTANEOUS SPECTROSCOPY AND OPTICAL INTERFEROMETRY

Energy Technology Data Exchange (ETDEWEB)

Sigut, T. A. A. [Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, N6A 3K7 (Canada); Tycner, C.; Jansen, B. [Department of Physics, Central Michigan University, Mount Pleasant, MI 48859 (United States); Zavala, R. T. [US Naval Observatory, Flagstaff Station, 10391 W. Naval Observatory Rd, Flagstaff, AZ 86001 (United States)

2015-12-01

Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric Hα emission line. We combine Hα interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with Hα spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of o Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of 75° ±  3° with a position angle on the sky of 110° ±  8° measured East from North. From the best-fit disk density model, we find that 90% of the Hα emission arises from within 9.5 stellar radii, and the mass associated with this Hα disk is ∼1.8 × 10{sup −10} of the stellar mass, and that the associated angular momentum, assuming Keplerian rotation for the disk, is ∼1.6 × 10{sup −8} of the total stellar angular momentum. The occurrence of a central quasi-emission feature in Mg ii λ4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999. To obtain consistency between the Hα line profile modeling and the other constraints, it was necessary in the profile fitting to weight the line core (emission peaks and central depression) more heavily than the line wings, which were not well reproduced by our models. This may reflect the limitation of assuming a single power law for the disk's variation in equatorial density. The best-fit disk density model for o Aqr predicts that Hα is near its maximum strength as a function of disk density, and hence the Hα equivalent width and line profile change only weakly in response to large (factor of ∼5) changes in the disk density. This may in part explain the remarkable observed stability of o Aqr's Hα emission line profile.

On the absence of radio haloes in clusters with double relics

Science.gov (United States)

Bonafede, A.; Cassano, R.; Brüggen, M.; Ogrean, G. A.; Riseley, C. J.; Cuciti, V.; de Gasperin, F.; Golovich, N.; Kale, R.; Venturi, T.; van Weeren, R. J.; Wik, D. R.; Wittman, D.

2017-09-01

Pairs of radio relics are believed to form during cluster mergers, and are best observed when the merger occurs in the plane of the sky. Mergers can also produce radio haloes, through complex processes likely linked to turbulent re-acceleration of cosmic ray electrons. However, only some clusters with double relics also show a radio halo. Here, we present a novel method to derive upper limits on the radio halo emission, and analyse archival X-ray Chandra data, as well as galaxy velocity dispersions and lensing data, in order to understand the key parameter that switches on radio halo emission. We place upper limits on the halo power below the P1.4 GHz-M500 correlation for some clusters, confirming that clusters with double relics have different radio properties. Computing X-ray morphological indicators, we find that clusters with double relics are associated with the most disturbed clusters. We also investigate the role of different mass-ratios and time-since-merger. Data do not indicate that the merger mass-ratio has an impact on the presence or absence of radio haloes (the null hypothesis that the clusters belong to the same group cannot be rejected). However, the data suggest that the absence of radio haloes could be associated with early and late mergers, but the sample is too small to perform a statistical test. Our study is limited by the small number of clusters with double relics. Future surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to better address this issue.

Mass outflow in the nearby proto-planetary system, Beta Pictoris

International Nuclear Information System (INIS)

Bruhweiler, F.C.; Grady, C.A.; Kondo, Yoji

1991-01-01

Previous spectral studies of circumstallar dust around the nearby, candidate proto-planetary system, Beta Pictoris, has detected only infalling gas. The lack of detectable mass outflow has been critical in the interpretation of the origin of the circumstellar gas and in our understanding of the evolutionary status of the Beta Pictoris system. IUE high-dispersion spectra are presented which show, in addition to infall, the presence of mass outflow, with a maximum observed outflow velocity of -60 km/s, and a corresponding instantaneous outflow rate of 1.1 x 10 to the -14th solar mass/yr, or 1.1 x 10 to the -11th Jupiter mass/yr. This mass outflow rate and terminal velocity are comparable to the magnitudes of mass infall rates and terminal velocities observed from late 1986 through early 1988. The implications of these observations on our understanding of the mechanisms producing infall from the surrounding circumstellar disk are discussed, as are the implications for our understanding of the evolutionary status of the Beta Pic system. 23 refs

SHAKEN, NOT STIRRED: THE DISRUPTED DISK OF THE STARBURST GALAXY NGC 253

International Nuclear Information System (INIS)

Davidge, T. J.

2010-01-01

Near-infrared images obtained with WIRCam on the Canada-France-Hawaii Telescope are used to investigate the recent history of the nearby Sculptor Group spiral NGC 253, which is one of the nearest starburst galaxies. Bright asymptotic giant branch (AGB) stars are traced out to projected distances of ∼22-26 kpc (∼13-15 disk scale lengths) along the major axis. The distribution of stars in the disk is lopsided, in the sense that the projected density of AGB stars in the northeast portion of the disk between 10 and 20 kpc from the galaxy center is ∼0.5 dex higher than on the opposite side of the galaxy. A large population of red supergiants is also found in the northeast portion of the disk and, with the exception of the central 2 kpc, this area appears to have been the site of the highest levels of star-forming activity in the galaxy during the past ∼0.1 Gyr. It is argued that such high levels of localized star formation may have produced a fountain that ejected material from the disk, and the extraplanar H I detected by Boomsma et al. may be one manifestation of such activity. Diffuse stellar structures are found in the periphery of the disk, and the most prominent of these is to the south and east of the galaxy. Bright AGB stars, including cool C stars that are identified based on their J - K colors, are detected out to 15 kpc above the disk plane, and these are part of a diffusely distributed, flattened extraplanar component. Comparisons between observed and model luminosity functions suggest that the extraplanar regions contain stars that formed throughout much of the age of the universe. Additional evidence of a diffuse, extraplanar stellar component that contains moderately young stars comes from archival Galaxy Evolution Explorer images. It is suggested that the disk of NGC 253 was disrupted by a tidal encounter with a now defunct companion. This encounter introduced asymmetries that remain to this day, and the projected distribution of stars in and

THE ARDUOUS JOURNEY TO BLACK HOLE FORMATION IN POTENTIAL GAMMA-RAY BURST PROGENITORS

International Nuclear Information System (INIS)

Dessart, Luc; O'Connor, Evan; Ott, Christian D.

2012-01-01

We present a quantitative study on the properties at death of fast-rotating massive stars evolved at low-metallicity—objects that are proposed as likely progenitors of long-duration γ-ray bursts (LGRBs). We perform one-dimensional+rotation stellar-collapse simulations on the progenitor models of Woosley and Heger, and critically assess their potential for the formation of a black hole and a Keplerian disk (namely, a collapsar) or a proto-magnetar. We note that theoretical uncertainties in the treatment of magnetic fields and the approximate handling of rotation compromise the accuracy of stellar-evolution models. We find that only the fastest rotating progenitors achieve sufficient compactness for black hole formation while the bulk of models possess a core density structure typical of garden-variety core-collapse supernova (SN) progenitors evolved without rotation and at solar metallicity. Of the models that do have sufficient compactness for black hole formation, most of them also retain a large amount of angular momentum in the core, making them prone to a magneto-rotational explosion, therefore preferentially leaving behind a proto-magnetar. A large progenitor angular-momentum budget is often the sole criterion invoked in the community today to assess the suitability for producing a collapsar. This simplification ignores equally important considerations such as the core compactness, which conditions black hole formation, the core angular momentum, which may foster a magneto-rotational explosion preventing black hole formation, or the metallicity and the residual envelope mass which must be compatible with inferences from observed LGRB/SNe. Our study suggests that black hole formation is non-trivial, that there is room for accommodating both collapsars and proto-magnetars as LGRB progenitors, although proto-magnetars seem much more easily produced by current stellar-evolutionary models.

THE ARDUOUS JOURNEY TO BLACK HOLE FORMATION IN POTENTIAL GAMMA-RAY BURST PROGENITORS

Energy Technology Data Exchange (ETDEWEB)

Dessart, Luc [Laboratoire d' Astrophysique de Marseille, Universite Aix-Marseille and CNRS, UMR7326, 38 rue Frederic Joliot-Curie, 13388 Marseille (France); O' Connor, Evan; Ott, Christian D., E-mail: Luc.Dessart@oamp.fr, E-mail: evanoc@tapir.caltech.edu, E-mail: cott@tapir.caltech.edu [TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125 (United States)

2012-07-20

We present a quantitative study on the properties at death of fast-rotating massive stars evolved at low-metallicity-objects that are proposed as likely progenitors of long-duration {gamma}-ray bursts (LGRBs). We perform one-dimensional+rotation stellar-collapse simulations on the progenitor models of Woosley and Heger, and critically assess their potential for the formation of a black hole and a Keplerian disk (namely, a collapsar) or a proto-magnetar. We note that theoretical uncertainties in the treatment of magnetic fields and the approximate handling of rotation compromise the accuracy of stellar-evolution models. We find that only the fastest rotating progenitors achieve sufficient compactness for black hole formation while the bulk of models possess a core density structure typical of garden-variety core-collapse supernova (SN) progenitors evolved without rotation and at solar metallicity. Of the models that do have sufficient compactness for black hole formation, most of them also retain a large amount of angular momentum in the core, making them prone to a magneto-rotational explosion, therefore preferentially leaving behind a proto-magnetar. A large progenitor angular-momentum budget is often the sole criterion invoked in the community today to assess the suitability for producing a collapsar. This simplification ignores equally important considerations such as the core compactness, which conditions black hole formation, the core angular momentum, which may foster a magneto-rotational explosion preventing black hole formation, or the metallicity and the residual envelope mass which must be compatible with inferences from observed LGRB/SNe. Our study suggests that black hole formation is non-trivial, that there is room for accommodating both collapsars and proto-magnetars as LGRB progenitors, although proto-magnetars seem much more easily produced by current stellar-evolutionary models.

The 0.5-2.22 μm Scattered Light Spectrum of the Disk around TW Hya: Detection of a Partially Filled Disk Gap at 80 AU

Science.gov (United States)

Debes, John H.; Jang-Condell, Hannah; Weinberger, Alycia J.; Roberge, Aki; Schneider, Glenn

2013-07-01

We present a 0.5-2.2 μm scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances >40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at ~80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady α-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 M ⊕. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 10167, 8624, 7226, and 7233.

THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Bae, Jaehan; Hartmann, Lee [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105 (United States); Zhu Zhaohuan [Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, NJ 08544 (United States); Gammie, Charles, E-mail: jaehbae@umich.edu, E-mail: lhartm@umich.edu, E-mail: zhuzh@astro.princeton.edu, E-mail: gammie@illinois.edu [Department of Astronomy, University of Illinois Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801 (United States)

2013-09-01

We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for {approx}< 20% of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that the initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the M-dot-R{sub wall} plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU.

Few Skewed Results from IOTA Interferometer YSO Disk Survey

Science.gov (United States)

Monnier, J. D.; Millan-Gabet, R.; Berger, J.-P.; Pedretti, E.; Traub, W.; Schloerb, F. P.

2005-12-01

The 3-telescope IOTA interferometer is capable of measuring closure phases for dozens of Herbig Ae/Be stars in the near-infrared. The closure phase unambiguously identifies deviations from centro-symmetry (i.e., skew) in the brightness distribution, at the scale of 4 milliarcseconds (sub-AU physical scales) for our work. Indeed, hot dust emission from the inner circumstellar accretion disk is expected to be skewed for (generic) flared disks viewed at intermediate inclination angles, as has been observed for LkHa 101. Surprisingly, we find very little evidence for skewed disk emission in our IOTA3 sample, setting strong constraints on the geometry of the inner disk. In particular, we rule out the currently-popular model of a VERTICAL hot inner wall of dust at the sublimation radius. Instead, our data is more consistent with a curved inner wall that bends away from the midplane as might be expected from the pressure-dependence of dust sublimation or limited absorption of stellar luminosity in the disk midplane by gas.

THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

International Nuclear Information System (INIS)

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 around young Sun-like stars (K1-M5) and cool stars/brown dwarfs (M5-M9). The comparison of these two large samples of over 60 sources reveal major differences in the evolution of both the dust and gas components. We report the first detection of organic molecules in disks around brown dwarfs. The detection rate statistics and the line flux ratios of HCN and C 2 H 2 show a striking difference between the two samples, demonstrating a significant underabundance of HCN relative to C 2 H 2 in the disk surface of cool stars. We propose this to originate from the large difference in the UV irradiation around the two types of sources. The statistical comparison of the 10 μm silicate emission features also reveals a difference between the two samples. Cool stars and brown dwarfs show weaker features arising from more processed silicate grains in the disk atmosphere. These findings complement previous indications of flatter disk structures and longer disk lifetimes around cool stars. Our results highlight important differences in the chemical and physical evolution of protoplanetary disks as a function of stellar mass, temperature, and radiation field which should be taken into account in planet formation models. We note that the different chemistry of preplanetary materials in the disk may also influence the bulk composition and volatile content of the forming planets. In particular, if exogenous HCN has played a key role in the synthesis of prebiotic molecules on Earth as proposed, then prebiotic chemistry may unfold differently on planets around cool stars.

THE DISK WIND IN THE RAPIDLY SPINNING STELLAR-MASS BLACK HOLE 4U 1630–472 OBSERVED WITH NuSTAR

Energy Technology Data Exchange (ETDEWEB)

King, Ashley L.; Miller, Jon M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Walton, Dominic J.; Fürst, Felix; Harrison, Fiona A. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Barret, Didier [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); Boggs, Steven E.; Craig, William W.; Krivonos, Roman; Tomsick, John A. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States); Christensen, Finn E. [DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Fabian, Andy C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Hailey, Charles J.; Mori, Kaya [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Natalucci, Lorenzo [Istituto Nazionale di Astrofisica, INAF-IAPS, via del Fosso del Cavaliere, I-00133 Roma (Italy); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States); Zhang, William W., E-mail: ashking@umich.edu [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2014-03-20

We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630–472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a{sub ∗}=0.985{sub −0.014}{sup +0.005} (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 ± 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log ξ=3.6{sub −0.3}{sup +0.2}) and is dominated by He-like Fe XXV, the wind has a velocity of v/c=0.043{sub −0.007}{sup +0.002} (12900{sub −2100}{sup +600} km s{sup –1}). If the line is instead associated with a more highly ionized gas (log ξ=6.1{sub −0.6}{sup +0.7}), and is dominated by Fe XXVI, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

The low-mass stellar population in the young cluster Tr 37. Disk evolution, accretion, and environment

Science.gov (United States)

Sicilia-Aguilar, Aurora; Kim, Jinyoung Serena; Sobolev, Andrej; Getman, Konstantin; Henning, Thomas; Fang, Min

2013-11-01

Aims: We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution. Methods: We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Results: Including the new members and the known solar-type stars, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. Conclusions: The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr 37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play an important role in the disk evolution and dispersal. Finally, we

“The Godly Greedy Appetite”: New Relic Circulation in the Early Modern World

Directory of Open Access Journals (Sweden)

Igor Pérez Tostado

2017-05-01

Full Text Available Having lost all monasteries and a good deal of its medieval Christian movable assets, England became one of the greatest producers of new Catholic relics during the sixteenth and seventeenth centuries. This article aims to look, from a material point of view, at the circulation and consumption of English relics on the Catholic continent. In this case, these products were created because of violence and circulated as an answer to it. Gifts and the exchange of relics served to obtain support for the exiled Catholics and for the institutions providing for their education created in the continent, and allowed them to participate in the necropolitics of the Spanish Monarchy. Relics, artifacts and printed and manuscript narratives brought back from all over the world helped construct a selfimage of an English Catholic as a necrocommunity imbued by a sense of historical continuity and connected to a global imagined community.

