A UKIDSS-based search for low-mass stars and small stellar clumps in off-cloud parts of young star-forming regions* **

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Barrado y Navascués D.

2011-07-01

Full Text Available The form and universality of the mass function of young and nearby star-forming regions is still under debate. Its relation to the stellar density, its mass peak and the dependency on most recent models shows significant differencies for the various regions and remains unclear up to date. We aim to get a more complete census of two of such regions. We investigate yet unexplored areas of Orion and Taurus-Auriga, observed by the UKIDSS survey. In the latter, we search for low-mass stars via photometric and proper motion criteria and signs for variability. In Orion, we search for small stellar clumps via nearest-neighbor methods. Highlights in Taurus would be the finding of the missing low-mass stars and the detection of a young cluster T dwarf. In Orion, we discovered small stellar associations of its OB1b and OB1c populations. Combined with what is known in literature, we will provide by this investigations a general picture of the results of the star-forming processes in large areas of Taurus and Orion and probe the most recent models.

STAR FORMATION IN THE TAURUS FILAMENT L 1495: FROM DENSE CORES TO STARS

International Nuclear Information System (INIS)

Schmalzl, Markus; Kainulainen, Jouni; Henning, Thomas; Launhardt, Ralf; Quanz, Sascha P.; Alves, Joao; Goodman, Alyssa A.; Pineda, Jaime E.; Roman-Zuniga, Carlos G.

2010-01-01

We present a study of dense structures in the L 1495 filament in the Taurus Molecular Cloud and examine its star-forming properties. In particular, we construct a dust extinction map of the filament using deep near-infrared observations, exposing its small-scale structure in unprecedented detail. The filament shows highly fragmented substructures and a high mass-per-length value of M line = 17 M sun pc -1 , reflecting star-forming potential in all parts of it. However, a part of the filament, namely B 211, is remarkably devoid of young stellar objects. We argue that in this region the initial filament collapse and fragmentation is still taking place and star formation is yet to occur. In the star-forming part of the filament, we identify 39 cores with masses from 0.4 to 10 M sun and preferred separations in agreement with the local Jeans length. Most of these cores exceed the Bonnor-Ebert critical mass, and are therefore likely to collapse and form stars. The dense core mass function follows a power law with exponent Γ = 1.2 ± 0.2, a form commonly observed in star-forming regions.

T Tauri stars in Taurus - the IRAS view

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Harris, Stella; Clegg, Peter; Hughes, Joanne

1988-01-01

Statistical studies of star-formation have traditionally been beset with selection effects. We have developed a technique, using the completeness of the IRAS catalogue, which circumvents these effects. We have taken the properties of known T Tau stars within Taurus as a template to establish a purely IRAS-based definition of such sources. We then use this definition to extract, from the IRAS catalogue, all sources within a specific region of Taurus having those same IRAS properties. This wider class of source is examined and discussed. (author)

Far-infrared to Millimeter Data of Protoplanetary Disks: Dust Growth in the Taurus, Ophiuchus, and Chamaeleon I Star-forming Regions

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Ribas, Álvaro; Espaillat, Catherine C.; Macías, Enrique [Department of Astronomy, Boston University, Boston, MA 02215 (United States); Bouy, Hervé [Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, F-33615 Pessac (France); Andrews, Sean; Wilner, David [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 91023 (United States); Calvet, Nuria [Astronomy Department, University of Michigan, Ann Arbor, MI 48109 (United States); Naylor, David A.; Van der Wiel, Matthijs H. D. [Institute for Space Imaging Science, Department of Physics and Astronomy, University of Lethbridge (Canada); Riviere-Marichalar, Pablo, E-mail: aribas@bu.edu [Instituto de Ciencia de Materiales de Madrid (CSIC). Calle Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Madrid (Spain)

2017-11-01

Far-infrared and (sub)millimeter fluxes can be used to study dust in protoplanetary disks, the building blocks of planets. Here, we combine observations from the Herschel Space Observatory with ancillary data of 284 protoplanetary disks in the Taurus, Chamaeleon I, and Ophiuchus star-forming regions, covering from the optical to mm/cm wavelengths. We analyze their spectral indices as a function of wavelength and determine their (sub)millimeter slopes when possible. Most disks display observational evidence of grain growth, in agreement with previous studies. No correlation is found between other tracers of disk evolution and the millimeter spectral indices. A simple disk model is used to fit these sources, and we derive posterior distributions for the optical depth at 1.3 mm and 10 au, the disk temperature at this same radius, and the dust opacity spectral index β . We find the fluxes at 70 μ m to correlate strongly with disk temperatures at 10 au, as derived from these simple models. We find tentative evidence for spectral indices in Chamaeleon I being steeper than those of disks in Taurus/Ophiuchus, although more millimeter observations are needed to confirm this trend and identify its possible origin. Additionally, we determine the median spectral energy distribution of each region and find them to be similar across the entire wavelength range studied, possibly due to the large scatter in disk properties and morphologies.

Star Formation in Taurus: Preliminary Results from 2MASS

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Beichman, C. A.; Jarrett, T.

1993-01-01

Data with the 2MASS prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from IRAS observations to contain a number of very young solar type stars.

THE SPITZER INFRARED SPECTROGRAPH SURVEY OF T TAURI STARS IN TAURUS

International Nuclear Information System (INIS)

Furlan, E.; Luhman, K. L.; Espaillat, C.

2011-01-01

We present 161 Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars and young brown dwarfs in the Taurus star-forming region. All of the targets were selected based on their infrared excess and are therefore surrounded by protoplanetary disks; they form the complete sample of all available IRS spectra of T Tauri stars with infrared excesses in Taurus. We also present the IRS spectra of seven Class 0/I objects in Taurus to complete the sample of available IRS spectra of protostars in Taurus. We use spectral indices that are not significantly affected by extinction to distinguish between envelope- and disk-dominated objects. Together with data from the literature, we construct spectral energy distributions for all objects in our sample. With spectral indices derived from the IRS spectra we infer disk properties such as dust settling and the presence of inner disk holes and gaps. We find a transitional disk frequency, which is based on objects with unusually large 13-31 μm spectral indices indicative of a wall surrounding an inner disk hole, of about 3%, and a frequency of about 20% for objects with unusually large 10 μm features, which could indicate disk gaps. The shape and strength of the 10 μm silicate emission feature suggests weaker 10 μm emission and more processed dust for very low mass objects and brown dwarfs (spectral types M6-M9). These objects also display weaker infrared excess emission from their disks, but do not appear to have more settled disks than their higher-mass counterparts. We find no difference for the spectral indices and properties of the dust between single and multiple systems.

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

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

2010-01-01

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

FAR-INFRARED OBSERVATIONS OF THE VERY LOW LUMINOSITY EMBEDDED SOURCE L1521F-IRS IN THE TAURUS STAR-FORMING REGION

International Nuclear Information System (INIS)

Terebey, Susan; Fich, Michel; Noriega-Crespo, Alberto; Padgett, Deborah L.; Brooke, Tim; Carey, Sean; McCabe, Caer-Eve; Rebull, Luisa; Fukagawa, Misato; Audard, Marc; Evans, Neal J.; Guedel, Manuel; Hines, Dean; Huard, Tracy; Knapp, Gillian R.; Menard, Francois; Monin, Jean-Louis

2009-01-01

We investigate the environment of the very low luminosity object L1521F-IRS using data from the Taurus Spitzer Legacy Survey. The MIPS 160 μm image shows both extended emission from the Taurus cloud and emission from multiple cold cores over a 1 0 x 2 0 region. Analysis shows that the cloud dust temperature is 14.2 ± 0.4 K and the extinction ratio is A 160 /A K = 0.010 ± 0.001 up to A V ∼ 4 mag. We find κ 160 = 0.23 ± 0.046 cm 2 g -1 for the specific opacity of the gas-dust mixture. Therefore, for dust in the Taurus cloud we find that the 160 μm opacity is significantly higher than that measured for the diffuse interstellar medium, but not too different from dense cores, even at modest extinction values. Furthermore, the 160 μm image shows features that do not appear in the IRAS 100 μm image. We identify six regions as cold cores, i.e., colder than 14.2 K, all of which have counterparts in extinction maps or C 18 O maps. Three of the six cores contain embedded young stellar objects, which demonstrates the cores are sites of current star formation. We compare the effects of L1521F-IRS on its natal core and find there is no evidence for dust heating at 160 or 100 μm by the embedded source. From the infrared luminosity L TIR = 0.024 L sun we find L bol-int =0.034-0.046 L odot , thus confirming the source's low luminosity. Comparison of L1521F-IRS with theoretical simulations for the very early phases of star formation appears to rule out the first core collapse phase. The evolutionary state appears similar to or younger than the class 0 phase, and the estimated mass is likely to be substellar.

The Gould's Belt Distances Survey (GOBELINS). IV. Distance, Depth, and Kinematics of the Taurus Star-forming Region

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Galli, Phillip A. B.; Loinard, Laurent; Ortiz-Léon, Gisela N.; Kounkel, Marina; Dzib, Sergio A.; Mioduszewski, Amy J.; Rodríguez, Luis F.; Hartmann, Lee; Teixeira, Ramachrisna; Torres, Rosa M.; Rivera, Juana L.; Boden, Andrew F.; Evans, Neal J., II; Briceño, Cesar; Tobin, John J.; Heyer, Mark

2018-05-01

We present new trigonometric parallaxes and proper motions of young stellar objects in the Taurus molecular cloud complex from observations collected with the Very Long Baseline Array as part of the Gould’s Belt Distances Survey. We detected 26 young stellar objects and derived trigonometric parallaxes for 18 stars with an accuracy of 0.3% to a few percent. We modeled the orbits of six binaries and determined the dynamical masses of the individual components in four of these systems (V1023 Tau, T Tau S, V807 Tau, and V1000 Tau). Our results are consistent with the first trigonometric parallaxes delivered by the Gaia satellite and reveal the existence of significant depth effects. We find that the central portion of the dark cloud Lynds 1495 is located at d =129.5 ± 0.3 pc, while the B216 clump in the filamentary structure connected to it is at d = 158.1 ± 1.2 pc. The closest and remotest stars in our sample are located at d = 126.6 ± 1.7 pc and d = 162.7 ± 0.8 pc, yielding a distance difference of about 36 pc. We also provide a new distance estimate for HL Tau that was recently imaged. Finally, we compute the spatial velocity of the stars with published radial velocity and investigate the kinematic properties of the various clouds and gas structures in this region.

Rotation and kinematics of the premain-sequence stars in Taurus-Auriga with Ca II emission

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Hartmann, Lee W.; Soderblom, David R.; Stauffer, John R.

1987-01-01

Radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren 'HVR', (1986) are reported. Most of the velocities are determined to better than 2 km/s precision. The kinematic properties of the Ca II emission stars with strong Li are found to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. It is suggested following Jones and Herbig (1979), that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.

Rotation and kinematics of the premain-sequence stars in Taurus-Auriga with CA II emission

Science.gov (United States)

Hartmann, Lee W.; Soderblom, David R.; Stauffer, John R.

1987-04-01

The authors report radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren (HVR). Most of the velocities are determined to better than 2 km s-1 precision. The authors find the kinematic properties of the Ca II emission stars with strong Li to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. The authors suggest, following Jones and Herbig, that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.

MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS-AURIGA

International Nuclear Information System (INIS)

Kraus, Adam L.; Ireland, Michael J.; Martinache, Frantz; Hillenbrand, Lynne A.

2011-01-01

We have conducted a high-resolution imaging study of the Taurus-Auriga star-forming region in order to characterize the primordial outcome of multiple star formation and the extent of the brown dwarf desert. Our survey identified 16 new binary companions to primary stars with masses of 0.25-2.5 M sun , raising the total number of binary pairs (including components of high-order multiples) with separations of 3-5000 AU to 90. We find that ∼2/3-3/4 of all Taurus members are multiple systems of two or more stars, while the other ∼1/4-1/3 appear to have formed as single stars; the distribution of high-order multiplicity suggests that fragmentation into a wide binary has no impact on the subsequent probability that either component will fragment again. The separation distribution for solar-type stars (0.7-2.5 M sun ) is nearly log-flat over separations of 3-5000 AU, but lower-mass stars (0.25-0.7 M sun ) show a paucity of binary companions with separations of ∼>200 AU. Across this full mass range, companion masses are well described with a linear-flat function; all system mass ratios (q = M B /M A ) are equally probable, apparently including substellar companions. Our results are broadly consistent with the two expected modes of binary formation (free-fall fragmentation on large scales and disk fragmentation on small scales), but the distributions provide some clues as to the epochs at which the companions are likely to form.

Optical polarimetry of star-forming regions

Energy Technology Data Exchange (ETDEWEB)

Gledhill, T M

1987-01-01

The polarimetric investigation of nebulosity associated with loss-mass pre-main sequence (PMS) stellar objects is detailed. Three regions of on-going star formation are considered, specifically, the Haro 6-5 and the HL/XZ Tau systems - both associated with dark clouds in the Taurus complex - and the PV Cephei nebulosity near NGC7023. In each region the imaging observations suggest bipolarity in the optical structure of the nebulosity, and the polarimetric data are used to determine the locations of the illuminating sources. Evidence is found for the association of circumstellar discs of obscuration with the PMS objects Haro 6-5A (FS Tau), Haro 6-5B, HL Tau, and PV Cephei. In each case the polarimetric data suggest that the local magnetic field has played an important role in the evolution of the star and the circumstellar material. Examination of the source-region polarization maps suggests that at least one of the objects considered is surrounded by a dust grain-aligning magnetic field with a predominantly toroidal geometry in the plane of the circumstellar disc. Implications for current theories of outflow acceleration and cloud evolution are discussed.

VLBA Changes Picture of Famous Star-Forming Region

Science.gov (United States)

2007-10-01

capable of the measurement we made," he added. "Knowing the accurate distance to this region is vitally important to properly understanding the general characteristics of the star-formation processes there," Sandstrom said. The new distance to the region, determined with the VLBA, is 1270 light-years, compared with the best previous measurement of 1565 light-years. The old measurement had an uncertainty of about 17 percent, while the new VLBA measurement has an uncertainty of 6 percent. Because the newly-measured distance to the region is 20 percent closer than the earlier measurement, the stars in the region are intrinisically fainter by a factor of 1.5. This has a major impact on scientists' understanding of their ages. "These stars are nearly twice as old as previously thought," said Bower. "Getting a more-accurate distance is going to pay off in many ways by improving our understanding of what is one of the most frequently-studied star-forming regions in the Universe," Peek said. "By using the same technique on other stars in the region, it would be possible to build up a three-dimensional picture of the area," he added. The VLBA, a system of 10 radio-telescope antennas stretching from Hawaii to the Caribbean, provides the best ability to see fine detail, called resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope. The VLBA's tremendous resolving power is what permits the astronomers to make the precise distance determinations. In addition to the new measurement to the Orion star-forming region, the VLBA has made precise distance measurements to star-forming regions in the constellations Taurus and Ophiuchus, to a number of pulsars within our Milky Way Galaxy, and to one of our Galaxy's spiral arms. In 1999, astronomers using the VLBA announced the most precise distance measurement to a galaxy that is not a satellite of the Milky Way. That

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Science.gov (United States)

Marks, M.; Martín, E. L.; Béjar, V. J. S.; Lodieu, N.; Kroupa, P.; Manjavacas, E.; Thies, I.; Rebolo López, R.; Velasco, S.

2017-08-01

Context. One of the key questions of the star formation problem is whether brown dwarfs (BDs) form in the manner of stars directly from the gravitational collapse of a molecular cloud core (star-like) or whether BDs and some very low-mass stars (VLMSs) constitute a separate population that forms alongside stars comparable to the population of planets, for example through circumstellar disk (peripheral) fragmentation. Aims: For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above ≈ 0.2 M⊙, while for BDs the binary fraction is computations. A small amount of dynamical processing of the stellar component was accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results: The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the mass limits for star-like and peripheral formation. Such a trend might be unique to low density regions, such as Taurus, which host binary populations that are largely unprocessed dynamically in which the binary fraction is large for stars down to M-dwarfs and small for BDs. Conclusions: The existence of a strong decline in the binary fraction - primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star-forming region. The binary fraction - primary mass diagram is a diagnostic of the (non-)continuity of star formation along the mass scale, the separateness of the stellar and BD populations, and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

CLOSE COMPANIONS TO YOUNG STARS. I. A LARGE SPECTROSCOPIC SURVEY IN CHAMAELEON I AND TAURUS-AURIGA

International Nuclear Information System (INIS)

Nguyen, Duy Cuong; Brandeker, Alexis; Van Kerkwijk, Marten H.; Jayawardhana, Ray

2012-01-01

We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m telescope. From these data, we achieved a typical radial velocity (RV) precision of ∼80 m s –1 with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on RV variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Chamaeleon I (7%) and Taurus-Auriga (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient RV precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.

SPECTROSCOPY OF PUTATIVE BROWN DWARFS IN TAURUS

International Nuclear Information System (INIS)

Luhman, K. L.; Mamajek, E. E.

2010-01-01

Quanz and coworkers have reported the discovery of the coolest known member of the Taurus star-forming complex (L2 ± 0.5), and Barrado and coworkers have identified a possible protostellar binary brown dwarf in the same region. We have performed infrared spectroscopy on the former and the brighter component of the latter to verify their substellar nature. The resulting spectra do not exhibit the strong steam absorption bands that are expected for cool objects, demonstrating that they are not young brown dwarfs. The optical magnitudes and colors for these sources are also indicative of background stars rather than members of Taurus. Although the fainter component of the candidate protostellar binary lacks spectroscopy, we conclude that it is a galaxy rather than a substellar member of Taurus based on its colors and the constraints on its proper motion.

A Pan-STARRS1 Proper-Motion Survey for Young Brown Dwarfs in the Nearest Star-Forming Regions and a Reddening-Free Classification Method for Ultracool Dwarfs

Science.gov (United States)

Zhang, Zhoujian; Liu, Michael C.; Best, William M. J.; Magnier, Eugene; Aller, Kimberly

2018-01-01

Young brown dwarfs are of prime importance to investigate the universality of the initial mass function (IMF). Based on photometry and proper motions from the Pan-STARRS1 (PS1) 3π survey, we are conducting the widest and deepest brown dwarf survey in the nearby star-forming regions, Taurus–Auriga (Taurus) and Upper Scorpius (USco). Our work is the first to measure proper motions, a robust proxy of membership, for brown dwarf candidates in Taurus and USco over such a large area and long time baseline (≈ 15 year) with such high precision (≈ 4 mas yr-1). Since extinction complicates spectral classification, we have developed a new approach to quantitatively determine reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (≈ 100–5 MJup), using low-resolution near-infrared spectra. So far, our IRTF/SpeX spectroscopic follow-up has increased the substellar and planetary-mass census of Taurus by ≈ 50% and almost doubled the substellar census of USco, constituting the largest single increases of brown dwarfs and free-floating planets found in both regions to date. Most notably, our new discoveries reveal an older (> 10 Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. In addition, the mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes. Upon completion, our survey will establish the most complete substellar and planetary-mass census in both Taurus and USco associations, make a significant addition to the low-mass IMF in both regions, and deliver more comprehensive pictures of star formation histories.

A CENSUS OF ROTATION AND VARIABILITY IN L1495: A UNIFORM ANALYSIS OF TRANS-ATLANTIC EXOPLANET SURVEY LIGHT CURVES FOR PRE-MAIN-SEQUENCE STARS IN TAURUS

International Nuclear Information System (INIS)

Xiao Hongyu; Covey, Kevin R.; Lloyd, James P.; Rebull, Luisa; Charbonneau, David; Mandushev, Georgi; O'Donovan, Francis; Slesnick, Catherine

2012-01-01

disks, with only a 10% probability of the two populations sharing the same parent period distribution. K-S tests do suggest, however, that the updated Taurus period distribution now more closely resembles those measured in other young star-forming clusters (i.e., NGC 2264, NGC 6530, and the ONC). This improved agreement may reflect the exclusion of long rotation periods which are detected in Taurus at lower significance, and which may be beyond the limits of detectability in more distant star-forming regions.

THE GOULD'S BELT VERY LARGE ARRAY SURVEY. IV. THE TAURUS-AURIGA COMPLEX

Energy Technology Data Exchange (ETDEWEB)

Dzib, Sergio A. [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Loinard, Laurent; Rodríguez, Luis F.; Ortiz-León, Gisela N.; Pech, Gerardo; Rivera, Juana L. [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México Apartado Postal 3-72, 58090 Morelia, Michoacán (Mexico); Mioduszewski, Amy J. [National Radio Astronomy Observatory, Domenici Science Operations Center, 1003 Lopezville Road, Socorro, NM 87801 (United States); Kounkel, Marina A.; Hartmann, Lee [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105 (United States); Torres, Rosa M. [Instituto de Astronomía y Meteorología, Universidad de Guadalajara, Avenida Vallarta No. 2602, Col. Arcos Vallarta, CP 44130 Guadalajara, Jalisco, México (Mexico); Boden, Andrew F. [Division of Physics, Math, and Astronomy, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Evans II, Neal J. [Department of Astronomy, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712 (United States); Briceño, Cesar [Cerro Tololo Interamerican Observatory, Casilla 603, La Serena (Chile); Tobin, John, E-mail: sdzib@mpifr-bonn.mpg.de [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)

2015-03-10

We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5 GHz and 7.5 GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects (YSOs) and 18 to field stars. The properties of 56% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved YSOs tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star-forming regions. By comparing our results with previously reported X-ray observations, we notice that YSOs in Taurus-Auriga follow a Güdel-Benz relation with κ = 0.03, as we previously suggested for other regions of star formation. In general, YSOs in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of ∼1 dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature.

THE GOULD'S BELT VERY LARGE ARRAY SURVEY. IV. THE TAURUS-AURIGA COMPLEX

International Nuclear Information System (INIS)

Dzib, Sergio A.; Loinard, Laurent; Rodríguez, Luis F.; Ortiz-León, Gisela N.; Pech, Gerardo; Rivera, Juana L.; Mioduszewski, Amy J.; Kounkel, Marina A.; Hartmann, Lee; Torres, Rosa M.; Boden, Andrew F.; Evans II, Neal J.; Briceño, Cesar; Tobin, John

2015-01-01

We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5 GHz and 7.5 GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects (YSOs) and 18 to field stars. The properties of 56% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved YSOs tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star-forming regions. By comparing our results with previously reported X-ray observations, we notice that YSOs in Taurus-Auriga follow a Güdel-Benz relation with κ = 0.03, as we previously suggested for other regions of star formation. In general, YSOs in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of ∼1 dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature

X-ray sources in regions of star formation. I. The naked T Tauri stars

International Nuclear Information System (INIS)

Walter, F.M.

1986-01-01

Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but naked T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope. 72 references

Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

Science.gov (United States)

Lundquist, Michael; Kobulnicky, Henry

2018-01-01

The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

The Pan-STARRS1 Proper-motion Survey for Young Brown Dwarfs in Nearby Star-forming Regions. I. Taurus Discoveries and a Reddening-free Classification Method for Ultracool Dwarfs

Science.gov (United States)

Zhang, Zhoujian; Liu, Michael C.; Best, William M. J.; Magnier, Eugene A.; Aller, Kimberly M.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Metcalfe, N.; Wainscoat, R. J.; Waters, C.

2018-05-01

We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3π Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370 deg2) and deeper (down to ≈3 M Jup) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution (R ≈ 100) near-infrared spectra to quantify reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (≲100–3 M Jup in Taurus). We have discovered 25 low-gravity (VL-G) and the first 11 intermediate-gravity (INT-G) substellar (M6–L1) members of Taurus, constituting the largest single increase of Taurus brown dwarfs to date. We have also discovered 1 new Pleiades member and 13 new members of the Perseus OB2 association, including a candidate very wide separation (58 kau) binary. We homogeneously reclassify the spectral types and extinctions of all previously known Taurus brown dwarfs. Altogether our discoveries have thus far increased the substellar census in Taurus by ≈40% and added three more L-type members (≲5–10 M Jup). Most notably, our discoveries reveal an older (>10 Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. The mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes.

New insights on multiplicity and clustering in Taurus.

Science.gov (United States)

Joncour, Isabelle; Duchene, Gaspard; Moraux, Estelle; Mundy, Lee

2018-01-01

Multiplicity and clustering of young stars are critical clues to constraint star formation process. The Taurus molecular complex is the archetype of a quiescent star forming region that may retain primeval signature of star formation.Using statistical and clustering tools such as nearest neighbor statistics, correlation functions and the density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, this work reveals new spatial substructures in Taurus.We have identified unexpected ultra wide pairs (UWPs) candidates of high order multiplicity in Taurus in the 5-60 kAU separation range (Joncour et al 2017), beyond the separation assessed for wide pairs (Kraus & Hillenbrand 2009).Our work reveals 20 local stellar substructures, the Nested Elementary Structures (NESTs). These NESTs contain nearly half the stars of Taurus and 75% of the Class 0/I objects probing that they are the preferred sites of star formation (Joncour et al, sub.). The NESTs size ranges from few kAU up to 80 kAU making a length scale bridge between wide pairs and loose group (few hundreds kAU, Kirk & Myers, 2011). The NESTs mass ranges from 0.5-10 solar mass. The balance between Class I, II and III in NESTs suggests that they may be ordered as an evolutionary temporal scheme, some of them got infertile, while other shelter stars in infancy.The UWPs and the NESTs may be pristine imprints of their spatial configuration at birth. The UWPs population may result from a cascade fragmentation scenario of the natal molecular core. They could be the older counterparts, to the 0.5 Myr prestellar cores/Class 0 multiple objects observed at radio/millimeter wavelengths (Tobin et al 2010, 2016) and the precursors of the large number of UWPs (10–100 kAU) recently identified in older moving groups (Floriano-Alonso et al, 2015 ; Elliot et al 2016). The NESTs may result from the gravitational collapse of a gas clump that fragments to give a tight collection of stars within few millions years

Radial Velocity Survey of T Tauri Stars in Taurus-Auriga

Science.gov (United States)

Crockett, Christopher; Mahmud, N.; Huerta, M.; Prato, L.; Johns-Krull, C.; Hartigan, P.; Jaffe, D.

2009-01-01

Is the frequency of giant planet companions to young stars similar to that seen around old stars? Is the "brown dwarf desert" a product of how low-mass companion objects form, or of how they evolve? Some models indicate that both giant planets and brown dwarfs should be common at young ages within 3 AU of a primary star, but migration induced by massive disks drive brown dwarfs into the parent stars, leaving behind proportionally more giant planets. Our radial velocity survey of young stars will provide a census of the young giant planet and brown dwarf population in Taurus-Auriga. In this poster we present our progress in quantifying how spurious radial velocity signatures are caused by stellar activity and in developing models to help distinguish between companion induced and spot induced radial velocity variations. Early results stress the importance of complementary observations in both visible light and NIR. We present our technique to determine radial velocities by fitting telluric features and model stellar features to our observed spectra. Finally, we discuss ongoing observations at McDonald Observatory, KPNO, and the IRTF, and several new exoplanet host candidates.

Polarimetric study of the interstellar medium in Taurus Dark Clouds

International Nuclear Information System (INIS)

Hsu, J.

1985-01-01

An optical linear polarimetric survey was completed for more than 300 stars in an area of 6.5 0 x 10 0 toward the Taurus Dark Clouds Complex. It was found that the orientation of the magnetic field is roughly perpendicular to the elongation direction of the dust lanes, indicating cloud contraction along the magnetic field lines. The distance to the front edge of the dark clouds in Taurus is determined to be 126 pc. There is only insignificant amount of obscuring material between the cloud complex and the Sun. Besides the polarization data, the reddenings of about 250 stars were also obtained from the UBV photometry. The mean polarization to reddening ratio in the Taurus region is 4.6, which is similar to that of the general interstellar matter. The wavelengths of maximum polarization were determined for 30 stars in Taurus. They show an average value of lambda/sub max/ = 0.57 μm, which is only slightly higher than the mean value of the general interstellar medium, lambda/sub max/ = 0.55 μm. A few stars that show higher values of lambda/sub max/ are found near the small isolated regions of very high extinction. One such highly obscured small region where very complex long chain molecules have been discovered in the ratio spectra, is the Taurus Molecular Cloud 1

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.

ULTRAVIOLET-SELECTED FIELD AND PRE-MAIN-SEQUENCE STARS TOWARD TAURUS AND UPPER SCORPIUS

International Nuclear Information System (INIS)

Findeisen, K.; Hillenbrand, L.

2010-01-01

We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest investigator program covering 56 deg 2 near the Taurus T association and 12 deg 2 along the northern edge of the Upper Scorpius OB association. We combined photometry in the GALEX far-ultraviolet and near-ultraviolet bands with data from the Two Micron All Sky Survey to identify candidate young (∼<100 Myr old) stars as those with an ultraviolet excess relative to older main-sequence stars. Follow-up spectroscopy of a partial sample of these candidates suggests five new members of Taurus, with 8-20 expected from additional observations, and five new members of Upper Scorpius, with three to six expected from additional observations. These candidate new members appear to represent a distributed, non-clustered population in either region, although our sample statistics are as of yet too poor to constrain the nature or extent of this population. Rather, our study demonstrates the ability of GALEX observations to identify young stellar populations distributed over a wide area of the sky. We also highlight the necessity of a better understanding of the Galactic ultraviolet source population to support similar investigations. In particular, we report a large population of stars with an ultraviolet excess but no optical indicators of stellar activity or accretion, and briefly argue against several interpretations of these sources.

NEW YOUNG STAR CANDIDATES IN THE TAURUS-AURIGA REGION AS SELECTED FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

International Nuclear Information System (INIS)

Rebull, L. M.; Padgett, D. L.; Noriega-Crespo, A.

2011-01-01

The Taurus Molecular Cloud subtends a large solid angle on the sky, in excess of 250 deg 2 . The search for legitimate Taurus members to date has been limited by sky coverage as well as the challenge of distinguishing members from field interlopers. The Wide-field Infrared Survey Explorer has recently observed the entire sky, and we take advantage of the opportunity to search for young stellar object (YSO) candidate Taurus members from a ∼260 deg 2 region designed to encompass previously identified Taurus members. We use near- and mid-infrared colors to select objects with apparent infrared excesses and incorporate other catalogs of ancillary data to present a list of rediscovered Taurus YSOs with infrared excesses (taken to be due to circumstellar disks), a list of rejected YSO candidates (largely galaxies), and a list of 94 surviving candidate new YSO-like Taurus members. There is likely to be contamination lingering in this candidate list, and follow-up spectra are warranted.

Flares of Orion population variables in the association Taurus T3

International Nuclear Information System (INIS)

Khodzhaev, A.S.; AN Armyanskoj SSR, Byurakan. Astrofizicheskaya Observatoriya)

1987-01-01

Thirteen new flare stars, proved to be irregular variables of Orion Population, were discovered from a study of the Taurus Dark Cloud region by the homogeneous photographic multipose method on the wide angle Schmidt telescopes of the Byurakan Astorphysical Observatory. Seventeen flares on these stars were detected for about 750 hours of the effective observing time. The analysis of the complicated light curves of these flares shows a great variety and multiplicity of this phenomenon and various dynamics of flare energy release processes. The existence of flare stars with some properties typical for both of the T Tauri and UV Ceti stars simulteneously indicates nonstable stars. The population of flare stars in the Taurus Dark Cloud region is apparently as young as in Orion and Monoceros

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.

Photometric peculiarities of the RY Taurus

International Nuclear Information System (INIS)

Zajtseva, G.V.

1982-01-01

The results are presented of photoelectric UBV-observations of RY Taurus carried out in 1965-80 at the Crimean Station of the State Sternberg Astronomical Institute. Two components of brightness variations are observed: fast (days) and slow (years). During fast variations the colour indices U-B and B-V change independently of brightness, however, in particular time inter-- vals the rather strong correlation with the star brightness is observed, positive or negative. During the slow variations only the reverse dependence is observed; the brightness increase is followed by the increase of colour indices (reddening of the star). The comparison of the RY TAURUS intrinsic polarization variations has shown that the dependence of polarization degree on brightness is nonmonotonic. At minimum and maximum brightness the RY TAURUS intrinsic polarization is maximum and reaches 5-6 %. At the general amplitude of RY TAURUS brightness variations in V rays from 10.sup(m)1 to 11.sup(m)7 the V=11.sup(m)0 value is singled out. First a certain ''avoidance'' of this brightness value by the star is observed. Second, the fracture in the course of polarization dependence on brightness occurs as well in the V=11sup(m) region

DISK BRAKING IN YOUNG STARS: PROBING ROTATION IN CHAMAELEON I AND TAURUS-AURIGA

International Nuclear Information System (INIS)

Duy Cuong Nguyen; Jayawardhana, Ray; Van Kerkwijk, Marten H.; Damjanov, Ivana; Brandeker, Alexis; Scholz, Alexander

2009-01-01

We present a comprehensive study of rotation, disk, and accretion signatures for 144 T Tauri stars in the young (∼2 Myr old) Chamaeleon I and Taurus-Auriga star-forming regions based on multi-epoch high-resolution optical spectra from the Magellan Clay 6.5 m telescope supplemented by mid-infrared photometry from the Spitzer Space Telescope. In contrast to previous studies in the Orion Nebula Cluster and NGC 2264, we do not see a clear signature of disk braking in Tau-Aur and Cha I. We find that both accretors and non-accretors have similar distributions of vsin i. This result could be due to different initial conditions, insufficient time for disk braking, or a significant age spread within the regions. The rotational velocities in both regions show a clear mass dependence, with F-K stars rotating on average about twice as fast as M stars, consistent with results reported for other clusters of similar age. Similarly, we find the upper envelope of the observed values of specific angular momentum j varies as M 0.5 for our sample which spans a mass range of ∼0.16-3 M sun . This power law complements previous studies in Orion which estimated j ∝ M 0.25 for ∼ sun . Furthermore, the overall specific angular momentum of this ∼10 Myr population is five times lower than that of non-accretors in our sample, and implies a stellar braking mechanism other than disk braking could be at work. For a subsample of 67 objects with mid-infrared photometry, we examine the connection between accretion signatures and dusty disks: in the vast majority of cases (63/67), the two properties correlate well, which suggests that the timescale of gas accretion is similar to the lifetime of inner disks.