X-ray Ionization of Heavy Elements Applied to Protoplanetary Disks

NARCIS (Netherlands)

Ádámkovics, Máté; Glassgold, Alfred E.; Meijerink, Rowin

The consequences of the Auger effect on the population of heavy-element ions are analyzed for the case of relatively cool gas irradiated by keV X-rays with intended applications to the accretion disks of young stellar objects. Highly charged ions are rapidly reduced to the doubly charged state in

THE FORMATION OF A MILKY WAY-SIZED DISK GALAXY. I. A COMPARISON OF NUMERICAL METHODS

Energy Technology Data Exchange (ETDEWEB)

Zhu, Qirong; Li, Yuexing, E-mail: qxz125@psu.edu [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)

2016-11-01

The long-standing challenge of creating a Milky Way- (MW-) like disk galaxy from cosmological simulations has motivated significant developments in both numerical methods and physical models. We investigate these two fundamental aspects in a new comparison project using a set of cosmological hydrodynamic simulations of an MW-sized galaxy. In this study, we focus on the comparison of two particle-based hydrodynamics methods: an improved smoothed particle hydrodynamics (SPH) code Gadget, and a Lagrangian Meshless Finite-Mass (MFM) code Gizmo. All the simulations in this paper use the same initial conditions and physical models, which include star formation, “energy-driven” outflows, metal-dependent cooling, stellar evolution, and metal enrichment. We find that both numerical schemes produce a late-type galaxy with extended gaseous and stellar disks. However, notable differences are present in a wide range of galaxy properties and their evolution, including star-formation history, gas content, disk structure, and kinematics. Compared to Gizmo, the Gadget simulation produced a larger fraction of cold, dense gas at high redshift which fuels rapid star formation and results in a higher stellar mass by 20% and a lower gas fraction by 10% at z = 0, and the resulting gas disk is smoother and more coherent in rotation due to damping of turbulent motion by the numerical viscosity in SPH, in contrast to the Gizmo simulation, which shows a more prominent spiral structure. Given its better convergence properties and lower computational cost, we argue that the MFM method is a promising alternative to SPH in cosmological hydrodynamic simulations.

VLA and CARMA observations of protostars in the Cepheus clouds: Sub-arcsecond proto-binaries formed via disk fragmentation

Energy Technology Data Exchange (ETDEWEB)

Tobin, John J.; Looney, Leslie W. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Chandler, Claire J. [National Radio Astronomy Observatory, Socorro, NM (United States); Wilner, David J.; Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Loinard, Laurent; D' Alessio, Paola [Centro de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Chiang, Hsin-Fang [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii at Manoa, Hilo, HI 96720 (United States); Hartmann, Lee; Calvet, Nuria [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Kwon, Woojin, E-mail: jtobin@nrao.edu [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen (Netherlands)

2013-12-20

We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G. Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of λ = 7.3 mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of ∼0.''06 (18 AU) at 7.3 mm. The L1165-SMM1 CARMA observations were taken at λ = 1.3 mm with a best resolution of ∼0.''3 (100 AU) and the CB230 IRS1 observations were taken at λ = 3.4 mm with a best resolution of ∼3'' (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of ∼0.''3 (100 AU) from detections of secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to the direction of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggest that these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentially arrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3 mm emission show evidence of a large (R > 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230 IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with ∼20 AU radius disks. For the other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii <20 AU.

Grand-design Spiral Arms in a Young Forming Circumstellar Disk

Energy Technology Data Exchange (ETDEWEB)

Tomida, Kengo; Lin, Chia Hui [Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Nishi-ku, Fukuoka 819-0395 (Japan); Hosokawa, Takashi [Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Sakurai, Yuya, E-mail: tomida@vega.ess.sci.osaka-u.ac.jp [Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan)

2017-01-20

We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues, and its radius becomes as large as 200 au toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk, soon becoming unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phases. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2–27, whose circumstellar disk has grand-design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand-design spiral arms around Elias 2–27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.

Grand-design Spiral Arms in a Young Forming Circumstellar Disk

International Nuclear Information System (INIS)

Tomida, Kengo; Lin, Chia Hui; Machida, Masahiro N.; Hosokawa, Takashi; Sakurai, Yuya

2017-01-01

We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues, and its radius becomes as large as 200 au toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk, soon becoming unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phases. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2–27, whose circumstellar disk has grand-design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand-design spiral arms around Elias 2–27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.

A PETAL OF THE SUNFLOWER: PHOTOMETRY OF THE STELLAR TIDAL STREAM IN THE HALO OF MESSIER 63 (NGC 5055)

International Nuclear Information System (INIS)

Chonis, Taylor S.; Martínez-Delgado, David; Gabany, R. Jay; Majewski, Steven R.; Hill, Gary J.; Gralak, Ray; Trujillo, Ignacio

2011-01-01

We present deep surface photometry of a very faint, giant arc-loop feature in the halo of the nearby spiral galaxy NGC 5055 (M63) that is consistent with being a part of a stellar stream resulting from the disruption of a dwarf satellite galaxy. This faint feature was first detected in early photographic studies by van der Kruit; more recently, in the study of Martínez-Delgado and as presented in this work, from the loop has been realized to be the result of a recent minor merger through evidence obtained by wide-field, deep images taken with a telescope of only 0.16 m aperture. The stellar stream is clearly confirmed in additional deep images taken with the 0.5 m telescope of the BlackBird Remote Observatory and the 0.8 m telescope of the McDonald Observatory. This low surface brightness (μ R ≈ 26 mag arcsec –2 ) arc-like structure around the disk of the galaxy extends 14.'0 (∼29 kpc projected) from its center, with a projected width of 1.'6 (∼3.3 kpc). The stream's morphology is consistent with that of the visible part of a giant, 'great-circle' type stellar stream originating from the recent accretion of a ∼10 8 M ☉ dwarf satellite in the last few Gyr. The progenitor satellite's current position and final fate are not conclusive from our data. The color of the stream's stars is consistent with dwarfs in the Local Group and is similar to the outer faint regions of M63's disk and stellar halo. From our photometric study, we detect other low surface brightness 'plumes'; some of these may be extended spiral features related to the galaxy's complex spiral structure, and others may be tidal debris associated with the disruption of the galaxy's outer stellar disk as a result of the accretion event. We are able to differentiate between features related to the tidal stream and faint, blue extended features in the outskirts of the galaxy's disk previously detected by the Galaxy Evolution Explorer satellite. With its highly warped H I gaseous disk (∼20�

On the Dynamical Structure of the Jet System in the Disk with the Keplerian Rotation

Directory of Open Access Journals (Sweden)

Kyung-Sook Jeong

1989-06-01

Full Text Available The classical sloar wind theory proposed by Parker(1963 explains well the dynamics of the wind pheonomena such as stellar wind accretion disk. While the stellar wind system like the solar wind has the spherically symmetric wind structure, there are various jet phenomena which collimate the system into the narrow space. We can find these dynamical structures in SS433, in the optical jet of M87, and around the active galactic nulei. We present the dynamical structure of the jet system in disks, which conserves the angular momentum, with the Keplerian rotation and the strong relation between the geometrical cross section and the physical change of the jet stream on the basis of the hydrodynamic equations.

Could a Proto-Ribosome Emerge Spontaneously in the Prebiotic World?

Directory of Open Access Journals (Sweden)

Ilana C. Agmon

2016-12-01

Full Text Available An indispensable prerequisite for establishing a scenario of life emerging by natural processes is the requirement that the first simple proto-molecules could have had a realistic probability of self-assembly from random molecular polymers in the prebiotic world. The vestige of the proto-ribosome, which is believed to be still embedded in the contemporary ribosome, is used to assess the feasibility of such spontaneous emergence. Three concentric structural elements of different magnitudes, having a dimeric nature derived from the symmetrical region of the ribosomal large subunit, were suggested to constitute the vestige of the proto-ribosome. It is assumed to have materialized spontaneously in the prebiotic world, catalyzing non-coded peptide bond formation and simple elongation. Probabilistic and energetic considerations are applied in order to evaluate the suitability of the three contenders for being the initial proto-ribosome. The analysis points to the simplest proto-ribosome, comprised of a dimer of tRNA-like molecules presently embedded in the core of the symmetrical region, as the only one having a realistic statistical likelihood of spontaneous emergence from random RNA chains. Hence it offers a feasible starting point for a continuous evolutionary path from the prebiotic matter, through natural processes, into the intricate modern translation system.

Time-dependent simulations of disk-embedded planetary atmospheres

Science.gov (United States)

Stökl, A.; Dorfi, E. A.

2014-03-01

At the early stages of evolution of planetary systems, young Earth-like planets still embedded in the protoplanetary disk accumulate disk gas gravitationally into planetary atmospheres. The established way to study such atmospheres are hydrostatic models, even though in many cases the assumption of stationarity is unlikely to be fulfilled. Furthermore, such models rely on the specification of a planetary luminosity, attributed to a continuous, highly uncertain accretion of planetesimals onto the surface of the solid core. We present for the first time time-dependent, dynamic simulations of the accretion of nebula gas into an atmosphere around a proto-planet and the evolution of such embedded atmospheres while integrating the thermal energy budget of the solid core. The spherical symmetric models computed with the TAPIR-Code (short for The adaptive, implicit RHD-Code) range from the surface of the rocky core up to the Hill radius where the surrounding protoplanetary disk provides the boundary conditions. The TAPIR-Code includes the hydrodynamics equations, gray radiative transport and convective energy transport. The results indicate that diskembedded planetary atmospheres evolve along comparatively simple outlines and in particular settle, dependent on the mass of the solid core, at characteristic surface temperatures and planetary luminosities, quite independent on numerical parameters and initial conditions. For sufficiently massive cores, this evolution ultimately also leads to runaway accretion and the formation of a gas planet.

RADIALLY MAGNETIZED PROTOPLANETARY DISK: VERTICAL PROFILE

Energy Technology Data Exchange (ETDEWEB)

Russo, Matthew [Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 (Canada); Thompson, Christopher [Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada)

2015-11-10

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field B{sub r} ∼ (10{sup −4}–10{sup −2})(r/ AU){sup −2} G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ∼1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10{sup −8} M{sub ⊙} yr{sup −1} are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper.

Discussion of impact of relics activation on protection and utilization approaches-take the old summer palace as an example

Science.gov (United States)

Xiaoqi, J.

2015-08-01

As the popularization of cultural relics and the rapid development of cultural tourism industry, a large number of cultural relic tourism resources goes into public eyes. Activation of relics has became an important way for tourist to contact and understand culture relics. The way of how to properly interpret the historical sense and cultural uniqueness to the masses of tourists in order to achieve social service functions of relic resources has always been research focal point of site protection and utilization, so nowadays it has important significance to protection and utilization of heritage resources in our country. From the point of activation of relics and based on the analysis of resource characteristic, the paper in depth discuss ways of activation of relics of the Old Summer Palace, in order to provide reference for sustainable development of sites tourism in China.

The Andromeda Optical and Infrared Disk Survey

Science.gov (United States)

Sick, J.; Courteau, S.; Cuillandre, J.-C.

2014-03-01

The Andromeda Optical and Infrared Disk Survey has mapped M31 in u* g' r' i' JKs wavelengths out to R = 40 kpc using the MegaCam and WIRCam wide-field cameras on the Canada-France-Hawaii Telescope. Our survey is uniquely designed to simultaneously resolve stars while also carefully reproducing the surface brightness of M31, allowing us to study M31's global structure in the context of both resolved stellar populations and spectral energy distributions. We use the Elixir-LSB method to calibrate the optical u* g' r' i' images by building real-time maps of the sky background with sky-target nodding. These maps are stable to μg ≲ 28.5 mag arcsec-2 and reveal warps in the outer M31 disk in surface brightness. The equivalent WIRCam mapping in the near-infrared uses a combination of sky-target nodding and image-to-image sky offset optimization to produce stable surface brightnesses. This study enables a detailed analysis of the systematics of spectral energy distribution fitting with near-infrared bands where asymptotic giant branch stars impose a significant, but ill-constrained, contribution to the near-infrared light of a galaxy. Here we present panchromatic surface brightness maps and initial results from our near-infrared resolved stellar catalog.

Prospects for relic neutrino detection

International Nuclear Information System (INIS)

Smith, P.F.

1991-03-01

The standard big bang model predicts a universal background of relic neutrinos, comparable in number density to the background microwave photons. This neutrino background is undetectable at the present time firstly because the neutrino energy is very low (10 -4 -10 -5 eV) resulting in a very low energy transfer to any conceivable detector, and secondly the low energy gives a lower interaction cross section and hence a very low event rate per unit mass. These obstacles have so far precluded any realistic proposal for relic neutrino detection. The aim of this paper is to illustrate the difficulties in detecting these neutrinos by summarizing six detection ideas which have been previously considered, indicating in each case the problems which have prevented the idea being developed into an experimental proposal. The most promising direction for further study would appear to be that of coherent interactions. So far, no investigations of this idea have resulted in a practical detection scheme, but in this paper one new variation is suggested which could in principle give an observable effect, if the necessary stringent experimental conditions could be created. It is suggested that this may become possible with the aid of foreseeable 21st century developments in nanotechnology. (author)

The vertical metallicity gradient of the Milky Way disk: transitions in [α/Fe] populations

International Nuclear Information System (INIS)

Schlesinger, Katharine J.; Johnson, Jennifer A.; Rockosi, Constance M.; Lee, Young Sun; Beers, Timothy C.; Harding, Paul; Allende Prieto, Carlos; Bird, Jonathan C.; Schönrich, Ralph; Yanny, Brian; Schneider, Donald P.; Weaver, Benjamin A.; Brinkmann, Jon

2014-01-01

Using G dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, we have determined the vertical metallicity gradient in the Milky Way's disk and examined how this gradient varies for different [α/Fe] subsamples. Our sample contains over 40,000 stars with low-resolution spectroscopy over 144 lines of sight. It also covers a significant disk volume, between ∼0.3 and 1.6 kpc from the Galactic plane, and allows us to examine the disk in situ, whereas previous analyses were more limited in scope. Furthermore, this work does not presuppose a disk structure, whether composed of a single complex population or distinct thin and thick disk components. We employ the SEGUE Stellar Parameter Pipeline to obtain estimates of stellar parameters, [Fe/H], and [α/Fe] and extract multiple volume-complete subsamples of approximately 1000 stars each. Based on SEGUE's target-selection algorithm, we adjust each subsample to determine an unbiased picture of disk chemistry; consequently, each individual star represents the properties of many. The metallicity gradient is –0.243 −0.053 +0.039 dex kpc –1 for the entire sample, which we compare to various literature results. This gradient stems from the different [α/Fe] populations inhabiting different ranges of height above the Galactic plane. Each [α/Fe] subsample shows little change in median [Fe/H] with height. If we associate [α/Fe] with age, the negligible gradients of our [α/Fe] subsamples suggest that stars formed in different epochs exhibit comparable vertical structure, implying similar star formation processes and evolution.

NO EVIDENCE FOR A DARK MATTER DISK WITHIN 4 kpc FROM THE GALACTIC PLANE

International Nuclear Information System (INIS)

Moni Bidin, C.; Carraro, G.; Mendez, R. A.; Van Altena, W. F.

2010-01-01

We estimated the dynamical surface mass density (Σ) at the solar Galactocentric distance between 2 and 4 kpc from the Galactic plane, as inferred from the observed kinematics of the thick disk. We find Σ(z = 2 kpc) = 57.6 ± 5.8 M sun pc -2 , and it shows only a tiny increase in the z range considered by our investigation. We compared our results with the expectations for the visible mass, adopting the most recent estimates in the literature for contributions of the Galactic stellar disk and interstellar medium, and proposed models of the dark matter distribution. Our results match the expectation for the visible mass alone, never differing from it by more than 0.8 M sun pc -2 at any z, and thus we find little evidence for any dark component. We assume that the dark halo could be undetectable with our method, but the dark disk, recently proposed as a natural expectation of the ΛCDM models, should be detected. Given the good agreement with the visible mass alone, models including a dark disk are less likely, but within errors its existence cannot be excluded. In any case, these results put constraints on its properties: thinner models (scale height lower than 4 kpc) reconcile better with our results and, for any scale height, the lower-density models are preferred. We believe that successfully predicting the stellar thick disk properties and a dark disk in agreement with our observations could be a challenging theoretical task.