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.

Star Formation Activity Beyond the Outer Arm. I. WISE -selected Candidate Star-forming Regions

Energy Technology Data Exchange (ETDEWEB)

Izumi, Natsuko; Yasui, Chikako; Saito, Masao [National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan); Kobayashi, Naoto; Hamano, Satoshi, E-mail: natsuko.izumi@nao.ac.jp [Laboratory of Infrared High-resolution spectroscopy (LIH), Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)

2017-10-01

The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at R {sub G} ≥ 13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer ( WISE ) mid-infrared all-sky survey. From their color distribution, we developed a simple identification criterion of star-forming regions in the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at R {sub G} ≥ 13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) {sup 12}CO survey of the outer Galaxy, of which the survey region is 102.°49 ≤  l  ≤ 141.°54, −3.°03 ≤  b  ≤ 5.°41, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star formation properties, including star formation rate, star formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.

Stellar Feedback in Massive Star-Forming Regions

Science.gov (United States)

Baldwin, Jack; Pellegrini, Eric; Ferland, Gary; Murray, Norm; Hanson, Margaret

2008-02-01

Star formation rates and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study in the two nearest giant star-forming regions to nail down the physics that produces the 10-20 parsec bubbles seen to surround young massive clusters in the Milky Way. This will determine if and how the clusters disrupt their natal giant molecular clouds (GMCs). Here we request 4 nights on the Blanco telescope to obtain dense grids of optical long-slit spectra criss-crossing each nebula. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3000 different spots in each nebula. From this we can determine a number of dynamically important quantities, such as the gas density and temperature, hence pressure in and around these bubbles. These quantities can be compared to the dynamical (gravitationally induced) pressure, and the radiation pressure. All can be employed in dynamical models for the evolution of a GMC under the influence of an embedded massive star cluster. This research will elucidate the detailed workings of the star-forming regions which dominate the star formation rate in the Milky Way, and also will steadily improve our calibration and understanding of more distant, less well-resolved objects such as ULIRGS, Lyman break, and submillimeter galaxies.

Spatial and kinematic structure of Monoceros star-forming region

Science.gov (United States)

Costado, M. T.; Alfaro, E. J.

2018-05-01

The principal aim of this work is to study the velocity field in the Monoceros star-forming region using the radial velocity data available in the literature, as well as astrometric data from the Gaia first release. This region is a large star-forming complex formed by two associations named Monoceros OB1 and OB2. We have collected radial velocity data for more than 400 stars in the area of 8 × 12 deg2 and distance for more than 200 objects. We apply a clustering analysis in the subspace of the phase space formed by angular coordinates and radial velocity or distance data using the Spectrum of Kinematic Grouping methodology. We found four and three spatial groupings in radial velocity and distance variables, respectively, corresponding to the Local arm, the central clusters forming the associations and the Perseus arm, respectively.

NGVLA Observations of Dense Gas Filaments in Star-Forming Regions

Science.gov (United States)

Di Francesco, James; Chen, Mike; Keown, Jared; GAS Team, KEYSTONE Team

2018-01-01

Recent observations of continuum emission from nearby star-forming regions with Herschel and JCMT have revealed that filaments are ubiquitous structures within molecular clouds. Such filaments appear to be intimately connected to star formation, with those having column densities of AV > 8 hosting the majority of prestellar cores and young protostars in clouds. Indeed, this “threshold” can be explained simply as the result of supercritical cylinder fragmentation. How specifically star-forming filaments form in molecular clouds, however, remains unclear, though gravity and turbulence are likely involved. Observations of their kinematics are needed to understand how mass flows both onto and through these filaments. We show here results from two recent surveys, the Green Bank Ammonia Survey (GAS) and the K-band Examinations of Young Stellar Object Natal Environments (KEYSTONE) that have used the Green Bank Telescope’s K-band Focal Plane Array instrument to map NH3 (1,1) emission from dense gas in nearby star-forming regions. Data from both surveys show that NH3 emission traces extremely well the high column density gas across these star-forming regions. In particular, the GAS results for NGC 1333 show NH3-based velocity gradients either predominantly parallel or perpendicular to the filament spines. Though the GAS and KEYSTONE data are vital for probing filaments, higher resolutions than possible with the GBT alone are needed to examine the kinematic patterns on the 0.1-pc scales of star-forming cores within filaments. We describe how the Next Generation Very Large Array (NGVLA) will uniquely provide the key wide-field data of high sensitivity needed to explore how ambient gas in molecular clouds forms filaments that evolve toward star formation.

Orion star-forming region - far-infrared and radio molecular observations

International Nuclear Information System (INIS)

Thronson, H.A. Jr.; Harper, D.A.; Bally, J.; Dragovan, M.; Mozurkewich, D.; Yerkes Observatory, Williams Bay, WI; ATandT Bell Labs., Holmdel, NJ; Chicago Uni., IL; E. O. Hulburt Center for Space Research, Washington, DC)

1986-01-01

New J = 1-0 CO and far-infrared maps of the Orion star-forming region are presented and discussed. The total infrared luminosity of the Orion star-forming ridge is 250,000 solar luminosities. The material that is emitting strongly at 60 microns is traced and found to be highly centrally concentrated. However, the majority of the extended emission from this region comes from dust that is ultimately heated by the visible Trapezium cluster stars. The luminosity of IRc 2, the most luminous member of the infrared cluster, is estimated to be 40,000-50,000 solar luminosities. A schematic drawing of the Ori MC 1 region is presented. 30 references

Polarization and infrared imaging of regions of star formation

International Nuclear Information System (INIS)

Moneti, A.

1985-01-01

Observational studies of two regions of star formation, the Taurus cloud and the BN-KL region of Orion, are presented. The magnetic field structure in the Taurus cloud was studied in order to investigate its possible role in the evolution of the cloud. It was found that the magnetic field is generally perpendicular to the elongated structures that make up the cloud, and it is deduced that the observed structure could be due to the effects of the magnetic field during the early stages of collapse. In addition, it was found that the magnetic field may have prevented the formation of massive stars by inhibiting the collapse of large cores, while not affecting the collapse of the small ones. Using a new near-infrared array camera, high resolution (1'') images of several young stars embedded in the cloud were obtained. Most of these sources have extended, spatially resolved circumstellar shells. High resolution images of the BN-KL region of Orion at four wavelengths between 1.65 and 4.7 μm were also obtained. At 1.65 μm a large trough is seen in the overall nebulosity; it is suggested that the observed trough is due to the doughnut of material around IRc2 as it obscures the background nebulosity

A radio survey of weak T Tauri stars in Taurus-Auriga

International Nuclear Information System (INIS)

O'neal, D.; Feigelson, E.D.; Mathieu, R.D.; Myers, P.C.

1990-01-01

A multi-epoch 5 GHz survey of candidate or confirmed weak T Tauri stars in the Taurus-Auriga molecular cloud complex was conducted with the Very Large Array. The stars were chosen from those having detectable X-ray or chromospheric emission, and weak-emission-line pre-main-sequence stars found by other means. Snapshots of 99 VLA fields containing 119 candidate stars were obtained with a sensitivity of 0.7 mJy; most fields were observed on two or three dates. Nine radio sources coincident with cataloged stars were found. One may be an RS CVn binary system; the other eight are pre-main-sequence stars. Three of the detected stars - HD 283447, V410 Tau, and FK X-ray 1 - were previously known radio sources. Five new detections are Herbig's Anon 1, Hubble 4, HDE 283572, Elias 12, and HK Tau/c. At least five of the sources are variable, and no linear or circular polarization was found. Several lines of evidence suggest that the radio-detected weak T Tauri stars are quite young, perhaps younger on average than nondetected stars. 54 refs

YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

Energy Technology Data Exchange (ETDEWEB)

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

2015-11-01

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

Multimolecular studies of Galactic star-forming regions

NARCIS (Netherlands)

Baan, W. A.; Loenen, A. F.; Spaans, M.

2014-01-01

Molecular emission-line observations of isolated Galactic star-forming regions are used to model the physical properties of the molecular interstellar medium in these systems. Observed line ratios are compared with the results predicted by models that incorporate gas-phase chemistry and the heating

HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

Science.gov (United States)

2002-01-01

NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

Insights from Synthetic Star-forming Regions. III. Calibration of Measurement and Techniques of Star Formation Rates

Energy Technology Data Exchange (ETDEWEB)

Koepferl, Christine M.; Robitaille, Thomas P. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Dale, James E., E-mail: koepferl@usm.lmu.de [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany)

2017-11-01

Through an extensive set of realistic synthetic observations (produced in Paper I), we assess in this part of the paper series (Paper III) how the choice of observational techniques affects the measurement of star formation rates (SFRs) in star-forming regions. We test the accuracy of commonly used techniques and construct new methods to extract the SFR, so that these findings can be applied to measure the SFR in real regions throughout the Milky Way. We investigate diffuse infrared SFR tracers such as those using 24 μ m, 70 μ m and total infrared emission, which have been previously calibrated for global galaxy scales. We set up a toy model of a galaxy and show that the infrared emission is consistent with the intrinsic SFR using extra-galactic calibrated laws (although the consistency does not prove their reliability). For local scales, we show that these techniques produce completely unreliable results for single star-forming regions, which are governed by different characteristic timescales. We show how calibration of these techniques can be improved for single star-forming regions by adjusting the characteristic timescale and the scaling factor and give suggestions of new calibrations of the diffuse star formation tracers. We show that star-forming regions that are dominated by high-mass stellar feedback experience a rapid drop in infrared emission once high-mass stellar feedback is turned on, which implies different characteristic timescales. Moreover, we explore the measured SFRs calculated directly from the observed young stellar population. We find that the measured point sources follow the evolutionary pace of star formation more directly than diffuse star formation tracers.

Wide-Field Infrared Survey Explorer Observations of the Evolution of Massive Star-Forming Regions

Science.gov (United States)

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Asslef, R. J.

2012-01-01

We present the results of a mid-infrared survey of II outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

WIDE-FIELD INFRARED SURVEY EXPLORER OBSERVATIONS OF THE EVOLUTION OF MASSIVE STAR-FORMING REGIONS

International Nuclear Information System (INIS)

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Padgett, D. L.; Rebull, L. M.; Assef, R. J.

2012-01-01

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the 'fireworks hypothesis' since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

Correlations between the stellar and disc properties of Taurus PMS stars in the GASPS sample

NARCIS (Netherlands)

Alonso-Martínez, Miguel; Riviere-Marichalar, Pablo; Pascual, Natalia; Montesinos, Benjamín; Howard, Christian D.; Sandell, Göran; Meeus, Gwendolyn; Eiroa, Carlos; Dent, Bill

The Herschel Open Time Key Programme GASPS (P.I. B. Dent) has observed a large number of pre-main sequence TTauri stars in Taurus with PACS (photometry and spectroscopy). In addition, we have also carried out new ground-based optical and near-IR observations (photometry and spectroscopy) of most of

Classifying the embedded young stellar population in Perseus and Taurus and the LOMASS database

DEFF Research Database (Denmark)

Carney, M. T.; Ylldlz, U. A.; Mottram, J. C.

2016-01-01

. An additional 16% are confused sources with an uncertain evolutionary stage. Outflows are found to make a negligible contribution to the integrated HCO+ intensity for the majority of sources in this study. Conclusions. Separating classifications by cloud reveals that a high percentage of the Class 0+I sources...... in the Perseus star forming region are truly embedded Stage I sources (71%), while the Taurus cloud hosts a majority of evolved PMS stars with disks (68%). The concentration factor method is useful to correct misidentified embedded YSOs, yielding higher accuracy for YSO population statistics and Stage timescales...

New far infrared images of bright, nearby, star-forming regions

Science.gov (United States)

Harper, D. AL, Jr.; Cole, David M.; Dowell, C. Darren; Lees, Joanna F.; Lowenstein, Robert F.

1995-01-01

Broadband imaging in the far infrared is a vital tool for understanding how young stars form, evolve, and interact with their environment. As the sensitivity and size of detector arrays has increased, a richer and more detailed picture has emerged of the nearest and brightest regions of active star formation. We present data on M 17, M 42, and S 106 taken recently on the Kuiper Airborne Observatory with the Yerkes Observatory 60-channel far infrared camera, which has pixel sizes of 17 in. at 60 microns, 27 in. at 100 microns, and 45 in. at 160 and 200 microns. In addition to providing a clearer view of the complex central cores of the regions, the images reveal new details of the structure and heating of ionization fronts and photodissociation zones where radiation form luminous stars interacts with adjacent molecular clouds.

YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

Energy Technology Data Exchange (ETDEWEB)

Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Kuhn, Michael A. [Millennium Institute of Astrophysics, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Povich, Matthew S., E-mail: edf@astro.psu.edu [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Ave., Pomona, CA 91768 (United States)

2016-12-20

The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

International Nuclear Information System (INIS)

Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Povich, Matthew S.

2016-01-01

The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

Water in low-mass star-forming regions with Herschel

DEFF Research Database (Denmark)

Kristensen, L. E.; Visser, R.; Van Dishoeck, E. F.

2010-01-01

"Water In Star-forming regions with Herschel" (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIF...

THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS

Energy Technology Data Exchange (ETDEWEB)

Barnes, Kate L.; Van Zee, Liese [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Dowell, Jayce D., E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: jdowell@unm.edu [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States)

2013-09-20

We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and Hα colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; τ model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and Hα observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub α}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing τ and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ∼2 × 10{sup –6} M{sub ☉} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical

The distribution of warm gas in the G327.3-0.6 star forming region

NARCIS (Netherlands)

Leurini, S.; Wyrowski, F.; van der Tak, F.; Herpin, F.; Herschel WISH Team, [Unknown

Water is a key molecule for determining the physical chemical structure of star forming regions because of its large abundance variations between warm and cold regions. As a part of the HIFI-led Key Program WISH (P.I. E. van Dishoeck), we are mapping six massive star forming region in different H2O

SEQUENTIAL STAR FORMATION IN RCW 34: A SPECTROSCOPIC CENSUS OF THE STELLAR CONTENT OF HIGH-MASS STAR-FORMING REGIONS

International Nuclear Information System (INIS)

Bik, A.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Puga, E.; Waters, L.B.F.M.; Waelkens, Ch.; Horrobin, M.; Kaper, L.; De Koter, A.; Van den Ancker, M.; Comeron, F.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; Thi, W. F.

2010-01-01

In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M sun ) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H 2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is

Interstellar ice grains in the Taurus molecular clouds

International Nuclear Information System (INIS)

Whittet, D.C.B.; Bode, M.F.; Baines, D.W.T.; Evans, A.

1983-01-01

Observations made in November 1981 using the United Kingdom Infrared Telescope (UKIRT) at Mauna Kea of the 3 μm ice absorption feature in the spectra of several obscured stars in the Taurus interstellar clouds are reported. The feature correlated in strength with extinction at visual wavelengths (Asub(v)), and is present in stars with Asub(v) as low as 4-6 mag. Ice may be widespread in the Taurus clouds, vindicating ideas on grain composition and growth first reported nearly 50 yr ago. (author)

OH outflows in star-forming regions

International Nuclear Information System (INIS)

Mirabel, I.F.; Ruiz, A.; Rodriguez, L.F.; Canto, J.; Universidad de Puer; Universidad de Puerto Rico, Rio Piedras; Universidad Nacional Autonoma de Mexico, Mexico City)

1987-01-01

The results from a survey for high-velocity OH in molecular outflows in star-forming regions are reported. High-velocity OH was detected in absorption in nine of these regions. When the telescope beam can resolve the outflows, they show similar anisotropic angular distribution as the redshifted and blueshifted CO. The OH transitions are markedly subthermal since for several sources it is found that the radiation that is being absorbed is a background continuum constituted by the cosmic component plus a small Galactic contribution. The absorbing OH appears to trace gas with higher velocities and lower densities than does the CO and, in some cases, provides information on the structure of the outflows at larger distances from the central source. At scales of 0.1 pc, the outflows are elongated in the direction of the steepest density gradient of the ambient cloud, suggesting that the large-scale collimation of the outflow is produced by the density structure of the ambient cloud. 29 references

Molecular line study of massive star-forming regions from the Red MSX Source survey

Science.gov (United States)

Yu, Naiping; Wang, Jun-Jie

2014-05-01

In this paper, we have selected a sample of massive star-forming regions from the Red MSX Source survey, in order to study star formation activities (mainly outflow and inflow signatures). We have focused on three molecular lines from the Millimeter Astronomy Legacy Team Survey at 90 GHz: HCO+(1-0), H13CO+(1-0) and SiO(2-1). According to previous observations, our sources can be divided into two groups: nine massive young stellar object candidates (radio-quiet) and 10 H II regions (which have spherical or unresolved radio emissions). Outflow activities have been found in 11 sources, while only three show inflow signatures in all. The high outflow detection rate means that outflows are common in massive star-forming regions. The inflow detection rate was relatively low. We suggest that this was because of the beam dilution of the telescope. All three inflow candidates have outflow(s). The outward radiation and thermal pressure from the central massive star(s) do not seem to be strong enough to halt accretion in G345.0034-00.2240. Our simple model of G318.9480-00.1969 shows that it has an infall velocity of about 1.8 km s-1. The spectral energy distribution analysis agrees our sources are massive and intermediate-massive star formation regions.

Extreme Variables in Star Forming Regions

Science.gov (United States)

Contreras Peña, Carlos Eduardo

2015-01-01

in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to far-infrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with ΔK > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| explained as arising from shock-excited emission caused by molecular outflows. Whether these molecular outflows are related to outbursts events cannot be confirmed from our data. Adding the GPS and VVV spectroscopic results, we find that between 6 and 14 objects are new additions to the FUor class from their close resemblance to the near-infrared spectra of FUors, and at least 23 more objects are new additions to the eruptive variable class. For most of these we are unable to classify them into any of the original definitions for this variable class. In any case, we are adding up to 37 new stars to the eruptive variable class which would double the current number of known objects. We note that most objects are found to be deeply embedded optically invisible stars, thus increasing the number of objects belonging to this subclass by a much larger factor. In general, objects in our samples which are found to be likely eruptive variable stars show a mixture of

A RESOLVED CENSUS OF MILLIMETER EMISSION FROM TAURUS MULTIPLE STAR SYSTEMS

International Nuclear Information System (INIS)

Harris, Robert J.; Andrews, Sean M.; Wilner, David J.; Kraus, Adam L.

2012-01-01

We present a high angular resolution millimeter-wave dust continuum imaging survey of circumstellar material associated with the individual components of 23 multiple star systems in the Taurus-Auriga young cluster. Combined with previous measurements in the literature, these new data permit a comprehensive look at how the millimeter luminosity (a rough tracer of disk mass) relates to the separation and mass of a stellar companion. Approximately one-third (28%-37%) of the individual stars in multiple systems have detectable millimeter emission, an incidence rate half that for single stars (∼62%) which does not depend on the number of companions. There is a strong, positive correlation between the luminosity and projected separation (a p ) of a stellar pair. Wide pairs (a p > 300 AU) have a similar luminosity distribution as single stars, medium pairs (a p ≈ 30-300 AU) are a factor of five fainter, and close pairs (a p < 30 AU) are ∼5× fainter yet (aside from a small, but notable population of bright circumbinary disks). In most cases, the emission is dominated by a disk around the primary (or a wide tertiary in hierarchical triples), but there is no clear relationship between luminosity and stellar mass ratio. A direct comparison of resolved disk sizes with predictions from tidal truncation models yields mixed results; some disks are much larger than expected given the projected distances of their companions. We suggest that the presence of a stellar companion impacts disk properties at a level comparable to the internal evolution mechanisms that operate in an isolated system, with both the multiple star formation process itself and star-disk tidal interactions likely playing important roles in the evolution of circumstellar material. From the perspective of the mass content of the disk reservoir, we expect that (giant) planet formation is inhibited around the components of close pairs or secondaries, but should be as likely as for single stars around the

Global Infrared–Radio Spectral Energy Distributions of Galactic Massive Star-Forming Regions

Science.gov (United States)

Povich, Matthew Samuel; Binder, Breanna Arlene

2018-01-01

We present a multiwavelength study of 30 Galactic massive star-forming regions. We fit multicomponent dust, blackbody, and power-law continuum models to 3.6 µm through 10 mm spectral energy distributions obtained from Spitzer, MSX, IRAS, Herschel, and Planck archival survey data. Averaged across our sample, ~20% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ~50% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates NC ≥ 1050 s–1 and total infrared luminosity LTIR ≥ 106.8 L⊙) have higher percentages of absorbed Lyman continuum photons (~40%) and dust-reprocessed starlight (~80%). The monochromatic 70-µm luminosity L70 is linearly correlated with LTIR, and on average L70/LTIR = 50%, in good agreement with extragalactic studies. Calibrated against the known massive stellar content in our sampled H II regions, we find that star formation rates based on L70 are in reasonably good agreement with extragalactic calibrations, when corrected for the smaller physical sizes of the Galactic regions. We caution that absorption of Lyman continuum photons prior to contributing to the observed ionizing photon rate may reduce the attenuation-corrected Hα emission, systematically biasing extragalactic calibrations toward lower star formation rates when applied to spatially-resolved studies of obscured star formation.This work was supported by the National Science Foundation under award CAREER-1454333.

Observations of star-forming regions with the Midcourse Space Experiment

NARCIS (Netherlands)

Kraemer, KE; Shipman, RF; Price, SD; Mizuno, DR; Kuchar, T; Carey, SJ

We have imaged seven nearby star-forming regions, the Rosette Nebula, the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5, with the Spatial Infrared Imaging Telescope on the Midcourse Space Experiment (MSX) satellite at 1800 resolution at 8.3, 12.1, 14.7, and 21.3 mum. The large

The Structure of the Nearby Giant Star-Forming Region 30 Doradus

Science.gov (United States)

Pellegrini, Eric; Baldwin, Jack; Hanson, Margaret; Ferland, Gary; Troland, Thomas

2007-08-01

The rates of star formation and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study of these processes in the two nearest giant star-forming regions, 30 Doradus and NGC 3603, as an aide in understanding the nature of Giant Extragalactic H II Regions, starbursts, and Ultra-Luminous IR Galaxies. We recently completed our observations of NGC 3603. Here we request 2 nights on the Blanco telescope to obtain a dense grid of optical long-slit spectra criss- crossing 30 Dor. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3800 different spots in the nebula. We also request 3 nights on SOAR to take K-band long slit spectra covering H^+ Br(gamma) and several H_2 lines across three representative edge-on ionization fronts in 30 Dor. The IR spectra will be taken in locations also covered by the optical spectra, and will tell us about the structure, pressure support and heating mechanisms in the photo-dissociation regions (PDRs) at these points. Either half of this project can stand on its own, but both parts together will permit the PI to complete his PhD thesis.

Water in massive star-forming regions with Herschel Space Observatory

Science.gov (United States)

Chavarria, L.; Herpin, F.; Bontemps, S.; Jacq, T.; Baudry, A.; Braine, J.; van der Tak, F.; Wyrowski, F.; van Dishoeck, E. F.

2011-05-01

High-mass stars formation process is much less understood than the low-mass case: short timescales, high opacities and long distance to the sources challenge the study of young massive stars. The instruments on board the Heschel Space Observatory permit us to investigate molecular species at high spectral resolution in the sub-milimeter wavelengths. Water, one of the most abundant molecules in the Universe, might elucidate key episodes in the process of stellar birth and it may play a major role in the formation of high-mass stars. This contribution presents the first results of the Heschel Space Observatory key-program WISH (Water In Star forming regions with Herschel) concerning high-mass protostars. The program main purpose is to follow the process of star formation during the various stages using the water molecule as a physical diagnostic throughout the evolution. In general, we aim to adress the following questions: How does protostars interact with their environment ? How and where water is formed ? How is it transported from cloud to disk ? When and where water becomes a dominant cooling or heating agent ? We use the HIFI and PACS instruments to obtain maps and spectra of ~20 water lines in ~20 massive protostars spanning a large range in physical parameters, from pre-stellar cores to UCHII regions. I will review the status of the program and focus specifically on the spectroscopic results. I will show how powerful are the HIFI high-resolution spectral observations to resolve different physical source components such as the dense core, the outflows and the extended cold cloud around the high-mass object. We derive water abundances between 10-7 and 10-9 in the outer envelope. The abundance variations derived from our models suggest that different chemical mechanisms are at work on these scales (e.g. evaporation of water-rich icy grain mantles). The detection and derived abundance ratios for rare isotopologues will be discussed. Finally, a comparison in tems

THE SCHMIDT-KENNICUTT LAW OF MATCHED-AGE STAR-FORMING REGIONS; Paα OBSERVATIONS OF THE EARLY-PHASE INTERACTING GALAXY TAFFY I

International Nuclear Information System (INIS)

Komugi, S.; Tateuchi, K.; Motohara, K.; Kato, N.; Konishi, M.; Koshida, S.; Morokuma, T.; Takahashi, H.; Tanabé, T.; Yoshii, Y.; Takagi, T.; Iono, D.; Kaneko, H.; Ueda, J.; Saitoh, T. R.

2012-01-01

In order to test a recent hypothesis that the dispersion in the Schmidt-Kennicutt law arises from variations in the evolutionary stage of star-forming molecular clouds, we compared molecular gas and recent star formation in an early-phase merger galaxy pair, Taffy I (UGC 12915/UGC 12914, VV 254) which went through a direct collision 20 Myr ago and whose star-forming regions are expected to have similar ages. Narrowband Paα image is obtained using the ANIR near-infrared camera on the mini-TAO 1 m telescope. The image enables us to derive accurate star formation rates within the galaxy directly. The total star formation rate, 22.2 M ☉ yr –1 , was found to be much higher than previous estimates. Ages of individual star-forming blobs estimated from equivalent widths indicate that most star-forming regions are ∼7 Myr old, except for a giant H II region at the bridge which is much younger. Comparison between star formation rates and molecular gas masses for the regions with the same age exhibits a surprisingly tight correlation, a slope of unity, and star formation efficiencies comparable to those of starburst galaxies. These results suggest that Taffy I has just evolved into a starburst system after the collision, and the star-forming sites are at a similar stage in their evolution from natal molecular clouds except for the bridge region. The tight Schmidt-Kennicutt law supports the scenario that dispersion in the star formation law is in large part due to differences in evolutionary stage of star-forming regions.

Wide-field Infrared Survey Explorer Observations of the Evolution of Massive Star-forming Regions

OpenAIRE

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Assef, R. J.

2012-01-01

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from th...

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

The embedded young stars in the Taurus-Auriga molecular cloud. I - Models for spectral energy distributions

Science.gov (United States)

Kenyon, Scott J.; Calvet, Nuria; Hartmann, Lee

1993-01-01

We describe radiative transfer calculations of infalling, dusty envelopes surrounding pre-main-sequence stars and use these models to derive physical properties for a sample of 21 heavily reddened young stars in the Taurus-Auriga molecular cloud. The density distributions needed to match the FIR peaks in the spectral energy distributions of these embedded sources suggest mass infall rates similar to those predicted for simple thermally supported clouds with temperatures about 10 K. Unless the dust opacities are badly in error, our models require substantial departures from spherical symmetry in the envelopes of all sources. These flattened envelopes may be produced by a combination of rotation and cavities excavated by bipolar flows. The rotating infall models of Terebey et al. (1984) models indicate a centrifugal radius of about 70 AU for many objects if rotation is the only important physical effect, and this radius is reasonably consistent with typical estimates for the sizes of circumstellar disks around T Tauri stars.

STAR-FORMING OR STARBURSTING? THE ULTRAVIOLET CONUNDRUM

International Nuclear Information System (INIS)

Boquien, M.; Calzetti, D.; Hong, S.; Kennicutt, R.; Dale, D.; Engelbracht, C.; Portouw, J.; Gordon, K. D.; Lee, J. C.

2009-01-01

Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-β diagram (the IR/UV ratio 'IRX' versus the UV color 'β'). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of eight nearby galaxies, and examined the properties of individual UV and 24 μm selected star-forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies. We find that (1) the dispersion is not correlated with the mean age of the stellar populations; (2) a range of dust geometries and dust extinction curves are the most likely causes for the observed dispersion in the IRX-β diagram, (3) together with some potential dilution of the most recent star-forming population by older unrelated bursts, at least in the case of star-forming regions within galaxies; and (4) we also recover some general characteristics of the regions, including a tight positive correlation between the amount of dust attenuation and the metal content. Although generalizing our results to whole galaxies may not be immediate, the possibility of a range of dust extinction laws and geometries should be accounted for in the latter systems as well.

Water in Star-forming Regions with Herschel (WISH): recent results and trends

Science.gov (United States)

van Dishoeck, E. F.

2012-03-01

Water is a key molecule in the physics and chemistry of star- and planet-forming regions. In the `Water in Star-forming Regions with Herschel' (WISH) Key Program, we have obtained a comprehensive set of water data toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities --from the lowest to the highest mass protostars--, as well as evolutionary stages --from pre-stellar cores to disks. Lines of both ortho- and para-H_2O and their isotopologues, as well as chemically related hydrides, are observed with the HIFI and PACS instruments. The data elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets (outflow, infall, expansion), test basic chemical processes and reveal the chemical evolution of water and the oxygen-reservoir into planet-forming disks. In this brief talk a few recent WISH highlights will be presented, including determinations of the water abundance in each of the different physical components (inner and outer envelope, outflow) and constraints on the ortho/para ratio. Special attention will be given to trends found across the sample, especially the similarity in profiles from low to high-mass protostars and the evolution of the gas-phase water abundance from prestellar cores to disks. More details can be found at http://www.strw.leidenuniv.nl/WISH, whereas overviews are given in van Dishoeck et al. (2011, PASP 123, 138), Kristensen & van Dishoeck (2011, Astronomische Nachrichten 332, 475) and Bergin & van Dishoeck (2012, Phil. Trans. Royal Soc. A).

Anomalous strength of the 2200 Angstroem feature in Cassiopeia-Taurus association

International Nuclear Information System (INIS)

Morales, C.; Ruiz del Arbol, J.A.; Llorente de Andres, F.

1980-01-01

From a large sample of reddened stars we computed the individual extinction curves which agree with that calculated by Nandy et al. (1976), except for four stars which show that the extinction at the 2200 Angstroem feature is greater than that deduced for the rest of stars. These four stars belong to the Cassiopeia-Taurus association. (orig.)

Star-forming galaxy models: Blending star formation into TREESPH

Science.gov (United States)

Mihos, J. Christopher; Hernquist, Lars

1994-01-01

We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

Ratio of total-to-selective extinction in the Taurus dark cloud complex

International Nuclear Information System (INIS)

Vrba, F.J.; Rydgren, A.E.; Space Telescope Science Institute, Baltimore, MD)

1985-01-01

UBVRI and JHK photometry, as well as spectral classifications are presented for seven reddened early-type field stars that are observed through the Taurus dark cloud complex. The ratio of total-to-selective extinction is derived for each star by the color-difference method. For six stars with absolute magnitudes in violet of more than 1.7 and less than 3.2 mag, a normal ratio R of total-to-selective extinction of about 3.1 is found. The mildly anomalous R value of about 3.5 for the well-studied star HD 29647 was also confirmed. The results provide further evidence that the interstellar extinction law in the Taurus dark cloud complex is basically normal for lines of sight with absolute magnitudes in violet of less than 3 mag. 24 references

Investigation of conspicuous infrared star cluster and star-forming region RCW 38 IR Cluster

International Nuclear Information System (INIS)

Gyulbudaghian, A.L.; May, J.