Expanded calculation of weak-interaction-mediated neutrino cooling rates due to 56Ni in stellar matter

International Nuclear Information System (INIS)

Nabi, Jameel-Un

2010-01-01

An accurate estimate of the neutrino cooling rates is required in order to study the various stages of stellar evolution of massive stars. Neutrino losses from proto-neutron stars play a crucial role in deciding whether these stars would be crushed into black holes or explode as supernovae. Both pure leptonic and weak-interaction processes contribute to the neutrino energy losses in stellar matter. At low temperatures and densities, the characteristics of the early phase of presupernova evolution, cooling through neutrinos produced via the weak interaction, are important. Proton-neutron quasi-particle random phase approximation (pn-QRPA) theory has recently been used with success for the calculation of stellar weak-interaction rates of fp-shell nuclide. The lepton-to-baryon ratio (Y e ) during early phases of stellar evolution of massive stars changes substantially, mainly due to electron captures on 56 Ni. The stellar matter is transparent to the neutrinos produced during the presupernova evolution of massive stars. These neutrinos escape the site and assist the stellar core in maintaining a lower entropy. Here, an expanded calculation of weak-interaction-mediated neutrino and antineutrino cooling rates due to 56 Ni in stellar matter using the pn-QRPA theory is presented. This detailed scale is appropriate for interpolation purposes and is of greater utility for simulation codes. The calculated rates are compared with earlier calculations. During the relevant temperature and density regions of stellar matter the reported rates show few differences compared with the shell model rates and might contribute in fine-tuning of the lepton-to-baryon ratio during the presupernova phases of stellar evolution of massive stars.

SPITZER OBSERVATIONS OF LONG-TERM INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN CHAMAELEON I

Energy Technology Data Exchange (ETDEWEB)

Flaherty, Kevin M.; Herbst, William [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); DeMarchi, Lindsay [Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, NY 13346 (United States); Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Balog, Zoltan [Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg (Germany); Megeath, S. Thomas [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Furlan, Elise [Infrared Processing and Analysis Center, California Institute of Technology, 770 S. Wilson Avenue, Pasadena, CA 91125 (United States); Gutermuth, Robert [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)

2016-12-10

Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring in ∼80% of the detected cluster members. The change in [3.6]–[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ∼0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.

Calibrated Tully-fisher Relations For Improved Photometric Estimates Of Disk Rotation Velocities

NARCIS (Netherlands)

Reyes, Reinabelle; Mandelbaum, R.; Gunn, J. E.; Pizagno II, Jim

We present calibrated scaling relations (also referred to as Tully-Fisher relations or TFRs) between rotation velocity and photometric quantities-- absolute magnitude, stellar mass, and synthetic magnitude (a linear combination of absolute magnitude and color)-- of disk galaxies at z 0.1. First, we

Infrared radiative transfer in dense disks around young stars

International Nuclear Information System (INIS)

Dent, W.R.F.

1988-01-01

A two-dimensional radiative transfer program has been used to determine the temperature distribution within cylindrically symmetric, centrally heated dust clouds. In particular, the disk-shaped structures observed around young luminous stars have been modeled. Changing the dust distribution in these disks primarily affected the observed morphology in the near-infrared and far-infrared, and at millimeter wavelengths. The overall cloud spectrum, however, was mainly determined by the characteristics of the grains themselves. Comparison with published far-infrared and molecular line data has indicated that the dust density can generally be modeled by a power-law distribution in r with index of -2 and an exponential in z with disk thickness proportional to 1/r. When observed nearly edge-on, scattered direct stellar radiation is observed in the polar regions in the form of comet-shaped lobes of emission. 26 references

Initial proto II pulsed power tests

International Nuclear Information System (INIS)

Johnson, D.L.

1976-01-01

The Proto II electron beam accelerator is being developed by Sandia Laboratories to study engineering and physics aspects of electron beam pellet fusion. Currently the Marx generator-water capacitor portion of Proto II is undergoing high voltage testing and timing measurements. Eight 112 kJ Marx generators form the primary energy storage system. Each Marx generator pulse charges two parallel 7.5 nF water capacitors to 3 MV. The water capacitors act as intermediate energy storage elements and will transfer their energy to the water insulated pulse-forming lines in 250 ns by means of eight SF 6 gas insulated, trigatron switches. Test data and design considerations of the trigger systems, Marx generators, water capacitors, and trigatron switches are presented

PROTOPLANETARY DISK MASSES IN IC348: A RAPID DECLINE IN THE POPULATION OF SMALL DUST GRAINS AFTER 1 Myr

International Nuclear Information System (INIS)

Lee, Nicholas; Williams, Jonathan P.; Cieza, Lucas A.

2011-01-01

We present a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old cluster, IC348, with the Submillimeter Array. We observed 85 young stellar objects and detected 10 with 1.3 mm fluxes greater than 2 mJy. The brightest source is a young embedded protostar driving a molecular outflow. The other nine detections are dusty disks around optically visible stars. Our millimeter flux measurements translate into total disk masses ranging from 2 to 6 Jupiter masses. Each detected disk has strong mid-infrared emission in excess of the stellar photosphere and has Hα equivalent widths larger than the average in the cluster and indicative of ongoing gas accretion. The disk mass distribution, however, is shifted by about a factor of 20 to lower masses, compared to that in the ∼1 Myr old Taurus and Ophiuchus regions. These observations reveal the rapid decline in the number of small dust grains in disks with time and probably their concomitant growth beyond millimeter sizes. Moreover, if IC348 is to form planets in the same proportion as detected in the field, these faint millimeter detections may represent the best candidates in the cluster to study the progression from planetesimals to planets.

Properties of the outer regions of spiral disks: abundances, colors and ages

Science.gov (United States)

Mollá, Mercedes; Díaz, Angeles I.; Gibson, Brad K.; Cavichia, Oscar; López-Sánchez, Ángel-R.

2017-03-01

We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.

Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion: T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

International Nuclear Information System (INIS)

Torbett, M.V.

1984-01-01

A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction βapprox.10 -2 to 10 -3 of the accreted mass. These winds are driven by a mechanism that accelerates the flow perpendicular to the plane of the disk and can therefore account for the bipolar geometry of the mass loss observed near young stars. The mass loss contained in these winds is comparable to that inferred for young stars. Thus, disk accretion-driven winds may constitute the T Tauri phase of stellar evolution. This mechanism is generally applicable, and thus massive pre-main-sequence objects as well as cataclysmic variables at times of enhanced accretion are predicted to eject bipolar outflows as well. Unmagnetized accreting neutron stas are also expected to eject bipolar flows. Since this mechanism requires stellar surfaces, however, it will not operate in disk accretion onto black holes

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk Around PDS 70: Observations of the Disk

Science.gov (United States)

Hashimoto, J.; Dong, R.; Kudo, T.; Honda, M.; McClure, M. K.; Zhu, Z.; Muto, T.; Wisniewski, J.; Abe, L.; Brandner, W.;

Accretion Disk Assembly During Common Envelope Evolution: Implications for Feedback and LIGO Binary Black Hole Formation

Energy Technology Data Exchange (ETDEWEB)

Murguia-Berthier, Ariadna; Ramirez-Ruiz, Enrico; Antoni, Andrea; Macias, Phillip [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); MacLeod, Morgan, E-mail: armurgui@ucsc.edu [School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540 (United States)

2017-08-20

During a common envelope (CE) episode in a binary system, the engulfed companion spirals to tighter orbital separations under the influence of drag from the surrounding envelope material. As this object sweeps through material with a steep radial gradient of density, net angular momentum is introduced into the flow, potentially leading to the formation of an accretion disk. The presence of a disk would have dramatic consequences for the outcome of the interaction because accretion might be accompanied by strong, polar outflows with enough energy to unbind the entire envelope. Without a detailed understanding of the necessary conditions for disk formation during CE, therefore, it is difficult to accurately predict the population of merging compact binaries. This paper examines the conditions for disk formation around objects embedded within CEs using the “wind tunnel” formalism developed by MacLeod et al. We find that the formation of disks is highly dependent on the compressibility of the envelope material. Disks form only in the most compressible of stellar envelope gas, found in envelopes’ outer layers in zones of partial ionization. These zones are largest in low-mass stellar envelopes, but comprise small portions of the envelope mass and radius in all cases. We conclude that disk formation and associated accretion feedback in CE is rare, and if it occurs, transitory. The implication for LIGO black hole binary assembly is that by avoiding strong accretion feedback, CE interactions should still result in the substantial orbital tightening needed to produce merging binaries.

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.

Near-infrared imaging of white dwarfs with candidate debris disks

International Nuclear Information System (INIS)

Wang, Zhongxiang; Tziamtzis, Anestis; Wang, Xuebing

2014-01-01

We have carried out JHK s imaging of 12 white dwarf debris disk candidates from the WIRED Sloan Digital Sky Survey Data Release 7 catalog, aiming to confirm or rule out disks among these sources. On the basis of positional identification and the flux density spectra, we find that seven white dwarfs have excess infrared emission, but mostly at Wide-field Infrared Survey Explorer W1 and W2 bands. Four are due to nearby red objects consistent with background galaxies or very low mass dwarfs, and one exhibits excess emission at JHK s consistent with an unresolved L0 companion at the correct distance. While our photometry is not inconsistent with all seven excesses arising from disks, the stellar properties are distinct from the known population of debris disk white dwarfs, making the possibility questionable. In order to further investigate the nature of these infrared sources, warm Spitzer imaging is needed, which may help resolve galaxies from the white dwarfs and provide more accurate flux measurements.

Neutrino Coannihilation on Dark-Matter Relics?

Energy Technology Data Exchange (ETDEWEB)

Barenboim, Gabriela; /Valencia U.; Mena Requejo, Olga; Quigg, Chris; /Fermilab

2006-04-01

High-energy neutrinos may resonate with relic background neutralinos to form short-lived sneutrinos. In some circumstances, the decay chain that leads back to the lightest supersymmetric particle would yield few-GeV gamma rays or charged-particle signals. Although resonant coannihilation would occur at an appreciable rate in our galaxy, the signal in any foreseeable detector is unobservably small.

The National Programme of Stellar Physics. Assessment 2011-2014. Prospective 2015-2018

International Nuclear Information System (INIS)

Bontemps, Sylvain; Bouchy, Francois; Charbonnel, Corinne; Chieze, Jean-Pierre; Dessart, Luc; Dintrans, Boris; Dougados, Catherine; Josselin, Eric; Kervella, Pierre; Martins, Fabrice; Michel, Eric; Moraux, Estelle; Recio-Blanco, Alejandra; Ristorcelli, Isabelle; Reyle, Celine; Alecian, Evelyne; Bouchy, Francois; Ciardi, Andrea; Dintrans, Boris; Herpin, Fabrice; Jouve, Laurene; Lebreton, Yveline; Motte, Frederique; Nardetto, Nicolas; Robin, Annie; Royer, Frederic; Samadi, Reza

2015-04-01

After an introduction which outlines the role of stellar physics as a keystone of research in astrophysics, this report proposes a presentation of the operation of the French national programme of stellar physics (PNPS): status and general operation, annual operation, statistics of budget and calls for bids, scientific animation, education, communication, community census, assessment of projects and thesis. It presents an overview of priority research theses between 2011 and 2014, according to their theme: stellar formation and protoplanetary disks, stellar structure and evolutions, origin and impact of magnetism, and atmospheres, winds and mass loss. Transverse theses are also presented the same way for the same period, with the following themes: basic physics, numeric simulations. The last part presents prospectives in terms of events (colloquium), bodies (new scientific council), themes to be studied, operation (interdisciplinarity and interfaces), means, general recommendations, and strengths and weaknesses of the national community

Unveiling the sources of disk heating in spiral galaxies with the CALIFA survey

NARCIS (Netherlands)

Pinna, F.; Falcón-Barroso, J.; Martig, M.; van de Ven, G.; Lyubenova, M.; Leaman, R.

The stellar velocity ellipsoid (SVE) quantifies the amount of velocity dispersion in the vertical, radial and azimuthal directions. Since different disk heating mechanisms (e.g. spiral arms, giant molecular clouds, mergers, etc) affect these components differently, the SVE can constrain the sources

ALMA observations of a misaligned binary protoplanetary disk system in Orion

Energy Technology Data Exchange (ETDEWEB)

Williams, Jonathan P. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96816 (United States); Mann, Rita K.; Francesco, James Di; Johnstone, Doug; Matthews, Brenda [NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Andrews, Sean M.; Ricci, Luca [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hughes, A. Meredith [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Bally, John, E-mail: jpw@ifa.hawaii.edu [CASA, University of Colorado, CB 389, Boulder, CO 80309 (United States)

2014-12-01

We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a wide binary system in Orion, with projected separation 440 AU, in which we detect submillimeter emission from the protoplanetary disks around each star. Both disks appear moderately massive and have strong line emission in CO 3-2, HCO{sup +} 4-3, and HCN 3-2. In addition, CS 7-6 is detected in one disk. The line-to-continuum ratios are similar for the two disks in each of the lines. From the resolved velocity gradients across each disk, we constrain the masses of the central stars, and show consistency with optical-infrared spectroscopy, both indicative of a high mass ratio ∼9. The small difference between the systemic velocities indicates that the binary orbital plane is close to face-on. The angle between the projected disk rotation axes is very high, ∼72°, showing that the system did not form from a single massive disk or a rigidly rotating cloud core. This finding, which adds to related evidence from disk geometries in other systems, protostellar outflows, stellar rotation, and similar recent ALMA results, demonstrates that turbulence or dynamical interactions act on small scales well below that of molecular cores during the early stages of star formation.

INNER EDGES OF COMPACT DEBRIS DISKS AROUND METAL-RICH WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Rafikov, Roman R.; Garmilla, Jose A., E-mail: rrr@astro.princeton.edu, E-mail: garmilla@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)

2012-12-01

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems, the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations, we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogs, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim toward the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range {approx}0.03-30 cm.

INNER EDGES OF COMPACT DEBRIS DISKS AROUND METAL-RICH WHITE DWARFS

International Nuclear Information System (INIS)

Rafikov, Roman R.; Garmilla, José A.

2012-01-01

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems, the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations, we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogs, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim toward the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range ∼0.03-30 cm.

Inner Edges of Compact Debris Disks around Metal-rich White Dwarfs

Science.gov (United States)

Rafikov, Roman R.; Garmilla, José A.

2012-12-01

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems, the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations, we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogs, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim toward the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range ~0.03-30 cm.

Precision Scaling Relations for Disk Galaxies in the Local Universe

Science.gov (United States)

Lapi, A.; Salucci, P.; Danese, L.

2018-05-01

We build templates of rotation curves as a function of the I-band luminosity via the mass modeling (by the sum of a thin exponential disk and a cored halo profile) of suitably normalized, stacked data from wide samples of local spiral galaxies. We then exploit such templates to determine fundamental stellar and halo properties for a sample of about 550 local disk-dominated galaxies with high-quality measurements of the optical radius R opt and of the corresponding rotation velocity V opt. Specifically, we determine the stellar M ⋆ and halo M H masses, the halo size R H and velocity scale V H, and the specific angular momenta of the stellar j ⋆ and dark matter j H components. We derive global scaling relationships involving such stellar and halo properties both for the individual galaxies in our sample and for their mean within bins; the latter are found to be in pleasing agreement with previous determinations by independent methods (e.g., abundance matching techniques, weak-lensing observations, and individual rotation curve modeling). Remarkably, the size of our sample and the robustness of our statistical approach allow us to attain an unprecedented level of precision over an extended range of mass and velocity scales, with 1σ dispersion around the mean relationships of less than 0.1 dex. We thus set new standard local relationships that must be reproduced by detailed physical models, which offer a basis for improving the subgrid recipes in numerical simulations, that provide a benchmark to gauge independent observations and check for systematics, and that constitute a basic step toward the future exploitation of the spiral galaxy population as a cosmological probe.

Proto-jet configurations in RADs orbiting a Kerr SMBH: symmetries and limiting surfaces

Science.gov (United States)

Pugliese, D.; Stuchlík, Z.

2018-05-01

Ringed accretion disks (RADs) are agglomerations of perfect-fluid tori orbiting around a single central attractor that could arise during complex matter inflows in active galactic nuclei. We focus our analysis to axi-symmetric accretion tori orbiting in the equatorial plane of a supermassive Kerr black hole; equilibrium configurations, possible instabilities, and evolutionary sequences of RADs were discussed in our previous works. In the present work we discuss special instabilities related to open equipotential surfaces governing the material funnels emerging at various regions of the RADs, being located between two or more individual toroidal configurations of the agglomerate. These open structures could be associated to proto-jets. Boundary limiting surfaces are highlighted, connecting the emergency of the jet-like instabilities with the black hole dimensionless spin. These instabilities are observationally significant for active galactic nuclei, being related to outflows of matter in jets emerging from more than one torus of RADs orbiting around supermassive black holes.

The continuous rise of bulges out of galactic disks

Science.gov (United States)

Breda, Iris; Papaderos, Polychronis

2018-06-01

Context. A key subject in extragalactic astronomy concerns the chronology and driving mechanisms of bulge formation in late-type galaxies (LTGs). The standard scenario distinguishes between classical bulges and pseudo-bulges (CBs and PBs, respectively), the first thought to form monolithically prior to disks and the second gradually out of disks. These two bulge formation routes obviously yield antipodal predictions on the bulge age and bulge-to-disk age contrast, both expected to be high (low) in CBs (PBs). Aims: Our main goal is to explore whether bulges in present-day LTGs segregate into two evolutionary distinct classes, as expected from the standard scenario. Other questions motivating this study center on evolutionary relations between LTG bulges and their hosting disks, and the occurrence of accretion-powered nuclear activity as a function of bulge stellar mass ℳ⋆ and stellar surface density Σ⋆. Methods: In this study, we have combined three techniques - surface photometry, spectral modeling of integral field spectroscopy data and suppression of stellar populations younger than an adjustable age cutoff with the code REMOVEYOUNG (ℛ𝒴) - toward a systematic analysis of the physical and evolutionary properties (e.g., ℳ⋆, Σ⋆ and mass-weighted stellar age ℳ and metallicity ℳ, respectively) of a representative sample of 135 nearby (≤ 130 Mpc) LTGs from the CALIFA survey that cover a range between 108.9 M⊙ and 1011.5 M⊙ in total stellar mass ℳ⋆,T. In particular, the analysis here revolves around ⟨δμ9G⟩, a new distance- and formally extinction-independent measure of the contribution by stellar populations of age ≥ 9 Gyr to the mean r-band surface brightness of the bulge. We argue that ⟨δμ9G⟩ offers a handy semi-empirical tracer of the physical and evolutionary properties of LTG bulges and a promising means for their characterization. Results: The essential insight from this study is that LTG bulges form over 3 dex

Constraints on observing brightness asymmetries in protoplanetary disks at solar system scale

Science.gov (United States)

Brunngräber, Robert; Wolf, Sebastian

2018-04-01

We have quantified the potential capabilities of detecting local brightness asymmetries in circumstellar disks with the Very Large Telescope Interferometer (VLTI) in the mid-infrared wavelength range. The study is motivated by the need to evaluate theoretical models of planet formation by direct observations of protoplanets at early evolutionary stages, when they are still embedded in their host disk. Up to now, only a few embedded candidate protoplanets have been detected with semi-major axes of 20-50 au. Due to the small angular separation from their central star, only long-baseline interferometry provides the angular resolving power to detect disk asymmetries associated to protoplanets at solar system scales in nearby star-forming regions. In particular, infrared observations are crucial to observe scattered stellar radiation and thermal re-emission in the vicinity of embedded companions directly. For this purpose we performed radiative transfer simulations to calculate the thermal re-emission and scattered stellar flux from a protoplanetary disk hosting an embedded companion. Based on that, visibilities and closure phases are calculated to simulate observations with the future beam combiner MATISSE, operating at the L, M and N bands at the VLTI. We find that the flux ratio of the embedded source to the central star can be as low as 0.5 to 0.6% for a detection at a feasible significance level due to the heated dust in the vicinity of the embedded source. Furthermore, we find that the likelihood for detection is highest for sources at intermediate distances r ≈ 2-5 au and disk masses not higher than ≈10-4 M⊙.

Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation

Science.gov (United States)

Silich, Sergiy; Tenorio-Tagle, Guillermo

2018-05-01

Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds and supernova explosions, or that the enrichment of the residual gas and the formation of the second stellar generation occur so rapidly, that the negative stellar feedback is not significant. Here we continue our study of the early development of star clusters in the extreme environments and discuss the restrictions that strong radiative cooling and stellar mass segregation provide on the gas expulsion from dense star-forming clouds. A large range of physical initial conditions in star-forming clouds which include the star-forming cloud mass, compactness, gas metallicity, star formation efficiency and effects of massive stars segregation are discussed. It is shown that in sufficiently massive and compact clusters hot shocked winds around individual massive stars may cool before merging with their neighbors. This dramatically reduces the negative stellar feedback, prevents the development of the global star cluster wind and expulsion of the residual and the processed matter into the ambient interstellar medium. The critical lines which separate the gas expulsion and the gas retention regimes are obtained.

Mapping the ecological dimensions and potential distributions of endangered relic shrubs in western Ordos biodiversity center.

Science.gov (United States)

Zhu, Geng-Ping; Li, Hui-Qi; Zhao, Li; Man, Liang; Liu, Qiang

2016-05-20

Potential distributions of endemic relic shrubs in western Ordos were poorly mapped, which hindered our implementation of proper conservation. Here we investigated the applicability of ecological niche modeling for endangered relic shrubs to detect areas of priority for biodiversity conservation and analyze differences in ecological niche spaces used by relic shrubs. We applied ordination and niche modeling techniques to assess main environmental drivers of five endemic relic shrubs in western Ordos, namely, Ammopiptanthus mongolicus, Amygdalus mongolica, Helianthemum songaricum, Potaninia mongolica, and Tetraena mongolica. We calculated niche overlap metrics in gridded environmental spaces and compared geographical projections of ecological niches to determine similarities and differences of niches occupied by relic shrubs. All studied taxa presented different responses to environmental factors, which resulted in a unique combination of niche conditions. Precipitation availability and soil quality characteristics play important roles in the distributions of most shrubs. Each relic shrub is constrained by a unique set of environmental conditions, the distribution of one species cannot be implied by the distribution of another, highlighting the inadequacy of one-fits-all type of conservation measure. Our stacked habitat suitability maps revealed regions around Yellow River, which are highly suitable for most species, thereby providing high conservation value.

MULTI-FREQUENCY STUDIES OF RADIO RELICS IN THE GALAXY CLUSTERS A4038, A1664, AND A786

Energy Technology Data Exchange (ETDEWEB)

Kale, Ruta; Dwarakanath, K. S., E-mail: ruta@iucaa.ernet.in [Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bangalore 560 080 (India)

2012-01-01

We present a multi-frequency study of radio relics associated with the galaxy clusters A4038, A1664, and A786. Radio images, integrated spectra, spectral index maps, and fits to the integrated spectra in the framework of the adiabatic compression model are presented. Images of the relic in A4038 at 150, 240, and 606 MHz with the Giant Meterwave Radio Telescope have revealed extended ultra-steep spectrum ({alpha} {approx} -1.8 to -2.7) emission of extent 210 Multiplication-Sign 80 kpc{sup 2}. The model of passively evolving radio lobes compressed by a shock fits the integrated spectrum best. The relic with a circular morphology at the outskirts of the cluster A1664 has an integrated spectral index of {approx} - 1.10 {+-} 0.06 and is best fit by the model of radio lobes lurking for {approx}4 Multiplication-Sign 10{sup 7} yr. The relic near A786 has a curved spectrum and is best fit by a model of radio lobes lurking for {approx}3 Multiplication-Sign 10{sup 7} yr. At 4.7 GHz, a compact radio source, possibly the progenitor of the A786 relic, is detected near the center of the radio relic. The A786 radio relic is thus likely a lurking radio galaxy rather than a site of cosmological shock as has been considered in earlier studies.

MID-INFRARED SPECTRA OF TRANSITIONAL DISKS IN THE CHAMAELEON I CLOUD

International Nuclear Information System (INIS)

Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Sargent, B.; McClure, M. K.; Green, J. D.; Harrold, Samuel T.; Furlan, E.; Najita, J.; Espaillat, C.; Calvet, N.; Luhman, K. L.

2009-01-01

We present 5-40 μm Spitzer Infrared Spectrograph spectra of a collection of transitional disks, objects for which the spectral energy distribution (SED) indicates central clearings (holes) or gaps in the dust distribution, in the Chamaeleon I star-forming region. Like their counterparts in the Taurus-Auriga star-forming region that we have previously observed, the spectra of these young objects (1-3 Myr old) reveal that the central clearings or gaps are very sharp-edged, and are surrounded by optically thick dusty disks similar to those around other classical T Tauri stars in the Chamaeleon I association. Also like the Taurus transitional disks, the Chamaeleon I transitional disks have extremely large depletion factors for small dust grains in their gaps, compared to the full accretion disks whose SEDs are represented by the median SED of Class II objects in the region. We find that the fraction of transitional disks in the Chamaeleon I cloud is somewhat higher than that in the Taurus-Auriga cloud, possibly indicating that the frequency of transitional disks, on average, increases with cluster age. We also find a significant correlation between the stellar mass and the radius of the outer edge of the gap. We discuss the disk structures implied by the spectra and the constraints they place on gap-formation mechanisms in protoplanetary disks.

The Earliest Chinese Proto-Porcelain Excavated from Kiln Sites: An Elemental Analysis

OpenAIRE

Li, Yu; Zhang, Bin; Cheng, Huansheng; Zheng, Jianming

2015-01-01

In June 2012, the Piaoshan kiln site was excavated in Huzhou, Zhejiang Province, which hitherto proved to be the earliest known Chinese proto-porcelain kiln. Judging from the decorative patterns of unearthed impressed stoneware and proto-porcelain sherds, the site was determined to date to the late Xia (c. 2070-c. 1600 BC), the first dynasty of China. Here, we report on proton-induced X-ray emission analyses of 118 proto-porcelain and 35 impressed stoneware sherds from Piaoshan and five subse...

The SLUGGS survey: wide-field stellar kinematics of early-type galaxies

Energy Technology Data Exchange (ETDEWEB)

Arnold, Jacob A. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Romanowsky, Aaron J.; Brodie, Jean P.; Woodley, Kristin A. [University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Forbes, Duncan A.; Blom, Christina; Kartha, Sreeja S.; Pastorello, Nicola; Pota, Vincenzo; Usher, Christopher [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Strader, Jay [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Spitler, Lee R. [Department of Physics and Astronomy, Faculty of Sciences, Macquarie University, Sydney, NSW 2109 (Australia); Foster, Caroline, E-mail: romanow@ucolick.org [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW (Australia)

2014-08-20

We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ∼2-4 R {sub e} (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (σ{sub inst} ∼ 25 km s{sup –1}) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, σ, h {sub 3}, and h {sub 4}) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R {sub e} often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS{sup 3D} survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

EFFECT OF PHOTODESORPTION ON THE SNOW LINES AT THE SURFACE OF OPTICALLY THICK CIRCUMSTELLAR DISKS AROUND HERBIG Ae/Be STARS

International Nuclear Information System (INIS)

Oka, Akinori; Nakamoto, Taishi; Inoue, Akio K.; Honda, Mitsuhiko

2012-01-01

We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find that photodesorption induced by far-ultraviolet radiation from the central star depresses the ice-condensation front toward the mid-plane and pushes the surface snow line significantly outward when the stellar effective temperature exceeds a certain critical value. This critical effective temperature depends on the stellar luminosity and mass, the water abundance in the disk, and the yield of photodesorption. We present an approximate analytic formula for the critical temperature. We separate Herbig Ae/Be stars into two groups on the HR diagram according to the critical temperature: one is the disks where photodesorption is effective and from which we may not find ice particles at the surface, and the other is the disks where photodesorption is not effective. We estimate the snow line position at the surface of the disk around HD142527 to be 100-300 AU, which is consistent with the water ice detection at >140 AU in the disk. All the results depend on the dust grain size in a complex way, and this point requires more work in the future.

Helicon normal modes in Proto-MPEX

Science.gov (United States)

Piotrowicz, P. A.; Caneses, J. F.; Green, D. L.; Goulding, R. H.; Lau, C.; Caughman, J. B. O.; Rapp, J.; Ruzic, D. N.

2018-05-01

The Proto-MPEX helicon source has been operating in a high electron density ‘helicon-mode’. Establishing plasma densities and magnetic field strengths under the antenna that allow for the formation of normal modes of the fast-wave are believed to be responsible for the ‘helicon-mode’. A 2D finite-element full-wave model of the helicon antenna on Proto-MPEX is used to identify the fast-wave normal modes responsible for the steady-state electron density profile produced by the source. We also show through the simulation that in the regions of operation in which core power deposition is maximum the slow-wave does not deposit significant power besides directly under the antenna. In the case of a simulation where a normal mode is not excited significant edge power is deposited in the mirror region. ).

Implications of Stellar Feedback for Dynamical Modeling of the Milky Way and Dwarf Galaxies

Science.gov (United States)

Wetzel, Andrew

2018-04-01

I will present recent results on dynamical modeling of stellar populations from the FIRE cosmological zoom-in baryonic simulations of Milky Way-like and dwarf galaxies. First, I will discuss the dynamical formation of the Milky Way, including the origin of thin+thick stellar disk morphology. I also will discuss the curious origin of metal-rich stars on halo-like orbits near the Sun, as recently measured by Gaia, with new insights from FIRE simulations on stellar radial migration/heating. Next, I will discuss role of stellar feedback in generating non-equilibrium fluctuations of the gravitational potential in low-mass 'dwarf' galaxies, which can explain the origin of cores in their dark-matter density profiles. In particular, we predict significant observable effects on stellar dynamics, including radial migration, size fluctuations, and population gradients, which can provide observational tests of feedback-driven core formation. Finally, this scenario can explain the formation of newly discovered 'ultra-diffuse' galaxies.

UNSTABLE PLANETARY SYSTEMS EMERGING OUT OF GAS DISKS

International Nuclear Information System (INIS)

Matsumura, Soko; Thommes, Edward W.; Chatterjee, Sourav; Rasio, Frederic A.

2010-01-01

The discovery of over 400 extrasolar planets allows us to statistically test our understanding of the formation and dynamics of planetary systems via numerical simulations. Traditional N-body simulations of multiple-planet systems without gas disks have successfully reproduced the eccentricity (e) distribution of the observed systems by assuming that the planetary systems are relatively closely packed when the gas disk dissipates, so that they become dynamically unstable within the stellar lifetime. However, such studies cannot explain the small semimajor axes a of extrasolar planetary systems, if planets are formed, as the standard planet formation theory suggests, beyond the ice line. In this paper, we numerically study the evolution of three-planet systems in dissipating gas disks, and constrain the initial conditions that reproduce the observed a and e distributions simultaneously. We adopt initial conditions that are motivated by the standard planet formation theory, and self-consistently simulate the disk evolution and planet migration, by using a hybrid N-body and one-dimensional gas disk code. We also take into account eccentricity damping, and investigate the effect of saturation of corotation resonances on the evolution of planetary systems. We find that the a distribution is largely determined in a gas disk, while the e distribution is determined after the disk dissipation. We also find that there may be an optimum disk mass which leads to the observed a-e distribution. Our simulations generate a larger fraction of planetary systems trapped in mean-motion resonances (MMRs) than the observations, indicating that the disk's perturbation to the planetary orbits may be important to explain the observed rate of MMRs. We also find a much lower occurrence of planets on retrograde orbits than the current observations of close-in planets suggest.

Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon

DEFF Research Database (Denmark)

Schiller, Martin; Bizzarro, Martin; Fernandes, Vera Assis

2018-01-01

Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth-Moon system. Using this approach......, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner...... into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The identical calcium isotope composition of Earth and the Moon reported here is a prediction of our model if the Moon-forming impact involved protoplanets or precursors that completed their accretion near...

DYNAMICAL EVOLUTION OF VISCOUS DISKS AROUND Be STARS. I. PHOTOMETRY

Energy Technology Data Exchange (ETDEWEB)

Haubois, X.; Carciofi, A. C. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP 05508-900 (Brazil); Rivinius, Th. [European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19 (Chile); Okazaki, A. T. [Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605 (Japan); Bjorkman, J. E., E-mail: xhaubois@astro.iag.usp.br [Ritter Observatory, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)

2012-09-10

Be stars possess gaseous circumstellar disks that modify in many ways the spectrum of the central B star. Furthermore, they exhibit variability at several timescales and for a large number of observables. Putting the pieces together of this dynamical behavior is not an easy task and requires a detailed understanding of the physical processes that control the temporal evolution of the observables. There is an increasing body of evidence that suggests that Be disks are well described by standard {alpha}-disk theory. This paper is the first of a series that aims at studying the possibility of inferring several disk and stellar parameters through the follow-up of various observables. Here we study the temporal evolution of the disk density for different dynamical scenarios, including the disk build-up as a result of a long and steady mass injection from the star, the disk dissipation that occurs after mass injection is turned off, as well as scenarios in which active periods are followed by periods of quiescence. For those scenarios, we investigate the temporal evolution of continuum photometric observables using a three-dimensional non-LTE radiative transfer code. We show that light curves for different wavelengths are specific of a mass loss history, inclination angle, and {alpha} viscosity parameter. The diagnostic potential of those light curves is also discussed.

Education Policy as Proto-Fascism: The Aesthetics of Racial Neo-Liberalism

Science.gov (United States)

Webb, P. Taylor; Gulson, Kalervo N.

2011-01-01

We argue that neo-liberal educational policy has emerged as a proto-fascist governmentality. This contemporary technology relies on State racisms and racial orderings manifested from earlier liberal and neo-liberal practices of biopower. As a proto-fascist technology, education policy, and school choice policies in particular, operate within a…

The Single-Phase ProtoDUNE Technical Design Report

Energy Technology Data Exchange (ETDEWEB)

Abi, B. [Univ. of Padova (Italy); et al.

2017-06-21

ProtoDUNE-SP is the single-phase DUNE Far Detector prototype that is under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018. ProtoDUNE-SP, a crucial part of the DUNE effort towards the construction of the first DUNE 10-kt fiducial mass far detector module (17 kt total LAr mass), is a significant experiment in its own right. With a total liquid argon (LAr) mass of 0.77 kt, it represents the largest monolithic single-phase LArTPC detector to be built to date. It's technical design is given in this report.

Heat flux estimates of power balance on Proto-MPEX with IR imaging

Energy Technology Data Exchange (ETDEWEB)

Showers, M., E-mail: mshower1@vols.utk.edu [Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996 (United States); Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Biewer, T. M.; Caughman, J. B. O.; Goulding, R. H.; Rapp, J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Donovan, D. C. [Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996 (United States)

2016-11-15

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory (ORNL) is a precursor linear plasma device to the Material Plasma Exposure eXperiment (MPEX), which will study plasma material interactions (PMIs) for future fusion reactors. This paper will discuss the initial steps performed towards completing a power balance on Proto-MPEX to quantify where energy is lost from the plasma, including the relevant diagnostic package implemented. Machine operating parameters that will improve Proto-MPEX’s performance may be identified, increasing its PMI research capabilities.

Heat flux estimates of power balance on Proto-MPEX with IR imaging

International Nuclear Information System (INIS)

Showers, M.; Biewer, T. M.; Caughman, J. B. O.; Goulding, R. H.; Rapp, J.; Donovan, D. C.

2016-01-01

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory (ORNL) is a precursor linear plasma device to the Material Plasma Exposure eXperiment (MPEX), which will study plasma material interactions (PMIs) for future fusion reactors. This paper will discuss the initial steps performed towards completing a power balance on Proto-MPEX to quantify where energy is lost from the plasma, including the relevant diagnostic package implemented. Machine operating parameters that will improve Proto-MPEX’s performance may be identified, increasing its PMI research capabilities.

Tidal Disruption Events from Eccentric Nuclear Disks

Science.gov (United States)

Wernke, Heather N.; Madigan, Ann-Marie

2018-04-01

Stars that get too close to a supermassive black hole are in danger of being tidally disrupted. Stellar two-body relaxation is commonly assumed to be the main driver of these events. Recent work has shown, however, that secular gravitational torques from eccentric nuclear disks can push stars to extreme eccentricities at much higher rates than predicted by two-body relaxation. This work did not include the effects of general relativity, however, which could quench secular torques via rapid apsidal precession. Here we show that, for a star in danger of disruption, general relativity acts on a timescale of less than an orbital period. This short timescale means that general relativity does not have enough time to have a major effect on the orbit. When driven by secular torques from eccentric nuclear disks, tidal disruption event rates are not affected by general relativity.

THE STELLAR AND GAS KINEMATICS OF THE LITTLE THINGS DWARF IRREGULAR GALAXY NGC 1569

International Nuclear Information System (INIS)

Johnson, Megan; Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly; Oh, Se-Heon; Elmegreen, Bruce; Brinks, Elias; Tollerud, Erik

2012-01-01

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, σ z , coupled with the maximum rotational velocity derived from H I observations, V max , gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V max /σ z = 2.4 ± 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, ∼1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V max , shows that the disk may be dark matter deficient in the inner region, although, when compared to the

THE PHOTOMETRIC PROPERTIES OF A VAST STELLAR SUBSTRUCTURE IN THE OUTSKIRTS OF M33

International Nuclear Information System (INIS)

McConnachie, Alan W.; Ferguson, Annette M. N.; Irwin, Michael J.; Dubinski, John; Widrow, Lawrence M.; Dotter, Aaron; Ibata, Rodrigo; Lewis, Geraint F.

2010-01-01

We have surveyed approximately 40 deg 2 surrounding M33 with Canada-France-Hawaii Telescope MegaCam/MegaPrime in the g and i filters out to a maximum projected radius from this galaxy of 50 kpc, as part of the Pan-Andromeda Archaeological Survey (PAndAS). Our observations are deep enough to resolve the top ∼4 mag of the red giant branch population in this galaxy. We have previously shown that the disk of M33 is surrounded by a large, irregular, low surface brightness substructure. Here, we quantify the stellar populations and structure of this feature using the PAndAS data. We show that the stellar populations of this feature are consistent with an old population with ([Fe/H]) ∼ -1.6 dex and an interquartile range in metallicity of ∼0.5 dex. We construct a surface brightness map of M33 that traces this feature to μ V ≅ 33 mag arcsec -2 . At these low surface brightness levels, the structure extends to projected radii of ∼40 kpc from the center of M33 in both the northwest and southeast quadrants of the galaxy. Overall, the structure has an 'S-shaped' appearance that broadly aligns with the orientation of the H I disk warp. We calculate a lower limit to the integrated luminosity of the structure of -12.7 ± 0.5 mag, comparable to a bright dwarf galaxy such as Fornax or Andromeda II and slightly less than 1% of the total luminosity of M33. Further, we show that there is tentative evidence for a distortion in the distribution of young stars near the edge of the H I disk that occurs at similar azimuth to the warp in H I. The data also hint at a low-level, extended stellar component at larger radius that may be an M33 halo component. We revisit studies of M33 and its stellar populations in light of these new results and discuss possible formation scenarios for the vast stellar structure. Our favored model is that of the tidal disruption of M33 in its orbit around M31.

Stellar X-Ray Polarimetry

Science.gov (United States)

Swank, J.

2011-01-01

Most of the stellar end-state black holes, pulsars, and white dwarfs that are X-ray sources should have polarized X-ray fluxes. The degree will depend on the relative contributions of the unresolved structures. Fluxes from accretion disks and accretion disk corona may be polarized by scattering. Beams and jets may have contributions of polarized emission in strong magnetic fields. The Gravity and Extreme Magnetism Small Explorer (GEMS) will study the effects on polarization of strong gravity of black holes and strong magnetism of neutron stars. Some part of the flux from compact stars accreting from companion stars has been reflected from the companion, its wind, or accretion streams. Polarization of this component is a potential tool for studying the structure of the gas in these binary systems. Polarization due to scattering can also be present in X-ray emission from white dwarf binaries and binary normal stars such as RS CVn stars and colliding wind sources like Eta Car. Normal late type stars may have polarized flux from coronal flares. But X-ray polarization sensitivity is not at the level needed for single early type stars.

An Extreme X-ray Disk Wind in the Black Hole Candidate IGR J17091-3624

Science.gov (United States)

King, A. L.; Miller, J. M.; Raymond, J.; Fabian, A. C.; Reynolds, C. S.; Kallman, T. R.; Maitra, D.; Cackett, E. M.; Rupen, M. P.

2012-01-01

Chandra spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk-dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized. dense. and to have typical velocities of approx 1000 km/s or less projected along our line of sight. Here. we present an analysis of two Chandra High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091-3624 and contemporaneous EVLA radio observations. obtained in 2011. The second Chandra observation reveals an absorption line at 6.91+/-0.01 keV; associating this line with He-like Fe XXV requires a blue-shift of 9300(+500/-400) km/ s (0.03c. or the escape velocity at 1000 R(sub schw)). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of approx 14600 km/s (0.05c), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091-3624 may originate within 43,300 Schwarzschild radii of the black hole, and may be expelling more gas than accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our Chandra observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems

Possible Imprints of Cold-mode Accretion on the Present-day Properties of Disk Galaxies

Science.gov (United States)

Noguchi, Masafumi

2018-01-01

Recent theoretical studies suggest that a significant part of the primordial gas accretes onto forming galaxies as narrow filaments of cold gas without building a shock and experiencing heating. Using a simple model of disk galaxy evolution that combines the growth of dark matter halos predicted by cosmological simulations with a hypothetical form of cold-mode accretion, we investigate how this cold-accretion mode affects the formation process of disk galaxies. It is found that the shock-heating and cold-accretion models produce compatible results for low-mass galaxies owing to the short cooling timescale in such galaxies. However, cold accretion significantly alters the evolution of disk galaxies more massive than the Milky Way and puts observable fingerprints on their present properties. For a galaxy with a virial mass {M}{vir}=2.5× {10}12 {M}ȯ , the scale length of the stellar disk is larger by 41% in the cold-accretion model than in the shock-heating model, with the former model reproducing the steep rise in the size–mass relation observed at the high-mass end. Furthermore, the stellar component of massive galaxies becomes significantly redder (0.66 in u ‑ r at {M}{vir}=2.5× {10}12 {M}ȯ ), and the observed color–mass relation in nearby galaxies is qualitatively reproduced. These results suggest that large disk galaxies with red optical colors may be the product of cold-mode accretion. The essential role of cold accretion is to promote disk formation in the intermediate-evolution phase (0.5< z< 1.5) by providing the primordial gas having large angular momentum and to terminate late-epoch accretion, quenching star formation and making massive galaxies red.

Multiwavelength Imaging Of YSOs With Disk In South Pillars Of Eta Carina

Science.gov (United States)

Reyes, J. A.; Porras, B. A.

2013-04-01

We present multiwavelength imaginery and spectral energy distributions (SEDs) of 15 Young Stellar Objects (YSOs) with disk components lying on the South Pillars region close to Eta Carina (η Car). The SEDs include IR fluxes from 2MASS, IRAC, MSX, AKARI, and MIPS-24 μm, and 1.1 mm flux from AzTEC camera at the ASTE antenna. Millimeter fluxes help to constrain the number of fitted models, which provide the list of physical parameters for the star, the disk and the envelope. We then compare the parameters of the YSOs and their spatial location within the star forming region.

Digging for red nuggets: discovery of hot halos surrounding massive, compact, relic galaxies

Science.gov (United States)

Werner, N.; Lakhchaura, K.; Canning, R. E. A.; Gaspari, M.; Simionescu, A.

2018-04-01

We present the results of Chandra X-ray observations of the isolated, massive, compact, relic galaxies MRK 1216 and PGC 032873. Compact massive galaxies observed at z > 2, also called red nuggets, formed in quick dissipative events and later grew by dry mergers into the local giant ellipticals. Due to the stochastic nature of mergers, a few of the primordial massive galaxies avoided the mergers and remained untouched over cosmic time. We find that the hot atmosphere surrounding MRK 1216 extends far beyond the stellar population and has an 0.5-7 keV X-ray luminosity of LX = (7.0 ± 0.2) × 1041 erg s-1, which is similar to the nearby X-ray bright giant ellipticals. The hot gas has a short central cooling time of ˜50 Myr and the galaxy has a ˜13 Gyr old stellar population. The presence of an X-ray atmosphere with a short nominal cooling time and the lack of young stars indicate the presence of a sustained heating source, which prevented star formation since the dissipative origin of the galaxy 13 Gyrs ago. The central temperature peak and the presence of radio emission in the core of the galaxy indicate that the heating source is radio-mechanical AGN feedback. Given that both MRK 1216 and PGC 032873 appear to have evolved in isolation, the order of magnitude difference in their current X-ray luminosity could be traced back to a difference in the ferocity of the AGN outbursts in these systems. Finally, we discuss the potential connection between the presence of hot halos around such massive galaxies and the growth of super/over-massive black holes via chaotic cold accretion.

Accreting planets as dust dams in 'transition' disks

International Nuclear Information System (INIS)

Owen, James E.

2014-01-01

We investigate under what circumstances an embedded planet in a protoplanetary disk may sculpt the dust distribution such that it observationally presents as a 'transition' disk. We concern ourselves with 'transition' disks that have large holes (≳ 10 AU) and high accretion rates (∼10 –9 -10 –8 M ☉ yr –1 ), particularly, those disks which photoevaporative models struggle to explain. Adopting the observed accretion rates in 'transition' disks, we find that the accretion luminosity from the forming planet is significant, and can dominate over the stellar luminosity at the gap edge. This planetary accretion luminosity can apply a significant radiation pressure to small (s ≲ 1 μm) dust particles provided they are suitably decoupled from the gas. Secular evolution calculations that account for the evolution of the gas and dust components in a disk with an embedded, accreting planet, show that only with the addition of the radiation pressure can we explain the full observed characteristics of a 'transition' disk (NIR dip in the spectral energy distribution (SED), millimeter cavity, and high accretion rate). At suitably high planet masses (≳ 3-4 M J ), radiation pressure from the accreting planet is able to hold back the small dust particles, producing a heavily dust-depleted inner disk that is optically thin to infrared radiation. The planet-disk system will present as a 'transition' disk with a dip in the SED only when the planet mass and planetary accretion rate are high enough. At other times, it will present as a disk with a primordial SED, but with a cavity in the millimeter, as observed in a handful of protoplanetary disks.

Establishing a relation between the mass and the spin of stellar-mass black holes.