2008-01-01

An infrared star cluster RCW 38 IR Cluster, which is also a massive star-forming region, is investigated. The results of observations with SEST (Cerro is Silla, Chile) telescope on 2.6-mm 12 CO spectral line and with SIMBA on 1.2-mm continuum are given. The 12 CO observations revealed the existence of several molecular clouds, two of which (clouds I and 2) are connected with the object RCW 38 IR Cluster. Cloud 1 is a massive cloud, which has a depression in which the investigated object is embedded. It is not excluded that the depression was formed by the wind and/or emission from the young bright stars belonging to the star cluster. Rotation of cloud 2, around the axis having SE-NW direction, with an angular velocity ω 4.6 · 10 -14 s -1 is also found. A red-shifted outflow with velocity ∼+5.6 km/s, in the SE direction and perpendicular to the elongation of cloud 2 has been also found. The investigated cluster is associated with an IR point source IRAS 08573-4718, which has IR colours typical for a, non-evolved embedded (in the cloud) stellar object. The cluster is also connected with a water maser. The SIMBA image shoves the existence of a central bright condensation, coinciding with the cluster itself, and two extensions. One of these extensions (the one with SW-NE direction) coincides, both in place and shape, with cloud 2, so that it is not excluded the possibility that this extension might be also rotating like cloud 2. In the vicinity of these extensions there are condensations resembling HH objects

Neutral and Ionized Hydrides in Star-forming Regions. Observations with Herschel/HIFI

DEFF Research Database (Denmark)

O. Benz, Arnold; Bruderer, Simon; F. van Dishoeck, Ewine

2013-01-01

of OH, CH, NH, SH and their ions OH+, CH+, NH+, SH+, H2O+, and H3O+ were observed in star-forming regions by the HIFI spectrometer onboard the Herschel Space Observatory. Molecular column densities are derived from observed ground-state lines, models, or rotational diagrams. We report here on two...

Extended high circular polarization in the Orion massive star forming region: implications for the origin of homochirality in the solar system.

Science.gov (United States)

Fukue, Tsubasa; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hough, James H; Bailey, Jeremy; Whittet, Douglas C B; Lucas, Philip W; Nakajima, Yasushi; Hashimoto, Jun

2010-06-01

We present a wide-field (approximately 6' x 6') and deep near-infrared (K(s) band: 2.14 mum) circular polarization image in the Orion nebula, where massive stars and many low-mass stars are forming. Our results reveal that a high circular polarization region is spatially extended (approximately 0.4 pc) around the massive star-forming region, the BN/KL nebula. However, other regions, including the linearly polarized Orion bar, show no significant circular polarization. Most of the low-mass young stars do not show detectable extended structure in either linear or circular polarization, in contrast to the BN/KL nebula. If our solar system formed in a massive star-forming region and was irradiated by net circularly polarized radiation, then enantiomeric excesses could have been induced, through asymmetric photochemistry, in the parent bodies of the meteorites and subsequently delivered to Earth. These could then have played a role in the development of biological homochirality on Earth.

The comparison of physical properties derived from gas and dust in a massive star-forming region

Energy Technology Data Exchange (ETDEWEB)

Battersby, Cara; Bally, John; Ginsburg, Adam; Darling, Jeremy [Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 80309 (United States); Dunham, Miranda [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Longmore, Steve [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)

2014-05-10

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH{sub 3} on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH{sub 3} abundance, χ{sub NH{sub 3}} = 4.6 × 10{sup –8}. In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T {sub dust,} {sub avg} ∼ 11.6 ± 0.2 K versus T {sub gas,} {sub avg} ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH{sub 3}, which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

The comparison of physical properties derived from gas and dust in a massive star-forming region

International Nuclear Information System (INIS)

Battersby, Cara; Bally, John; Ginsburg, Adam; Darling, Jeremy; Dunham, Miranda; Longmore, Steve

2014-01-01

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH 3 on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH 3 abundance, χ NH 3 = 4.6 × 10 –8 . In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T dust, avg ∼ 11.6 ± 0.2 K versus T gas, avg ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH 3 , which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

TADPOL: A 1.3 mm Survey of Dust Polarization in Star-forming Cores and Regions

OpenAIRE

Hull, Charles L. H.; Plambeck, Richard L.; Kwon, Woojin; Bower, Geoffrey C.; Carpenter, John M.; Crutcher, Richard M.; Fiege, Jason D.; Franzmann, Erica; Hakobian, Nicholas S.; Heiles, Carl; Houde, Martin; Hughes, A. Meredith; Lamb, James W.; Looney, Leslie W.; Marrone, Daniel P.

2014-01-01

We present λ 1.3 mm Combined Array for Research in Millimeter-wave Astronomy observations of dust polarization toward 30 star-forming cores and eight star-forming regions from the TADPOL survey. We show maps of all sources, and compare the ~2".5 resolution TADPOL maps with ~20" resolution polarization maps from single-dish submillimeter telescopes. Here we do not attempt to interpret the detailed B-field morphology of each object. Rather, we use average B-field orientations to derive conclusi...

NEAR-INFRARED IMAGING OF THE STAR-FORMING REGIONS SH2-157 AND SH2-152

International Nuclear Information System (INIS)

Chen Yafeng; Yang Ji; Zeng Qin; Yao Yongqiang; Sato, Shuji

2009-01-01

Near-infrared JHK' and H 2 v = 1-0 S (1) imaging observations of the star-forming regions Sh2-157 and Sh2-152 are presented. The data reveal a cluster of young stars associated with H 2 line emission in each region. Additionally, many IR point sources are found in the dense core of each molecular cloud. Most of these sources exhibit infrared color excesses typical of T Tauri stars, Herbig Ae/Be stars, and protostars. Several display the characteristics of massive stars. We calculate histograms of the K'-magnitude and [H - K'] color for all sources, as well as two-color and color-magnitude diagrams. The stellar populations inside and outside the clusters are similar, suggesting that these systems are rather evolved. Shock-driven H 2 emission knots are also detected, which may be related to evident subclusters in an earlier evolutionary stage.

NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin A. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

2013-04-15

We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

H2O masers in star-forming regions

International Nuclear Information System (INIS)

Downes, D.

1985-01-01

Water vapour near star forming regions was first detected by Cheung et al. (1969) and shortly thereafter was recognised to be maser emission. In spite of this 15 year history of H 2 O observations, the problem of interpreting such strong H 2 O masers as W49 and Orion is still very acute. Not one of the models now available can explain in an unconstrained fashion why a very large maser flux can emanate from clouds of such small size. Whereas some models proposed to explain OH masers have retained their plausibility under the pressure of new observations, H 2 O models have not. The author outlines the background of the H 2 O problem, stating that the strongest of the masers discovered are still not satisfactorily explained today. (Auth.)

THE MASSIVE STAR-FORMING REGION CYGNUS OB2. II. INTEGRATED STELLAR PROPERTIES AND THE STAR FORMATION HISTORY

International Nuclear Information System (INIS)

Wright, N. J.; Drake, J. J.; Drew, J. E.; Vink, J. S.

2010-01-01

Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 M sun (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5 +0.75 -1.0 and 5.25 +1.5 -1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = -1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 x 10 4 M sun , similar to that of many of our Galaxy's most massive SFRs.

MOLECULAR OUTFLOWS IN THE SUBSTELLAR DOMAIN: MILLIMETER OBSERVATIONS OF YOUNG VERY LOW MASS OBJECTS IN TAURUS AND ρ OPHIUCHI

International Nuclear Information System (INIS)

Ngoc Phan-Bao; Lee, Chin-Fei; Ho, Paul T. P.; Tang, Ya-Wen

2011-01-01

We report here our search for molecular outflows from young very low mass stars and brown dwarfs in Taurus and ρ Ophiuchi. Using the Submillimeter Array and the Combined Array for Research in Millimeter-wave Astronomy, we have observed four targets at 1.3 mm wavelength (230 GHz) to search for CO J = 2 → 1 outflows. A young very low mass star MHO 5 (in Taurus) with an estimated mass of 90 M J , which is just above the hydrogen-burning limit, shows two gas lobes that are likely outflows. While the CO map of MHO 5 does not show a clear structure of outflow, possibly due to environment gas, its position-velocity diagram indicates two distinct blue- and redshifted components. We therefore conclude that they are components of a bipolar molecular outflow from MHO 5. We estimate an outflow mass of 7.0 x 10 -5 M sun and a mass-loss rate of 9.0 x 10 -10 M sun . These values are over two orders of magnitude smaller than the typical ones for T Tauri stars and somewhat weaker than those we have observed in the young brown dwarf ISO-Oph 102 of 60 M J in ρ Ophiuchi. This makes MHO 5 the first young very low mass star showing a bipolar molecular outflow in Taurus. The detection boosts the scenario that very low mass objects form like low-mass stars but in a version scaled down by a factor of over 100.

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.

X-ray sources in regions of star formation. II. The pre-main-sequence G star HDE 283572

International Nuclear Information System (INIS)

Walter, F.M.; Brown, A.; Linsky, J.L.; Rydgren, A.E.; Vrba, F.; Joint Institute for Laboratory Astrophysics, Boulder, CO; Computer Sciences Corp., El Segundo, CA; Naval Observatory, Flagstaff, AZ)

1987-01-01

This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a naked T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars. 49 references

Molecular Hydrogen Images of Star Forming Regions in the Magellanic Clouds

Science.gov (United States)

Probst, Ronald G.; Barba, R.; Bolatto, A.; Chu, Y.; Points, S.; Rubio, M.; Smith, C.

2011-01-01

The Large and Small Magellanic Clouds exhibit a variety of star formation physics with multiple phase components in low metallicity, gas rich environments. The 10 K, 100 K, and 104 K regimes are well explored. We are imaging LMC and SMC star forming regions in 2.12 micron H2 emission which arises in the 1000 K transition zone of molecular clouds. This is an NOAO Survey program using the widefield IR camera NEWFIRM on the CTIO 4-m Blanco telescope during its limited southern deployment. The data set will have immediate morphological applications and will provide target selection for followup infrared spectroscopy. We will provide a public archive of fully calibrated images with no proprietary period. NOAO is operated by the Association of Universities for Research in Astronomy, under cooperative agreement with the National Science Foundation.

Dynamical evolution of star-forming regions - II. Basic kinematics

Science.gov (United States)

Parker, Richard J.; Wright, Nicholas J.

2016-04-01

We follow the dynamical evolution of young star-forming regions with a wide range of initial conditions and examine how the radial velocity dispersion, σ, evolves over time. We compare this velocity dispersion to the theoretically expected value for the velocity dispersion if a region were in virial equilibrium, σvir and thus assess the virial state (σ/σvir) of these systems. We find that in regions that are initially subvirial, or in global virial equilibrium but subvirial on local scales, the system relaxes to virial equilibrium within several million years, or roughly 25-50 crossing times, according to the measured virial ratio. However, the measured velocity dispersion, σ, appears to be a bad diagnostic of the current virial state of these systems as it suggests that they become supervirial when compared to the velocity dispersion estimated from the virial mass, σvir. We suggest that this discrepancy is caused by the fact that the regions are never fully relaxed, and that the early non-equilibrium evolution is imprinted in the one-dimensional velocity dispersion at these early epochs. If measured early enough (interquartile range (IQR) dispersion, with measures of spatial structure, places stronger constraints on the dynamical history of a region than using the velocity dispersion in isolation.

Close Binaries in the Orion Nebula Cluster: On the Universality of Stellar Multiplicity and the Origin of Field Stars

Science.gov (United States)

Duchene, Gaspard; Lacour, Sylvestre; Moraux, Estelle; Bouvier, Jerome; Goodwin, Simon

2018-01-01

While stellar multiplicity is an ubiquitous outcome of star formation, there is a clear dichotomy between the multiplicity properties of young (~1 Myr-old) stellar clusters, like the ONC, which host a mostly field-like population of visual binaries, and those of equally young sparse populations, like the Taurus-Auriga region, which host twice as many stellar companions. Two distinct scenarios can account for this observation: one in which different star-forming regions form different number of stars, and one in which multiplicity properties are universal at birth but where internal cluster dynamics destroy many wide binaries. To solve this ambiguity, one must probe binaries that are sufficiently close so as not to be destroyed through interactions with other cluster members. To this end, we have conducted a survey for 10-100 au binaries in the ONC using the aperture masking technique with the VLT adaptive optics system. Among our sample of the 42 ONC members, we discovered 13 companions in this range of projected separations. This is consistent with the companion frequency observed in the Taurus population and twice as high as that observed among field stars. This survey thus strongly supports the idea that stellar multiplicity is characterized by near-universal initial properties that can later be dynamically altered. On the other hand, this exacerbates the question of the origin of field stars, since only clusters much denser than the ONC can effectively destroyed binaries closer than 100 au.

Diffuse Matter from Star Forming Regions to Active Galaxies A Volume Honouring John Dyson

CERN Document Server

Hartquist, T W

2006-01-01

John Dyson has contributed to the study of the hydrodynamic processes that govern a wide variety of astrophysical sources which he has helped explain. In this volume dedicated to him, introductory reviews to a number of the key processes and to the sources themselves are given by leading experts. The mechanisms in which the multi-component natures of media affect their dynamics receive particular attention, but the roles of hydromagnetic effects are also highlighted. The importance of cosmic ray moderation and mass transfer between different thermal phases for cosmic ray moderation and mass transfer between different thermal phases for the evolution of flows are amongst the topics treated. The main types of regions considered include those where stars form, the circumstellar environments of evolved stars, the larger scale interstellar structures caused by the mass loss of stars, and those where the lines of AGNs form. The reviews complement one another and together provide a coherent introduction to the astro...

THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

2012-01-01

Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction (∼60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of ∼2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last ∼5 Myr. The central cluster NGC 602 was formed first

A WISE survey of circumstellar disks in Taurus

International Nuclear Information System (INIS)

Esplin, T. L.; Luhman, K. L.; Mamajek, E. E.

2014-01-01

We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M ☉ ).

A WISE survey of circumstellar disks in Taurus

Energy Technology Data Exchange (ETDEWEB)

Esplin, T. L.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Mamajek, E. E., E-mail: taran.esplin@psu.edu [Department of Physics and Astronomy, The University of Rochester, Rochester, NY 14627 (United States)

2014-04-01

We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M {sub ☉}).

Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

International Nuclear Information System (INIS)

Yu, Jincheng; Puzia, Thomas H.; Lin, Congping; Zhang, Yiwei

2017-01-01

We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

Energy Technology Data Exchange (ETDEWEB)

Yu, Jincheng; Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Católica, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22 (Chile); Lin, Congping; Zhang, Yiwei, E-mail: yujc.astro@gmail.com, E-mail: tpuzia@gmail.com, E-mail: congpinglin@gmail.com, E-mail: yiweizhang831129@gmail.com [Center for Mathematical Science, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 4370074 (China)

2017-05-10

We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

SMA and CARMA observations of young brown dwarfs in ρ Ophiuchi and Taurus

Directory of Open Access Journals (Sweden)

Lee C.-F.

2011-07-01

Full Text Available Molecular outflows provide vital information about the earliest stages in the birth of stars, studying the molecular outflow properties is therefore crucial for understanding how stars form. Brown dwarfs with masses between that of stars and planets are not massive enough to maintain stable hydrogen-burning fusion reactions during most of their lifetime. Their origins are subject to much debate in recent literature because their masses are far below the typical mass where core collapse is expected to occur. Based on Submillimeter Array (SMA and Combined Array for Research in Millimeter-wave Astronomy (CARMA observations, we present the first detections of bipolar molecular outflows from young brown dwarfs in ρ Ophiuchi and Taurus. Our results demonstrate that the bipolar molecular outflow operates down to brown dwarf masses, occurring in brown dwarfs as a scaled-down version of the universal process seen in young low-mass stars. This demonstrates that brown dwarfs and low-mass stars likely share the same formation mechanism.

Atomic hydrogen in the Orion star-forming region

International Nuclear Information System (INIS)

Chromey, F.R.; Elmegreen, B.G.; Elmegreen, D.M.

1989-01-01

A large-scale survey of atomic hydrogen in Orion reveals low-density material with a total mass comparable to that in dense molecular clouds. The atomic gas is sufficiently dense that it can shield the molecular material from photodissociative radiation and provide a pressure link to the low-density intercloud medium. An excess of H I emission comes from photodissociation fronts near the bright stars and from a giant shell in the Orion Belt region. This shell may have caused the apparent bifurcation between the Orion A and B clouds, and the associated pressures may have induced peculiar motions and star formation in NGC 2023 and 2024. 49 refs

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

Energy Technology Data Exchange (ETDEWEB)

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

2017-04-20

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

Infrared spectroscopy of dust in the Taurus dark clouds: solid carbon monoxide

International Nuclear Information System (INIS)

Whittet, D.C.B.; McFadzean, A.D.

1989-01-01

Spectra centred on the spectral feature of solid CO at 4.67 μm wavelength are presented for eight stars in or behind the quiescent dark cloud complex in Taurus. The solid CO profile is dominated by a sharp component centred at 4.673 μm (2140 cm -1 ). As in previous observations of the feature, asymmetry in the profile is consistent with the presence of a weaker, somewhat broader, overlapping component centred at ∼ 4.682 μm (2136 cm -1 ). New and previously published data for Taurus stars are combined to study the correlation of the peak optical depth in the CO feature with visual extinction and with the depth of the water-ice feature at 3.0 μm. (author)

Mid-Infrared Observations of Possible Intergalactic Star Forming Regions in the Leo Ring

Science.gov (United States)

Giroux, Mark; Smith, B.; Struck, C.

2011-05-01

Within the Leo group of galaxies lies a gigantic loop of intergalactic gas known as the Leo Ring. Not clearly associated with any particular galaxy, its origin remains uncertain. It may be a primordial intergalactic cloud alternatively, it may be a collision ring, or have a tidal origin. Combining archival Spitzer images of this structure with published UV and optical data, we investigate the mid-infrared properties of possible knots of star formation in the ring. These sources are very faint in the mid-infrared compared to star forming regions in the tidal features of interacting galaxies. This suggests they are either deficient in dust, or they may not be associated with the ring.

A Study of THT Cold Cores Population in the Star-Forming Region in Serpens

Science.gov (United States)

Fiorellino, Eleonora

2017-11-01

The purpose of this work is to produce the Core Mass Function (CMF) of the Serpens star-forming region and confront it with the Initial Mass Function (IMF), the statistical distribution of initial star mass. As Testi & Sergent (1998) discovered, the power-law index of the slope of the CMF is very close to the one of the Salpeter's IMF (Salpeter, 1955): dN/dM / M2.35. This strongly suggests that the stellar IMF results from the fragmentation process in turbulent cloud cores rather than from stellar accretion mechanisms and gives a huge contribute to undestanding the star formation. For this work, we started from the data delivered by the European satellite Herschel and produced the maps of the Serpens with Unimap code (Piazzo et al, 2015). Hence we obtained a core catalogue with two different softwares getsources (Men'shchikov et al, 2012) and CuTEx (Molinari et al, 2011) and we eliminated from it any source that is not a core. A full discussion of the cores physical propreties as well as the whole region is under preparation.

Anomalou OH emission in galactic star-forming regions - A clue to the megamaser phenomenon?

International Nuclear Information System (INIS)

Mirabel, I.F.; Rodriguez, L.F.; Ruiz, A.

1989-01-01

The detection of spatially extended, anomalous OH emission in galactic star-forming regions is reported. This OH emission is similar to, although much weaker than, that produced by extragalactic megamasers. This new type of galactic emission may provide clues to elucidate the nature of the extragalactic OH megamaser phenomenon observed in luminous IR galaxies. 10 refs

Molecular Diagnostics of the Interstellar Medium and Star Forming Regions

Science.gov (United States)

Hartquist, T. W.; Dalgarno, A.

1996-03-01

Selected examples of the use of observationally inferred molecular level populations and chemical compositions in the diagnosis of interstellar sources and processes important in them (and in other diffuse astrophysical sources) are given. The sources considered include the interclump medium of a giant molecular cloud, dark cores which are the progenitors of star formation, material responding to recent star formation and which may form further stars, and stellar ejecta (including those of supernovae) about to merge with the interstellar medium. The measurement of the microwave background, mixing of material between different nuclear burning zones in evolved stars and turbulent boundary layers (which are present in and influence the structures and evolution of all diffuse astrophysical sources) are treated.

Zeeman effect in sulfur monoxide. A tool to probe magnetic fields in star forming regions

Science.gov (United States)

Cazzoli, Gabriele; Lattanzi, Valerio; Coriani, Sonia; Gauss, Jürgen; Codella, Claudio; Ramos, Andrés Asensio; Cernicharo, José; Puzzarini, Cristina

2017-09-01

Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN. Aims: We decided to investigate the suitability of sulfur monoxide (SO), which is one of the most abundant species in star forming regions, for probing the intensity of magnetic fields via the Zeeman effect. Methods: We investigated the Zeeman effect for several rotational transitions of SO in the (sub-)mm spectral regions by using a frequency-modulated, computer-controlled spectrometer, and by applying a magnetic field parallel to the radiation propagation (I.e., perpendicular to the oscillating magnetic field of the radiation). To support the experimental determination of the g factors of SO, a systematic quantum-chemical investigation of these parameters for both SO and O2 has been carried out. Results: An effective experimental-computational strategy for providing accurate g factors as well as for identifying the rotational transitions showing the strongest Zeeman effect has been presented. Revised g factors have been obtained from a large number of SO rotational transitions between 86 and 389 GHz. In particular, the rotational transitions showing the largest Zeeman shifts are: N,J = 2, 2 ← 1, 1 (86.1 GHz), N,J = 4, 3 ← 3, 2 (159.0 GHz), N,J = 1, 1 ← 0, 1 (286.3 GHz), N,J = 2, 2 ← 1, 2 (309.5 GHz), and N,J = 2, 1 ← 1, 0 (329.4 GHz). Our investigation supports SO as a good candidate for probing magnetic fields in high-density star forming regions. The complete list of measured Zeeman components is only available at the CDS via anonymous ftp to http

Water in star-forming regions with Herschel (WISH) : IV. A survey of low-J H2O line profiles toward high-mass protostars

NARCIS (Netherlands)

van der Tak, F. F. S.; Chavarria, L.; Herpin, F.; Wyrowski, F.; Walmsley, C. M.; van Dishoeck, E. F.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Hogerheijde, M. R.; Johnstone, D.; Kristensen, L. E.; Liseau, R.; Nisini, B.; Tafalla, M.

Context. Water is a key constituent of star-forming matter, but the origin of its line emission and absorption during high-mass star formation is not well understood. Aims. We study the velocity profiles of low-excitation H2O lines toward 19 high-mass star-forming regions and search for trends with

Interstellar extinction in the Taurus dark clouds

International Nuclear Information System (INIS)

Meistas, E.; Straizys, V.

1981-01-01

The results of photoelectric photometry of 89 stars in the Vilnius seven-color system in the area of the Taurus dark clouds with corrdinates (1950) 4sup(h)16sup(m)-4sup(h)33sup(m), +16 0 -+20 0 are presented. Photometric spectral types, absolute magnitude, color excesses, interstellar extinctions and distances of the stars are determined. The distance of the dark nebula is found to be 140 pc and is in a good agreement with the distance determined for the dark nebula Khavtassi 286, 278. The average extinction Asub(v) in the investigated area is of the order of 1.4. (author)

New Insights into the Nature of Transition Disks from a Complete Disk Survey of the Lupus Star-forming Region

Science.gov (United States)

van der Marel, Nienke; Williams, Jonathan P.; Ansdell, M.; Manara, Carlo F.; Miotello, Anna; Tazzari, Marco; Testi, Leonardo; Hogerheijde, Michiel; Bruderer, Simon; van Terwisga, Sierk E.; van Dishoeck, Ewine F.

2018-02-01

Transition disks with large dust cavities around young stars are promising targets for studying planet formation. Previous studies have revealed the presence of gas cavities inside the dust cavities, hinting at recently formed, giant planets. However, many of these studies are biased toward the brightest disks in the nearby star-forming regions, and it is not possible to derive reliable statistics that can be compared with exoplanet populations. We present the analysis of 11 transition disks with large cavities (≥20 au radius) from a complete disk survey of the Lupus star-forming region, using ALMA Band 7 observations at 0.″3 (22–30 au radius) resolution of the 345 GHz continuum, 13CO and C18O 3–2 observations, and the spectral energy distribution of each source. Gas and dust surface density profiles are derived using the physical–chemical modeling code DALI. This is the first study of transition disks of large cavities within a complete disk survey within a star-forming region. The dust cavity sizes range from 20 to 90 au radius, and in three cases, a gas cavity is resolved as well. The deep drops in gas density and large dust cavity sizes are consistent with clearing by giant planets. The fraction of transition disks with large cavities in Lupus is ≳ 11 % , which is inconsistent with exoplanet population studies of giant planets at wide orbits. Furthermore, we present a hypothesis of an evolutionary path for large massive disks evolving into transition disks with large cavities.

Star-forming Filament Models

International Nuclear Information System (INIS)

Myers, Philip C.

2017-01-01

New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density ( N -pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

Star-forming Filament Models

Energy Technology Data Exchange (ETDEWEB)

Myers, Philip C., E-mail: pmyers@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2017-03-20

New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density ( N -pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

Energy Technology Data Exchange (ETDEWEB)

Montes, V. A.; Hofner, P.; Anderson, C.; Rosero, V. [Physics Department, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801 (United States)

2015-08-15

We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.

Radio continuum interferometry of dark clouds: A search for newly formed HII regions

International Nuclear Information System (INIS)

Gilmore, W.S.

1978-01-01

A search for compact HII regions embedded in dark clouds has been carried out in an effort to study local massive star formation. Approximately 20% of the total area of opaque dark cloud material in the sky with Av greater than or equal to 6 mag was surveyed with the NRAO three-element interferometer at 2695 MHz, and at least 5% more was surveyed with the NRAO 300-foot telescope at 4750 MHz. The regions surveyed include the dark cloud complexes in Perseus, Taurus, Orion, and Ophiuchus, as well as several smaller cloud complexes and individual clouds. No hidden compact HII regions embedded inside dark clouds were detected with certainty in the radio continuum. However, eleven HII regions with associated visible emission and eighteen other possible HII regions were detected. Five infrared sources thought to have the luminosities of early B stars were not detected in the radio continuum. These five sources showed high correlation with the presence of CO self-absorption, CO emission over a wide range of velocities, and type I OH masers, but an absence of coincident visible nebulosity and detectable radio continuum emission. Therefore, it is suggested that they represent an earlier evolutionary stage than those HII region detected in the radio continuum. This first evolutionary state marks the presence of ''pre-emergent'' (with respect to the molecular cloud) cocoon stars. HII regions in the second evolutionary state are marked by the presence of detectable radio continuum emission, i.e., they are stronger than 10 mJy at 2695 MHz. They have associated visible nebulosity, are relatively large, and appear to be located at the edges of molecular clouds. These are designated as ''emergent edge'' HII regions. The fact that many young HII regions are edge HII regions implies that massive stars are born near the edges of clouds, a phenomenon previously suggested by several other investigators

Stars Form Surprisingly Close to Milky Way's Black Hole

Science.gov (United States)

2005-10-01

million low mass, sun-like stars in and around the ring, whereas in the disk model, the number of low mass stars could be much less. Nayakshin and his coauthor, Rashid Sunyaev of the Max Plank Institute for Physics in Garching, Germany, used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found that the Sgr A* star cluster contains only about 10,000 low mass stars, thereby ruling out the migration model. "We can now say that the stars around Sgr A* were not deposited there by some passing star cluster, rather they were born there," said Sunyaev . "There have been theories that this was possible, but this is the first real evidence. Many scientists are going to be very surprised by these results." Because the Galactic Center is shrouded in dust and gas, it has not been possible to look for the low-mass stars in optical observations. In contrast, X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars. Scenario Dismissed by Chandra Results Scenario Dismissed by Chandra Results "In one of the most inhospitable places in our Galaxy, stars have prevailed," said Nayakshin. "It appears that star formation is much more tenacious than we previously believed." The results suggest that the "rules" of star formation change when stars form in the disk of a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes. And, when these massive stars explode as supernovae, they will "fertilize" the region with heavy elements such as oxygen. This may explain the large amounts of such elements observed in the disks of young supermassive black holes. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for

[O I] disk emission in the Taurus star-forming region

NARCIS (Netherlands)

Aresu, G.; Kamp, I.; Meijerink, R.; Spaans, M.; Vicente, S.; Podio, L.; Woitke, P.; Menard, F.; Thi, W.-F.; Güdel, M.; Liebhart, A.

2014-01-01

Context. The structure of protoplanetary disks is thought to be linked to the temperature and chemistry of their dust and gas. Whether the disk is flat or flaring depends on the amount of radiation that it absorbs at a given radius and on the efficiency with which this is converted into thermal

Detection of warm water vapour in Taurus protoplanetary discs by Herschel

NARCIS (Netherlands)

Riviere-Marichalar, P.; Menard, F.; Thi, W. F.; Kamp, I.; Montesinos, B.; Meeus, G.; Woitke, P.; Howard, C.; Sandell, G.; Podio, L.; Dent, W. R. F.; Mendigutia, I.; Pinte, C.; White, G. J.; Barrado, D.

Line spectra of 68 Taurus T Tauri stars were obtained with the Herschel-PACS (Photodetector Array Camera and Spectrometer) instrument as part of the GASPS (GAS evolution in Protoplanetary Systems) survey of protoplanetary discs. A careful examination of the linescans centred on the [OI] 63.18 mu m

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

EXTERNALLY HEATED PROTOSTELLAR CORES IN THE OPHIUCHUS STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Lindberg, Johan E.; Charnley, Steven B.; Cordiner, Martin A. [NASA Goddard Space Flight Center, Astrochemistry Laboratory, Mail Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Jørgensen, Jes K.; Bjerkeli, Per, E-mail: johan.lindberg@nasa.gov [Centre for Star and Planet Formation, Niels Bohr Institute and Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K (Denmark)

2017-01-20

We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H{sub 2}CO and c -C{sub 3}H{sub 2} rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H{sub 2}CO temperatures range between 16 K and 124 K, with the highest H{sub 2}CO temperatures toward the hot corino source IRAS 16293-2422 (69–124 K) and the sources in the ρ Oph A cloud (23–49 K) located close to the luminous Herbig Be star S1, which externally irradiates the ρ Oph A cores. On the other hand, the c -C{sub 3}H{sub 2} rotational temperature is consistently low (7–17 K) in all sources. Our results indicate that the c -C{sub 3}H{sub 2} emission is primarily tracing more shielded parts of the envelope whereas the H{sub 2}CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS 16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.

CHEMICAL EVOLUTION IN HIGH-MASS STAR-FORMING REGIONS: RESULTS FROM THE MALT90 SURVEY

Energy Technology Data Exchange (ETDEWEB)

Hoq, Sadia; Jackson, James M.; Foster, Jonathan B.; Sanhueza, Patricio; Claysmith, Christopher [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States); Guzmán, Andrés [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Whitaker, J. Scott [Physics Department, Boston University, Boston, MA 02215 (United States); Rathborne, Jill M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Epping, NSW (Australia); Vasyunina, Tatiana; Vasyunin, Anton, E-mail: shoq@bu.edu, E-mail: jackson@bu.edu, E-mail: patricio@bu.edu, E-mail: claysmit@bu.edu, E-mail: jonathan.b.foster@yale.edu, E-mail: aguzmanf@cfa.harvard.edu, E-mail: scott@bu.edu, E-mail: rathborne@csiro.au, E-mail: tv3h@virginia.edu, E-mail: aiv3f@virginia.edu [Department of Chemistry, University of Virginia, Charlottesville, VA 22904 (United States)

2013-11-10

The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H{sub 2} column densities for each clump from Herschel/Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N{sub 2}H{sup +}, HCO{sup +}, HCN and HNC (1-0) lines, and derive the column densities and abundances of N{sub 2}H{sup +} and HCO{sup +}. The Herschel dust temperatures increase as a function of the IR-based Spitzer evolutionary classification scheme, with the youngest clumps being the coldest, which gives confidence that this classification method provides a reliable way to assign evolutionary stages to clumps. Both N{sub 2}H{sup +} and HCO{sup +} abundances increase as a function of evolutionary stage, whereas the N{sub 2}H{sup +} (1-0) to HCO{sup +} (1-0) integrated intensity ratios show no discernable trend. The HCN (1-0) to HNC(1-0) integrated intensity ratios show marginal evidence of an increase as the clumps evolve.

The Tarantula Nebula as a template for extragalactic star forming regions from VLT/MUSE and HST/STIS

Science.gov (United States)

Crowther, Paul A.; Caballero-Nieves, Saida M.; Castro, Norberto; Evans, Christopher J.

2017-11-01

We present VLT/MUSE observations of NGC 2070, the dominant ionizing nebula of 30 Doradus in the LMC, plus HST/STIS spectroscopy of its central star cluster R136. Integral Field Spectroscopy (MUSE) and pseudo IFS (STIS) together provides a complete census of all massive stars within the central 30×30 parsec2 of the Tarantula. We discuss the integrated far-UV spectrum of R136, of particular interest for UV studies of young extragalactic star clusters. Strong He iiλ1640 emission at very early ages (1-2 Myr) from very massive stars cannot be reproduced by current population synthesis models, even those incorporating binary evolution and very massive stars. A nebular analysis of the integrated MUSE dataset implies an age of ~4.5 Myr for NGC 2070. Wolf-Rayet features provide alternative age diagnostics, with the primary contribution to the integrated Wolf-Rayet bumps arising from R140 rather than the more numerous H-rich WN stars in R136. Caution should be used when interpreting spatially extended observations of extragalactic star-forming regions.