Science.gov (United States)

Banerjee, Indrani; Mukhopadhyay, Banibrata

2013-08-09

Stellar mass black holes (SMBHs), forming by the core collapse of very massive, rapidly rotating stars, are expected to exhibit a high density accretion disk around them developed from the spinning mantle of the collapsing star. A wide class of such disks, due to their high density and temperature, are effective emitters of neutrinos and hence called neutrino cooled disks. Tracking the physics relating the observed (neutrino) luminosity to the mass, spin of black holes (BHs) and the accretion rate (M) of such disks, here we establish a correlation between the spin and mass of SMBHs at their formation stage. Our work shows that spinning BHs are more massive than nonspinning BHs for a given M. However, slowly spinning BHs can turn out to be more massive than spinning BHs if M at their formation stage was higher compared to faster spinning BHs.

arXiv Squeezed relic photons beyond the horizon

CERN Document Server

Giovannini, Massimo

2017-11-14

Owing to the analogy with the ordinary photons in the visible range of the electromagnetic spectrum, the Glauber theory is generalized to address the quantum coherence of the gauge field fluctuations parametrically amplified during an inflationary stage of expansion. The first and second degrees of quantum coherence of relic photons are then computed beyond the effective horizon defined by the evolution of the susceptibility. In the zero-delay limit the Hanbury Brown-Twiss correlations exhibit a super-Poissonian statistics which is however different from the conventional results of the single-mode approximation customarily employed, in quantum optics, to classify the coherence properties of visible light. While in the case of large-scale curvature perturbations the degrees of quantum coherence coincide with the naive expectation of the single-mode approximation, the net degree of second-order coherence computed for the relic photons diminishes thanks to the effect of the polarizations. We suggest that the Han...

Making the most of the relic density for dark matter searches at the LHC 14 TeV Run

International Nuclear Information System (INIS)

Busoni, Giorgio; Simone, Andrea De; Jacques, Thomas; Morgante, Enrico; Riotto, Antonio

2015-01-01

As the LHC continues to search for new weakly interacting particles, it is important to remember that the search is strongly motivated by the existence of dark matter. In view of a possible positive signal, it is essential to ask whether the newly discovered weakly interacting particle can be be assigned the label 'dark matter'. Within a given set of simplified models and modest working assumptions, we reinterpret the relic abundance bound as a relic abundance range, and compare the parameter space yielding the correct relic abundance with projections of the Run II exclusion regions. Assuming that dark matter is within the reach of the LHC, we also make the comparison with the potential 5σ discovery regions. Reversing the logic, relic density calculations can be used to optimize dark matter searches by motivating choices of parameters where the LHC can probe most deeply into the dark matter parameter space. In the event that DM is seen outside of the region giving the correct relic abundance, we will learn that either thermal relic DM is ruled out in that model, or the DM-quark coupling is suppressed relative to the DM coupling strength to other SM particles

THE AGORA HIGH-RESOLUTION GALAXY SIMULATIONS COMPARISON PROJECT. II. ISOLATED DISK TEST

Energy Technology Data Exchange (ETDEWEB)

Kim, Ji-hoon [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 (United States); Agertz, Oscar [Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH (United Kingdom); Teyssier, Romain; Feldmann, Robert [Centre for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Zurich, 8057 (Switzerland); Butler, Michael J. [Max-Planck-Institut für Astronomie, D-69117 Heidelberg (Germany); Ceverino, Daniel [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, D-69120 Heidelberg (Germany); Choi, Jun-Hwan [Department of Astronomy, University of Texas, Austin, TX 78712 (United States); Keller, Ben W. [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada); Lupi, Alessandro [Institut d’Astrophysique de Paris, Sorbonne Universites, UPMC Univ Paris 6 et CNRS, F-75014 Paris (France); Quinn, Thomas; Wallace, Spencer [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Revaz, Yves [Institute of Physics, Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Gnedin, Nickolay Y. [Particle Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Leitner, Samuel N. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Shen, Sijing [Kavli Institute for Cosmology, University of Cambridge, Cambridge, CB3 0HA (United Kingdom); Smith, Britton D., E-mail: me@jihoonkim.org [Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom); Collaboration: AGORA Collaboration; and others

2016-12-20

Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt–Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of ∼3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

Finger of a saint, thumb of a priest: medieval relics in the Diocese of Turku, and the archaeology of lived bodies

Directory of Open Access Journals (Sweden)

Visa Immonen

2011-01-01

Full Text Available The relics of Turku Cathedral are remains belonging to the bodies of holy persons, different from ours, even today, although the cathedral is the see for the archbishop of the Evangelical Lutheran Church of Finland, and relics are not on public display. Among the relics of the cathedral, there is a fragment of a radius, which according to its authentica, belongs to St Henry. Relics and reliquaries were in the core of medieval piety, and the cult of saints had infused throughout the society. Due to their central position in culture, relics offer glimpses at a range of material, social and cultural phenomena related to medieval embodiment.The Department of Archaeology at the University of Turku began to study the finger relic of St Eric and other items in the assemblage of Turku Cathedral in 2007. Relics and reliquaries are being opened and documented and organic as well as inorganic samples are being taken for a range of scientific analyses. So far the project has concentrated on building a chronological chart of individual artefacts. The majority of the relics date to the fourteenth century, although much more recent datings have also been obtained. The challenge of the project is not to stop when a better understanding of materials, their origins and age has been accomplished, but to use the results as a steppingstone into a study of the practices of medieval relic veneration. Medieval bodies and those material processes which authenticate relics, or distinguish saints’ bodies from other human remains, are thus at the heart of this article discussing embodiment.

Confronting Standard Models of Proto-planetary Disks with New Mid-infrared Sizes from the Keck Interferometer

OpenAIRE

Millan-Gabet, Rafael; Che, Xiao; Monnier, John D.; Sitko, Michael L.; Russell, Ray W.; Grady, Carol A.; Day, Amanda N.; Perry, R. B.; Harries, Tim J.; Aarnio, Alicia N.; Colavita, Mark M.; Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien

2016-01-01

We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inne...

High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind

Science.gov (United States)

Bujarrabal, V.; Castro-Carrizo, A.; Winckel, H. Van; Alcolea, J.; Contreras, C. Sánchez; Santander-García, M.; Hillen, M.

2018-06-01

similar disks suggest that the size of the stellar orbits has significantly decreased as a consequence of disk formation.

Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

Energy Technology Data Exchange (ETDEWEB)

Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Martínez-Delgado, David [Max Planck Institut fur Astronomie, D-69117 Heidelberg (Germany); D' Onghia, Elena [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Zibetti, Stefano [INAF-Osservatorio Astrofisico di Arcetri, I-50125 Firenze (Italy); Gabany, R. Jay [Black Bird II Observatory, Alder Springs, CA 93602 (United States); Blanton, Michael, E-mail: rbeaton@virginia.edu [Department of Physics, New York University, New York, NY 10003 (United States)

2014-08-01

We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10{sup 8} M{sub ☉}, which implies a 1:50 merger ratio, has a circular radius, R{sub circ} ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10{sup 10} M{sub ☉}. Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M{sub ☉} yr{sup –1}). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

International Nuclear Information System (INIS)

Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne; Martínez-Delgado, David; D'Onghia, Elena; Zibetti, Stefano; Gabany, R. Jay; Blanton, Michael

2014-01-01

We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10 8 M ☉ , which implies a 1:50 merger ratio, has a circular radius, R circ ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10 10 M ☉ . Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M ☉ yr –1 ). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

First results from the Thomson scattering diagnostic on proto-MPEX

Energy Technology Data Exchange (ETDEWEB)

Biewer, T. M., E-mail: biewertm@ornl.gov; Meitner, S.; Rapp, J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Ray, H.; Shaw, G. [Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996 (United States)

2016-11-15

A Thomson scattering (TS) diagnostic has been successfully implemented on the prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory. The diagnostic collects the light scattered by plasma electrons and spectroscopically resolves the Doppler shift imparted to the light by the velocity of the electrons. The spread in velocities is proportional to the electron temperature, while the total number of photons is proportional to the electron density. TS is a technique used on many devices to measure the electron temperature (T{sub e}) and electron density (n{sub e}) of the plasma. A challenging aspect of the technique is to discriminate the small number of Thomson scattered photons against the large peak of background photons from the high-power laser used to probe the plasma. A variety of methods are used to mitigate the background photons in Proto-MPEX, including Brewster angled windows, viewing dumps, and light baffles. With these methods, first results were measured from argon plasmas in Proto-MPEX, indicating T{sub e} ∼ 2 eV and n{sub e} ∼ 1 × 10{sup 19} m{sup −3}. The configuration of the Proto-MPEX TS diagnostic will be described and plans for improvement will be given.

Aragonite precipitation by "proto-polyps" in coral cell cultures.

Directory of Open Access Journals (Sweden)

Tali Mass

Full Text Available The mechanisms of coral calcification at the molecular, cellular and tissue levels are poorly understood. In this study, we examine calcium carbonate precipitation using novel coral tissue cultures that aggregate to form "proto-polyps". Our goal is to establish an experimental system in which calcification is facilitated at the cellular level, while simultaneously allowing in vitro manipulations of the calcifying fluid. This novel coral culturing technique enables us to study the mechanisms of biomineralization and their implications for geochemical proxies. Viable cell cultures of the hermatypic, zooxanthellate coral, Stylophora pistillata, have been maintained for 6 to 8 weeks. Using an enriched seawater medium with aragonite saturation state similar to open ocean surface waters (Ω(arag~4, the primary cell cultures assemble into "proto-polyps" which form an extracellular organic matrix (ECM and precipitate aragonite crystals. These extracellular aragonite crystals, about 10 µm in length, are formed on the external face of the proto-polyps and are identified by their distinctive elongated crystallography and X-ray diffraction pattern. The precipitation of aragonite is independent of photosynthesis by the zooxanthellae, and does not occur in control experiments lacking coral cells or when the coral cells are poisoned with sodium azide. Our results demonstrate that proto-polyps, aggregated from primary coral tissue culture, function (from a biomineralization perspective similarly to whole corals. This approach provides a novel tool for investigating the biophysical mechanism of calcification in these organisms.

CORONAL MASS EJECTIONS AS A MECHANISM FOR PRODUCING IR VARIABILITY IN DEBRIS DISKS

International Nuclear Information System (INIS)

Osten, Rachel; Livio, Mario; Lubow, Steve; Pringle, J. E.; Soderblom, David; Valenti, Jeff

2013-01-01

Motivated by recent observations of short-timescale variations in the infrared emission of circumstellar disks, we propose that coronal mass ejections can remove dust grains on timescales as short as a few days. Continuous monitoring of stellar activity, coupled with infrared observations, can place meaningful constraints on the proposed mechanism.

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.

The Earliest Chinese Proto-Porcelain Excavated from Kiln Sites: An Elemental Analysis.

Science.gov (United States)

Li, Yu; Zhang, Bin; Cheng, Huansheng; Zheng, Jianming

2015-01-01

In June 2012, the Piaoshan kiln site was excavated in Huzhou, Zhejiang Province, which hitherto proved to be the earliest known Chinese proto-porcelain kiln. Judging from the decorative patterns of unearthed impressed stoneware and proto-porcelain sherds, the site was determined to date to the late Xia (c. 2070-c. 1600 BC), the first dynasty of China. Here, we report on proton-induced X-ray emission analyses of 118 proto-porcelain and 35 impressed stoneware sherds from Piaoshan and five subsequent kiln sites in the vicinity. Using principal components analysis on the major chemical compositions, we reveal the relationships between impressed stoneware and proto-porcelain samples from the six kiln sites. The sherds from different sites have distinctive chemical profiles. The results indicate that the raw materials were procured locally. We find a developmental tendency for early glazes towards mature calcium-based glaze. It is most likely that woody plant ashes with increased calcia-potash ratios were applied to the formula.

The Earliest Chinese Proto-Porcelain Excavated from Kiln Sites: An Elemental Analysis.

Directory of Open Access Journals (Sweden)

Yu Li

Full Text Available In June 2012, the Piaoshan kiln site was excavated in Huzhou, Zhejiang Province, which hitherto proved to be the earliest known Chinese proto-porcelain kiln. Judging from the decorative patterns of unearthed impressed stoneware and proto-porcelain sherds, the site was determined to date to the late Xia (c. 2070-c. 1600 BC, the first dynasty of China. Here, we report on proton-induced X-ray emission analyses of 118 proto-porcelain and 35 impressed stoneware sherds from Piaoshan and five subsequent kiln sites in the vicinity. Using principal components analysis on the major chemical compositions, we reveal the relationships between impressed stoneware and proto-porcelain samples from the six kiln sites. The sherds from different sites have distinctive chemical profiles. The results indicate that the raw materials were procured locally. We find a developmental tendency for early glazes towards mature calcium-based glaze. It is most likely that woody plant ashes with increased calcia-potash ratios were applied to the formula.

Equipotential surfaces in the Proto-Cleo Torsatron

International Nuclear Information System (INIS)

Trost, P.K.; Shohet, J.L.

1986-01-01

Plasma potential measurements are made in electron cyclotron resonance plasmas in the Proto-Cleo Torsatron with an emissive probe. Plots of equipotential surfaces are presented and compared with the numerical calculated vacuum magnetic surfaces

The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

Science.gov (United States)

Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

2016-02-01

Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.

PROTOPLANETARY DISKS IN THE ORION OMC1 REGION IMAGED WITH ALMA

Energy Technology Data Exchange (ETDEWEB)

Eisner, J. A.; Sheehan, P. D. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Bally, J. M. [Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389, Boulder, CO 80309 (United States); Ginsburg, A., E-mail: jeisner@email.arizona.edu [ESO Headquarters, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen (Germany)

2016-07-20

We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing ∼600 near-IR-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. Approximately 100 sources are known proplyds identified with the Hubble Space Telescope . We detect continuum emission at 1 mm wavelengths toward ∼20% of the proplyd sample, and ∼8% of the larger sample of near-IR objects. The noise in our maps allows 4 σ detection of objects brighter than ∼1.5 mJy, corresponding to protoplanetary disk masses larger than 1.5 M {sub J} (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or C{sup 18}O(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in Orion Nebula cluster (ONC) disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC.

THE COUPLED PHYSICAL STRUCTURE OF GAS AND DUST IN THE IM Lup PROTOPLANETARY DISK

Energy Technology Data Exchange (ETDEWEB)

Cleeves, L. Ilsedore; Öberg, Karin I.; Wilner, David J.; Huang, Jane; Loomis, Ryan A.; Andrews, Sean M.; Czekala, Ian, E-mail: ilse.cleeves@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2016-12-01

The spatial distribution of gas and solids in protoplanetary disks determines the composition and formation efficiency of planetary systems. A number of disks show starkly different distributions for the gas and small grains compared to millimeter–centimeter-sized dust. We present new Atacama Large Millimeter/Submillimeter Array observations of the dust continuum, CO, {sup 13}CO, and C{sup 18}O in the IM Lup protoplanetary disk, one of the first systems where this dust–gas dichotomy was clearly seen. The {sup 12}CO is detected out to a radius of 970 au, while the millimeter continuum emission is truncated at just 313 au. Based upon these data, we have built a comprehensive physical and chemical model for the disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. We constrain the distributions of gas and dust, the gas temperatures, the CO abundances, the CO optical depths, and the incident external radiation field. We find that the reduction/removal of dust from the outer disk exposes this region to higher stellar and external radiation and decreases the rate of freeze-out, allowing CO to remain in the gas out to large radial distances. We estimate a gas-phase CO abundance of 5% of the interstellar medium value and a low external radiation field ( G {sub 0} ≲ 4). The latter is consistent with that expected from the local stellar population. We additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo.

X-RAY IRRADIATION OF THE LkCa 15 PROTOPLANETARY DISK

Energy Technology Data Exchange (ETDEWEB)

Skinner, Stephen L. [CASA, University of Colorado, Boulder, CO 80309-0389 (United States); Guedel, Manuel, E-mail: stephen.skinner@colorado.edu, E-mail: manuel.guedel@univie.ac.at [Department of Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria)

2013-03-01

LkCa 15 in the Taurus star-forming region has recently gained attention as the first accreting T Tauri star likely to host a young protoplanet. High spatial resolution infrared observations have detected the suspected protoplanet within a dust-depleted inner gap of the LkCa 15 transition disk at a distance of {approx}15 AU from the star. If this object's status as a protoplanet is confirmed, then LkCa 15 will serve as a unique laboratory for constraining physical conditions within a planet-forming disk. Previous models of the LkCa 15 disk have accounted for disk heating by the stellar photosphere but have ignored the potential importance of X-ray ionization and heating. We report here the detection of LkCa 15 as a bright X-ray source with Chandra. The X-ray emission is characterized by a cool, heavily absorbed plasma component at kT {sub cool} Almost-Equal-To 0.3 keV and a harder component at kT {sub hot} Almost-Equal-To 5 keV. We use the observed X-ray properties to provide initial estimates of the X-ray ionization and heating rates within the tenuous inner disk. These estimates and the observed X-ray properties of LkCa 15 can be used as a starting point for developing more realistic disk models of this benchmark system.

LONG-TERM EVOLUTION OF PROTOSTELLAR AND PROTOPLANETARY DISKS. I. OUTBURSTS

International Nuclear Information System (INIS)

Zhu Zhaohuan; Hartmann, Lee; Gammie, Charles F.; Book, Laura G.; Simon, Jacob B.; Engelhard, Eric

2010-01-01

As an initial investigation into the long-term evolution of protostellar disks, we explore the conditions required to explain the large outbursts of disk accretion seen in some young stellar objects. We use one-dimensional time-dependent disk models with a phenomenological treatment of the magnetorotational instability (MRI) and gravitational torques to follow disk evolution over long timescales. Comparison with our previous two-dimensional disk model calculations indicates that the neglect of radial effects and two-dimensional disk structure in the one-dimensional case makes only modest differences in the results; this allows us to use the simpler models to explore parameter space efficiently. We find that the mass infall rates typically estimated for low-mass protostars generally result in AU-scale disk accretion outbursts, as predicted by our previous analysis. We also confirm quasi-steady accretion behavior for high mass infall rates if the values of α-parameter for the MRI are small, while at this high accretion rate convection from the thermal instability may lead to some variations. We further constrain the combinations of the α-parameter and the MRI critical temperature, which can reproduce observed outburst behavior. Our results suggest that dust sublimation may be connected with full activation of the MRI. This is consistent with the idea that small dust captures ions and electrons to suppress the MRI. In a companion paper, we will explore both long-term outburst and disk evolution with this model, allowing for infall from protostellar envelopes with differing angular momenta.

Bound-state formation for thermal relic dark matter and unitarity

International Nuclear Information System (INIS)

Harling, Benedict von; Petraki, Kalliopi

2014-01-01

We show that the relic abundance of thermal dark matter annihilating via a long-range interaction, is significantly affected by the formation and decay of dark matter bound states in the early universe, if the dark matter mass is above a few TeV . We determine the coupling required to obtain the observed dark matter density, taking into account both the direct 2-to-2 annihilations and the formation of bound states, and provide an analytical fit. We argue that the unitarity limit on the inelastic cross-section is realized only if dark matter annihilates via a long-range interaction, and we determine the upper bound on the mass of thermal-relic dark matter to be about 197 (139) TeV for (non)-self-conjugate dark matter

Low inductance diode design on the Proto II accelerator for imploding plasma loads

International Nuclear Information System (INIS)

Hsing, W.W.; Coats, R.; McDaniel, D.H.; Spielman, R.B.

1985-01-01

A new water transmission line convolute, single piece insulator, and double disk feed has been designed and tested on the .125 ohm, 10 TW Proto II accelerator. The water transmission lines have a 5 cm gap to eliminate any water arcing. A two-dimensional magnetic field code was used to calculate the convolute inductance. We used an acrylic insulator as well as a single piece, laminated polycarbonate insulator. They have been succuessfully tested at over 90% of the Shipman criteria for classical insulator breakdown, although the laminations in the polycarbonate insulator failed after a few shots. The anode and cathode each have two pieces and are held together mechanically. The vacuum MITL tapers to a 3 mm minimum gap. The total inductance is 8.4 nH for gas puff loads and 7.8 nH for imploding foil loads. Out of a forward-going energy of 290 kJ, 175 kJ has been delivered past the insulator, and 100 kJ has been successfully delivered to the load

The first observations of wide-band interferometers and the spectra of relic gravitons

CERN Document Server

Giovannini, Massimo

2016-01-01

Stochastic backgrounds of relic gravitons of cosmological origin extend from frequencies of the order of the aHz up to the GHz range. Since the temperature and polarization anisotropies constrain the low frequency normalization of the spectra, in the concordance paradigm the strain amplitude corresponding to the frequency window of wide-band interferometers turns out to be, approximately, nine orders of magnitude smaller than the astounding signal recently reported and attributed to a binary black hole merger. The backgrounds of relic gravitons expected from the early Universe are compared with the stochastic foregrounds stemming from the estimated multiplicity of the astrophysical sources. It is suggested that while the astrophysical foregrounds are likely to dominate between few Hz and 10 kHz, relic gravitons with frequencies exceeding 100 kHz represent a potentially uncontaminated signal for the next generation of high-frequency detectors currently under scrutiny.

The structure of protostellar dense cores: a millimeter continuum study

International Nuclear Information System (INIS)

Motte, Frederique

1998-01-01

A comprehensive theoretical scenario explains low-mass star formation and describes the gravitational collapse of an isolated 'ideal' dense core. The major aim of this thesis is to check the standard model predictions on the structure of protostellar dense cores (or envelopes). The earliest stages of star formation remain poorly known because the protostars are still deeply embedded in massive, opaque circumstellar cocoons. On the one hand, sensitive bolometer arrays very recently allow us to measure the millimeter continuum emission arising from dense cores. Such observations are a powerful tool to constrain the density structure of proto-stellar dense cores (on large length scale). In particular, we studied the structure of isolated proto-stellar envelopes in Taurus and protostars in the ρ Ophiuchi cluster. In order to accurately derive their envelope density power law, we simulated the observation of several envelope models. Then we show that most of the Taurus protostars present a density structure consistent with the standard model predictions. In contrast, dense cores in ρ Ophiuchi main cloud are highly fragmented and protostellar envelope have finite size. Moreover fragmentation appears to be essential in determining the final stellar mass of ρ Oph forming stars. In clusters, fragmentation may thus be at the origin of the stellar initial mass function (IMF). On the other hand, our interferometric millimeter continuum observations are tracing (with higher angular resolution) the inner part of protostellar envelopes. Our study show that disks during protostellar stages are not yet massive and thus do not perturb the analysis of envelope density structure. (author) [fr

FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS

International Nuclear Information System (INIS)

Dekel, Avishai; Sari, Re'em; Ceverino, Daniel

2009-01-01

We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps migrate into a bulge in ∼ sun yr -1 , and each clump converts into stars in ∼0.5 Gyr. While the clumps coalesce dissipatively to a compact bulge, the star-forming disk is extended because the incoming streams keep the outer disk dense and susceptible to instability and because of angular momentum transport. Passive spheroid-dominated galaxies form when the streams are more clumpy: the external clumps merge into a massive bulge and stir up disk turbulence that stabilize the disk and suppress in situ clump and star formation. We predict a bimodality in galaxy type by z ∼ 3, involving giant-clump star-forming disks and spheroid-dominated galaxies of suppressed star formation. After z ∼ 1, the disks tend to be stabilized by the dominant stellar disks and bulges. Most of the high-z massive disks are likely to end up as today's early-type galaxies.

A CANDIDATE PLANETARY-MASS OBJECT WITH A PHOTOEVAPORATING DISK IN ORION

Energy Technology Data Exchange (ETDEWEB)

Fang, Min; Kim, Jinyoung Serena; Apai, Dániel [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Pascucci, Ilaria [Department of Planetary Sciences, University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721 (United States); Manara, Carlo Felice [Scientific Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk (Netherlands)

2016-12-20

In this work, we report the discovery of a candidate planetary-mass object with a photoevaporating protoplanetary disk, Proplyd 133-353, which is near the massive star θ {sup 1} Ori C at the center of the Orion Nebula Cluster (ONC). The object was known to have extended emission pointing away from θ {sup 1} Ori C, indicating ongoing external photoevaporation. Our near-infrared spectroscopic data and the location on the H–R diagram suggest that the central source of Proplyd 133-353 is substellar (∼M9.5) and has a mass probably less than 13 Jupiter mass and an age younger than 0.5 Myr. Proplyd 133-353 shows a similar ratio of X-ray luminosity to stellar luminosity to other young stars in the ONC with a similar stellar luminosity and has a similar proper motion to the mean one of confirmed ONC members. We propose that Proplyd 133-353 formed in a very low-mass dusty cloud or an evaporating gas globule near θ {sup 1} Ori C as a second generation of star formation, which can explain both its young age and the presence of its disk.

THE TUCANA/HOROLOGIUM, COLUMBA, AB DORADUS, AND ARGUS ASSOCIATIONS: NEW MEMBERS AND DUSTY DEBRIS DISKS

International Nuclear Information System (INIS)

Zuckerman, B.; Rhee, Joseph H.; Song, Inseok; Bessell, M. S.

2011-01-01

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.

The Building History of XUV disks of M83& NGC2403 with TRGB Archaeology

Science.gov (United States)

Koda, Jin

2015-06-01

We propose deep HSC g & i-band imaging of two extended ultraviolet (XUV) disks of M83 and NGC2403. These galaxies have the prototype XUV disks with the largest size ( 1 deg and 30 arcmin). The Subaru HSC permits unprecedentedly deep imaging over these gigantic XUV disks, including sufficient surrounding areas which are used for sky subtraction and statistical estimation of background contamination. This project probes the building history of the XUV disks using archeological stellar populations, especially the tip of red giant branch (TRGB) stars (age 2-14 Gyr). Their presence and distribution over the XUV disks will reveal any star formation (SF) occurring over the past 2 Gyr, 4-6 Gyr, and beyond - i.e., the epochs preceding the recent (UV-traced) state of SF. Their color depends strongly on metallicity, thus providing an additional measure of star-gas recycling during the evolution of the XUV disks. In addition, we will detect young & massive main sequence stars (<100 Myr) and He-burning stars (100-500 Myr). Comparing various generations of stars, in terms of number densities and spatial distributions, will reveal the much-unexplored SF history in the XUV disks.

RESOLVING THE PLANET-HOSTING INNER REGIONS OF THE LkCa 15 DISK

Energy Technology Data Exchange (ETDEWEB)

Thalmann, C.; Garufi, A.; Quanz, S. P.; Daemgen, S.; Engler, N. [ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, 8093 Zurich (Switzerland); Janson, M. [Department of Astronomy, Stockholm University, SE-106 91 Stockholm (Sweden); Boccaletti, A. [LESIA, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Paris 6, Sorbonne Université, 5 place Jules Janssen, F-92195 Meudon CEDEX (France); Sissa, E.; Gratton, R.; Desidera, S. [INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Salter, G.; Langlois, M. [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Benisty, M.; Bonnefoy, M.; Chauvin, G.; Lagrange, A.-M.; Lannier, J. [Université Grenoble Alpes, IPAG, F-38000 Grenoble (France); Dominik, C. [Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Feldt, M.; Henning, T., E-mail: thalmann@phys.ethz.ch [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); and others

2016-09-10

LkCa 15 hosts a pre-transitional disk as well as at least one accreting protoplanet orbiting in its gap. Previous disk observations have focused mainly on the outer disk, which is cleared inward of ∼50 au. The planet candidates, on the other hand, reside at orbital radii around 15 au, where disk observations have been unreliable until recently. Here, we present new J -band imaging polarimetry of LkCa 15 with SPHERE IRDIS, yielding the most accurate and detailed scattered-light images of the disk to date down to the planet-hosting inner regions. We find what appear to be persistent asymmetric structures in the scattering material at the location of the planet candidates, which could be responsible at least for parts of the signals measured with sparse-aperture masking. These images further allow us to trace the gap edge in scattered light at all position angles and search the inner and outer disks for morphological substructure. The outer disk appears smooth with slight azimuthal variations in polarized surface brightness, which may be due to shadowing from the inner disk or a two-peaked polarized phase function. We find that the near-side gap edge revealed by polarimetry matches the sharp crescent seen in previous ADI imaging very well. Finally, the ratio of polarized disk to stellar flux is more than six times larger in the J -band than in the RI bands.

a Method of 3d Measurement and Reconstruction for Cultural Relics in Museums

Science.gov (United States)

Zheng, S.; Zhou, Y.; Huang, R.; Zhou, L.; Xu, X.; Wang, C.

2012-07-01

Three-dimensional measurement and reconstruction during conservation and restoration of cultural relics have become an essential part of a modem museum regular work. Although many kinds of methods including laser scanning, computer vision and close-range photogrammetry have been put forward, but problems still exist, such as contradiction between cost and good result, time and fine effect. Aimed at these problems, this paper proposed a structure-light based method for 3D measurement and reconstruction of cultural relics in museums. Firstly, based on structure-light principle, digitalization hardware has been built and with its help, dense point cloud of cultural relics' surface can be easily acquired. To produce accurate 3D geometry model from point cloud data, multi processing algorithms have been developed and corresponding software has been implemented whose functions include blunder detection and removal, point cloud alignment and merge, 3D mesh construction and simplification. Finally, high-resolution images are captured and the alignment of these images and 3D geometry model is conducted and realistic, accurate 3D model is constructed. Based on such method, a complete system including hardware and software are built. Multi-kinds of cultural relics have been used to test this method and results prove its own feature such as high efficiency, high accuracy, easy operation and so on.

Detecting relic gravitational waves in the CMB: Optimal parameters and their constraints

International Nuclear Information System (INIS)

Zhao, W.; Baskaran, D.

2009-01-01

The prospect of detecting relic gravitational waves, through their imprint in the cosmic microwave background radiation, provides an excellent opportunity to study the very early Universe. In the simplest viable theoretical models the relic gravitational wave background is characterized by two parameters, the tensor-to-scalar ratio r and the tensor spectral index n t . In this paper, we analyze the potential joint constraints on these two parameters, r and n t , using the data from the upcoming cosmic microwave background radiation experiments. Introducing the notion of the best-pivot multipole l t *, we find that at this pivot multipole the parameters r and n t are uncorrelated, and have the smallest variances. We derive the analytical formulas for the best-pivot multipole number l t *, and the variances of the parameters r and n t . We verify these analytical calculations using numerical simulation methods, and find agreement to within 20%. The analytical results provide a simple way to estimate the detection ability for the relic gravitational waves by the future observations of the cosmic microwave background radiation.

PIXE analysis of proto-porcelain excavated from the Huoshaoshan kiln site in Deqing County, Zhejiang Province

International Nuclear Information System (INIS)

Zhang Bin; Cheng Huansheng; Zheng Jianming

2014-01-01

Background: Zhejiang Province is an important producing area of proto-porcelain. Huoshaoshan kiln site in Deqing County is the only kiln known currently for firing proto-porcelain from the late Western Zhou Dynasty to the late Spring and Autumn Period. Also it is the earliest kiln site unearthed for only firing proto-porcelain so far. It is of great significance for the exploration of Chinese early celadon firing technology. Purpose: The aim is to disclose the elemental characteristics of these proto-porcelains and study the sources of the raw materials and relationship between these proto-porcelains. Methods: We selected 18 samples made at the early period (from the late Western Zhou Dynasty to the early Spring and Autumn Period), 15 samples made at the middle and last period (the last period of the middle Spring and Autumn Period), and 17 samples made at the last period (the last period of the late Spring and Autumn Period). Proton Induced X-ray Emission (PIXE) was used to analyze these samples and measure the chemical compositions of these proto-porcelains. The factor analysis is used to study the sources of the raw materials and relationship between these proto-porcelains made in the different periods. Results: The results show that for the raw materials of body and glaze, the proto-porcelains at the last period are different from those at the early period, while the same as those at the middle and last period. Conclusion: PIXE combining with factor analysis can be used to study effectively the sources of the raw materials and relationship between these proto-porcelains. (authors)

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

Science.gov (United States)

Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

2017-03-15

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high

METALLICITY GRADIENTS OF THICK DISK DWARF STARS

Energy Technology Data Exchange (ETDEWEB)

Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2012-12-01

We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

Magnetic diagnostics for the proto-eta Tokamak

International Nuclear Information System (INIS)

Ferreira, J.L.; Aso, Y.; Ueda, M.; Ferreira, J.G.