CHEMICAL SEGREGATION TOWARD MASSIVE HOT CORES: THE AFGL2591 STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Jimenez-Serra, I.; Zhang, Q. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Viti, S. [Department of Physics and Astronomy, University College London, Gower Place, London WC1E 6BT (United Kingdom); Martin-Pintado, J. [Centro de Astrobiologia (CSIC/INTA), Ctra. de Torrejon a Ajalvir km 4, E-28850 Torrejon de Ardoz, Madrid (Spain); De Wit, W.-J., E-mail: ijimenez-serra@cfa.harvard.edu, E-mail: qzhang@cfa.harvard.edu, E-mail: sv@star.ucl.ac.uk, E-mail: jmartin@cab.inta-csic.es, E-mail: wdewit@eso.org [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile)

2012-07-01

We present high angular resolution observations (0.''5 Multiplication-Sign 0.''3) carried out with the Submillimeter Array (SMA) toward the AFGL2591 high-mass star-forming region. Our SMA images reveal a clear chemical segregation within the AFGL2591 VLA 3 hot core, where different molecular species (Types I, II, and III) appear distributed in three concentric shells. This is the first time that such a chemical segregation is ever reported at linear scales {<=}3000 AU within a hot core. While Type I species (H{sub 2}S and {sup 13}CS) peak at the AFGL2591 VLA 3 protostar, Type II molecules (HC{sub 3}N, OCS, SO, and SO{sub 2}) show a double-peaked structure circumventing the continuum peak. Type III species, represented by CH{sub 3}OH, form a ring-like structure surrounding the continuum emission. The excitation temperatures of SO{sub 2}, HC{sub 3}N, and CH{sub 3}OH (185 {+-} 11 K, 150 {+-} 20 K, and 124 {+-} 12 K, respectively) show a temperature gradient within the AFGL2591 VLA 3 envelope, consistent with previous observations and modeling of the source. By combining the H{sub 2}S, SO{sub 2}, and CH{sub 3}OH images, representative of the three concentric shells, we find that the global kinematics of the molecular gas follow Keplerian-like rotation around a 40 M{sub Sun} star. The chemical segregation observed toward AFGL2591 VLA 3 is explained by the combination of molecular UV photodissociation and a high-temperature ({approx}1000 K) gas-phase chemistry within the low extinction innermost region in the AFGL2591 VLA 3 hot core.

The embedded young stars in the Taurus-Auriga molecular cloud. II - Models for scattered light images

Science.gov (United States)

Kenyon, Scott J.; Whitney, Barbara A.; Gomez, Mercedes; Hartmann, Lee

1993-01-01

We describe NIR imaging observations of embedded young stars in the Taurus-Auriga molecular cloud. We find a large range in J-K and H-K colors for these class I sources. The bluest objects have colors similar to the reddest T Tauri stars in the cloud; redder objects lie slightly above the reddening line for standard ISM dust and have apparent K extinctions of up to 5 mag. Most of these sources also show extended NIR emission on scales of 10-20 arcsec which corresponds to linear sizes of 1500-3000 AU. The NIR colors and nebular morphologies for this sample and the magnitude of linear polarization in several sources suggest scattered light produces most of the NIR emission in these objects. We present modeling results that suggest mass infall rates that agree with predictions for cold clouds and are generally consistent with rates estimated from radiative equilibrium models. For reasonable dust grain parameters, the range of colors and extinctions require flattened density distributions with polar cavities evacuated by bipolar outflows. These results support the idea that infall and outflow occur simultaneously in deeply embedded bipolar outflow sources. The data also indicate fairly large centrifugal radii and large inclinations to the rotational axis for a typical source.

Complex organic molecules toward low-mass and high-mass star forming regions

Science.gov (United States)

Favre, C.; Ceccarelli, C.; Lefloch, B.; Bergin, E.; Carvajal, M.; Brouillet, N.; Despois, D.; Jørgensen, J.; Kleiner, I.

2016-12-01

One of the most important questions in molecular astrophysics is how, when, and where complex organic molecules, COMs (≥ 6 atoms) are formed. In the Interstellar-Earth connection context, could this have a bearing on the origin of life on Earth? Formation mechanisms of COMs, which include potentially prebiotic molecules, are still debated and may include grain-mantle and/or gas-phase chemistry. Understanding the mechanisms that lead to the interstellar molecular complexification, along with the involved physicochemical processes, is mandatory to answer the above questions. In that context, active researches are ongoing in theory, laboratory experiment, chemical modeling and observations. Thanks to recent progress in radioastronomy instrumentation for both single-dish and millimeter array (e.g. Herschel, NOEMA, ALMA), new results have been obtained. I will review some notable results on the detection of COMs, including prebiotic molecules, towards star forming regions.

Do All O Stars Form in Star Clusters?

Science.gov (United States)

Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

The Star Formation in Radio Survey: Jansky Very Large Array 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-forming Regions

Science.gov (United States)

Murphy, E. J.; Dong, D.; Momjian, E.; Linden, S.; Kennicutt, R. C., Jr.; Meier, D. S.; Schinnerer, E.; Turner, J. L.

2018-02-01

We present 33 GHz imaging for 112 pointings toward galaxy nuclei and extranuclear star-forming regions at ≈2″ resolution using the Karl G. Jansky Very Large Array (VLA) as part of the Star Formation in Radio Survey. A comparison with 33 GHz Robert C. Byrd Green Bank Telescope single-dish observations indicates that the interferometric VLA observations recover 78% ± 4% of the total flux density over 25″ regions (≈kpc scales) among all fields. On these scales, the emission being resolved out is most likely diffuse non-thermal synchrotron emission. Consequently, on the ≈30–300 pc scales sampled by our VLA observations, the bulk of the 33 GHz emission is recovered and primarily powered by free–free emission from discrete H II regions, making it an excellent tracer of massive star formation. Of the 225 discrete regions used for aperture photometry, 162 are extranuclear (i.e., having galactocentric radii r G ≥ 250 pc) and detected at >3σ significance at 33 GHz and in Hα. Assuming a typical 33 GHz thermal fraction of 90%, the ratio of optically-thin 33 GHz to uncorrected Hα star formation rates indicates a median extinction value on ≈30–300 pc scales of A Hα ≈ 1.26 ± 0.09 mag, with an associated median absolute deviation of 0.87 mag. We find that 10% of these sources are “highly embedded” (i.e., A Hα ≳ 3.3 mag), suggesting that on average, H II regions remain embedded for ≲1 Myr. Finally, we find the median 33 GHz continuum-to-Hα line flux ratio to be statistically larger within r G < 250 pc relative to the outer disk regions by a factor of 1.82 ± 0.39, while the ratio of 33 GHz to 24 μm flux densities is lower by a factor of 0.45 ± 0.08, which may suggest increased extinction in the central regions.

Herschel/HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region

DEFF Research Database (Denmark)

Yildiz, U. A.; van Dishoeck, E. F.; Kristensen, L. E.

2010-01-01

Herschel/HIFI observations of high-J lines (up to Ju = 10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved......Herschel/HIFI observations of high-J lines (up to Ju = 10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally....... Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia...... and with important participation from NASA.Appendices and acknowledgements (pages 5 to 7) are only available in electronic form at http://www.aanda.org...

Overlapping Open Clusters NGC 1750 and NGC 1758 behind the Taurus Dark Clouds. II. CCD Photometry in the Vilnius System

Directory of Open Access Journals (Sweden)

Straižys V.

2003-09-01

Full Text Available Seven-color photometry in the Vilnius system has been obtained for 420 stars down to V = 16 mag in the area containing the overlapping open clusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosity classes, color excesses, interstellar extinctions and distances are given for 287 stars. The classification of stars is based on their reddening-free Q-parameters. 18 stars observed photoelectrically were used as standards. The extinction vs. distance diagram exhibits the presence of one dust cloud at a distance of 175 pc which almost coincides with a distance of other dust clouds in the Taurus complex. The clusters NGC 1750 and NGC 1758 are found to be at the same distance of ~760 pc and may penetrate each other. Their interstellar extinction AV is 1.06 mag which corresponds to EB-V = 0.34 mag.

Effect of monensin withdrawal on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay

Science.gov (United States)

Effects of monensin withdrawal and cattle subspecies on the utilization of bermudagrass hay (14.3% CP, 72.3% NDF, and 36.9% ADF) were evaluated using ruminally cannulated steers (5 Bos Taurus indicus [BI] and 5 Bos taurus taurus [BT]). Subspecies were concurrently subjected to a 2-period, 2-treatme...

Insights from Synthetic Star-forming Regions. I. Reliable Mock Observations from SPH Simulations

Energy Technology Data Exchange (ETDEWEB)

Koepferl, Christine M.; Robitaille, Thomas P.; Biscani, Francesco [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Dale, James E., E-mail: koepferl@usm.lmu.de [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany)

2017-11-01

Through synthetic observations of a hydrodynamical simulation of an evolving star-forming region, we assess how the choice of observational techniques affects the measurements of properties that trace star formation. Testing and calibrating observational measurements requires synthetic observations that are as realistic as possible. In this part of the series (Paper I), we explore different techniques for mapping the distributions of densities and temperatures from the particle-based simulations onto a Voronoi mesh suitable for radiative transfer and consequently explore their accuracy. We further test different ways to set up the radiative transfer in order to produce realistic synthetic observations. We give a detailed description of all methods and ultimately recommend techniques. We have found that the flux around 20 μ m is strongly overestimated when blindly coupling the dust radiative transfer temperature with the hydrodynamical gas temperature. We find that when instead assuming a constant background dust temperature in addition to the radiative transfer heating, the recovered flux is consistent with actual observations. We present around 5800 realistic synthetic observations for Spitzer and Herschel bands, at different evolutionary time-steps, distances, and orientations. In the upcoming papers of this series (Papers II, III, and IV), we will test and calibrate measurements of the star formation rate, gas mass, and the star formation efficiency using our realistic synthetic observations.

Effect of monensin inclusion on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay

Science.gov (United States)

Effects of monensin inclusion and cattle subspecies on utilization of bermudagrass hay (13.7% CP, 77.3% NDF, and 38.8% ADF) were evaluated using ruminally cannulated steers (5 Bos taurus indicus [BI] and 5 Bos taurus taurus [BT]; 398 kg BW). Subspecies were concurrently subjected to a 2-period, 2-t...

Characterizing filaments in regions of high-mass star formation: High-resolution submilimeter imaging of the massive star-forming complex NGC 6334 with ArTéMiS

Science.gov (United States)

André, Ph.; Revéret, V.; Könyves, V.; Arzoumanian, D.; Tigé, J.; Gallais, P.; Roussel, H.; Le Pennec, J.; Rodriguez, L.; Doumayrou, E.; Dubreuil, D.; Lortholary, M.; Martignac, J.; Talvard, M.; Delisle, C.; Visticot, F.; Dumaye, L.; De Breuck, C.; Shimajiri, Y.; Motte, F.; Bontemps, S.; Hennemann, M.; Zavagno, A.; Russeil, D.; Schneider, N.; Palmeirim, P.; Peretto, N.; Hill, T.; Minier, V.; Roy, A.; Rygl, K. L. J.

2016-07-01

Context. Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of ~0.1 pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation. Aims: In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350 μm. Methods: We used the large-format bolometer camera ArTéMiS on the APEX telescope and combined the high-resolution ArTéMiS data at 350 μm with Herschel/HOBYS data at 70-500 μm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8″ or Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.The final ArTéMiS+SPIRE 350 μm map (Fig. 1b) is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A54

Abundances and Excitation of H2, H3+ & CO in Star-Forming Regions

Science.gov (United States)

Kulesa, Craig A.

Although most of the 123 reported interstellar molecules to date have been detected through millimeter-wave emission-line spectroscopy, this technique is inapplicable to non-polar molecules like H2 and H3+, which are central to our understanding of interstellar chemistry. Thus high resolution infrared absorption-line spectroscopy bears an important role in interstellar studies: chemically important non-polar molecules can be observed, and their abundances and excitation conditions can be referred to the same ``pencil beam'' absorbing column. In particular, through a weak quadrupole absorption line spectrum at near-infrared wavelengths, the abundance of cold H2 in dark molecular clouds and star forming regions can now be accurately measured and compared along the same ``pencil beam'' line of sight with the abundance of its most commonly cited surrogate, CO, and its rare isotopomers. Also detected via infrared line absorption is the pivotal molecular ion H3+, whose abundance provides the most direct measurement of the cosmic ray ionization rate in dark molecular clouds, a process that initiates the formation of many other observed molecules there. Our growing sample of H2 and CO detections now includes detailed multi-beam studies of the ρ Ophiuchi molecular cloud and NGC 2024 in Orion. We explore the excitation and degree of ortho- and para-H2 thermalization in dark clouds, variation of the CO abundance over a cloud, and the relation of H2 column density to infrared extinction mapping, far-infrared/submillimeter dust continuum emission, and large scale submillimeter CO, [C I] and HCO+ line emission -- all commonly invoked to indirectly trace H2 during the past 30+ years. For each of the distinct velocity components seen toward some embedded young stellar objects, we are also able to determine the temperature, density, and a CO/H2 abundance ratio, thus unraveling some of the internal structure of a star-forming cloud. H2 and H3+ continue to surprise and delight us

Field O stars: formed in situ or as runaways?

Science.gov (United States)

Gvaramadze, V. V.; Weidner, C.; Kroupa, P.; Pflamm-Altenburg, J.

2012-08-01

A significant fraction of massive stars in the Milky Way and other galaxies are located far from star clusters and star-forming regions. It is known that some of these stars are runaways, i.e. possess high space velocities (determined through the proper motion and/or radial velocity measurements), and therefore most likely were formed in embedded clusters and then ejected into the field because of dynamical few-body interactions or binary-supernova explosions. However, there exists a group of field O stars whose runaway status is difficult to prove via direct proper motion measurements (e.g. in the Magellanic Clouds) or whose (measured) low space velocities and/or young ages appear to be incompatible with their large separation from known star clusters. The existence of this group led some authors to believe that field O stars can form in situ. Since the question of whether or not O stars can form in isolation is of crucial importance for star formation theory, it is important to thoroughly test candidates of such stars in order to improve the theory. In this paper, we examine the runaway status of the best candidates for isolated formation of massive stars in the Milky Way and the Magellanic Clouds by searching for bow shocks around them, by using the new reduction of the Hipparcos data, and by searching for stellar systems from which they could originate within their lifetimes. We show that most of the known O stars thought to have formed in isolation are instead very likely runaways. We show also that the field must contain a population of O stars whose low space velocities and/or young ages are in apparent contradiction to the large separation of these stars from their parent clusters and/or the ages of these clusters. These stars (the descendants of runaway massive binaries) cannot be traced back to their parent clusters and therefore can be mistakenly considered as having formed in situ. We argue also that some field O stars could be detected in optical

YOUNG, ULTRAVIOLET-BRIGHT STARS DOMINATE DUST HEATING IN STAR-FORMING GALAXIES

International Nuclear Information System (INIS)

Law, Ka-Hei; Gordon, Karl D.; Misselt, K. A.

2011-01-01

In star-forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAHs), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region-the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the IR emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star-forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.

THE STRUCTURAL EVOLUTION OF FORMING AND EARLY STAGE STAR CLUSTERS

International Nuclear Information System (INIS)

Jaehnig, Karl O.; Da Rio, Nicola; Tan, Jonathan C.

2015-01-01

We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young (∼1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray Survey and the statistical analysis of the angular dispersion parameter, δ ADP, N . We find statistically significant correlation between δ ADP, N and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters

Observations of HC5N and NH3 in Taurus

International Nuclear Information System (INIS)

Myers, P.C.; Ho, P.T.P.; Benson, P.J.

1979-01-01

Observations of HC 5 N lines toward TMC-2 indicate that it is a small (Lapprox.0.1 pc), dense (napprox.4 x 10 4 cm -3 ), low-mass (Mapprox.1 M/sub sun/) fragment in the Taurus complex, with velocity dispersion at the emission peak only about twice thermal (Δvapprox.0.2 km s -1 ). The HC 5 N emission region in TMC-2 has roughly half the projected area of that in TMC-1, and is more round than filamentary. The HC 5 N and NH 3 emission regions in TMC-2 are coincident, with N (HC 5 N)/N (NH 3 ) approx.0.1. The line width is much smaller than the free-fall width; the deduced values of L, n, and T satisfy the virial-theorem requirement for stable equilibrium. The temporary equilibrium of such fragments may serve to lengthen the time scales for formation of low-mass stars and long-chain molecules

CH+(1-0) and 13CH+(1-0) absorption lines in the direction of massive star-forming regions

NARCIS (Netherlands)

Falgarone, E.; Godard, B.; Cernicharo, J.; de Luca, M.; Gerin, M.; Phillips, T. G.; Black, J. H.; Lis, D. C.; Bell, T. A.; Boulanger, F.; Coutens, A.; Dartois, E.; Encrenaz, P.; Giesen, T.; Goicoechea, J. R.; Goldsmith, P. F.; Gupta, H.; Gry, C.; Hennebelle, P.; Herbst, E.; Hily-Blant, P.; Joblin, C.; Kaźmierczak, M.; Kołos, R.; Krełowski, J.; Martin-Pintado, J.; Monje, R.; Mookerjea, B.; Neufeld, D. A.; Perault, M.; Pearson, J. C.; Persson, C.; Plume, R.; Salez, M.; Schmidt, M.; Sonnentrucker, P.; Stutzki, J.; Teyssier, D.; Vastel, C.; Yu, S.; Menten, K.; Geballe, T. R.; Schlemmer, S.; Shipman, R.; Tielens, A. G. G. M.; Philipp, S.; Cros, A.; Zmuidzinas, J.; Samoska, L. A.; Klein, K.; Lorenzani, A.; Szczerba, R.; Péron, I.; Cais, P.; Gaufre, P.; Ravera, L.; Morris, P.; Lord, S.; Planesas, P.

2010-01-01

We report the detection of the ground-state rotational transition of the methylidyne cation CH+ and its isotopologue 13CH+ toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the

ASSESSING RADIATION PRESSURE AS A FEEDBACK MECHANISM IN STAR-FORMING GALAXIES

International Nuclear Information System (INIS)

Andrews, Brett H.; Thompson, Todd A.

2011-01-01

Radiation pressure from the absorption and scattering of starlight by dust grains may be an important feedback mechanism in regulating star-forming galaxies. We compile data from the literature on star clusters, star-forming subregions, normal star-forming galaxies, and starbursts to assess the importance of radiation pressure on dust as a feedback mechanism, by comparing the luminosity and flux of these systems to their dust Eddington limit. This exercise motivates a novel interpretation of the Schmidt law, the L IR -L' CO correlation, and the L IR -L' HCN correlation. In particular, the linear L IR -L' HCN correlation is a natural prediction of radiation pressure regulated star formation. Overall, we find that the Eddington limit sets a hard upper bound to the luminosity of any star-forming region. Importantly, however, many normal star-forming galaxies have luminosities significantly below the Eddington limit. We explore several explanations for this discrepancy, especially the role of 'intermittency' in normal spirals-the tendency for only a small number of subregions within a galaxy to be actively forming stars at any moment because of the time dependence of the feedback process and the luminosity evolution of the stellar population. If radiation pressure regulates star formation in dense gas, then the gas depletion timescale is 6 Myr, in good agreement with observations of the densest starbursts. Finally, we highlight the importance of observational uncertainties, namely, the dust-to-gas ratio and the CO-to-H 2 and HCN-to-H 2 conversion factors, that must be understood before a definitive assessment of radiation pressure as a feedback mechanism in star-forming galaxies.

A Comparative Observational Study of YSO Classification in Four Small Star-forming H ii Regions

Energy Technology Data Exchange (ETDEWEB)

Kang, Sung-Ju; Choi, Minho; Kang, Miju [Korea Astronomy and Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, Daejeon, 34055 (Korea, Republic of); Kerton, C. R., E-mail: sjkang@kasi.re.kr, E-mail: kerton@iastate.edu [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States)

2017-08-10

We have developed a new young stellar object (YSO) identification and classification technique using mid-infrared Wide-field Infrared Survey Explorer (WISE) data. We compare this new technique with previous WISE YSO detection and classification methods that used either infrared colors or spectral energy distribution slopes. In this study, we also use the new technique to detect and examine the YSO population associated with four small H ii regions: KR 7, KR 81, KR 120, and KR 140. The relatively simple structure of these regions allows us to effectively use both spatial and temporal constraints to identify YSOs that are potential products of triggered star formation. We are also able to identify regions of active star formation around these H ii regions that are clearly not influenced by the H ii region expansion, and thus demonstrate that star formation is on-going on megayear timescales in some of these molecular clouds.

Star-Forming Clouds Feed, Churn, and Fall

Science.gov (United States)

Kohler, Susanna

2017-12-01

Molecular clouds, the birthplaces of stars in galaxies throughout the universe, are complicated and dynamic environments. A new series of simulations has explored how these clouds form, grow, and collapse over their lifetimes.This composite image shows part of the Taurus Molecular Cloud. [ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey]Stellar BirthplacesMolecular clouds form out of the matter in between stars, evolving through constant interactions with their turbulent environments. These interactions taking the form of accretion flows and surface forces, while gravity, turbulence, and magnetic fields interplay are thought to drive the properties and evolution of the clouds.Our understanding of the details of this process, however, remains fuzzy. How does mass accretion affect these clouds as they evolve? What happens when nearby supernova explosions blast the outsides of the clouds? What makes the clouds churn, producing the motion within them that prevents them from collapsing? The answers to these questions can tellus about the gas distributed throughout galaxies, revealing information about the environments in which stars form.A still from the simulation results showing the broader population of molecular clouds that formed in the authors simulations, as well as zoom-in panels of three low-mass clouds tracked in high resolution. [Ibez-Meja et al. 2017]Models of TurbulenceIn a new study led by Juan Ibez-Meja (MPI Garching and Universities of Heidelberg and Cologne in Germany, and American Museum of Natural History), scientists have now explored these questions using a series of three-dimensional simulations of a population of molecular clouds forming and evolving in the turbulent interstellar medium.The simulations take into account a whole host of physics, including the effects of nearby supernova explosions, self-gravitation, magnetic fields, diffuse heating, and radiative cooling. After looking at the behavior of the broader population of

Wind bubbles within H ii regions around slowly moving stars

Science.gov (United States)

Mackey, Jonathan; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert

2015-01-01

Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H ii region RCW 120) show arcs of dust emission around O stars, contained well within the H ii region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H ii regions around massive stars moving through a dense (nH = 3000 cm-3), uniform medium with velocities ranging from 4 to 16 km s-1. The H ii region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H ii regions (we find filling factors of 10-20 per cent), at least for a main sequence star with mass M⋆ ~ 30 M⊙. Furthermore, even for supersonic velocities the wind bow shock does not significantly trap the ionization front. X-ray emission from the wind bubble is soft, faint, and comes mainly from the turbulent mixing layer between the wind bubble and the H ii region. The wind bubble radiates <1 per cent of its energy in X-rays; it loses most of its energy by turbulent mixing with cooler photoionized gas. Comparison of the simulations with the H ii region RCW 120 shows that its dynamical age is ≲0.4 Myr and that stellar motion ≲4 km s-1 is allowed, implying that the ionizing source is unlikely to be a runaway star but more likely formed in situ. The region's youth, and apparent isolation from other O or B stars, makes it very interesting for studies of massive star formation and of initial mass functions. Movies are available in electronic form at http://www.aanda.org

THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

Energy Technology Data Exchange (ETDEWEB)

Myers, Andrew T.; McKee, Christopher F. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Cunningham, Andrew J. [Lawrence Livermore National Laboratory, P.O. Box 808, L-23, Livermore, CA 94550 (United States); Klein, Richard I. [Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720 (United States); Krumholz, Mark R., E-mail: atmyers@berkeley.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2013-04-01

We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

THE COMPACT STAR-FORMING COMPLEX AT THE HEART OF NGC 253

Energy Technology Data Exchange (ETDEWEB)

Davidge, T. J., E-mail: tim.davidge@nrc.ca [Dominion Astrophysical Observatory, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

2016-02-20

We discuss integral field spectra of the compact star-forming complex that is the brightest near-infrared (NIR) source in the central regions of the starburst galaxy NGC 253. The spectra cover the H and K passbands and were recorded with the Gemini NIR Spectrograph during subarcsecond seeing conditions. Absorption features in the spectrum of the star-forming complex are weaker than in the surroundings. An absorption feature is found near 1.78 μm that coincides with the location of a C{sub 2} bandhead. If this feature is due to C{sub 2} then the star-forming complex has been in place for at least a few hundred Myr. Emission lines of Brγ, [Fe ii], and He i 2.06 μm do not track the NIR continuum light. Pockets of star-forming activity that do not have associated concentrations of red supergiants, and so likely have ages <8 Myr, are found along the western edge of the complex, and there is evidence that one such pocket contains a rich population of Wolf–Rayet stars. Unless the star-forming complex is significantly more metal-poor than the surroundings, then a significant fraction of its total mass is in stars with ages <8 Myr. If the present-day star formation rate is maintained then the timescale to double its stellar mass ranges from a few Myr to a few tens of Myr, depending on the contribution made by stars older than ∼8 Myr. If—as suggested by some studies—the star-forming complex is centered on the galaxy’s nucleus, which presumably contains a large population of old and intermediate-age stars, then the nucleus of NGC 253 is currently experiencing a phase of rapid growth in its stellar mass.

Interstellar extinction in the dark Taurus clouds. Pt. 1

International Nuclear Information System (INIS)

Straizys, V.; Meistas, E.

1980-01-01

The results of photoelectric photometry of 74 stars in the Vilnius seven-color system in the area of Taurus dark clouds with coordinates (1950) 4sup(h)20sup(m)-4sup(h)48sup(m)+24 0 .5-+27 0 are presented. Photometric spectral types, absolute magnitudes, color excesses, interstellar extinctions and distances of the stars are determined. The dark cloud Khavtassi 286, 278 and the surrounding absorbing nebulae are found to extend from 140 to 175 pc from the sun. The average interstellar extinction Asub(V) on both sides of the dark cloud is of the order of 1sup(m).5. We find no evidence of the existence of several absorbing clouds situated at various distances. (author)

THE STRUCTURE OF THE STAR-FORMING CLUSTER RCW 38

Energy Technology Data Exchange (ETDEWEB)

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

2011-12-20

We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8 {mu}m) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region. Three subclusters were identified surrounding the central cluster, with massive and variable stars in each subcluster. The central region shows evidence of distinct spatial distributions of the protostars and pre-main-sequence stars. A previously detected IR cluster, DB2001{sub O}bj36, has been established as a subcluster of RCW 38. This suggests that star formation in RCW 38 occurs over a more extended area than previously thought. The gas-to-dust ratio is examined using the X-ray derived hydrogen column density, N{sub H} and the K-band extinction, and found to be consistent with the diffuse interstellar medium, in contrast with Serpens and NGC 1333. We posit that the high photoionizing flux of massive stars in RCW 38 affects the agglomeration of the dust grains.

VERY LARGE ARRAY OH ZEEMAN OBSERVATIONS OF THE STAR-FORMING REGION S88B

Energy Technology Data Exchange (ETDEWEB)

Sarma, A. P.; Eftimova, M. [Physics Department, DePaul University, 2219 N. Kenmore Ave., Byrne Hall 211, Chicago, IL 60614 (United States); Brogan, C. L. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Troland, T. H., E-mail: asarma@depaul.edu [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States)

2013-04-10

We present observations of the Zeeman effect in OH thermal absorption main lines at 1665 and 1667 MHz taken with the Very Large Array toward the star-forming region S88B. The OH absorption profiles toward this source are complicated, and contain several blended components toward a number of positions. Almost all of the OH absorbing gas is located in the eastern parts of S88B, toward the compact continuum source S88B-2 and the eastern parts of the extended continuum source S88B-1. The ratio of 1665/1667 MHz OH line intensities indicates the gas is likely highly clumped, in agreement with other molecular emission line observations in the literature. S88-B appears to present a similar geometry to the well-known star-forming region M17, in that there is an edge-on eastward progression from ionized to molecular gas. The detected magnetic fields appear to mirror this eastward transition; we detected line-of-sight magnetic fields ranging from 90 to 400 {mu}G, with the lowest values of the field to the southwest of the S88B-1 continuum peak, and the highest values to its northeast. We used the detected fields to assess the importance of the magnetic field in S88B by a number of methods; we calculated the ratio of thermal to magnetic pressures, we calculated the critical field necessary to completely support the cloud against self-gravity and compared it to the observed field, and we calculated the ratio of mass to magnetic flux in terms of the critical value of this parameter. All these methods indicated that the magnetic field in S88B is dynamically significant, and should provide an important source of support against gravity. Moreover, the magnetic energy density is in approximate equipartition with the turbulent energy density, again pointing to the importance of the magnetic field in this region.

VERY LARGE ARRAY OH ZEEMAN OBSERVATIONS OF THE STAR-FORMING REGION S88B

International Nuclear Information System (INIS)

Sarma, A. P.; Eftimova, M.; Brogan, C. L.; Bourke, T. L.; Troland, T. H.

2013-01-01

We present observations of the Zeeman effect in OH thermal absorption main lines at 1665 and 1667 MHz taken with the Very Large Array toward the star-forming region S88B. The OH absorption profiles toward this source are complicated, and contain several blended components toward a number of positions. Almost all of the OH absorbing gas is located in the eastern parts of S88B, toward the compact continuum source S88B-2 and the eastern parts of the extended continuum source S88B-1. The ratio of 1665/1667 MHz OH line intensities indicates the gas is likely highly clumped, in agreement with other molecular emission line observations in the literature. S88-B appears to present a similar geometry to the well-known star-forming region M17, in that there is an edge-on eastward progression from ionized to molecular gas. The detected magnetic fields appear to mirror this eastward transition; we detected line-of-sight magnetic fields ranging from 90 to 400 μG, with the lowest values of the field to the southwest of the S88B-1 continuum peak, and the highest values to its northeast. We used the detected fields to assess the importance of the magnetic field in S88B by a number of methods; we calculated the ratio of thermal to magnetic pressures, we calculated the critical field necessary to completely support the cloud against self-gravity and compared it to the observed field, and we calculated the ratio of mass to magnetic flux in terms of the critical value of this parameter. All these methods indicated that the magnetic field in S88B is dynamically significant, and should provide an important source of support against gravity. Moreover, the magnetic energy density is in approximate equipartition with the turbulent energy density, again pointing to the importance of the magnetic field in this region.

Characterizing the Interstellar and Circumgalactic Medium in Star-forming Galaxies

Science.gov (United States)

Du, Xinnan; Shapley, Alice; Crystal Martin, Alison Coil, Charles Steidel, Tucker Jones, Daniel Stark, Allison Strom

2018-01-01

Rest-frame UV and optical spectroscopy provide valuable information on the physical properties of the neutral and ionized interstellar medium (ISM) in star-forming galaxies, including both the systemic interstellar component originating from HII regions, and the multi-phase outflowing component associated with star-formation feedback. My thesis focuses on both the systemic and outflowing ISM in star-forming galaxies at redshift z ~ 1-4. With an unprecedented sample at z~1 with the rest-frame near-UV coverage, we examined how the kinematics of the warm and cool phrases of gas, probed by the interstellar CIV and low-ionization features, respectively, relate to each other. The spectral properties of CIV strongly correlate with the current star-formation rate, indicating a distinct nature of highly-ionized outflowing gas being driven by massive star formation. Additionally, we used the same set of z~1 galaxies to study the properties of the systemic ISM in HII regions by analyzing the nebular CIII] emission. CIII] emission tends to be stronger in lower-mass, bluer, and fainter galaxies with lower metallicity, suggesting that the strong CIII] emitters at lower redshifts can be ideal analogs of young, bursty galaxies at z > 6, which are possibly responsible for reionizing the universe. We are currently investigating the redshift evolution of the neutral, circumgalactic gas in a sample of ~1100 Lyman Break Galaxies at z ~ 2-4. The negative correlation between Lya emission and low-ionization interstellar absorption line strengths appears to be universal across different redshifts, but the fine-structure line emitting regions are found to be more compact for higher-redshift galaxies. With the detailed observational constraints provided by the rest-UV and rest-optical spectroscopy, our study sheds light on how the interstellar and circumgalactic gas components and different phases of gas connect to each other, and therefore provides a comprehensive picture of the overall

The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst

Science.gov (United States)

Motte, F.; Nony, T.; Louvet, F.; Marsh, K. A.; Bontemps, S.; Whitworth, A. P.; Men'shchikov, A.; Nguyáën Luong, Q.; Csengeri, T.; Maury, A. J.; Gusdorf, A.; Chapillon, E.; Könyves, V.; Schilke, P.; Duarte-Cabral, A.; Didelon, P.; Gaudel, M.

2018-04-01

Understanding the processes that determine the stellar initial mass function (IMF) is a critical unsolved problem, with profound implications for many areas of astrophysics1. In molecular clouds, stars are formed in cores—gas condensations sufficiently dense that gravitational collapse converts a large fraction of their mass into a star or small clutch of stars. In nearby star-formation regions, the core mass function (CMF) is strikingly similar to the IMF, suggesting that the shape of the IMF may simply be inherited from the CMF2-5. Here, we present 1.3 mm observations, obtained with the Atacama Large Millimeter/submillimeter Array telescope, of the active star-formation region W43-MM1, which may be more representative of the Galactic-arm regions where most stars form6,7. The unprecedented resolution of these observations reveals a statistically robust CMF at high masses, with a slope that is markedly shallower than the IMF. This seriously challenges our understanding of the origin of the IMF.

The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst

Science.gov (United States)

Motte, F.; Nony, T.; Louvet, F.; Marsh, K. A.; Bontemps, S.; Whitworth, A. P.; Men'shchikov, A.; Nguyen Luong, Q.; Csengeri, T.; Maury, A. J.; Gusdorf, A.; Chapillon, E.; Könyves, V.; Schilke, P.; Duarte-Cabral, A.; Didelon, P.; Gaudel, M.

2018-06-01

Understanding the processes that determine the stellar initial mass function (IMF) is a critical unsolved problem, with profound implications for many areas of astrophysics1. In molecular clouds, stars are formed in cores—gas condensations sufficiently dense that gravitational collapse converts a large fraction of their mass into a star or small clutch of stars. In nearby star-formation regions, the core mass function (CMF) is strikingly similar to the IMF, suggesting that the shape of the IMF may simply be inherited from the CMF2-5. Here, we present 1.3 mm observations, obtained with the Atacama Large Millimeter/submillimeter Array telescope, of the active star-formation region W43-MM1, which may be more representative of the Galactic-arm regions where most stars form6,7. The unprecedented resolution of these observations reveals a statistically robust CMF at high masses, with a slope that is markedly shallower than the IMF. This seriously challenges our understanding of the origin of the IMF.

Stability of Stellar Periods in the Hyades and Taurus

Science.gov (United States)

Rebull, Luisa M.; Stauffer, John R.; K2 Clusters Team

2018-06-01

K2 has opened to us the study of high-precision light curves from which we can derive stellar rotation periods. We have presented period distributions for the Pleiades, Praesepe, Upper Sco and Rho Oph. But, how stable are the periods we are deriving from them? Early ground-based work in Orion (Rebull 2001) suggested that, for the youngest stars, about half the stars had sufficiently different spot distributions in two consecutive years such that periods could not be recovered in the second year. However, now that we have K2, precision and diurnal windowing functions are no longer really much of a concern. For a handful of stars in Hyades and Taurus, the K2 spacecraft monitored them for two non-consecutive 70d windows (campaigns 4, 2015 Feb and 13, 2017 Mar). In this poster, we examine whether or not the light curves are similar in the two epochs, and how accurately the same period can be recovered.

Individual taper models for natural cedar and Taurus fir mixed stands of Bucak Region, Turkey

Directory of Open Access Journals (Sweden)

Ramazan Özçelik

2017-11-01

Full Text Available In this study, we assessed the performance of different types of taper equations for predicting tree diameters at specific heights and total stem volumes for mixed stands of Taurus cedar (Cedrus libani A. Rich. and Taurus fir (Abies cilicica Carr.. We used data from mixed stands containing a total of 131 cedar and 124 Taurus fir trees. We evaluated six commonly used and well-known forestry taper functions developed by a variety of researchers (Biging (1984, Zakrzewski (1999, Muhairwe (1999, Fang et al. (2000, Kozak (2004, and Sharma and Zhang (2004. To address problems related to autocorrelation and multicollinearity in the hierarchical data associated with the construction of taper models, we used appropriate statistical procedures for the model fitting. We compared model performances based on the analysis of three goodness-of-fit statistics and found the compatible segmented model of Fang et al. (2000 to be superior in describing the stem profile and stem volume of both tree species in mixed stands. The equation used by Zakrzewski (1999 exhibited the poorest fitting results of the three taper equations. In general, we found segmented taper equations to provide more accurate predictions than variable-form models for both tree species. Results from the non-linear extra sum of squares method indicate that stem tapers differ among tree species in mixed stands. Therefore, a different taper function should be used for each tree species in mixed stands in the Bucak district. Using individual-specific taper equations yields more robust estimations and, therefore, will enhance the prediction accuracy of diameters at different heights and volumes in mixed stands.

TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. II. CEP A AND NGC 7538

International Nuclear Information System (INIS)

Moscadelli, L.; Reid, M. J.; Menten, K. M.; Brunthaler, A.; Xu, Y.; Zheng, X. W.

2009-01-01

We report trigonometric parallaxes for the sources NGC 7538 and Cep A, corresponding to distances of 2.65 +0.12 -0.11 and 0.70 +0.04 -0.04 kpc, respectively. The distance to NGC 7538 is considerably smaller than its kinematic distance and places it in the Perseus spiral arm. The distance to Cep A is also smaller than its kinematic distance and places it in the L ocalarm or spur. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star-forming regions. We find significant deviations from circular galactic orbits for these sources: both sources show large peculiar motions (greater than 10 km s -1 ) counter to galactic rotation and NGC 7538 has a comparable peculiar motion toward the Galactic center.

How Do Multiple-Star Systems Form? VLA Study Reveals "Smoking Gun"

Science.gov (United States)

2006-12-01

Astronomers have used the National Science Foundation's Very Large Array (VLA) radio telescope to image a young, multiple-star system with unprecedented detail, yielding important clues about how such systems are formed. Most Sun-sized or larger stars in the Universe are not single, like our Sun, but are members of multiple-star systems. Astronomers have been divided on how such systems can form, producing competing theoretical models for this process. Multiple Star Formation Graphic Proposed Formation Process for L1551 IRS5 CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for page of graphics and full information The new VLA study produced a "smoking gun" supporting one of the competing models, said Jeremy Lim, of the Institute of Astronomy & Astrophysics, Academia Sinica, in Taipei, Taiwan, whose study, done with Shigehisa Takakuwa of the National Astronomical Observatory of Japan, is published in the December 10 issue of the Astrophysical Journal. Ironically, their discovery of a third, previously-unknown, young star in the system may support a second theoretical model. "There may be more than one way to make a multiple-star system," Lim explained. The astronomers observed an object called L1551 IRS5, young, still-forming protostars enshrouded in a cloud of gas and dust, some 450 light-years from Earth in the direction of the constellation Taurus. Invisible to optical telescopes because of the gas and dust, this object was discovered in 1976 by astronomers using infrared telescopes. A VLA study in 1998 showed two young stars orbiting each other, each surrounded by a disk of dust that may, in time, congeal into a system of planets. Lim and Takakuwa re-examined the system, using improved technical capabilities that greatly boosted the quality of their images. "In the earlier VLA study, only half of the VLA's 27 antennas had receivers that could collect the radio waves, at a frequency of 43 GigaHertz (GHz), coming from the dusty disks. When we re-observed this

Millimetre wavelength methanol masers survey towards massive star forming regions

Science.gov (United States)

Umemoto, T.; Mochizuki, N.; Shibata, K. M.; Roh, D.-G.; Chung, H.-S.

2007-03-01

We present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above -25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

EGRET observations of diffuse gamma-ray emission in taurus and perseus

International Nuclear Information System (INIS)

Digel, Seth W.; Grenier, Isabelle A.

2001-01-01

We present an analysis of the interstellar gamma-ray emission observed toward the extensive molecular cloud complexes in Taurus and Perseus by the Energetic Gamma-Ray Experiment Telescope (EGRET). The region's large size (more than 300 square degrees) and location below the plane in the anticenter are advantageous for straightforward interpretation of the interstellar emission. The complex of clouds in Taurus has a distance of ∼140 pc and is near the center of the Gould Belt. The complex in Perseus, adjacent to Taurus on the sky, is near the rim of the Belt at a distance of ∼300 pc. The findings for the cosmic-ray density and the molecular mass-calibrating ratio N(H 2 )/W CO in Taurus and Perseus are compared with results for other nearby cloud complexes resolved by EGRET. The local clouds that now have been studied in gamma rays can be used to trace the distribution of high-energy cosmic rays within 1 kpc of the sun

FILAMENTARY STRUCTURE OF STAR-FORMING COMPLEXES

International Nuclear Information System (INIS)

Myers, Philip C.

2009-01-01

The nearest young stellar groups are associated with 'hubs' of column density exceeding 10 22 cm -2 , according to recent observations. These hubs radiate multiple 'filaments' of parsec length, having lower column density and fewer stars. Systems with many filaments tend to have parallel filaments with similar spacing. Such 'hub-filament structure' is associated with all of the nine young stellar groups within 300 pc, forming low-mass stars. Similar properties are seen in infrared dark clouds forming more massive stars. In a new model, an initial clump in a uniform medium is compressed into a self-gravitating, modulated layer. The outer layer resembles the modulated equilibrium of Schmid-Burgk with nearly parallel filaments. The filaments converge onto the compressed clump, which collapses to form stars with high efficiency. The initial medium and condensations have densities similar to those in nearby star-forming clouds and clumps. The predicted structures resemble observed hub-filament systems in their size, shape, and column density, and in the appearance of their filaments. These results suggest that HFS associated with young stellar groups may arise from compression of clumpy gas in molecular clouds.

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.

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

International Nuclear Information System (INIS)

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

2010-01-01

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

A Hard X-Ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR

DEFF Research Database (Denmark)

Yukita, M.; Hornschemeier, A. E.; Lehmer, B. D.

2016-01-01

We present the results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d = 4.6 Mpc). This is the first investigation to spatially resolve the hard (E > 10 keV) X-ray emission of this galaxy. The nuclear region and similar to 20 off-nuclear point sources......, including a previously discovered ultraluminous X-ray source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most...

Trigonometric parallaxes of star forming regions in the Scutum spiral arm

International Nuclear Information System (INIS)

Sato, M.; Wu, Y. W.; Immer, K.; Zhang, B.; Sanna, A.; Brunthaler, A.; Menten, K. M.; Reid, M. J.; Dame, T. M.

2014-01-01

We report measurements of trigonometric parallaxes for six high-mass star-forming regions in the Scutum spiral arm of the Milky Way as part of the BeSSeL Survey. Combining our measurements with 10 previous measurements from the BeSSeL Survey yields a total sample of 16 sources in the Scutum arm with trigonometric parallaxes in the Galactic longitude range from 5° to 32°. Assuming a logarithmic spiral model, we estimate a pitch angle of 19.°8 ± 3.°1 for the Scutum arm, which is larger than pitch angles reported for other spiral arms. The high pitch angle of the arm may be due to the arm's proximity to the Galactic bar. The Scutum arm sources show an average peculiar motion of 4 km s –1 slower than the Galactic rotation and 8 km s –1 toward the Galactic center. While the direction of this non-circular motion has the same sign as determined for sources in other spiral arms, the motion toward the Galactic center is greater for the Scutum arm sources.

Search for molecular outflows associated with peculiar nebulosities and regions of star formation

Energy Technology Data Exchange (ETDEWEB)

Torrelles, J M; Rodriguez, L F; Canto, J; Marcaide, J; Gyulbudaghian, A L

1983-01-01

We surveyed an extensive list of peculiar nebulosities and regions of star formation searching for conspicuous cases of high-velocity carbon monoxide emission. We detected an apparently isotropic outflow associated with the star-forming region GL 2591. Among the other sources surveyed, the cometary nebula GM 24 is of interest since it is located in a very hot molecular spot where formation of massive stars took place recently.

Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

International Nuclear Information System (INIS)

Juárez, Carmen; Girart, Josep M.; Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier; Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab; Zhang, Qizhou; Qiu, Keping

2017-01-01

We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s −1 , converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

Interstellar C2 molecules in a Taurus dark cloud

International Nuclear Information System (INIS)

Hobbs, L.M.; Black, J.H.; van Dishoeck, E.F.

1983-01-01

Five relatively strong interstellar absorption lines of the 2--0) Phillips band of C 2 near lambda8760 are detected in the spectrum of HD 29647, a late B star which lies behind a substantial part of the Taurus molecular cloud complex about 20triangle-solid from TMC-1. In combination with newly determined oscillator strengths, the observations yield a column density N(C 2 )roughly-equal9 x 10 13 cm -2 , which is comparable to those of widely distributed molecules like CH and H 2 O. Theoreticl models of the observed C 2 rotational level populations indicate a kinetic temperature T = 14 +8 /sub -/ 5 K and a mean density n 3 cm -3 . A narrow, anomalous strong, stellar Mn II line yields for HD 29647 a project rotational velocity v sin i -1 and is explained by previous identifications HD 29647 as a Hg-Mn peculiar star. Similar spectra of ν Cyg and omicron And give an upper limit W/sub lambda/ 2 lines in the 2--0) band, toward both stars

THE MAGNETIC FIELD IN TAURUS PROBED BY INFRARED POLARIZATION

International Nuclear Information System (INIS)

Chapman, Nicholas L.; Goldsmith, Paul F.; Pineda, Jorge L.; Li Di; Clemens, D. P.; Krco, Marko

2011-01-01

We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A V ∼ 9 mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82 μG and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales (∼2 pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.

Radiative transfer modelling of W33A MM1: 3-D structure and dynamics of a complex massive star forming region

Science.gov (United States)

Izquierdo, Andrés F.; Galván-Madrid, Roberto; Maud, Luke T.; Hoare, Melvin G.; Johnston, Katharine G.; Keto, Eric R.; Zhang, Qizhou; de Wit, Willem-Jan

2018-05-01

We present a composite model and radiative transfer simulations of the massive star forming core W33A MM1. The model was tailored to reproduce the complex features observed with ALMA at ≈0.2 arcsec resolution in CH3CN and dust emission. The MM1 core is fragmented into six compact sources coexisting within ˜1000 au. In our models, three of these compact sources are better represented as disc-envelope systems around a central (proto)star, two as envelopes with a central object, and one as a pure envelope. The model of the most prominent object (Main) contains the most massive (proto)star (M⋆ ≈ 7 M⊙) and disc+envelope (Mgas ≈ 0.4 M⊙), and is the most luminous (LMain ˜ 104 L⊙). The model discs are small (a few hundred au) for all sources. The composite model shows that the elongated spiral-like feature converging to the MM1 core can be convincingly interpreted as a filamentary accretion flow that feeds the rising stellar system. The kinematics of this filament is reproduced by a parabolic trajectory with focus at the center of mass of the region. Radial collapse and fragmentation within this filament, as well as smaller filamentary flows between pairs of sources are proposed to exist. Our modelling supports an interpretation where what was once considered as a single massive star with a ˜103 au disc and envelope, is instead a forming stellar association which appears to be virialized and to form several low-mass stars per high-mass object.

Lots of Small Stars Born in Starburst Region

Science.gov (United States)

1999-10-01

Decisive Study of NGC 3603 with the VLT and ISAAC An international group of astronomers [1] has used the ESO Very Large Telescope (VLT) at Paranal (Chile) to perform unique observations of an interstellar nebula in which stars are currently being born. Thanks to the excellent imaging properties of the first of the four 8.2-m VLT Unit Telescopes, ANTU, they were able to demonstrate, for the first time, the presence of large numbers of small and relatively light, new-born stars in NGC 3603, a well-known "starburst" region in the Milky Way Galaxy . Until now, it has only been possible to observe brighter and much heavier stars in such nebulae. The new observations show that stars of all masses are being born together in the same starburst event, a fundamental result for our understanding of the very complex process of star formation. Background of the project The present research programme was granted observing time with VLT ANTU in April 1999. Its general aim is to investigate collective, massive star formation, in particular the coalescence of high- and low-mass stars in the violent environments of starburst regions . These are areas in which the processes that lead to the birth of new stars are particularly active just now. Several fundamental questions arise in this context. A very basic one is whether low-mass stars form at all in such environments. And if so, do they form together with the most massive stars in a starburst event or do they form at different times, before or after or perhaps on different timescales? Are low-mass stars born with any "preferred" mass that may possibly give further clues to the ongoing processes? All of this is most important in order to understand the detailed mechanisms of star formation. Most current theoretical scenarios explain how single stars form in an isolated, contracting gas cloud, but most stars in the Universe did not form in that simple way. Once some massive stars have formed in some place and start to shine, they

VLBA DETERMINATION OF THE DISTANCE TO NEARBY STAR-FORMING REGIONS. V. DYNAMICAL MASS, DISTANCE, AND RADIO STRUCTURE OF V773 Tau A

Energy Technology Data Exchange (ETDEWEB)

Torres, Rosa M.; Franco-Hernandez, Ramiro; Vlemmings, Wouter H. T. [Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany); Loinard, Laurent [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Mioduszewski, Amy J. [Dominici Science Operations Center, National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801 (United States); Boden, Andrew F. [Division of Physics, Math, and Astronomy, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Rodriguez, Luis F., E-mail: rtorres@astro.uni-bonn.de [Centro de Radiostronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 72-3 (Xangari), 58089 Morelia, Michoacan (Mexico)

2012-03-01

We present multi-epoch Very Long Baseline Array (VLBA) observations of V773 Tau A, the 51 day binary subsystem in the multiple young stellar system V773 Tau. Combined with previous interferometric and radial velocity measurements, these new data enable us to improve the characterization of the physical orbit of the A subsystem. In particular, we infer updated dynamical masses for the primary and the secondary components of 1.55 {+-} 0.11 M{sub Sun} and 1.293 {+-} 0.068 M{sub Sun }, respectively, and an updated orbital parallax distance to the system of 135.7 {+-} 3.2 pc, all consistent with previous estimates. Using the improved orbit, we can calculate the absolute coordinates of the barycenter of V773 Tau A at each epoch of our VLBA observations, and fit for its trigonometric parallax and proper motion. This provides a direct measurement of the distance to the system almost entirely independent of the orbit modeling. The best fit yields a distance of 129.9 {+-} 3.2 pc, in good agreement (i.e., within 1{sigma}) with the distance estimate based on the orbital fit. Taking the mean value of the orbital and trigonometric parallaxes, we conclude that V773 Tau is located at d = 132.8 {+-} 2.3 pc. The accuracy of this determination is nearly one order of magnitude better than that of previous estimates. In projection, V773 Tau and two other young stars (Hubble 4 and HDE 283572) recently observed with the VLBA are located toward the dark cloud Lynds 1495, in the central region of Taurus. These three stars appear to have similar trigonometric parallaxes, radial velocities, and proper motions, and we argue that the weighted mean and dispersion of their distances (d = 131.4 pc and {sigma}{sub d} = 2.4 pc) provide a good estimate of the distance to and depth of Lynds 1495 and its associated stellar population. The radio emission from the two sources in V773 Tau A is largely of gyrosynchrotron origin. Interestingly, both sources are observed to become typically five times

Evidence for detection of 1--10 MeV emission from the Taurus region in 1971 August

International Nuclear Information System (INIS)

Gruber, D.E.; Ling, J.C.

1977-01-01

The Taurus region was scanned in mid-1971 during three balloon flights with an actively shielded NaI detector sensitive between 0.2 and 10 MeV. Below 1 MeV, these observations yielded measurements and upper limits consistent with extensions of the X-ray power laws of 0.0035 (E/1 MeV) -2 /sup ./ 2 photons (cm 2 s MeV) -1 and 0.0008(E/1 MeV) -2 /sup ./ 1 photons (cm 2 s MeV) -1 for the Crab Nebula and NP 0532, respectively. Above 1 MeV an apparent unpulsed flux, enhanced well above the extrapolated Crab Nebula power law, was observed during the 1971 August 8 flight; it was the most sensitive of the three. For the NP 0532 above 1 MeV on the same date, the measured upper limit of a factor of 8 above the extrapolated power law excludes only the possibility of a large flare-up. The possibility that the observation reported here for 1971 August 8 was a purely instrumental effect, or was produced by environmental radiations, is thoroughly examined, with negative results. If of cosmic origin, the emission must have been short-term (approx.days, months), because other observations in 1973 and 1974 have shown null results. The possibility of variable MeV range emission is discussed in the context of other reported variable emissions in recent years from the Crab and the Taurus region

One of the most massive stars in the Galaxy may have formed in isolation

OpenAIRE

Oskinova, L. M.; Steinke, M.; Hamann, W. -R.; Sander, A.; Todt, H.; Liermann, A.

2013-01-01

Very massive stars, 100 times heavier than the sun, are rare. It is not yet known whether such stars can form in isolation or only in star clusters. The answer to this question is of fundamental importance. The central region of our Galaxy is ideal for investigating very massive stars and clusters located in the same environment. We used archival infrared images to investigate the surroundings of apparently isolated massive stars presently known in the Galactic Center. We find that two such i...

Where are the stars of the bar of NGC 1530 forming?

NARCIS (Netherlands)

Zurita, A.; Perez, I.

Aims. NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its H II regions, to elucidate the conditions under which H II regions form and their spatial relation to the

Discovery of three x-ray luminous pre-main-sequence stars

International Nuclear Information System (INIS)

Feigelson, E.D.; Kriss, G.A.

1981-01-01

Three X-ray sources found serendipitously in Einstein images of the Taurus-Auriga cloud complex were observed at the McGraw-Hill Observatory and are found to be associated with approx.12 mag stars with weak Hα emission. The stars lie on the edges of dark clouds and are spectroscopically similar to the least active emission-line pre-main-sequence stars. Although they lie well above the ZAMS in the H-R diagram, they do not exhibit ultraviolet excess, strong optical variability, or evidence for mass outflow/inflow characteristics of the more active T Tauri stars. Their only unusual property is high X-ray luminosity (approx.10 30 ergs s1). It is suggested that the X-ray emission from pre-main-sequence stars is not closely linked to the conditions giving rise to their unusual spectroscopic properties. The emission may instead represent an enhanced form of the coronal activity producing X-rays observed in late-type main-sequence stars

ALMA OBSERVATIONS OF A HIGH-DENSITY CORE IN TAURUS: DYNAMICAL GAS INTERACTION AT THE POSSIBLE SITE OF A MULTIPLE STAR FORMATION

Energy Technology Data Exchange (ETDEWEB)

Tokuda, Kazuki; Onishi, Toshikazu [Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Saigo, Kazuya; Kawamura, Akiko [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Fukui, Yasuo; Inutsuka, Shu-ichiro; Tachihara, Kengo [Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Matsumoto, Tomoaki [Faculty of Humanity and Environment, Hosei University, Fujimi, Chiyoda-ku, Tokyo 102-8160 (Japan); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Tomida, Kengo, E-mail: s_k.tokuda@p.s.osakafu-u.ac.jp [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2014-07-01

Starless dense cores eventually collapse dynamically, forming protostars inside them, and the physical properties of the cores determine the nature of the forming protostars. We report ALMA observations of dust continuum emission and molecular rotational lines toward MC27 or L1521F, which is considered to be very close to the first protostellar core phase. We found a few starless high-density cores, one of which has a very high density of ∼10{sup 7} cm{sup –3}, within a region of several hundred AU around a very low-luminosity protostar detected by Spitzer. A very compact bipolar outflow with a dynamical timescale of a few hundred years was found toward the protostar. The molecular line observation shows several cores with an arc-like structure, possibly due to the dynamical gas interaction. These complex structures revealed in the present observations suggest that the initial condition of star formation is highly dynamical in nature, which is considered to be a key factor in understanding fundamental issues of star formation such as the formation of multiple stars and the origin of the initial mass function of stars.

Direct Measurement of Dust Attenuation in z approx. 1.5 Star-Forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

Science.gov (United States)

Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B; Conroy, Charlie; Schreiber, Natascha M. Foerster; Franx, Marijn; Fumagalli, Mattia; Lundren, Britt; Momcheva, Ivelina; Nelson, Erica J.;

Embedded star formation in the extended narrow line region of Centaurus A: Extreme mixing observed by MUSE

Science.gov (United States)

Santoro, F.; Oonk, J. B. R.; Morganti, R.; Oosterloo, T. A.; Tadhunter, C.

2016-05-01

We present a detailed study of the complex ionization structure in a small (~250 pc) extended narrow line region (ENLR) cloud near Centaurus A using the Multi Unit Spectroscopic Explorer. This cloud is located in the so-called outer filament of ionized gas (about 15 kpc from the nucleus) where jet-induced star formation has been suggested to occur by different studies. We find that, despite the small size, a mixture of ionization mechanisms is operating, resulting in considerable complexity in the spatial ionization structure. The area includes two H II regions where star formation is occurring and another location where star formation must have ceased very recently. Interestingly, the extreme Balmer decrement of one of the star forming regions (Hα/Hβobs ~ 6) indicates that it is still heavily embedded in its natal cocoon of gas and dust. At all three locations a continuum counterpart is found with spectra matching those of O/B stars local to Centaurus A. The H II regions are embedded in a larger gas complex which is photoionized by the radiation of the central active galactic nucleus (AGN), but the O/B stars affect the spatial ionization pattern in the ENLR cloud very locally. In particular, in the surroundings of the youngest star forming region, we can isolate a tight mixing sequence in the diagnostic diagram going from gas with ionization due to a pure stellar continuum to gas only photoionized by the AGN. These results emphasize the complexity and the mixture of processes occurring in star forming regions under the influence of an AGN radiation. This is relevant for our understanding of AGN-induced star formation suggested to occur in a number of objects, including this region of Centaurus A. They also illustrate that these young stars influence the gas over only a limited region.

SHOCKED SUPERWINDS FROM THE z {approx} 2 CLUMPY STAR-FORMING GALAXY, ZC406690

Energy Technology Data Exchange (ETDEWEB)

Newman, Sarah F.; Genzel, Reinhard [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States); Shapiro Griffin, Kristen [Aerospace Research Laboratories, Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278 (United States); Davies, Ric; Foerster-Schreiber, Natascha M.; Tacconi, Linda J.; Kurk, Jaron; Wuyts, Stijn; Genel, Shy; Buschkamp, Peter; Eisenhauer, Frank; Lutz, Dieter [Max-Planck-Institut fuer extraterrestrische Physik (MPE), Giessenbachstr.1, D-85748 Garching (Germany); Lilly, Simon J.; Carollo, C. Marcella [Institute of Astronomy, Department of Physics, Eidgenoessische Technische Hochschule, ETH Zuerich CH-8093 (Switzerland); Renzini, Alvio; Mancini, Chiara [Osservatorio Astronomico di Padova, Vicolo dellOsservatorio 5, Padova I-35122 (Italy); Bouche, Nicolas [Department of Physics and Astronomy, University of California, Santa Barbara, Santa Barbara, CA 93106 (United States); Burkert, Andreas [Department fuer Physik, Universitaets-Sternwarte Ludwig-Maximilians-Universitaet (USM), Scheinerstr. 1, Muenchen, D-81679 (Germany); Cresci, Giovanni [Istituto Nazionale di AstrofisicaOsservatorio Astronomico di Arcetri, Largo Enrico Fermi 5, I 50125 Firenze (Italy); Hicks, Erin, E-mail: sfnewman@berkeley.edu [Department of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580 (United States); and others

2012-06-20

We have obtained high-resolution data of the z {approx} 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with adaptive optics (in K band) and in seeing-limited mode (in H and J bands). Our data include all of the main strong optical emission lines: [O II], [O III], H{alpha}, H{beta}, [N II], and [S II]. We find broad, blueshifted H{alpha} and [O III] emission line wings in the spectra of the galaxy's massive, star-forming clumps ({sigma} {approx} 85 km s{sup -1}) and even broader wings (up to 70% of the total H{alpha} flux, with {sigma} {approx} 290 km s{sup -1}) in regions spatially offset from the clumps by {approx}2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1-8 Multiplication-Sign the star formation rate (SFR) of the clumps. Based on emission line ratio diagnostics ([N II]/H{alpha} and [S II]/H{alpha}) and photoionization and shock models, we find that the emission from the clumps is due to a combination of photoionization from the star-forming regions and shocks generated in the outflowing component, with 5%-30% of the emission deriving from shocks. In terms of the ionization parameter (6 Multiplication-Sign 10{sup 7} to 10{sup 8} cm s{sup -1}, based on both the SFR and the O{sub 32} ratio), density (local electron densities of 300-1800 cm{sup -3} in and around the clumps, and ionized gas column densities of 1200-8000 M{sub Sun }pc{sup -2}), and SFR (10-40 M{sub Sun} yr{sup -1}), these clumps more closely resemble nuclear starburst regions of local ultraluminous infrared galaxies and dwarf irregulars than H II regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal

Long-term Variability of H2CO Masers in Star-forming Regions

Science.gov (United States)

Andreev, N.; Araya, E. D.; Hoffman, I. M.; Hofner, P.; Kurtz, S.; Linz, H.; Olmi, L.; Lorran-Costa, I.

2017-10-01

We present results of a multi-epoch monitoring program on variability of 6 cm formaldehyde (H2CO) masers in the massive star-forming region NGC 7538 IRS 1 from 2008 to 2015, conducted with the Green Bank Telescope, the Westerbork Radio Telescope , and the Very Large Array. We found that the similar variability behaviors of the two formaldehyde maser velocity components in NGC 7538 IRS 1 (which was pointed out by Araya and collaborators in 2007) have continued. The possibility that the variability is caused by changes in the maser amplification path in regions with similar morphology and kinematics is discussed. We also observed 12.2 GHz methanol and 22.2 GHz water masers toward NGC 7538 IRS 1. The brightest maser components of CH3OH and H2O species show a decrease in flux density as a function of time. The brightest H2CO maser component also shows a decrease in flux density and has a similar LSR velocity to the brightest H2O and 12.2 GHz CH3OH masers. The line parameters of radio recombination lines and the 20.17 and 20.97 GHz CH3OH transitions in NGC 7538 IRS 1 are also reported. In addition, we observed five other 6 cm formaldehyde maser regions. We found no evidence of significant variability of the 6 cm masers in these regions with respect to previous observations, the only possible exception being the maser in G29.96-0.02. All six sources were also observed in the {{{H}}}213{CO} isotopologue transition of the 6 cm H2CO line; {{{H}}}213{CO} absorption was detected in five of the sources. Estimated column density ratios [{{{H}}}212{CO}]/[{{{H}}}213{CO}] are reported.

Structure of massive star forming clumps from the Red MSX Source Survey

Science.gov (United States)

Figura, Charles C.; Urquhart, J. S.; Morgan, L.

2014-01-01

We present ammonia (1,1) and (2,2) emission maps of 61 high-mass star forming regions drawn from the Red MSX Source (RMS) Survey and observed with the Green Bank Telescope's K-Band Focal Plane Array. We use these observations to investigate the spatial distribution of the environmental conditions associated with this sample of embedded massive young stellar objects (MYSOs). Ammonia is an excellent high-density tracer of star-forming regions as its hyperfine structure allows relatively simple characterisation of the molecular environment. These maps are used to measure the column density, kinetic gas temperature distributions and velocity structure across these regions. We compare the distribution of these properties to that of the associated dust and mid-infrared emission traced by the ATLASGAL 870 micron emission maps and the Spitzer GLIMPSE IRAC images. We present a summary of these results and highlight some of more interesting finds.

Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

Energy Technology Data Exchange (ETDEWEB)

Juárez, Carmen; Girart, Josep M. [Institut de Ciències de l’Espai, (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, S/N, E-08193 Cerdanyola del Vallès, Catalonia (Spain); Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090, Morelia, Michoacán (Mexico); Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 10617, Taiwan (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping, E-mail: juarez@ice.cat [School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 (China)

2017-07-20

We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s{sup −1}, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

Isolation and genetic diversity of endangered grey nurse shark (Carcharias taurus) populations.

Science.gov (United States)

Stow, Adam; Zenger, Kyall; Briscoe, David; Gillings, Michael; Peddemors, Victor; Otway, Nicholas; Harcourt, Robert

2006-06-22

Anthropogenic impacts are believed to be the primary threats to the eastern Australian population of grey nurse sharks (Carcharias taurus), which is listed as critically endangered, and the most threatened population globally. Analyses of 235 polymorphic amplified fragment length polymorphisms (AFLP) loci and 700 base pairs of mitochondrial DNA control region provide the first account of genetic variation and geographical partitioning (east and west coasts of Australia, South Africa) in C. taurus. Assignment tests, analysis of relatedness and Fst values all indicate that the Australian populations are isolated from South Africa, with negligible migration between the east and west Australian coasts. There are significant differences in levels of genetic variation among regions. Australian C. taurus, particularly the eastern population, has significantly less AFLP variation than the other sampling localities. Further, the eastern Australian sharks possess only a single mitochondrial haplotype, also suggesting a small number of founding individuals. Therefore, historical, rather than anthropogenic processes most likely account for their depauperate genetic variation. These findings have implications for the viability of the eastern Australian population of grey nurse sharks.

Insights from Synthetic Star-forming Regions. II. Verifying Dust Surface Density, Dust Temperature, and Gas Mass Measurements With Modified Blackbody Fitting

Energy Technology Data Exchange (ETDEWEB)

Koepferl, Christine M.; Robitaille, Thomas P. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Dale, James E., E-mail: koepferl@usm.lmu.de [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany)

2017-11-01

We use a large data set of realistic synthetic observations (produced in Paper I of this series) to assess how observational techniques affect the measurement physical properties of star-forming regions. In this part of the series (Paper II), we explore the reliability of the measured total gas mass, dust surface density and dust temperature maps derived from modified blackbody fitting of synthetic Herschel observations. We find from our pixel-by-pixel analysis of the measured dust surface density and dust temperature a worrisome error spread especially close to star formation sites and low-density regions, where for those “contaminated” pixels the surface densities can be under/overestimated by up to three orders of magnitude. In light of this, we recommend to treat the pixel-based results from this technique with caution in regions with active star formation. In regions of high background typical in the inner Galactic plane, we are not able to recover reliable surface density maps of individual synthetic regions, since low-mass regions are lost in the far-infrared background. When measuring the total gas mass of regions in moderate background, we find that modified blackbody fitting works well (absolute error: + 9%; −13%) up to 10 kpc distance (errors increase with distance). Commonly, the initial images are convolved to the largest common beam-size, which smears contaminated pixels over large areas. The resulting information loss makes this commonly used technique less verifiable as now χ {sup 2} values cannot be used as a quality indicator of a fitted pixel. Our control measurements of the total gas mass (without the step of convolution to the largest common beam size) produce similar results (absolute error: +20%; −7%) while having much lower median errors especially for the high-mass stellar feedback phase. In upcoming papers (Paper III; Paper IV) of this series we test the reliability of measured star formation rate with direct and indirect

Insights from Synthetic Star-forming Regions. II. Verifying Dust Surface Density, Dust Temperature, and Gas Mass Measurements with Modified Blackbody Fitting

Science.gov (United States)

Koepferl, Christine M.; Robitaille, Thomas P.; Dale, James E.