1991-04-01

This work gives a general view of the magnetic diagnostics rat will be used in the Proto-Eta Tokamak. These diagnostics will be useful tools to measure currents, electric and magnetic fields involved in the plasma magnetic confinement. (author)

THE FIRST DETERMINATION OF THE VISCOSITY PARAMETER IN THE CIRCUMSTELLAR DISK OF A Be STAR

Energy Technology Data Exchange (ETDEWEB)

Carciofi, Alex C.; Bjorkman, Jon E.; Haubois, Xavier [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, 05508-900, Sao Paulo, SP (Brazil); Otero, Sebastian A. [American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138 (United States); Okazaki, Atsuo T. [Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605 (Japan); Stefl, Stanislav; Rivinius, Thomas [European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19 (Chile); Baade, Dietrich, E-mail: carciofi@usp.br, E-mail: jon@physics.utoledo.edu [European Organisation for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen (Germany)

2012-01-15

Be stars possess gaseous circumstellar decretion disks, which are well described using standard {alpha}-disk theory. The Be star 28 CMa recently underwent a long outburst followed by a long period of quiescence, during which the disk dissipated. Here we present the first time-dependent models of the dissipation of a viscous decretion disk. By modeling the rate of decline of the V-band excess, we determine that the viscosity parameter {alpha} = 1.0 {+-} 0.2, corresponding to a mass injection rate M-dot =(3.5{+-}1.3) Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1}. Such a large value of {alpha} suggests that the origin of the turbulent viscosity is an instability in the disk whose growth is limited by shock dissipation. The mass injection rate is more than an order of magnitude larger than the wind mass-loss rate inferred from UV observations, implying that the mass injection mechanism most likely is not the stellar wind, but some other mechanism.

Proto-Acting as a New Concept: Personal Mimicry and the Origins of Role Playing

Directory of Open Access Journals (Sweden)

Steven Brown

2017-06-01

Full Text Available Proto-acting is introduced here as a new concept that refers to a set of processes that are intermediate between everyday role playing (in the Erving Goffman sense and dramatic acting. Its most characteristic process is the voluntary act of personal mimicry, which can occur in everyday contexts, such as quoting someone during conversation, or in performance contexts, such as impressionism. Proto-acting involves character portrayal, but on a much simpler and more transient scale than in dramatic acting, where a person may portray a character for an extended period of time during a stage performance. For example, this might involve impersonating the characters while reading a bedtime story to a child, or children themselves portraying characters while engaging in pretend play. Other key features of proto-acting are that it tends to be driven by gesture, have minimal scripting, and involve short bouts of alternation between the self and characters. Proto-acting, as based on personal mimicry, might provide a cognitive foundation for dramatic acting in human development. Moreover, proto-acting itself might be underlain evolutionarily by the process of pantomime, which often involves intentional mimicry of the actions of other people. Hence, the proto-acting concept is able to shed light on processes relevant to cognition, development, the performing arts, and human evolution.

Probing Protoplanetary Disks: From Birth to Planets

Science.gov (United States)

Cox, Erin Guilfoil

2018-01-01

49 pre main-sequence stellar systems and detected either gaps or cavities in ~6 of these sources. Combined, these results build upon how early protoplanetary disks can form around young protostars and thus how early planets can begin to form.

Late Quaternary sea level and environmental changes from relic ...

Indian Academy of Sciences (India)

Relic carbonate deposits along the western margin of India occur as dolomite crusts, aragonite sands (pelletal / oolitic) and aragonite-cemented limestones, oyster shells, corals, encrusted coralline algal and foraminiferal-dominated nodules. The petrology and mineralogy of the deposits indicate that except for aragonite ...

THE STELLAR AND GAS KINEMATICS OF THE LITTLE THINGS DWARF IRREGULAR GALAXY NGC 1569

Energy Technology Data Exchange (ETDEWEB)

Johnson, Megan [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States); Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Oh, Se-Heon [International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Elmegreen, Bruce [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Hts., NY 10598 (United States); Brinks, Elias [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB (United Kingdom); Tollerud, Erik, E-mail: mjohnson@nrao.edu, E-mail: dah@lowell.edu, E-mail: hxzhang@lowell.edu, E-mail: herrmann@lowell.edu, E-mail: se-heon.oh@uwa.edu.au, E-mail: bge@us.ibm.com, E-mail: E.Brinks@herts.ac.uk, E-mail: etolleru@uci.edu [Center For Cosmology, Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States)

2012-11-01

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, {sigma}{sub z}, coupled with the maximum rotational velocity derived from H I observations, V{sub max}, gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V{sub max}/{sigma}{sub z} = 2.4 {+-} 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, {approx}1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V{sub max}, shows that the disk may be dark matter deficient in the inner

A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48

Energy Technology Data Exchange (ETDEWEB)

Schworer, Guillaume; Lacour, Sylvestre; Du Foresto, Vincent Coudé [LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité (France); Huélamo, Nuria [Dpto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691, Villanueva de la Cañada (Spain); Pinte, Christophe; Chauvin, Gaël [Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble (France); Ehrenreich, David [Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix (Switzerland); Girard, Julien [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19 (Chile); Tuthill, Peter [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)

2017-06-20

For one decade, the spectral type and age of the ρ Oph object IRS-48 were subject to debate and mystery. Modeling its disk with mid-infrared to millimeter observations led to various explanations to account for the complex intricacy of dust holes and gas-depleted regions. We present multi-epoch high-angular-resolution interferometric near-infrared data of spatially resolved emissions in the first 15 au of IRS-48, known to have very strong polycyclic aromatic hydrocarbon (PAH) emissions within this dust-depleted region. We make use of new Sparse-Aperture-Masking data to instruct a revised radiative-transfer model, where spectral energy distribution fluxes and interferometry are jointly fitted. Neutral and ionized PAH, very small grains (VSG), and classical silicates are incorporated into the model; new stellar parameters and extinction laws are explored. A bright (42 L {sub ⊙}) and hence large (2.5 R {sub ⊙}) central star with A {sub v} = 12.5 mag and R {sub v} = 6.5 requires less near-infrared excess: the inner-most disk at ≈1 au is incompatible with the interferometric data. The revised stellar parameters place this system on a 4 Myr evolutionary track, four times younger than the previous estimations, which is in better agreement with the surrounding ρ Oph region and disk-lifetime observations. The disk-structure solution converges to a classical-grain outer disk from 55 au combined with an unsettled and fully resolved VSG and PAH ring, between 11 and 26 au. We find two overluminosities in the PAH ring at color-temperatures consistent with the radiative transfer simulations; one follows a Keplerian circular orbit at 14 au. We show a depletion of a factor of ≈5 of classical dust grains up to 0.3 mm compared to very small particles: the IRS-48 disk is nearly void of dust grains in the first 55 au. A 3.5 M {sub Jup} planet on a 40 au orbit can qualitatively explain the new disk structure.

Dynamical evolution of stars and gas of young embedded stellar sub-clusters

Science.gov (United States)

Sills, Alison; Rieder, Steven; Scora, Jennifer; McCloskey, Jessica; Jaffa, Sarah

2018-03-01

We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution which can include a filamentary structure in addition to gas surrounding the stellar subclusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young proto-star clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

Shedding light on the eccentricity valley: Gap heating and eccentricity excitation of giant planets in protoplanetary disks

International Nuclear Information System (INIS)

Tsang, David; Cumming, Andrew; Turner, Neal J.

2014-01-01

We show that the first order (non-co-orbital) corotation torques are significantly modified by entropy gradients in a non-barotropic protoplanetary disk. Such non-barotropic torques can dramatically alter the balance that, for barotropic cases, results in the net eccentricity damping for giant gap-clearing planets embedded in the disk. We demonstrate that stellar illumination can heat the gap enough for the planet's orbital eccentricity to instead be excited. We also discuss the 'Eccentricity Valley' noted in the known exoplanet population, where low-metallicity stars have a deficit of eccentric planets between ∼0.1 and ∼1 AU compared to metal-rich systems. We show that this feature in the planet distribution may be due to the self-shadowing of the disk by a rim located at the dust sublimation radius ∼0.1 AU, which is known to exist for several T Tauri systems. In the shadowed region between ∼0.1 and ∼1 AU, lack of gap insolation allows disk interactions to damp eccentricity. Outside such shadowed regions stellar illumination can heat the planetary gaps and drive eccentricity growth for giant planets. We suggest that the self-shadowing does not arise at higher metallicity due to the increased optical depth of the gas interior to the dust sublimation radius.

Shedding light on the eccentricity valley: Gap heating and eccentricity excitation of giant planets in protoplanetary disks

Energy Technology Data Exchange (ETDEWEB)

Tsang, David; Cumming, Andrew [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada); Turner, Neal J., E-mail: dtsang@physics.mcgill.ca [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2014-02-20

We show that the first order (non-co-orbital) corotation torques are significantly modified by entropy gradients in a non-barotropic protoplanetary disk. Such non-barotropic torques can dramatically alter the balance that, for barotropic cases, results in the net eccentricity damping for giant gap-clearing planets embedded in the disk. We demonstrate that stellar illumination can heat the gap enough for the planet's orbital eccentricity to instead be excited. We also discuss the 'Eccentricity Valley' noted in the known exoplanet population, where low-metallicity stars have a deficit of eccentric planets between ∼0.1 and ∼1 AU compared to metal-rich systems. We show that this feature in the planet distribution may be due to the self-shadowing of the disk by a rim located at the dust sublimation radius ∼0.1 AU, which is known to exist for several T Tauri systems. In the shadowed region between ∼0.1 and ∼1 AU, lack of gap insolation allows disk interactions to damp eccentricity. Outside such shadowed regions stellar illumination can heat the planetary gaps and drive eccentricity growth for giant planets. We suggest that the self-shadowing does not arise at higher metallicity due to the increased optical depth of the gas interior to the dust sublimation radius.

Stochastic Background of Relic Scalar Gravitational Waves tuned by Extended Gravity

International Nuclear Information System (INIS)

De Laurentis, Mariafelicia; Capozziello, Salvatore

2009-01-01

A stochastic background of relic gravitational waves is achieved by the so called adiabatically-amplified zero-point fluctuations process derived from early inflation. It provides a distinctive spectrum of relic gravitational waves. In the framework of scalar-tensor gravity, we discuss the scalar modes of gravitational waves and the primordial production of this scalar component which is generated beside tensorial one. Then analyze seven different viable f(R)-gravities towards the Solar System tests and stochastic gravitational waves background. It is demonstrated that seven viable f(R)-gravities under consideration not only satisfy the local tests, but additionally, pass the above PPN-and stochastic gravitational waves bounds for large classes of parameters.

EVOLUTION OF GASEOUS DISK VISCOSITY DRIVEN BY SUPERNOVA EXPLOSION. II. STRUCTURE AND EMISSIONS FROM STAR-FORMING GALAXIES AT HIGH REDSHIFT

International Nuclear Information System (INIS)

Yan Changshuo; Wang Jianmin

2010-01-01

High spatial resolution observations show that high-redshift galaxies are undergoing intensive evolution of dynamical structure and morphologies displayed by the Hα, Hβ, [O III], and [N II] images. It has been shown that supernova explosion (SNexp) of young massive stars during the star formation epoch, as kinetic feedback to host galaxies, can efficiently excite the turbulent viscosity. We incorporate the feedback into the dynamical equations through mass dropout and angular momentum transportation driven by the SNexp-excited turbulent viscosity. The empirical Kennicutt-Schmidt law is used for star formation rates (SFRs). We numerically solve the equations and show that there can be intensive evolution of structure of the gaseous disk. Secular evolution of the disk shows interesting characteristics: (1) high viscosity excited by SNexp can efficiently transport the gas from 10 kpc to ∼1 kpc forming a stellar disk whereas a stellar ring forms for the case with low viscosity; (2) starbursts trigger SMBH activity with a lag of ∼10 8 yr depending on SFRs, prompting the joint evolution of SMBHs and bulges; and (3) the velocity dispersion is as high as ∼100 km s -1 in the gaseous disk. These results are likely to vary with the initial mass function (IMF) that the SNexp rates rely on. Given the IMF, we use the GALAXEV code to compute the spectral evolution of stellar populations based on the dynamical structure. In order to compare the present models with the observed dynamical structure and images, we use the incident continuum from the simple stellar synthesis and CLOUDY to calculate emission line ratios of Hα, Hβ, [O III], and [N II], and Hα brightness of gas photoionized by young massive stars formed on the disks. The models can produce the main features of emission from star-forming galaxies. We apply the present model to two galaxies, BX 389 and BX 482 observed in the SINS high-z sample, which are bulge and disk-dominated, respectively. Two successive

Adiabatic invariants in stellar dynamics. 2: Gravitational shocking

Science.gov (United States)

Weinberg, Martin D.

1994-01-01

A new theory of gravitational shocking based on time-dependent perturbation theory shows that the changes in energy and angular momentum due to a slowly varying disturbance are not exponentially small for stellar dynamical systems in general. It predicts significant shock heating by slowly varying perturbations previously thought to be negligible according to the adiabatic criterion. The theory extends the scenarios traditionally computed only with the impulse approximation and is applicable to a wide class of disturbances. The approach is applied specifically to the problem of disk shocking of star clusters.

Relic gravitational waves and the generalized second law

International Nuclear Information System (INIS)

Izquierdo, German; Pavon, Diego

2004-01-01

The generalized second law of gravitational thermodynamics is applied to the present era of accelerated expansion of the Universe. In spite of the fact that the entropy of matter and relic gravitational waves inside the event horizon diminish, the mentioned law is fulfilled provided that the expression for the entropy density of the gravitational waves satisfies a certain condition

Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

Science.gov (United States)

Huang, Po-Chieh; Chen, Wen-Ping; Hu, Chia-Ling; Burkhonov, Otabek; Ehgamberdiev, Shuhrat; Liu, Jinzhong; Naito, Hiroyuki; Pakstiene, Erika; Qvam, Jan Kare Trandem; Rätz, Stefanie; Semkov, Evgeni

2018-04-01

UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual "blueing" phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g', r', and i' -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

Power accounting of plasma discharges in the linear device Proto-MPEX

Science.gov (United States)

Showers, M.; Piotrowicz, P. A.; Beers, C. J.; Biewer, T. M.; Caneses, J.; Canik, J.; Caughman, J. B. O.; Donovan, D. C.; Goulding, R. H.; Lumsdaine, A.; Kafle, N.; Owen, L. W.; Rapp, J.; Ray, H.

2018-06-01

Plasma material interaction (PMI) studies are crucial to the successful development of future fusion reactors. Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a prototype design for the MPEX, a steady-state linear device being developed to study PMI. The primary purpose of Proto-MPEX is developing the plasma heating source concepts for MPEX. A power accounting study of Proto-MPEX works to identify machine operating parameters that could improve its performance, thereby increasing its PMI research capabilities, potentially impacting the MPEX design concept. To build a comprehensive power balance, an analysis of the helicon region has been performed implementing a diagnostic suite and software modeling to identify mechanisms and locations of heat loss from the main plasma. Of the 106.3 kW of input power, up to 90.5% of the power has been accounted for in the helicon region. When the analysis was extended to encompass the device to its end plates, 49.2% of the input power was accounted for and verified diagnostically. Areas requiring further diagnostic analysis are identified. The required improvements will be implemented in future work. The data acquisition and analysis processes will be streamlined to form a working model for future power balance studies of Proto-MPEX. ).

TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A