2017-11-01

We use a large data set of realistic synthetic observations (produced in Paper I of this series) to assess how observational techniques affect the measurement physical properties of star-forming regions. In this part of the series (Paper II), we explore the reliability of the measured total gas mass, dust surface density and dust temperature maps derived from modified blackbody fitting of synthetic Herschel observations. We find from our pixel-by-pixel analysis of the measured dust surface density and dust temperature a worrisome error spread especially close to star formation sites and low-density regions, where for those “contaminated” pixels the surface densities can be under/overestimated by up to three orders of magnitude. In light of this, we recommend to treat the pixel-based results from this technique with caution in regions with active star formation. In regions of high background typical in the inner Galactic plane, we are not able to recover reliable surface density maps of individual synthetic regions, since low-mass regions are lost in the far-infrared background. When measuring the total gas mass of regions in moderate background, we find that modified blackbody fitting works well (absolute error: + 9%; -13%) up to 10 kpc distance (errors increase with distance). Commonly, the initial images are convolved to the largest common beam-size, which smears contaminated pixels over large areas. The resulting information loss makes this commonly used technique less verifiable as now χ 2 values cannot be used as a quality indicator of a fitted pixel. Our control measurements of the total gas mass (without the step of convolution to the largest common beam size) produce similar results (absolute error: +20%; -7%) while having much lower median errors especially for the high-mass stellar feedback phase. In upcoming papers (Paper III; Paper IV) of this series we test the reliability of measured star formation rate with direct and indirect techniques.

Where are the massive stars of the bar of NGC 1530 forming?

NARCIS (Netherlands)

Zurita, A.

2008-01-01

NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its Hii regions, to elucidate the conditions under which Hii regions form and their spatial relation to the principal

CO survey of the dark nebulae in Perseus, Taurus, and Auriga

International Nuclear Information System (INIS)

Ungerechts, H.; Thaddeus, P.

1987-01-01

A new SIS receiver with extremely low noise temperature, used on the Columbia 1.2-m telescope has permitted mapping CO rapidly with full sampling. Results are presented of a survey for which the angular resolution of the telescope was reduced to 0.5 deg, allowing the observations for the complete region of 750 square degrees to be finished within four months, while retaining sufficient resolution to see significant substructure. Most positions with emission are in the Taurus-Auriga dark nebulae, a cloud associated with IC 348 and NGC 1333, and a cloud associated with the California nebula (NGC 1499) and NGC 1579, which overlaps the northern Taurus-Auriga nebulae but is separated from them in velocity. Also seen were several small clouds at Galactic latitude -25 deg to -35 deg southwest of the Taurus clouds, and the L1558 and L1551 clouds in the south. 89 references

Direct Measurements of Dust Attenuation in z ~ 1.5 Star-forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

Science.gov (United States)

Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Förster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Skelton, Rosalind E.; van Dokkum, Pieter G.; Whitaker, Katherine E.; Wuyts, Stijn

2014-06-01

The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A V, H II ) and the integrated dust content (A V, star). We select a sample of 163 galaxies between 1.36 =5 and measure Balmer decrements from stacked spectra to calculate A V, H II . First, we stack spectra in bins of A V, star, and find that A V, H II = 1.86 A V, star, with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M *). We find that on average A V, H II increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

Infrared spectroscopy of dust in the Taurus dark clouds: ice and silicates

International Nuclear Information System (INIS)

Whittet, D.C.B.; Adamson, A.J.; McFadzean, A.D.; Aitken, D.K.

1988-01-01

Low-resolution spectra are presented of the 3 μm water-ice and 10 μm silicate dust features for stars in the direction of the extensive dark cloud complex in Taurus. A total of 22 stars were observed at 3 μm, and 16 at 10 μm. Our sample includes both dust-embedded objects and background field stars seen through the cloud. New and previously published results are combined to investigate the correlation of the strengths of both features with visual extinction A v , and we demonstrate the existence of a very close linear correlation between the peak optical depth in the 3 μm feature and A v for field stars. Ice is detected in all cases where A v exceeds a threshold value of 3.3 ± 0.1 mag, a result which provides a firm observational basis for models of volatile mantle growth on grains in the dark cloud environment. In contrast, the silicate feature is rather poorly correlated with A v . (author)

Wolf-Rayet stars associated to giant regions of star formation

International Nuclear Information System (INIS)

D'Odorico, S.; Rosa, M.

1982-01-01

Data on Wolf-Rayet (WR) stars in extragalactic H II regions and emission line galaxies are presented and discussed. The sample is still limited and inhomogeneous but two important points appear to be already established: a) The WR stars are more numerous than the blue supergiants at least in same phase of the evolution of the stellar clusters which ionize the giant H II regions, b) When the WR stars are detected, two cases are apparently observed, one in which only WN, the other in which both WN and WC, are present. (Auth.)

YSOVAR: Mid-infrared variability in the star-forming region Lynds 1688

Energy Technology Data Exchange (ETDEWEB)

Günther, H. M.; Poppenhaeger, K.; Wolk, S. J.; Hora, J. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Cody, A. M. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Covey, K. R. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Hillenbrand, L. A. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Plavchan, P. [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Rebull, L. M.; Stauffer, J. R. [Spitzer Science Center/Caltech, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Allen, L. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Bayo, A. [Max Planck Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Meng, H. Y. A. [Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Morales-Calderón, M. [Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Canada (Spain); Parks, J. R. [Department of Physics and Astronomy, Georgia State University, 25 Park Place South, Atlanta, GA 30303 (United States); Song, Inseok, E-mail: hguenther@cfa.harvard.edu [Physics and Astronomy Department, University of Georgia, Athens, GA 30602-2451 (United States)

2014-12-01

The emission from young stellar objects (YSOs) in the mid-infrared (mid-IR) is dominated by the inner rim of their circumstellar disks. We present IR data from the Young Stellar Object VARiability (YSOVAR) survey of ∼800 objects in the direction of the Lynds 1688 (L1688) star-forming region over four visibility windows spanning 1.6 yr using the Spitzer Space Telescope in its warm mission phase. Among all light curves, 57 sources are cluster members identified based on their spectral energy distribution and X-ray emission. Almost all cluster members show significant variability. The amplitude of the variability is larger in more embedded YSOs. Ten out of 57 cluster members have periodic variations in the light curves with periods typically between three and seven days, but even for those sources, significant variability in addition to the periodic signal can be seen. No period is stable over 1.6 yr. Nonperiodic light curves often still show a preferred timescale of variability that is longer for more embedded sources. About half of all sources exhibit redder colors in a fainter state. This is compatible with time-variable absorption toward the YSO. The other half becomes bluer when fainter. These colors can only be explained with significant changes in the structure of the inner disk. No relation between mid-IR variability and stellar effective temperature or X-ray spectrum is found.

Dark matter that can form dark stars

International Nuclear Information System (INIS)

Gondolo, Paolo; Huh, Ji-Haeng; Kim, Hyung Do; Scopel, Stefano

2010-01-01

The first stars to form in the Universe may be powered by the annihilation of weakly interacting dark matter particles. These so-called dark stars, if observed, may give us a clue about the nature of dark matter. Here we examine which models for particle dark matter satisfy the conditions for the formation of dark stars. We find that in general models with thermal dark matter lead to the formation of dark stars, with few notable exceptions: heavy neutralinos in the presence of coannihilations, annihilations that are resonant at dark matter freeze-out but not in dark stars, some models of neutrinophilic dark matter annihilating into neutrinos only and lighter than about 50 GeV. In particular, we find that a thermal DM candidate in standard Cosmology always forms a dark star as long as its mass is heavier than ≅ 50 GeV and the thermal average of its annihilation cross section is the same at the decoupling temperature and during the dark star formation, as for instance in the case of an annihilation cross section with a non-vanishing s-wave contribution

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

International Nuclear Information System (INIS)

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

2014-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-10-20

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

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.

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

DEFF Research Database (Denmark)

Coutens, Audrey; Vastel, C.; Hincelin, U.

2014-01-01

Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H_2^{18}O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the Heterodyne Instrument for the Far...... to an age of ˜105 yr after the infrared dark cloud stage....

Direct measurements of dust attenuation in z ∼ 1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates

International Nuclear Information System (INIS)

Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Schreiber, Natascha M. Förster; Wuyts, Stijn; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Van Dokkum, Pieter G.; Skelton, Rosalind E.; Whitaker, Katherine E.

2014-01-01

The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A V, H II ) and the integrated dust content (A V, star ). We select a sample of 163 galaxies between 1.36 ≤ z ≤ 1.5 with Hα signal-to-noise ratio ≥5 and measure Balmer decrements from stacked spectra to calculate A V, H II . First, we stack spectra in bins of A V, star , and find that A V, H II = 1.86 A V, star , with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M * ). We find that on average A V, H II increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

Star Formation in the Central Regions of Galaxies

Science.gov (United States)

Tsai, Mengchun

2015-08-01

The galactic central region connects the galactic nucleus to the host galaxy. If the central black hole co-evolved with the host galaxies, there should be some evidence left in the central region. We use the environmental properties in the central regions such as star-forming activity, stellar population and molecular abundance to figure out a possible scenario of the evolution of galaxies. In this thesis at first we investigated the properties of the central regions in the host galaxies of active and normal galaxies. We used radio emission around the nuclei of the host galaxies to represent activity of active galactic nuclei (AGNs), and used infrared ray (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs). We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst-AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies. For further investigation about the inner structure, we choose the most nearby and luminous

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

Science.gov (United States)

Panwar, Neelam

2018-04-01

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

Recent TAURUS results on Hα velocities in M83

International Nuclear Information System (INIS)

Allen, R.J.; Atherton, P.D.; Oosterloo, T.A.

1983-01-01

Preliminary Hα observations with the TAURUS imaging spectrometer confirm a pattern of systematic radial motions in a section of spiral arm in M83. The velocity gradients are not consistent with those predicted for the neutral gas. Non-circular motions have also been discovered in the central regions of the galaxy. (Auth.)

DISCOVERY OF A WIDE BINARY BROWN DWARF BORN IN ISOLATION

International Nuclear Information System (INIS)

Luhman, K. L.; Allen, P. R.; Mamajek, E. E.; Muench, A. A.; Finkbeiner, D. P.

2009-01-01

During a survey for stars with disks in the Taurus star-forming region using the Spitzer Space Telescope, we have discovered a pair of young brown dwarfs, FU Tau A and B, in the Barnard 215 dark cloud. They have a projected angular separation of 5.''7, corresponding to 800 AU at the distance of Taurus. To assess the nature of these two objects, we have obtained spectra of them and constructed spectral energy distributions. Both sources are young (∼1 Myr) according to their Hα emission, gravity-sensitive spectral features, and mid-infrared excess emission. The proper motion of FU Tau A provides additional evidence of its membership in Taurus. We measure spectral types of M7.25 and M9.25 for FU Tau A and B, respectively, which correspond to masses of ∼0.05 and ∼0.015 M sun according to the evolutionary models of Chabrier and Baraffe. FU Tau A is significantly overluminous relative to an isochrone passing through FU Tau B and relative to other members of Taurus near its spectral type, which may indicate that it is an unresolved binary. FU Tau A and B are likely to be components of a binary system based on the low probability (∼3 x 10 -4 ) that Taurus would produce two unrelated brown dwarfs with a projected separation of a ≤ 6''. Barnard 215 contains only one other young star and is in a remote area of Taurus, making FU Tau A and B the first spectroscopically confirmed brown dwarfs discovered forming in isolation rather than in a stellar cluster or aggregate. Because they were born in isolation and comprise a weakly bound binary, dynamical interactions with stars could not have played a role in their formation, and thus are not essential for the birth of brown dwarfs.

Accretion Disks around Young Stars: An Observational Perspective

Science.gov (United States)

Ménard, F.; Bertout, C.

Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

JHKL photometry of three Herbig-Haro jet sources and a nebulous T Tauri star

International Nuclear Information System (INIS)

Vrba, F.J.; Rydgren, A.E.; Zak, D.S.; Computer Sciences Corp., Baltimore, MD; Rensselaer Polytechnic Institute, Troy, NY)

1985-01-01

Infrared sources have been detected at the positions of the Herbig-Haro jet sources HH 30, DG Tau B, and Haro 6-5 B in the Taurus dark cloud complex. The colors of these Herbig-Haro jet sources in the 1-4 micron wavelength range are comparable to those of the dustiest T Tauri stars, while the K magnitudes corrected for likely interstellar extinction are actually somewhat fainter than those oftypical T Tauri stars in this region. These observations are consistent with the view that these Herbig-Haro jet sources are low-mass premain-sequence stars. The nebulous T Tauri star Haro 6-5 was also observed and found to show both a large infrared excess and an intrinsic-polarization of about 3 percent in visible light. Thus this star seems to resemble HL Tau and DG Tau, which have been suggested as examples of young stars with circumstellar disks. 17 references

TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS

International Nuclear Information System (INIS)

Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Kwon, Woojin; Carpenter, John M.; Lamb, James W.; Pillai, Thushara; Crutcher, Richard M.; Hakobian, Nicholas S.; Looney, Leslie W.; Fiege, Jason D.; Franzmann, Erica; Houde, Martin; Hughes, A. Meredith; Marrone, Daniel P.; Matthews, Brenda C.; Pound, Marc W.; Rahman, Nurur; Sandell, Göran

2014-01-01

We present λ 1.3 mm Combined Array for Research in Millimeter-wave Astronomy observations of dust polarization toward 30 star-forming cores and eight star-forming regions from the TADPOL survey. We show maps of all sources, and compare the ∼2.''5 resolution TADPOL maps with ∼20'' resolution polarization maps from single-dish submillimeter telescopes. Here we do not attempt to interpret the detailed B-field morphology of each object. Rather, we use average B-field orientations to derive conclusions in a statistical sense from the ensemble of sources, bearing in mind that these average orientations can be quite uncertain. We discuss three main findings. (1) A subset of the sources have consistent magnetic field (B-field) orientations between large (∼20'') and small (∼2.''5) scales. Those same sources also tend to have higher fractional polarizations than the sources with inconsistent large-to-small-scale fields. We interpret this to mean that in at least some cases B-fields play a role in regulating the infall of material all the way down to the ∼1000 AU scales of protostellar envelopes. (2) Outflows appear to be randomly aligned with B-fields; although, in sources with low polarization fractions there is a hint that outflows are preferentially perpendicular to small-scale B-fields, which suggests that in these sources the fields have been wrapped up by envelope rotation. (3) Finally, even at ∼2.''5 resolution we see the so-called polarization hole effect, where the fractional polarization drops significantly near the total intensity peak. All data are publicly available in the electronic edition of this article

CO survey of the dark nebulae in Taurus and Perseus

International Nuclear Information System (INIS)

Baran, G.P.

1986-01-01

The thesis reports a large-scale survey of carbon monoxide ( 12 CO) emission (at λ = 2.6 mm) from dark nebulae in Taurus and Perseus. CO spectra at 4395 points were obtained within an area of about 800 square degrees generally west of the galactic anti-center. The spatial resolution of the instrument was eight arcminutes and velocity resolution was 2.6 km s -1 /. CO emission is strongest wherever extinction by dust is greatest, spilling over the apparent outer boundaries of the dust clouds observed optically. Combining CO velocity for the nebulae with optically determined distances shows that the clouds in the survey area form several layers. The molecular cloud mass closest to the sun is the Taurus and Auriga complex about 150 +/- 50 pc). Nearer to the Per )B2 OB association (at 350 +/- 100 pc) than the Taurus clouds are the Per OB2 molecular cloud (350 +/- 100 pc) and the California Nebula = NGC15979 molecular clouds (at 400 +/- 150 pc). Cloud masses were determined from integrated CO emission intensity alone by assuming that γ-ray emission intensities can be used to relate H 2 column densities to CO emission intensities

A dearth of short-period massive binaries in the young massive star forming region M 17. Evidence for a large orbital separation at birth?

Science.gov (United States)

Sana, H.; Ramírez-Tannus, M. C.; de Koter, A.; Kaper, L.; Tramper, F.; Bik, A.

2017-03-01

Aims: The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties. Here, we aim to quantitatively investigate the strikingly low radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars (σ1D= 5.6 ± 0.2 km s-1) in the very young massive star forming region M 17, in order to obtain first constraints on the multiplicity properties of young massive stellar objects. Methods: We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained σ1D distributions to the observed value. We specifically investigate two scenarios: a low binary fraction and a dearth of short-period binary systems. Results: Simulated populations with low binary fractions () or with truncated period distributions (Pcutoff > 9 months) are able to reproduce the low σ1D observed within their 68%-confidence intervals. Furthermore, parent populations with fbin > 0.42 or Pcutoff < 47 d can be rejected at the 5%-significance level. Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old, well characterized OB-type populations. To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process. In the context of the second scenario, compact binaries must form later on, and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks. Conclusions: If the obtained constraints for the M 17's massive-star population are representative of the multiplicity properties of massive young stellar objects, our results may provide support to a massive star formation process in which binaries are initially formed at larger separations, then harden or migrate to produce the typical (untruncated) power-law period

New Herbig-Haro objects in star-forming regions

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Reipurth, BO; Graham, J. A.

1988-01-01

A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled. CCD images in the S II 6717, 6731 forbidden lines are presented for the objects, together with a few spectra and some IR observations. The individual objects and, when identified, their energy sources are discussed. HH 65 is located in the red lobe of the bipolar outflow associated with the highly variable reflection nebula Re 50. HH 67 is a 22-arcsec long sinusoidal jet. HH 68/69 consists of a long, linear chain of four HH knots. HH 72 emerges from a 120-solar luminosity IRAS source embedded in a Bok globule. HH 79 is the first HH object discovered in the Ophiuchus clouds. HH 80/81 in Sagittarius are among the brightest HH objects known, have complex velocities, high excitation conditions and emerge from a 6000-solar luminosity young B-star. HH 82 is associated with the bright variable star S Coronae Australis.

From gas to stars in energetic environments: dense gas clumps in the 30 Doradus region within the Large Magellanic Cloud

International Nuclear Information System (INIS)

Anderson, Crystal N.; Meier, David S.; Ott, Jürgen; Hughes, Annie; Wong, Tony; Looney, Leslie; Henkel, Christian; Chen, Rosie; Indebetouw, Remy; Muller, Erik; Pineda, Jorge L.; Seale, Jonathan

2014-01-01

We present parsec-scale interferometric maps of HCN(1-0) and HCO + (1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO + emission in the filament and signatures of recent star formation activity including H 2 O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO + (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30 Doradus region.

Formation of stars and star clusters in colliding galaxies

International Nuclear Information System (INIS)

Belles, Pierre-Emmanuel

2012-01-01

Mergers are known to be essential in the formation of large-scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC 7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the HI diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter-Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/HI ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower HI gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/HI ratios higher than in standard HI-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence

MERGER SIGNATURES IN THE DYNAMICS OF STAR-FORMING GAS

International Nuclear Information System (INIS)

Hung, Chao-Ling; Sanders, D. B.; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Martínez-Galarza, Juan R.; Zezas, Andreas; Lanz, Lauranne

2016-01-01

The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ∼0.2–0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ∼ 2–3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%–60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk

Smashing a Jet into a Cloud to Form Stars

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Kohler, Susanna

2017-12-01

What happens when the highly energetic jet from the center of an active galaxy rams into surrounding clouds of gas and dust? A new study explores whether this might be a way to form stars.The authors simulations at an intermediate (top) and final (bottom) stage show the compression in the gas cloud as a jet (red) enters from the left. Undisturbed cloud material is shown in blue, whereas green corresponds to cold, compressed gas actively forming stars. [Fragile et al. 2017]Impacts of FeedbackCorrelation between properties of supermassive black holes and their host galaxies suggest that there is some means of communication between them. For this reason, we suspect that feedback from an active galactic nucleus (AGN) in the form of jets, for instance controls the size of the galaxy by influencing star formation. But how does this process work?AGN feedback can be either negative or positive. In negative feedback, the gas necessary for forming stars is heated or dispersed by the jet, curbing or halting star formation. In positive feedback, jets propagate through the surrounding gas with energies high enough to create compression in the gas, but not so high that they heat it. The increased density can cause the gas to collapse, thereby triggering star formation.In a recent study, a team of scientists led by Chris Fragile (College of Charleston) modeled what happens when an enormous AGN jet slams into a dwarf-galaxy-sized, inactive cloud of gas. In particular, the team explored the possibility of star-forming positive feedback with the goal of reproducing recent observations of something called Minkowskis Object, a stellar nursery located at the endpoint of a radio jet emitted from the active galaxy NGC 541.The star formation rate in the simulated cloud increases dramatically as a result of the jets impact, reaching the rate currently observed for Minkowskis Objects within 20 million years. [Fragile et al. 2017]Triggering Stellar BirthFragile and collaborators used a

Infall and outflow motions towards a sample of massive star-forming regions from the RMS survey

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Cunningham, N.; Lumsden, S. L.; Moore, T. J. T.; Maud, L. T.; Mendigutía, I.

2018-06-01

We present the results of an outflow and infall survey towards a distance-limited sample of 31 massive star-forming regions drawn from the Red MSX source (RMS) survey. The presence of young, active outflows is identified from SiO (8-7) emission and the infall dynamics are explored using HCO+/H13CO+ (4-3) emission. We investigate if the infall and outflow parameters vary with source properties, exploring whether regions hosting potentially young active outflows show similarities or differences with regions harbouring more evolved, possibly momentum-driven, `fossil' outflows. SiO emission is detected towards approximately 46 per cent of the sources. When considering sources with and without an SiO detection (i.e. potentially active and fossil outflows, respectively), only the 12CO outflow velocity shows a significant difference between samples, indicating SiO is more prevalent towards sources with higher outflow velocities. Furthermore, we find the SiO luminosity increases as a function of the Herschel 70 μm to WISE 22 μm flux ratio, suggesting the production of SiO is prevalent in younger, more embedded regions. Similarly, we find tentative evidence that sources with an SiO detection have a smaller bolometric luminosity-to-mass ratio, indicating SiO (8-7) emission is associated with potentially younger regions. We do not find a prevalence towards sources displaying signatures of infall in our sample. However, the higher energy HCO+ transitions may not be the best suited tracer of infall at this spatial resolution in these regions.

A RAPIDLY EVOLVING REGION IN THE GALACTIC CENTER: WHY S-STARS THERMALIZE AND MORE MASSIVE STARS ARE MISSING

Energy Technology Data Exchange (ETDEWEB)

Chen, Xian; Amaro-Seoane, Pau, E-mail: Xian.Chen@aei.mpg.de, E-mail: Pau.Amaro-Seoane@aei.mpg.de [Max Planck Institut für Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany)

2014-05-10

The existence of ''S-stars'' within a distance of 1'' from Sgr A* contradicts our understanding of star formation, due to Sgr A* 's forbiddingly violent environment. A suggested possibility is that they form far away and were brought in by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities—without violating their young age—or cannot explain the problem of {sup i}nverse mass segregation{sup :} the fact that lighter stars (the S-stars) are closer to Sgr A* and more massive ones, Wolf-Rayet (WR) and O-stars, are farther out. In this Letter we propose that the mechanism responsible for both the distribution of the eccentricities and the paucity of massive stars is the Kozai-Lidov-like resonance induced by a sub-parsec disk recently discovered in the Galactic center. Considering that the disk probably extended to a smaller radius in the past, we show that in as short as (a few) 10{sup 6} yr, the stars populating the innermost 1'' region would redistribute in angular-momentum space and recover the observed ''super-thermal'' distribution. Meanwhile, WR and O-stars in the same region intermittently attain ample eccentricities that will lead to their tidal disruptions by the central massive black hole. Our results provide new evidences that Sgr A* was powered several millions years ago by an accretion disk as well as by tidal stellar disruptions.

Dissecting the intensely star-forming clumps in a z ~ 2 Einstein Ring

Science.gov (United States)

Rujopakarn, Wiphu

2013-10-01

Clumps of star formation spreading widely in galactic disks are common features of star-forming galaxies at 1 test cases to study the mechanism that drives intense star formation at z ~ 2. We propose WFC3 near-IR imaging and spatially-resolved spectroscopy of a gravitationally lensed, kinematically ordered, vigorously star-forming galaxy at z = 1.885 with physical resolutions up to 40 pc. This galaxy contains two luminous clumps that are forming stars at the rates of 100 solar mass/yr/clump. Spatially-resolved map of star formation from HST provides the most critical missing piece to interpret our existing observations of this galaxy in far-IR, CO emission lines, and radio continuum. We will probe the frontier research areas in z ~ 2 star formation, particularly the spatially-resolved star formation laws and dynamics of cold and ionized gases, which have never been probed at this spatial resolution. Our proposed observations will provide a benchmark against which to interpret the structures of vigorous star-forming clumps in general. This object can therefore have a unique impact on our understanding of the star-forming modes that dominate at z ~ 2.

WEAK AND COMPACT RADIO EMISSION IN EARLY HIGH-MASS STAR-FORMING REGIONS. I. VLA OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Rosero, V.; Hofner, P. [Physics Department, New Mexico Tech, 801 Leroy Pl., Socorro, NM 87801 (United States); Claussen, M. [National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM 87801 (United States); Kurtz, S.; Carrasco-González, C.; Rodríguez, L. F.; Loinard, L. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58090, México (Mexico); Cesaroni, R. [INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Araya, E. D. [Physics Department, Western Illinois University, 1 University Circle, Macomb, IL 61455 (United States); Menten, K. M.; Wyrowski, F. [Max-Planck-Institute für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Ellingsen, S. P. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania 7001 (Australia)

2016-12-01

We present a high-sensitivity radio continuum survey at 6 and 1.3 cm using the Karl G. Jansky Very Large Array toward a sample of 58 high-mass star-forming regions. Our sample was chosen from dust clumps within infrared dark clouds with and without IR sources (CMC–IRs and CMCs, respectively), and hot molecular cores (HMCs), with no previous, or relatively weak radio continuum detection at the 1 mJy level. Due to the improvement in the continuum sensitivity of the Very Large Array, this survey achieved map rms levels of ∼3–10  μ Jy beam{sup −1} at sub-arcsecond angular resolution. We extracted 70 continuum sources associated with 1.2 mm dust clumps. Most sources are weak, compact, and prime candidates for high-mass protostars. Detection rates of radio sources associated with the millimeter dust clumps for CMCs, CMC–IRs, and HMCs are 6%, 53%, and 100%, respectively. This result is consistent with increasing high-mass star formation activity from CMCs to HMCs. The radio sources located within HMCs and CMC–IRs occur close to the dust clump centers, with a median offset from it of 12,000 au and 4000 au, respectively. We calculated 5–25 GHz spectral indices using power-law fits and obtained a median value of 0.5 (i.e., flux increasing with frequency), suggestive of thermal emission from ionized jets. In this paper we describe the sample, observations, and detections. The analysis and discussion will be presented in Paper II.

TAURUS - a wide field imaging Fabry-Perot spectrometer

International Nuclear Information System (INIS)

Atherton, P.D.; Taylor, K.

1983-01-01

TAURUS, an imaging Fabry-Perot system developed by the Royal Greenwich Observatory and Imperial College London, is described. The imaging process is explained and the technique is compared with grating spectrographs. It is argued that TAURUS is superior for obtaining field information from extended emission line sources. (Auth.)

A study of the stellar population in the Lynds 1641 dark cloud - deep near-infrared imaging

International Nuclear Information System (INIS)

Strom, K.M.; Margulis, M.; Strom, S.E.

1989-01-01

Deep H and K photometry of a selection of IRAS point sources in the L1641 cloud is presented. Using these data in combination with IRAS data and previously published near-infrared photometry for sources in this region, it is found that the L1641 cloud contains newly born stars embedded within cores of unusually large visual extinction. A comparison of the properties of cores in L1641 with those in the Taurus-Auriga star-forming complex reveals that L1641 contains cores with higher visual extinctions, larger ammonia (J, K) = (1, 1) line widths, greater kinetic temperatures, and probably higher optical depths at 100 microns than any cores in Taurus-Auriga. These results are qualitatively consistent with recent suggestions that the process of protostellar collapse in cores in the L1641 cloud is dominated by gravity while this process is dominated by magnetic fields in Taurus-Auriga. 20 refs

The Maximum Flux of Star-Forming Galaxies

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Crocker, Roland M.; Krumholz, Mark R.; Thompson, Todd A.; Clutterbuck, Julie

2018-04-01

The importance of radiation pressure feedback in galaxy formation has been extensively debated over the last decade. The regime of greatest uncertainty is in the most actively star-forming galaxies, where large dust columns can potentially produce a dust-reprocessed infrared radiation field with enough pressure to drive turbulence or eject material. Here we derive the conditions under which a self-gravitating, mixed gas-star disc can remain hydrostatic despite trapped radiation pressure. Consistently taking into account the self-gravity of the medium, the star- and dust-to-gas ratios, and the effects of turbulent motions not driven by radiation, we show that galaxies can achieve a maximum Eddington-limited star formation rate per unit area \\dot{Σ }_*,crit ˜ 10^3 M_{⊙} pc-2 Myr-1, corresponding to a critical flux of F*, crit ˜ 1013L⊙ kpc-2 similar to previous estimates; higher fluxes eject mass in bulk, halting further star formation. Conversely, we show that in galaxies below this limit, our one-dimensional models imply simple vertical hydrostatic equilibrium and that radiation pressure is ineffective at driving turbulence or ejecting matter. Because the vast majority of star-forming galaxies lie below the maximum limit for typical dust-to-gas ratios, we conclude that infrared radiation pressure is likely unimportant for all but the most extreme systems on galaxy-wide scales. Thus, while radiation pressure does not explain the Kennicutt-Schmidt relation, it does impose an upper truncation on it. Our predicted truncation is in good agreement with the highest observed gas and star formation rate surface densities found both locally and at high redshift.

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.

MULTIPLICITY, DISKS, AND JETS IN THE NGC 2071 STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Carrasco-Gonzalez, Carlos [Max-Planck-Institut fuer Radioastronomie (MPIfR), Auf dem Huegel 69, 53121 Bonn (Germany); Osorio, Mayra; Anglada, Guillem; Gomez, Jose F. [Instituto de Astrofisica de Andalucia, CSIC, Camino Bajo de Huetor 50, E-18008 Granada (Spain); D' Alessio, Paola; Rodriguez, Luis F. [Centro de Radioastronomia y Astrofisica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacan (Mexico); Torrelles, Jose M., E-mail: carrasco@mpifr-bonn.mpg.de [Instituto de Ciencias del Espacio (CSIC)-UB/IEEC, Universitat de Barcelona, Marti i Franques 1, E-08028 Barcelona (Spain)

2012-02-10

We present centimeter (cm) and millimeter (mm) observations of the NGC 2071 star-forming region performed with the Very Large Array (VLA) and Combined Array for Research in Millimeter-wave Astronomy (CARMA). We detected counterparts at 3.6 cm and 3 mm for the previously known sources IRS 1, IRS 2, IRS 3, and VLA 1. All these sources show spectral energy distributions (SEDs) dominated by free-free thermal emission at cm wavelengths and thermal dust emission at mm wavelengths, suggesting that all of them are associated with young stellar objects (YSOs). IRS 1 shows a complex morphology at 3.6 cm, with changes in the direction of its elongation. We discuss two possible explanations to this morphology: the result of changes in the direction of a jet due to interactions with a dense ambient medium, or that we are actually observing the superposition of two jets arising from two components of a binary system. Higher angular resolution observations at 1.3 cm support the second possibility, since a double source is inferred at this wavelength. IRS 3 shows a clear jet-like morphology at 3.6 cm. Over a timespan of four years, we observed changes in the morphology of this source that we interpret as due to ejection of ionized material in a jet. The emission at 3 mm of IRS 3 is angularly resolved, with a deconvolved size (FWHM) of {approx}120 AU, and seems to be tracing a dusty circumstellar disk perpendicular to the radio jet. An irradiated accretion disk model around an intermediate-mass YSO can account for the observed SED and spatial intensity profile at 3 mm, supporting this interpretation.

MULTIPLICITY, DISKS, AND JETS IN THE NGC 2071 STAR-FORMING REGION

International Nuclear Information System (INIS)

Carrasco-González, Carlos; Osorio, Mayra; Anglada, Guillem; Gómez, José F.; D'Alessio, Paola; Rodríguez, Luis F.; Torrelles, José M.

2012-01-01

We present centimeter (cm) and millimeter (mm) observations of the NGC 2071 star-forming region performed with the Very Large Array (VLA) and Combined Array for Research in Millimeter-wave Astronomy (CARMA). We detected counterparts at 3.6 cm and 3 mm for the previously known sources IRS 1, IRS 2, IRS 3, and VLA 1. All these sources show spectral energy distributions (SEDs) dominated by free-free thermal emission at cm wavelengths and thermal dust emission at mm wavelengths, suggesting that all of them are associated with young stellar objects (YSOs). IRS 1 shows a complex morphology at 3.6 cm, with changes in the direction of its elongation. We discuss two possible explanations to this morphology: the result of changes in the direction of a jet due to interactions with a dense ambient medium, or that we are actually observing the superposition of two jets arising from two components of a binary system. Higher angular resolution observations at 1.3 cm support the second possibility, since a double source is inferred at this wavelength. IRS 3 shows a clear jet-like morphology at 3.6 cm. Over a timespan of four years, we observed changes in the morphology of this source that we interpret as due to ejection of ionized material in a jet. The emission at 3 mm of IRS 3 is angularly resolved, with a deconvolved size (FWHM) of ∼120 AU, and seems to be tracing a dusty circumstellar disk perpendicular to the radio jet. An irradiated accretion disk model around an intermediate-mass YSO can account for the observed SED and spatial intensity profile at 3 mm, supporting this interpretation.

Dynamics of H II regions around exiled O stars

Science.gov (United States)

Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

2013-11-01

At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

On the Onset of Secondary Stellar Generations in Giant Star-forming Regions and Massive Star Clusters

Czech Academy of Sciences Publication Activity Database

Palouš, Jan; Wünsch, Richard; Tenorio-Tagle, G.

2014-01-01

Roč. 792, č. 2 (2014), 105/1-105/10 ISSN 0004-637X R&D Projects: GA ČR GAP209/12/1795 Institutional support: RVO:67985815 Keywords : galaxies: ISM * star clusters: general * galaxies: star formation Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.993, year: 2014

Spitzer/IRAC view of Sh 2-284. Searching for evidence of triggered star formation in an isolated region in the outer Milky Way

NARCIS (Netherlands)

Puga, E.; Hony, S.; Neiner, C.; Lenorzer, A.; Hubert, A.M.; Waters, L.B.F.M.; Cusano, F.; Ripepi, V.

2009-01-01

Aims. Using Spitzer/IRAC observations of a region to be observed by the CoRoT satellite, we have unraveled a new complex star-forming region at low metallicity in the outer Galaxy. We perform a study of S284 in order to outline the chain of events in this star-forming region. Methods. We used

A GLOBAL STAR-FORMING EPISODE IN M31 2–4 GYR AGO

Energy Technology Data Exchange (ETDEWEB)

Williams, Benjamin F.; Dalcanton, Julianne J.; Weisz, Daniel R.; Lewis, Alexia R., E-mail: ben@astro.washington.edu, E-mail: jd@astro.washington.edu, E-mail: dweisz@astro.washington.edu [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States); and others

2015-06-10

We have identified a major global enhancement of star formation in the inner M31 disk that occurred between 2–4 Gyr ago, producing ∼60% of the stellar mass formed in the past 5 Gyr. The presence of this episode in the inner disk was discovered by modeling the optical resolved star color–magnitude diagrams of low extinction regions in the main disk of M31 (3 < R < 20 kpc) as part of the Panchromatic Hubble Andromeda Treasury. This measurement confirms and extends recent measurements of a widespread star formation enhancement of similar age in the outer disk, suggesting that this burst was both massive and global. Following the galaxy-wide burst, the star formation rate of M31 has significantly declined. We briefly discuss possible causes for these features of the M31 evolutionary history, including interactions with M32, M33, and/or a merger.

TAURUS, Post-processor of 3-D Finite Elements Plots

International Nuclear Information System (INIS)

Brown, B.E.; Hallquist, J.O.; Kennedy, T.

2002-01-01

Description of program or function: TAURUS reads the binary plot files generated by the LLNL three-dimensional finite element analysis codes, NIKE3D (NESC 9725), DYNA3D (NESC 9909), TACO3D (NESC 9838), TOPAZ3D (NESC9599) and GEMINI and plots contours, time histories, and deformed shapes. Contours of a large number of quantities may be plotted on meshes consisting of plate, shell, and solid type elements. TAURUS can compute a variety of strain measures, reaction forces along constrained boundaries, and momentum. TAURUS has three phases: initialization, geometry display with contouring, and time history processing

Star bursts and giant HII regions

International Nuclear Information System (INIS)

Pagel, B.E.J.

1990-01-01

Massive star formation bursts occur in a variety of galactic environments and can temporarily dominate the light output of a galaxy even when a relatively small proportion of its mass is involved. Inferences about their ages, the IMF and its dependence on chemical composition are still somewhat wobbly owing to an excess of unknowns, but certain things can be deduced from emission spectra of associated H II regions when due regard is paid to the effects of chemical composition and ionization parameter: In particular, largest ionization parameters and effective temperatures of exciting stars, at any given oxygen abundance, are anti-correlated with the abundance, and the second effect suggests an increasing proportion of more massive stars at lower abundances, although this is not yet satisfactorily quantified. A new blue compact galaxies could be very young, but it is equally possible that there is an older population of low surface brightness. Some giant H II regions may be self-polluted with nitrogen and helium due to winds from massive stars in the associated burst. (orig.)

The new Be-type star HD 147196 in the Rho Ophiuchi dark cloud region

Science.gov (United States)

The, P. S.; Perez, M. R.; De Winter, D.; Van Den Ancker, M. E.

1993-01-01

The newly discovered hot-emission line star, HD 147196 in the Rho Oph dark cloud region was observed spectroscopically and photometrically and high and low resolution IUE spectra were obtained. The finding of Irvine (1990) that this relatively bright star show its H-alpha-line in emission is confirmed. Previous H-alpha-surveys of the Rho Oph star-forming region did not detect HD 147196 as an H-alpha-emission star, meaning that it must recently be very active and has perhaps transformed itself from a B-type star at shell phase to a Be-phase. The Mg II h + k resonance lines are in absorption and they appear to be interstellar in nature, which means that either the abundance of Mg in the extended atmosphere of the star is low or that the shell is not extended enough to produce emission lines of Mg II. Photometric observations of this B8 V type star do not show any variations during at least the years covered by our monitoring or any excess of NIR radiation in its spectral energy distribution up to the M-passband at 4.8 microns.

PARALLAXES FOR W49N AND G048.60+0.02: DISTANT STAR FORMING REGIONS IN THE PERSEUS SPIRAL ARM

Energy Technology Data Exchange (ETDEWEB)

Zhang, B.; Menten, K. M.; Brunthaler, A. [Max-Plank-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Reid, M. J.; Dame, T. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Zheng, X. W. [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Xu, Y. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2013-09-20

We report trigonometric parallax measurements of 22 GHz H{sub 2}O masers in two massive star-forming regions from Very Long Baseline Array observations as part of the Bar and Spiral Structure Legacy Survey. The distances of 11.11{sup +0.79}{sub -0.69} kpc to W49N (G043.16+0.01) and 10.75{sup +0.61}{sub -0.55} kpc to G048.60+0.02 locate them in a distant section of the Perseus arm near the solar circle in the first Galactic quadrant. This allows us to locate accurately the inner portion of the Perseus arm for the first time. Combining the present results with sources measured in the outer portion of the arm in the second and third quadrants yields a global pitch angle of 9.°5 ± 1.°3 for the Perseus arm. We have found almost no H{sub 2}O maser sources in the Perseus arm for 50° star formation activity.

Molecular diagnostics of Galactic star-formation regions

Science.gov (United States)

Loenen, Edo; Baan, Willem; Spaans, Marco

2007-10-01

We propose a sensitive spectral survey of Galactic star-formation regions. Using the broadband correlator at two different frequencies, we expect to detect the (1-0) transition of CO, CN, HNC, HCN, HCO+, and HCO and various of their isotopes lines, as well as the (12-11) and (10-9) transitions of HC3N. The purpose of these observations is to create a consistent (public) database of molecular emission from galactic star-formation regions. The data will be interpreted using extensive physical and chemical modeling of the whole ensemble of lines, in order to get an accurate description of the molecular environment of these regions. In particular, this diagnostic approach will describe the optical depths, the densities, and the radiation fields in the medium and will allow the establishment of dominant temperature gradients. These observations are part of a program to study molecular emission on all scales, going from individual Galactic star-formation regions, through resolved nearby galaxies, to unresolved extra-galactic emission.

Absolute measurements of fluxes from Cassiopeia A, Cygnus A, Taurus A, Virgo A at seven wavelengths in the 1.8-4.2 cm band

International Nuclear Information System (INIS)

Dmitrenko, L.V.; Snegireva, V.V.; Turchin, V.I.; Tsejtlin, N.M.; Voronkov, L.A.; Dmitrenko, D.A.; Kuznetsova, N.A.; Kholodilov, N.N.

1981-01-01

Results of absolute measurements of fluxes from Cassiopeia A, Cygnus A, Taurus A, Virgo A at 1.8-4.17 cm wavelengths are presented. Spectra are built in the wave range of 1.8-100 cm with the use of results obtained earlier. Variability has been detected in radiation of Taurus A as well as ''steps'' in the spectrum of Taurus A with the spectral index α=0 in the region of 2 cm and 3-4 cm [ru

The ionisation parameter of star-forming galaxies evolves with the specific star formation rate

Science.gov (United States)

Kaasinen, Melanie; Kewley, Lisa; Bian, Fuyan; Groves, Brent; Kashino, Daichi; Silverman, John; Kartaltepe, Jeyhan

2018-04-01

We investigate the evolution of the ionisation parameter of star-forming galaxies using a high-redshift (z ˜ 1.5) sample from the FMOS-COSMOS survey and matched low-redshift samples from the Sloan Digital Sky Survey. By constructing samples of low-redshift galaxies for which the stellar mass (M*), star formation rate (SFR) and specific star formation rate (sSFR) are matched to the high-redshift sample we remove the effects of an evolution in these properties. We also account for the effect of metallicity by jointly constraining the metallicity and ionisation parameter of each sample. We find an evolution in the ionisation parameter for main-sequence, star-forming galaxies and show that this evolution is driven by the evolution of sSFR. By analysing the matched samples as well as a larger sample of z physically consistent with the definition of the ionisation parameter, a measure of the hydrogen ionising photon flux relative to the number density of hydrogen atoms.

Studies of Young, Star-forming Circumstellar Disks

Science.gov (United States)

Bae, Jaehan

2017-08-01

Disks of gas and dust around forming stars - circumstellar disks - last only a few million years. This is a very small fraction of the entire lifetime of Sun-like stars, several billion years. Nevertheless, by the time circumstellar disks dissipate stars complete building up their masses, giant planets finish accreting gas, and terrestrial bodies are nearly fully grown and ready for their final assembly to become planets. Understanding the evolution of circumstellar disks are thus crucial in many contexts. Using numerical simulations as the primary tool, my thesis has focused on the studies of various physical processes that can occur throughout the lifetime of circumstellar disks, from their formation to dispersal. Chapters 2, 3, and 4 emphasize the importance of early evolution, during which time a forming star-disk system obtains mass from its natal cloud: the infall phase. In Chapter 2 and 3, I have modeled episodic outbursts of accretion in protostellar systems resulting from disk instabilities - gravitational instability and magnetorotational instability. I showed that outbursts occur preferentially during the infall phase, because the mass addition provides more favorable conditions for gravitational instability to initiate the outburst cycle, and that forming stars build up a significant fraction of their masses through repeated short-lived, episodic outbursts. The infall phase can also be important for the formation of planets. Recent ALMA observations revealed sets of bright and dark rings in circumstellar disks of young, forming stars, potentially indicating early formation of planets. In Chapter 4, I showed that infall streams can create radial pressure bumps near the outer edge of the mass landing on the disk, from which vortices can form, collecting solid particles very efficiently to make initial seeds of planets. The next three chapters highlight the role of planets in setting the observational appearance and the evolution of circumstellar disks

A WIDE-FIELD NARROWBAND OPTICAL SURVEY OF THE BRAID NEBULA STAR FORMATION REGION IN CYGNUS OB7

International Nuclear Information System (INIS)

Magakian, Tigran Yu.; Nikogossian, Elena H.; Movsessian, Tigran; Aspin, Colin; Pyo, Tae-Soo; Khanzadyan, Tigran; Smith, Michael D.; Mitchison, Sharon; Davis, Chris J.; Beck, Tracy L.; Moriarty-Schieven, Gerald H.

2010-01-01

We study the population of Herbig-Haro (HH) flows and jets in an area of Cygnus OB7 designated the Braid Nebula star formation region. This complex forms part of the L 1003 dark cloud, and hosts two FU Orionis (FUor)-like objects as well as several other active young stars. To trace outflow activity and to relate both known and newly discovered flows to young star hosts we intercompare new, deep, narrowband Hα and [S II] optical images taken on the Subaru 8 m Telescope on Mauna Kea, Hawaii. Our images show that there is considerable outflow and jet activity in this region suggesting the presence of an extensive young star population. We confirm that both of the FUor-like objects drive extensive HH flows and document further members of the flows in both objects. The L 1003 star formation complex is a highly kinematically active region with young stars in several different stages of evolution. We trace collimated outflows from numerous young stars although the origin of some HH objects remains elusive.

The phylogenomic position of the grey nurse shark Carcharias taurus Rafinesque, 1810 (Lamniformes, Odontaspididae) inferred from the mitochondrial genome.

Science.gov (United States)

Bowden, Deborah L; Vargas-Caro, Carolina; Ovenden, Jennifer R; Bennett, Michael B; Bustamante, Carlos

2016-11-01

The complete mitochondrial genome of the grey nurse shark Carcharias taurus is described from 25 963 828 sequences obtained using Illumina NGS technology. Total length of the mitogenome is 16 715 bp, consisting of 2 rRNAs, 13 protein-coding regions, 22 tRNA and 2 non-coding regions thus updating the previously published mitogenome for this species. The phylogenomic reconstruction inferred from the mitogenome of 15 species of Lamniform and Carcharhiniform sharks supports the inclusion of C. taurus in a clade with the Lamnidae and Cetorhinidae. This complete mitogenome contributes to ongoing investigation into the monophyly of the Family Odontaspididae.

C III] EMISSION IN STAR-FORMING GALAXIES NEAR AND FAR

Energy Technology Data Exchange (ETDEWEB)

Rigby, J. R. [Astrophysics Science Division, Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Bayliss, M. B. [Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138 (United States); Gladders, M. D. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637 (United States); Sharon, K.; Johnson, T. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Wuyts, E. [Max Plank Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany); Dahle, H. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, NO-0315 Oslo (Norway); Peña-Guerrero, M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2015-11-20

We measure [C iii] 1907, C iii] 1909 Å emission lines in 11 gravitationally lensed star-forming galaxies at z ∼ 1.6–3, finding much lower equivalent widths than previously reported for fainter lensed galaxies. While it is not yet clear what causes some galaxies to be strong C iii] emitters, C iii] emission is not a universal property of distant star-forming galaxies. We also examine C iii] emission in 46 star-forming galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS on HST and IUE. Twenty percent of these local galaxies show strong C iii] emission, with equivalent widths < −5 Å. Three nearby galaxies show C iii] emission equivalent widths as large as the most extreme emitters yet observed in the distant universe; all three are Wolf–Rayet galaxies. At all redshifts, strong C iii] emission may pick out low-metallicity galaxies experiencing intense bursts of star formation. Such local C iii] emitters may shed light on the conditions of star formation in certain extreme high-redshift galaxies.

Water deuteration in star-forming regions: Contribution of Herschel/HIFI spectroscopic data

International Nuclear Information System (INIS)

Coutens, Audrey

2012-01-01

Water (H_2O) is one of the most abundant molecules in the interstellar medium. In addition to being a primordial ingredient in the emergence of life, this species plays an essential role in the process of star formation through the cooling of warm gas. It also controls the chemistry for many species, either in the gas phase or on the grain surfaces. Studying its deuterated form HDO is a unique opportunity, through the estimation of the HDO/H_2O ratio, to constrain the mechanisms of water formation and to better understand the origin of water contained in terrestrial oceans. Indeed, recent results obtained with the Herschel satellite show that the HDO/H_2O ratio observed in comets is similar to the value measured in oceans (∼1.5 10"-"4), which suggests that comets could have brought a large fraction to Earth to form the oceans during heavy bombardments (Hartogh et al. 2011). In this thesis, I was interested in the study of deuterated water in the first stages of star formation, the Class 0 stage, which precede the formation of the protoplanetary disk leading to the birth of comets and planets. Through a 1D non-Local Thermodynamic Equilibrium radiative transfer modeling of the line profiles of the numerous HDO and H_2"1"8O transitions detected with the HIFI (Heterodyne Instrument for Far-Infrared) instrument onboard the Herschel Space Observatory and ground-based telescopes (IRAM, JCMT), I determined that the HDO/H_2O ratios of the solar-type protostar IRAS 16293-2422 was about 2% in the hot corino, the inner part of the protostellar envelope sufficiently warm (T ≥ 100 K) to desorb in gas phase the water molecules trapped in the icy grain mantles, and about 0.5% in the colder part of the envelope. This study (Coutens et al. 2012) also allowed me to show that an absorbing layer rich in water surrounds the protostar. This layer could be produced by the photo-desorption through the UV field of the water molecules frozen on the grains, on the edges of the molecular

Discovery of new dipper stars with K2: a window into the inner disc region of T Tauri stars

Science.gov (United States)

Hedges, Christina; Hodgkin, Simon; Kennedy, Grant

2018-05-01

In recent years, a new class of young stellar object (YSO) has been defined, referred to as dippers, where large transient drops in flux are observed. These dips are too large to be attributed to stellar variability, last from hours to days and can reduce the flux of a star by 10-50 per cent. This variability has been attributed to occultations by warps or accretion columns near the inner edge of circumstellar discs. Here, we present 95 dippers in the Upper Scorpius association and ρ Ophiuchus cloud complex found in K2 Campaign 2 data using supervised machine learning with a random forest classifier. We also present 30 YSOs that exhibit brightening events on the order of days, known as bursters. Not all dippers and bursters are known members, but all exhibit infrared excesses and are consistent with belonging to either of the two young star-forming regions. We find 21.0 ± 5.5 per cent of stars with discs are dippers for both regions combined. Our entire dipper sample consists only of late-type (KM) stars, but we show that biases limit dipper discovery for earlier spectral types. Using the dipper properties as a proxy, we find that the temperature at the inner disc edge is consistent with interferometric results for similar and earlier type stars.

Pulsating stars in the region of Carina Nebula

Energy Technology Data Exchange (ETDEWEB)

Steslicki, Marek [Astronomical Institute, University of Wroclaw (Poland)], E-mail: steslicki@astro.uni.wroc.p1

2008-10-15

We present the results of a search for pulsating stars in the region of Carina Nebula which includes three very young open clusters: Trumpler 14, 15 and 16. The search was made with the Wide Field Imager (WFI) on the MPG/ESO 2.2-m telescope in La Silla (Chile). In total, about 16,000 stars have been analyzed using classical Fourier techniques. We found over 20 pulsating {delta}-Scuti type stars in this region. Most of them are probable members of open clusters at the pre-main sequence evolutionary stage.

Revolution evolution: tracing angular momentum during star and planetary system formation

Science.gov (United States)

Davies, Claire Louise

2015-04-01

Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 - 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the

The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

Science.gov (United States)

McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

2017-12-01

We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

Solid CO in the Taurus dark clouds

International Nuclear Information System (INIS)

Whittet, D.C.B.; McFadzean, A.D.

1985-01-01

The infrared vibrational feature of solid state CO at 4.67 μm wavelength is detected towards five sources in or behind the dark cloud complex in Taurus. A comparison with millimetre-wave data suggests that a significant fraction (up to 40 per cent) of the CO may be depleted on to grains. The adjacent CN feature at 4.62 μm observed in W33A by previous authors is absent from the present spectra, suggesting that the grain mantles in Taurus are unannealed. (author)

Discovery of a bright microlensing event with planetary features towards the Taurus region: a super-Earth planet

Science.gov (United States)

Nucita, A. A.; Licchelli, D.; De Paolis, F.; Ingrosso, G.; Strafella, F.; Katysheva, N.; Shugarov, S.

2018-05-01

The transient event labelled as TCP J05074264+2447555 recently discovered towards the Taurus region was quickly recognized to be an ongoing microlensing event on a source located at distance of only 700-800 pc from Earth. Here, we show that observations with high sampling rate close to the time of maximum magnification revealed features that imply the presence of a binary lens system with very low-mass ratio components. We present a complete description of the binary lens system, which host an Earth-like planet with most likely mass of 9.2 ± 6.6 M⊕. Furthermore, the source estimated location and detailed Monte Carlo simulations allowed us to classify the event as due to the closest lens system, being at a distance of ≃380 pc and mass ≃0.25 M⊙.

A Detached Protostellar Disk around a ˜0.2 M ⊙ Protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus

Science.gov (United States)

Tokuda, Kazuki; Onishi, Toshikazu; Saigo, Kazuya; Hosokawa, Takashi; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro; Machida, Masahiro N.; Tomida, Kengo; Kunitomo, Masanobu; Kawamura, Akiko; Fukui, Yasuo; Tachihara, Kengo

2017-11-01

We report ALMA observations in 0.87 mm continuum and 12CO (J = 3-2) toward a very low-luminosity (<0.1 L ⊙) protostar, which is deeply embedded in one of the densest cores, MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to ˜20 au, and we have clearly detected blueshifted/redshifted gas in 12CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of ˜10 au, a disk mass of ˜10-4 M ⊙, and a central stellar mass of ˜0.2 M ⊙. The observed disk seems to be detached from the surrounding dense gas, although it is still embedded at the center of the core whose density is ˜106 cm-3. The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of ˜0.2 M ⊙ protostar. However, we cannot explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar (˜0.65 {R}⊙ ). These facts may challenge our current understanding of the low mass star formation, in particular the mass accretion process onto the protostar and the circumstellar disk.

LOOKING INTO THE HEARTS OF BOK GLOBULES: MILLIMETER AND SUBMILLIMETER CONTINUUM IMAGES OF ISOLATED STAR-FORMING CORES

International Nuclear Information System (INIS)

Launhardt, R.; Henning, Th.; Khanzadyan, T.; Schmalzl, M.; Wolf, S.; Nutter, D.; Ward-Thompson, D.; Bourke, T. L.; Zylka, R.

2010-01-01

We present the results of a comprehensive infrared, submillimeter, and millimeter continuum emission study of isolated low-mass star-forming cores in 32 Bok globules, with the aim to investigate the process of star formation in these regions. The submillimeter and millimeter dust continuum emission maps together with the spectral energy distributions are used to model and derive the physical properties of the star-forming cores, such as luminosities, sizes, masses, densities, etc. Comparisons with ground-based near-infrared and space-based mid- and far-infrared images from Spitzer are used to reveal the stellar content of the Bok globules, association of embedded young stellar objects (YSOs) with the submillimeter dust cores, and the evolutionary stages of the individual sources. Submillimeter dust continuum emission was detected in 26 out of the 32 globule cores observed. For 18 globules with detected (sub)millimeter cores, we derive evolutionary stages and physical parameters of the embedded sources. We identify nine starless cores, most of which are presumably prestellar, nine Class 0 protostars, and twelve Class I YSOs. Specific source properties like bolometric temperature, core size, and central densities are discussed as a function of evolutionary stage. We find that at least two thirds (16 out of 24) of the star-forming globules studied here show evidence of forming multiple stars on scales between 1000 and 50,000 AU. However, we also find that most of these small prototstar and star groups are comprised of sources with different evolutionary stages, suggesting a picture of slow and sequential star formation in isolated globules.

Observations of the interstellar ice grain feature in the Taurus molecular clouds

International Nuclear Information System (INIS)

Whittet, D.C.B.; Longmore, A.J.; Baines, D.W.T.; Evans, A.

1984-01-01

Although water ice was originally proposed as a major constituent of the interstellar grain population, the advent of infrared astronomy has shown that the expected absorption due to O-H stretching vibrations at 3 μm is illusive. Observations have in fact revealed that the carrier of this feature is apparently restricted to regions deep within dense molecular clouds. However, the exact carrier of this feature is still controversial, and many questions remain as to the conditions required for its appearance. The Taurus molecular clouds were selected for observations, in the form of a preliminary survey in the 2-4 μm window. It is concluded that the carrier of the 3μm absorption feature appears to reside in the general cloud medium and is probably amorphous water ice. (author)

RECONCILING THE OBSERVED STAR-FORMING SEQUENCE WITH THE OBSERVED STELLAR MASS FUNCTION

International Nuclear Information System (INIS)

Leja, Joel; Van Dokkum, Pieter G.; Franx, Marijn; Whitaker, Katherine E.

2015-01-01

We examine the connection between the observed star-forming sequence (SFR ∝ M α ) and the observed evolution of the stellar mass function in the range 0.2 < z < 2.5. We find that the star-forming sequence cannot have a slope α ≲ 0.9 at all masses and redshifts because this would result in a much higher number density at 10 < log (M/M ☉ ) < 11 by z = 1 than is observed. We show that a transition in the slope of the star-forming sequence, such that α = 1 at log (M/M ☉ ) < 10.5 and α = 0.7-0.13z (Whitaker et al.) at log (M/M ☉ ) > 10.5, greatly improves agreement with the evolution of the stellar mass function. We then derive a star-forming sequence that reproduces the evolution of the mass function by design. This star-forming sequence is also well described by a broken power law, with a shallow slope at high masses and a steep slope at low masses. At z = 2, it is offset by ∼0.3 dex from the observed star-forming sequence, consistent with the mild disagreement between the cosmic star formation rate (SFR) and recent observations of the growth of the stellar mass density. It is unclear whether this problem stems from errors in stellar mass estimates, errors in SFRs, or other effects. We show that a mass-dependent slope is also seen in other self-consistent models of galaxy evolution, including semianalytical, hydrodynamical, and abundance-matching models. As part of the analysis, we demonstrate that neither mergers nor hidden low-mass quiescent galaxies are likely to reconcile the evolution of the mass function and the star-forming sequence. These results are supported by observations from Whitaker et al

STAR-FORMING ACTIVITY IN THE H ii REGIONS ASSOCIATED WITH THE IRAS 17160–3707 COMPLEX

Energy Technology Data Exchange (ETDEWEB)

Nandakumar, G.; Veena, V. S.; Vig, S.; Tej, A. [Indian Institute of Space Science and Technology, Thiruvananthapuram 695 547 (India); Ghosh, S. K.; Ojha, D. K. [Tata Institute of Fundamental Research, Mumbai (Bombay) 400 005 (India)

2016-11-01

We present a multiwavelength investigation of star formation activity toward the southern H ii regions associated with IRAS 17160–3707, located at a distance of 6.2 kpc with a bolometric luminosity of 8.3 × 10{sup 5} L {sub ⊙}. The ionized gas distribution and dust clumps in the parental molecular cloud are examined in detail using measurements at infrared, submillimeter and radio wavelengths. The radio continuum images at 1280 and 610 MHz obtained using the Giant Metrewave Radio Telescope reveal the presence of multiple compact sources as well as nebulous emission. At submillimeter wavelengths, we identify seven dust clumps and estimate their physical properties such as temperature: 24–30 K, mass: 300–4800 M {sub ⊙} and luminosity: 9–317 × 10{sup 2} L {sub ⊙} using modified blackbody fits to the spectral energy distributions (SEDs) between 70 and 870 μ m. We find 24 young stellar objects (YSOs) in the mid-infrared, with a few of them coincident with the compact radio sources. The SEDs of the YSOs have been fitted by the Robitaille models and the results indicate that those having radio compact sources as counterparts host massive objects in early evolutionary stages with best fit age ≤0.2 Myr. We compare the relative evolutionary stages of clumps using various signposts such as masers, ionized gas, presence of YSOs and infrared nebulosity, and find six massive star-forming clumps and one quiescent clump. Of the former, five are in a relatively advanced stage and one in an earlier stage.

The environment and star formation of H II region Sh2-163: a multi-wavelength study

Science.gov (United States)

Yu, Naiping; Wang, Jun-Jie; Li, Nan

2014-12-01

To investigate the environment of H II region Sh2-163 and search for evidence of triggered star formation in this region, we performed a multi-wavelength study of this H II region. Most of our data were taken from large-scale surveys: 2MASS, CGPS, MSX and SCUBA. We also made CO molecular line observations, using the 13.7-m telescope. The ionized region of Sh2-163 is detected by both the optical and radio continuum observations. Sh2-163 is partially bordered by an arc-like photodissociation region (PDR), which is coincident with the strongest optical and radio emissions, indicating interactions between the H II region and the surrounding interstellar medium. Two molecular clouds were discovered on the border of the PDR. The morphology of these two clouds suggests they are compressed by the expansion of Sh2-163. In cloud A, we found two molecular clumps. And it seems star formation in clump A2 is much more active than in clump A1. In cloud B, we found new outflow activities and massive star(s) are forming inside. Using 2MASS photometry, we tried to search for embedded young stellar object (YSO) candidates in this region. The very good agreement between CO emission, infrared shell and YSOs suggest that it is probably a star formation region triggered by the expansion of Sh2-163. We also found the most likely massive protostar related to IRAS 23314+6033.

The star-forming content of the W3 giant molecular cloud

Science.gov (United States)

Moore, T. J. T.; Bretherton, D. E.; Fujiyoshi, T.; Ridge, N. A.; Allsopp, J.; Hoare, M. G.; Lumsden, S. L.; Richer, J. S.

2007-08-01

We have surveyed a ˜0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to 2500 M⊙. Part of the W3 GMC is subject to an interaction with the H ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5-13 per cent in the undisturbed cloud but ˜25-37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation.

Trigonometric parallaxes of high mass star forming regions: the structure and kinematics of the Milky Way

Energy Technology Data Exchange (ETDEWEB)

Reid, M. J.; Dame, T. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Menten, K. M.; Brunthaler, A.; Wu, Y.; Zhang, B.; Sanna, A.; Sato, M.; Choi, Y. K.; Immer, K. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Zheng, X. W. [Department of Astronomy, Nanjing University Nanjing 210093 (China); Xu, Y. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Hachisuka, K. [Shanghai Astronomical Observatory, 80 Nandan Rd., Shanghai (China); Moscadelli, L. [Arcetri Observatory, Firenze (Italy); Rygl, K. L. J. [European Space Agency (ESA-ESTEC), Keplerlaan 1, P.O. Box 299, 2200 AG, Noordwijk (Netherlands); Bartkiewicz, A. [Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun (Poland)

2014-03-10

Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the Bar and Spiral Structure Legacy Survey, a Very Long Baseline Array key science project, the European VLBI Network, and the Japanese VLBI Exploration of Radio Astrometry project. These measurements provide strong evidence for the existence of spiral arms in the Milky Way, accurately locating many arm segments and yielding spiral pitch angles ranging from about 7° to 20°. The widths of spiral arms increase with distance from the Galactic center. Fitting axially symmetric models of the Milky Way with the three-dimensional position and velocity information and conservative priors for the solar and average source peculiar motions, we estimate the distance to the Galactic center, R {sub 0}, to be 8.34 ± 0.16 kpc, a circular rotation speed at the Sun, Θ{sub 0}, to be 240 ± 8 km s{sup –1}, and a rotation curve that is nearly flat (i.e., a slope of –0.2 ± 0.4 km s{sup –1} kpc{sup –1}) between Galactocentric radii of ≈5 and 16 kpc. Assuming a 'universal' spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44 ± 0.16 kpc. With this large data set, the parameters R {sub 0} and Θ{sub 0} are no longer highly correlated and are relatively insensitive to different forms of the rotation curve. If one adopts a theoretically motivated prior that high-mass star forming regions are in nearly circular Galactic orbits, we estimate a global solar motion component in the direction of Galactic rotation, V {sub ☉} = 14.6 ± 5.0 km s{sup –1}. While Θ{sub 0} and V {sub ☉} are significantly correlated, the sum of these parameters is well constrained, Θ{sub 0} + V {sub ☉} = 255.2 ± 5.1 km s{sup –1}, as is the angular speed of the Sun in its orbit about the Galactic center, (Θ{sub 0} + V {sub ☉})/R {sub 0} = 30.57 ± 0.43 km s{sup –1} kpc{sup –1}. These parameters improve the accuracy

Correlation analysis of the Taurus molecular cloud complex

International Nuclear Information System (INIS)

Kleiner, S.C.

1985-01-01

Autocorrelation and power spectrum methods were applied to the analysis of the density and velocity structure of the Taurus Complex and Heiles Cloud 2 as traced out by 13 CO J = 1 → 0 molecular line observations obtained with the 14m antenna of the Five College Radio Astronomy Observatory. Statistically significant correlations in the spacing of density fluctuations within the Taurus Complex and Heiles 2 were uncovered. The length scales of the observed correlations correspond in magnitude to the Jeans wavelengths characterizing gravitational instabilities with (i) interstellar atomic hydrogen gas for the case of the Taurus complex, and (ii) molecular hydrogen for Heiles 2. The observed correlations may be the signatures of past and current gravitational instabilities frozen into the structure of the molecular gas. The appendices provide a comprehensive description of the analytical and numerical methods developed for the correlation analysis of molecular clouds

THE RELATION BETWEEN GAS AND DUST IN THE TAURUS MOLECULAR CLOUD

International Nuclear Information System (INIS)

Pineda, Jorge L.; Goldsmith, Paul F.; Chapman, Nicholas; Li Di; Snell, Ronald L.; Cambresy, Laurent; Brunt, Chris

2010-01-01

We report a study of the relation between dust and gas over a 100 deg 2 area in the Taurus molecular cloud. We compare the H 2 column density derived from dust extinction with the CO column density derived from the 12 CO and 13 CO J = 1 → 0 lines. We derive the visual extinction from reddening determined from 2MASS data. The comparison is done at an angular size of 200'' corresponding to 0.14 pc at a distance of 140 pc. We find that the relation between visual extinction A V and N(CO) is linear between A V ≅ 3 and 10 mag in the region associated with the B213-L1495 filament. In other regions, the linear relation is flattened for A V ∼> 4 mag. We find that the presence of temperature gradients in the molecular gas affects the determination of N(CO) by ∼30%-70% with the largest difference occurring at large column densities. Adding a correction for this effect and accounting for the observed relation between the column density of CO and CO 2 ices and A V , we find a linear relationship between the column of carbon monoxide and dust for observed visual extinctions up to the maximum value in our data ≅23 mag. We have used these data to study a sample of dense cores in Taurus. Fitting an analytical column density profile to these cores we derive an average volume density of about 1.4 x 10 4 cm -3 and a CO depletion age of about 4.2 x 10 5 yr. At visual extinctions smaller than ∼3 mag, we find that the CO fractional abundance is reduced by up to two orders of magnitude. The data show a large scatter suggesting a range of physical conditions of the gas. We estimate the H 2 mass of Taurus to be about 1.5 x 10 4 M sun , independently derived from the A V and N(CO) maps. We derive a CO integrated intensity to H 2 conversion factor of about 2.1 x 10 20 cm -2 (K km s -1 ) -1 , which applies even in the region where the [CO]/[H 2 ] ratio is reduced by up to two orders of magnitude. The distribution of column densities in our Taurus maps resembles a log

THE STAR FORMATION LAWS OF EDDINGTON-LIMITED STAR-FORMING DISKS

International Nuclear Information System (INIS)

Ballantyne, D. R.; Armour, J. N.; Indergaard, J.

2013-01-01

Two important avenues into understanding the formation and evolution of galaxies are the Kennicutt-Schmidt (K-S) and Elmegreen-Silk (E-S) laws. These relations connect the surface densities of gas and star formation (Σ gas and Σ-dot * , respectively) in a galaxy. To elucidate the K-S and E-S laws for disks where Σ gas ∼> 10 4 M ☉ pc –2 , we compute 132 Eddington-limited star-forming disk models with radii spanning tens to hundreds of parsecs. The theoretically expected slopes (≈1 for the K-S law and ≈0.5 for the E-S relation) are relatively robust to spatial averaging over the disks. However, the star formation laws exhibit a strong dependence on opacity that separates the models by the dust-to-gas ratio that may lead to the appearance of a erroneously large slope. The total infrared luminosity (L TIR ) and multiple carbon monoxide (CO) line intensities were computed for each model. While L TIR can yield an estimate of the average Σ-dot * that is correct to within a factor of two, the velocity-integrated CO line intensity is a poor proxy for the average Σ gas for these warm and dense disks, making the CO conversion factor (α CO ) all but useless. Thus, observationally derived K-S and E-S laws at these values of Σ gas that uses any transition of CO will provide a poor measurement of the underlying star formation relation. Studies of the star formation laws of Eddington-limited disks will require a high-J transition of a high density molecular tracer, as well as a sample of galaxies with known metallicity estimates.

Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament

Energy Technology Data Exchange (ETDEWEB)

Choi, Yunhee; Lee, Jeong-Eun [School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104 (Korea, Republic of); Bourke, Tyler L. [Square Kilometre Array Organisation, Jodrell Bank Observatory, Lower Withington, Cheshire SK11 9DL (United Kingdom); II, Neal J. Evans, E-mail: yunhee.choi@khu.ac.kr, E-mail: jeongeun.lee@khu.ac.kr [Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States)

2017-04-01

We present observations and analyses of the low-mass star-forming region, Taurus Molecular Cloud-1 (TMC-1). CS ( J = 2–1)/N{sub 2}H{sup +} ( J = 1–0) and C{sup 17}O ( J = 2–1)/C{sup 18}O ( J = 2–1) were observed with the Five College Radio Astronomy Observatory and the Seoul Radio Astronomy Observatory, respectively. In addition, Spitzer infrared data and 1.2 mm continuum data observed with Max-Planck Millimetre Bolometer are used. We also perform chemical modeling to investigate the relative molecular distributions of the TMC-1 filament. Based on Spitzer observations, there is no young stellar object along the TMC-1 filament, while five Class II and one Class I young stellar objects are identified outside the filament. The comparison between column densities calculated from dust continuum and C{sup 17}O 2–1 line emission shows that CO is depleted much more significantly in the ammonia peak than in the cyanopolyyne peak, while the column densities calculated from the dust continuum are similar at the two peaks. N{sub 2}H{sup +} is not depleted much in either peak. According to our chemical calculation, the differential chemical distribution in the two peaks can be explained by different timescales required to reach the same density, i.e., by different dynamical processes.

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.

{sup 13}C-METHYL FORMATE: OBSERVATIONS OF A SAMPLE OF HIGH-MASS STAR-FORMING REGIONS INCLUDING ORION-KL AND SPECTROSCOPIC CHARACTERIZATION

Energy Technology Data Exchange (ETDEWEB)

Favre, Cécile; Bergin, Edwin A.; Crockett, Nathan R.; Neill, Justin L. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Carvajal, Miguel [Dpto. Física Aplicada, Unidad Asociada CSIC, Facultad de Ciencias Experimentales, Universidad de Huelva, E-21071 Huelva (Spain); Field, David [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Jørgensen, Jes K.; Bisschop, Suzanne E. [Centre for Star and Planet Formation, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø (Denmark); Brouillet, Nathalie; Despois, Didier; Baudry, Alain [Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France); Kleiner, Isabelle [Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS, UMR 7583, Université de Paris-Est et Paris Diderot, 61, Av. du Général de Gaulle, F-94010 Créteil Cedex (France); Margulès, Laurent; Huet, Thérèse R.; Demaison, Jean, E-mail: cfavre@umich.edu, E-mail: miguel.carvajal@dfa.uhu.es [Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, Université Lille I, F-59655 Villeneuve d' Ascq Cedex (France)

2015-01-01

We have surveyed a sample of massive star-forming regions located over a range of distances from the Galactic center for methyl formate, HCOOCH{sub 3}, and its isotopologues H{sup 13}COOCH{sub 3} and HCOO{sup 13}CH{sub 3}. The observations were carried out with the APEX telescope in the frequency range 283.4-287.4 GHz. Based on the APEX observations, we report tentative detections of the {sup 13}C-methyl formate isotopologue HCOO{sup 13}CH{sub 3} toward the following four massive star-forming regions: Sgr B2(N-LMH), NGC 6334 IRS 1, W51 e2, and G19.61-0.23. In addition, we have used the 1 mm ALMA science verification observations of Orion-KL and confirm the detection of the {sup 13}C-methyl formate species in Orion-KL and image its spatial distribution. Our analysis shows that the {sup 12}C/{sup 13}C isotope ratio in methyl formate toward the Orion-KL Compact Ridge and Hot Core-SW components (68.4 ± 10.1 and 71.4 ± 7.8, respectively) are, for both the {sup 13}C-methyl formate isotopologues, commensurate with the average {sup 12}C/{sup 13}C ratio of CO derived toward Orion-KL. Likewise, regarding the other sources, our results are consistent with the {sup 12}C/{sup 13}C in CO. We also report the spectroscopic characterization, which includes a complete partition function, of the complex H{sup 13}COOCH{sub 3} and HCOO{sup 13}CH{sub 3} species. New spectroscopic data for both isotopomers H{sup 13}COOCH{sub 3} and HCOO{sup 13}CH{sub 3}, presented in this study, have made it possible to measure this fundamentally important isotope ratio in a large organic molecule for the first time.

Subsonic islands within a high-mass star-forming infrared dark cloud

Science.gov (United States)

Sokolov, Vlas; Wang, Ke; Pineda, Jaime E.; Caselli, Paola; Henshaw, Jonathan D.; Barnes, Ashley T.; Tan, Jonathan C.; Fontani, Francesco; Jiménez-Serra, Izaskun; Zhang, Qizhou

2018-03-01

High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combined Very Large Array and Green Bank Telescope (VLA+GBT) observations of NH3 (1,1) and (2,2) in the infrared dark cloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast to previous, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermal motions (mean line width of 0.71 km s-1), and sonic Mach number distribution peaks around ℳ = 1. As possible observational and instrumental biases would only broaden the line profiles, our results provide strong upper limits to the actual value of ℳ, further strengthening our findings of narrow line widths. This finding calls for a re-evaluation of the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findings in G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH3 studies may have inhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamically important magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Our results offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-mass star and cluster formation.

Nitrogen fractionation in high-mass star-forming cores across the Galaxy

Science.gov (United States)

Colzi, L.; Fontani, F.; Rivilla, V. M.; Sánchez-Monge, A.; Testi, L.; Beltrán, M. T.; Caselli, P.

2018-04-01

The fractionation of nitrogen (N) in star-forming regions is a poorly understood process. To put more stringent observational constraints on the N-fractionation, we have observed with the IRAM-30m telescope a large sample of 66 cores in massive star-forming regions. We targeted the (1-0) rotational transition of HN13C, HC15N, H13CN and HC15N, and derived the 14N/15N ratio for both HCN and HNC. We have completed this sample with that already observed by Colzi et al. (2018), and thus analysed a total sample of 87 sources. The 14N/15N ratios are distributed around the Proto-Solar Nebula value with a lower limit near the terrestrial atmosphere value (˜272). We have also derived the 14N/15N ratio as a function of the Galactocentric distance and deduced a linear trend based on unprecedented statistics. The Galactocentric dependences that we have found are consistent, in the slope, with past works but we have found a new local 14N/15N value of ˜400, i.e. closer to the Prosolar Nebula value. A second analysis was done, and a parabolic Galactocentric trend was found. Comparison with Galactic chemical evolution models shows that the slope until 8 kpc is consistent with the linear analysis, while the flattening trend above 8 kpc is well reproduced by the parabolic analysis.

Physical and chemical differentiation of the luminous star-forming region W49A. Results from the JCMT Spectral Legacy Survey

Science.gov (United States)

Nagy, Z.; van der Tak, F. F. S.; Fuller, G. A.; Plume, R.

2015-05-01

Context. The massive and luminous star-forming region W49A is a well-known Galactic candidate to probe the physical conditions and chemistry similar to those expected in external starburst galaxies. Aims: We aim to probe the physical and chemical structure of W49A on a spatial scale of ~0.8 pc based on the JCMT Spectral Legacy Survey, which covers the frequency range between 330 and 373 GHz. Methods: The wide 2 × 2 arcmin field and the high spectral resolution of the HARP instrument on JCMT provides information on the spatial structure and kinematics of the cloud traced by the observed molecular lines. For species where multiple transitions are available, we estimate excitation temperatures and column densities using a population diagram method that takes beam dilution and optical depth corrections into account. Results: We detected 255 transitions corresponding to 63 species in the 330-373 GHz range at the center position of W49A. Excitation conditions can be probed for 14 molecules, including the complex organic molecules CH3CCH, CH3CN, and CH3OH. The chemical composition suggests the importance of shock, photon-dominated region (PDR), and hot core chemistry. Many molecular lines show a significant spatial extent across the maps including CO and its isotopologues, high density tracers (e.g., HCN, HNC, CS, HCO+), and tracers of UV irradiation (e.g., CN and C2H). The spatially extended species reveal a complex velocity-structure of W49A with possible infall and outflow motions. Large variations are seen between the subregions with mostly blue-shifted emission toward the eastern tail, mostly red-shifted emission toward the northern clump, and emission peaking around the expected source velocity toward the southwest clump. Conclusions: A comparison of column density ratios of characteristic species observed toward W49A to Galactic PDRs suggests that while the chemistry toward the W49A center is driven by a combination of UV irradiation and shocks, UV irradiation

Polarization Properties and Magnetic Field Structures in the High-mass Star-forming Region W51 Observed with ALMA

Science.gov (United States)

Koch, Patrick M.; Tang, Ya-Wen; Ho, Paul T. P.; Yen, Hsi-Wei; Su, Yu-Nung; Takakuwa, Shigehisa

2018-03-01

We present the first ALMA dust polarization observations toward the high-mass star-forming regions W51 e2, e8, and W51 North in Band 6 (230 GHz) with a resolution of about 0\\buildrel{\\prime\\prime}\\over{.} 26 (∼5 mpc). Polarized emission in all three sources is clearly detected and resolved. Measured relative polarization levels are between 0.1% and 10%. While the absolute polarization shows complicated structures, the relative polarization displays the typical anticorrelation with Stokes I, although with a large scatter. Inferred magnetic (B) field morphologies are organized and connected. Detailed substructures are resolved, revealing new features such as comet-shaped B-field morphologies in satellite cores, symmetrically converging B-field zones, and possibly streamlined morphologies. The local B-field dispersion shows some anticorrelation with the relative polarization. Moreover, the lowest polarization percentages together with largest dispersions coincide with B-field convergence zones. We put forward \\sin ω , where ω is the measurable angle between a local B-field orientation and local gravity, as a measure of how effectively the B field can oppose gravity. Maps of \\sin ω for all three sources show organized structures that suggest a locally varying role of the B field, with some regions where gravity can largely act unaffectedly, possibly in a network of narrow magnetic channels, and other regions where the B field can work maximally against gravity.

THE SPITZER c2d SURVEY OF WEAK-LINE T TAURI STARS. III. THE TRANSITION FROM PRIMORDIAL DISKS TO DEBRIS DISKS

International Nuclear Information System (INIS)

Wahhaj, Zahed; Cieza, Lucas; Koerner, David W.; Case, April; Stapelfeldt, Karl R.; Chapman, Nicholas; Padgett, Deborah L.; Brooke, Tim; Keller, James R.; MerIn, Bruno; Evans, Neal J.; Harvey, Paul; Sargent, Anneila; Van Dishoeck, Ewine F.; Allen, Lori; Blake, Geoff; Mundy, Lee; Myers, Philip C.

2010-01-01

We present 3.6 to 70 μm Spitzer photometry of 154 weak-line T Tauri stars (WTTSs) in the Chamaeleon, Lupus, Ophiuchus, and Taurus star formation regions, all of which are within 200 pc of the Sun. For a comparative study, we also include 33 classical T Tauri stars which are located in the same star-forming regions. Spitzer sensitivities allow us to robustly detect the photosphere in the IRAC bands (3.6 to 8 μm) and the 24 μm MIPS band. In the 70 μm MIPS band, we are able to detect dust emission brighter than roughly 40 times the photosphere. These observations represent the most sensitive WTTSs survey in the mid- to far-infrared to date and reveal the frequency of outer disks (r = 3-50 AU) around WTTSs. The 70 μm photometry for half the c2d WTTSs sample (the on-cloud objects), which were not included in the earlier papers in this series, those of Padgett et al. and Cieza et al., are presented here for the first time. We find a disk frequency of 19% for on-cloud WTTSs, but just 5% for off-cloud WTTSs, similar to the value reported in the earlier works. WTTSs exhibit spectral energy distributions that are quite diverse, spanning the range from optically thick to optically thin disks. Most disks become more tenuous than L disk /L * = 2 x 10 -3 in 2 Myr and more tenuous than L disk /L * = 5 x 10 -4 in 4 Myr.

Cosmic-ray energy densities in star-forming galaxies

Directory of Open Access Journals (Sweden)

Persic Massimo

2017-01-01

Full Text Available The energy density of cosmic ray protons in star forming galaxies can be estimated from π0-decay γ-ray emission, synchrotron radio emission, and supernova rates. To galaxies for which these methods can be applied, the three methods yield consistent energy densities ranging from Up ~ 0.1 − 1 eV cm−3 to Up ~ 102 − 103 eV cm−3 in galaxies with low to high star-formation rates, respectively.

X-Ray Flare Oscillations Track Plasma Sloshing along Star-disk Magnetic Tubes in the Orion Star-forming Region

Science.gov (United States)

Reale, Fabio; Lopez-Santiago, Javier; Flaccomio, Ettore; Petralia, Antonino; Sciortino, Salvatore

2018-03-01

Pulsing X-ray emission tracks the plasma “echo” traveling in an extremely long magnetic tube that flares in an Orion pre-main sequence (PMS) star. On the Sun, flares last from minutes to a few hours and the longest-lasting ones typically involve arcades of closed magnetic tubes. Long-lasting X-ray flares are observed in PMS stars. Large-amplitude (∼20%), long-period (∼3 hr) pulsations are detected in the light curve of day-long flares observed by the Advanced CCD Imaging Spectrometer on-board Chandra from PMS stars in the Orion cluster. Detailed hydrodynamic modeling of two flares observed on V772 Ori and OW Ori shows that these pulsations may track the sloshing of plasma along a single long magnetic tube, triggered by a sufficiently short (∼1 hr) heat pulse. These magnetic tubes are ≥20 solar radii long, enough to connect the star with the surrounding disk.

Star Formation in Irregular Galaxies.

Science.gov (United States)

Hunter, Deidre; Wolff, Sidney

1985-01-01

Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

THE STAR FORMATION LAWS OF EDDINGTON-LIMITED STAR-FORMING DISKS

Energy Technology Data Exchange (ETDEWEB)

Ballantyne, D. R.; Armour, J. N.; Indergaard, J., E-mail: david.ballantyne@physics.gatech.edu [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)

2013-03-10

Two important avenues into understanding the formation and evolution of galaxies are the Kennicutt-Schmidt (K-S) and Elmegreen-Silk (E-S) laws. These relations connect the surface densities of gas and star formation ({Sigma}{sub gas} and {Sigma}-dot{sub *}, respectively) in a galaxy. To elucidate the K-S and E-S laws for disks where {Sigma}{sub gas} {approx}> 10{sup 4} M{sub Sun} pc{sup -2}, we compute 132 Eddington-limited star-forming disk models with radii spanning tens to hundreds of parsecs. The theoretically expected slopes ( Almost-Equal-To 1 for the K-S law and Almost-Equal-To 0.5 for the E-S relation) are relatively robust to spatial averaging over the disks. However, the star formation laws exhibit a strong dependence on opacity that separates the models by the dust-to-gas ratio that may lead to the appearance of a erroneously large slope. The total infrared luminosity (L{sub TIR}) and multiple carbon monoxide (CO) line intensities were computed for each model. While L{sub TIR} can yield an estimate of the average {Sigma}-dot{sub *} that is correct to within a factor of two, the velocity-integrated CO line intensity is a poor proxy for the average {Sigma}{sub gas} for these warm and dense disks, making the CO conversion factor ({alpha}{sub CO}) all but useless. Thus, observationally derived K-S and E-S laws at these values of {Sigma}{sub gas} that uses any transition of CO will provide a poor measurement of the underlying star formation relation. Studies of the star formation laws of Eddington-limited disks will require a high-J transition of a high density molecular tracer, as well as a sample of galaxies with known metallicity estimates.

The Drifting Star

Science.gov (United States)

2008-04-01

temperature is 6150 K, its mass is 1.25 times that of the Sun, and its age is 625 million years. Moreover, the star is found to be more metal-rich than the Sun by about 50%. ESO PR Photo 09b/08 ESO PR Photo 09b/08 Constellations "These results show the power of asteroseismology when using a very precise instrument such as HARPS," says Vauclair. "It also shows that Iota Horologii has the same metal abundance and age as the Hyades cluster and this cannot be a coincidence." The Hyades is an ensemble of stars that is seen with the unaided eye in the Northern constellation Taurus ("The Bull"). This open cluster, located 151 light-years away, contains stars that were formed together 625 million years ago. The star Iota Horologii must have thus formed together with the stars of the Hyades cluster but must have slowly drifted away, being presently more than 130 light-years away from its original birthplace. This is an important result to understand how stars move on the galactic highways of the Milky Way. This also means that the amount of metals present in the star is due to the original cloud from which it formed and not because it engulfed planetary material. "The chicken and egg question of whether the star got planets because it is metal-rich, or whether it is metal-rich because it made planets that were swallowed up is at least answered in one case," says Vauclair. More information The astronomers' study is being published as a Letter to the Editor in Astronomy and Astrophysics ("The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster", by S. Vauclair et al.). The team is composed of Sylvie Vauclair, Marion Laymand, Gérard Vauclair, Alain Hui Bon Hoa, and Stéphane Charpinet (LATT, Toulouse, France), François Bouchy (IAP, Paris, France), and Michaël Bazot (University of Porto, Portugal).

Properties of symbiotic stars from studies in the optical region

International Nuclear Information System (INIS)

Ciatti, F.

1982-01-01

The author uses observations of symbiotic stars in the optical region to discuss the following aspects: definition, photometric and spectroscopic evolution, the three-component model, evidence for the binary nature, spectroscopic properties and anomalies, single-star interpretations, the ''very slow novae'' and BQ// stars and a comparison of symbiotic stars with other classes. (C.F.)

THE PRESSURE OF THE STAR-FORMING INTERSTELLAR MEDIUM IN COSMOLOGICAL SIMULATIONS

International Nuclear Information System (INIS)

Munshi, Ferah; Quinn, Thomas R.; Governato, Fabio; Christensen, Charlotte; Wadsley, James; Loebman, Sarah; Shen, Sijing

2014-01-01

We examine the pressure of the star-forming interstellar medium (ISM) of Milky-Way-sized disk galaxies using fully cosmological SPH+N-body, high-resolution simulations. These simulations include explicit treatment of metal-line cooling in addition to dust and self-shielding, H 2 -based star formation. The four simulated halos have masses ranging from a few times 10 10 to nearly 10 12 solar masses. Using a kinematic decomposition of these galaxies into present-day bulge and disk components, we find that the typical pressure of the star-forming ISM in the present-day bulge is higher than that in the present-day disk by an order of magnitude. We also find that the pressure of the star-forming ISM at high redshift is, on average, higher than ISM pressures at low redshift. This explains why the bulge forms at higher pressures: the disk assembles at lower redshift when the ISM exhibits lower pressure and the bulge forms at high redshift when the ISM has higher pressure. If ISM pressure and IMF variation are tied together, these results could indicate a time-dependent IMF in Milky-Way-like systems as well as a different IMF in the bulge and the disk

Central regions of LIRGs: rings, hidden starbursts, Supernovae and star clusters

International Nuclear Information System (INIS)

Väisänen, Petri; Randriamanakoto, Zara; Escala, Andres; Kankare, Erkki; Mattila, Seppo; Reunanen, Juha; Kotilainen, Jari; Rajpaul, Vinesh; Ryder, Stuart; Zijlstra, Albert

2012-01-01

We study star formation (SF) in very active environments, in luminous IR galaxies, which are often interacting. A variety of phenomena are detected, such as central starbursts, circumnuclear SF, obscured SNe tracing the history of recent SF, massive super star clusters, and sites of strong off-nuclear SF. All of these can be ultimately used to define the sequence of triggering and propagation of star-formation and interplay with nuclear activity in the lives of gas rich galaxy interactions and mergers. In this paper we present analysis of high-spatial resolution integral field spectroscopy of central regions of two interacting LIRGs. We detect a nuclear 3.3 μm PAH ring around the core of NGC 1614 with thermal-IR IFU observations. The ring's characteristics and relation to the strong star-forming ring detected in recombination lines are presented, as well as a scenario of an outward expanding starburst likely initiated with a (minor) companion detected within a tidal feature. We then present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an intriguing triple encounter. The third component is a minor one, but, nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows and outflows are detected in their nuclei locations. Finally, we briefly report on our on-going NIR adaptive optics imaging survey of several dozen LIRGs. We have detected highly obscured core-collapse SNe in the central kpc, and discuss the statistics of 'missing SNe' due to dust extinction. We are also determining the characteristics of hundreds of super star clusters in and around the core regions of LIRGs, as a function of host-galaxy properties.

Gas in the Terrestrial Planet Region of Disks: CO Fundamental Emission from T Tauri Stars

Science.gov (United States)

2003-06-01

planetary systems: protoplanetary disks — stars: variables: other 1. INTRODUCTION As the likely birthplaces of planets, the inner regions of young...both low column density regions, such as disk gaps , and temperature inversion regions in disk atmospheres can produce significant emission. The esti...which planetary systems form. The moti- vation to study inner disks is all the more intense today given the discovery of planets outside the solar system

INTERACTIONS BETWEEN FORMING STARS AND DENSE GAS IN THE SMALL LOW-MASS CLUSTER CEDERBLAD 110

Energy Technology Data Exchange (ETDEWEB)

Ladd, E. F. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Wong, T. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Thompson, K. L., E-mail: ladd@bucknell.edu [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States)

2011-12-20

We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaeleon I dark cloud complex. The region contains nine forming low-mass stars in evolutionary stages ranging from Class 0 to Class II/III crowded into a 0.2 pc region with high surface density ({Sigma}{sub YSO} {approx} 150 pc{sup -2}). The analysis of our N{sub 2}H{sup +} (J = 1{yields}0) maps indicates the presence of 13 {+-} 3 solar masses of dense (n {approx} 10{sup 5} cm{sup -3}) gas in this region, much of which is unstable against gravitational collapse. The most unstable material is located near the Class 0 source MMS-1, which is almost certainly actively accreting material from its dense core. Smaller column densities of more stable dense gas are found toward the region's Class I sources, IRS 4, 11, and 6. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from IRS 4 is interacting with the dense core associated with MMS-1. The molecular component of the outflow, measured in the (J = 1{yields}0) line of {sup 12}CO, appears to be deflected by the densest part of the core, after which it appears to plow through some of the lower column density portions of the core. The working surface between the head of the outflow lobe and the dense core material can be seen in the enhanced velocity dispersion of the dense gas. IRS 2, the Class III source that produces the optical reflection nebula that gives the Cederblad 110 region its name, may also be influencing the dense gas in the region. A dust temperature gradient across the MMS-1 dense core is consistent with warming from IRS 2, and a sharp gradient in dense gas column density may be caused by winds from this source. Taken together, our data indicate that this region has been producing several young stars in the recent past, and that sources which began forming first are interacting with the remaining dense gas in the region, thereby influencing current and future star

Hearily reddened Hg-Mn star HD 29647

International Nuclear Information System (INIS)

Strajzhis, V.; Glagolevskij, Yu.V.; Romanyuk, I.I.; Bychkov, V.D.; AN SSSR, Nizhnij Arkhyz. Spetsial'naya Astrofizicheskaya Observatoriya)

1982-01-01

A heavily reddened HD 29647 (V=8sup(m).4) star is investigated using the 6-meter telescope spectrograms with dispersions 9 and 28 A/mm and photometric observations in the Vilnius seven- color system. Parameters Tsub(e)=15600 K (corresponding spectral type B5) and log g=3.70 from hydrogen lines and Balmer jump were obtained. HD 29647 is a peculiar star of the Hg-Mn type. The radial velocity of the star is+14.1+-1.0 km/s, almost identical with that of the dark Taurus cloud and its T Tauri-type variables. If the star is near the front edge of the dark cloud at the distance of 165 pc and has Esub(B-V)=1.06, its visual absolute magnitude is - 0sup(m).9. Photometric observations permit to suspect a slight varia bility in the U, P, and X colors [ru

The Swift/UVOT catalogue of NGC 4321 star-forming sources: a case against density wave theory

Science.gov (United States)

Ferreras, Ignacio; Cropper, Mark; Kawata, Daisuke; Page, Mat; Hoversten, Erik A.

2012-08-01

We study the star-forming regions in the spiral galaxy NGC 4321 (M100). We take advantage of the spatial resolution (2.5 arcsec full width at half-maximum) of the Swift/Ultraviolet/Optical Telescope camera and the availability of three ultraviolet (UV) passbands in the region 1600 spiral arms. The Hα luminosities of the sources have a strong decreasing radial trend, suggesting more massive star-forming regions in the central part of the galaxy. When segregated with respect to near-UV (NUV)-optical colour, blue sources have a significant excess of flux in the IR at 8 μm, revealing the contribution from polycyclic aromatic hydrocarbons, although the overall reddening of these sources stays below E(B - V) = 0.2 mag. The distribution of distances to the spiral arms is compared for subsamples selected according to Hα luminosity, NUV-optical colour or ages derived from a population synthesis model. An offset would be expected between these subsamples as a function of radius if the pattern speed of the spiral arm were constant - as predicted by classic density wave theory. No significant offsets are found, favouring instead a mechanism where the pattern speed has a radial dependence.

A CENSUS OF OXYGEN IN STAR-FORMING GALAXIES: AN EMPIRICAL MODEL LINKING METALLICITIES, STAR FORMATION RATES, AND OUTFLOWS

International Nuclear Information System (INIS)

Zahid, H. J.; Dima, G. I.; Kewley, L. J.; Erb, D. K.; Davé, R.

2012-01-01

In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass-metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

Spectropolarimetry of the 3μm ice band in Elias 16 (Taurus Dark Cloud)

International Nuclear Information System (INIS)

Hough, J.H.; Sato, Shuji; Tamura, Motohide

1988-01-01

Polarization data between 1.2 and 3.8 μm, including spectro-polarimetry in the 3-μm ice feature, are presented for the highly reddened field star Elias 16 in the Taurus Dark Cloud. The polarization is observed to increase with optical depth in the ice feature in a manner similar to that found for the BN object, that is, consistent with dichroic absorption by aligned grains. The polarization feature can be well modelled assuming grains composed of ammonia-water ices, with the ratio of H 2 O:NH 3 greater than 3:1. The continuum polarization can be well fitted over most of the observed wavelength range assuming a mix of silicate and graphite grains with size ∼ 0.13μm. (author)

Spectral energy distribution analysis of class I and class II FU Orionis stars

Energy Technology Data Exchange (ETDEWEB)

Gramajo, Luciana V.; Gómez, Mercedes [Observatorio Astronómico, Universidad Nacional de Córdoba, Argentina, Laprida 854, 5000 Córdoba (Argentina); Rodón, Javier A., E-mail: luciana@oac.uncor.edu, E-mail: mercedes@oac.uncor.edu, E-mail: jrodon@eso.org [European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile)

2014-06-01

FU Orionis stars (FUors) are eruptive pre-main sequence objects thought to represent quasi-periodic or recurring stages of enhanced accretion during the low-mass star-forming process. We characterize the sample of known and candidate FUors in a homogeneous and consistent way, deriving stellar and circumstellar parameters for each object. We emphasize the analysis in those parameters that are supposed to vary during the FUor stage. We modeled the spectral energy distributions of 24 of the 26 currently known FUors, using the radiative transfer code of Whitney et al. We compare our models with those obtained by Robitaille et al. for Taurus class II and I sources in quiescence periods by calculating the cumulative distribution of the different parameters. FUors have more massive disks: we find that ∼80% of the disks in FUors are more massive than any Taurus class II and I sources in the sample. Median values for the disk mass accretion rates are ∼10{sup –7} M {sub ☉} yr{sup –1} versus ∼10{sup –5} M {sub ☉} yr{sup –1} for standard young stellar objects (YSOs) and FUors, respectively. While the distributions of envelope mass accretion rates for class I FUors and standard class I objects are similar, FUors, on average, have higher envelope mass accretion rates than standard class II and class I sources. Most FUors (∼70%) have envelope mass accretion rates above 10{sup –7} M {sub ☉} yr{sup –1}. In contrast, 60% of the classical YSO sample has an accretion rate below this value. Our results support the current scenario in which changes experimented by the circumstellar disk explain the observed properties of these stars. However, the increase in the disk mass accretion rate is smaller than theoretically predicted, although in good agreement with previous determinations.

CONTINUOUS MID-INFRARED STAR FORMATION RATE INDICATORS: DIAGNOSTICS FOR 0 < z < 3 STAR-FORMING GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Battisti, A. J.; Calzetti, D. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Johnson, B. D. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Elbaz, D., E-mail: abattist@astro.umass.edu [Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu, CNRS, Université Paris Diderot, Saclay, pt courrier 131, F-91191 Gif-sur-Yvette (France)

2015-02-20

We present continuous, monochromatic star formation rate (SFR) indicators over the mid-infrared wavelength range of 6–70 μm. We use a sample of 58 star-forming galaxies (SFGs) in the Spitzer–SDSS–GALEX Spectroscopic Survey at z < 0.2, for which there is a rich suite of multi-wavelength photometry and spectroscopy from the ultraviolet through to the infrared. The data from the Spitzer Infrared Spectrograph (IRS) of these galaxies, which spans 5–40 μm, is anchored to their photometric counterparts. The spectral region between 40–70 μm is interpolated using dust model fits to the IRS spectrum and Spitzer 70 and 160 μm photometry. Since there are no sharp spectral features in this region, we expect these interpolations to be robust. This spectral range is calibrated as a SFR diagnostic using several reference SFR indicators to mitigate potential bias. Our band-specific continuous SFR indicators are found to be consistent with monochromatic calibrations in the local universe, as derived from Spitzer, WISE, and Herschel photometry. Our local composite template and continuous SFR diagnostics are made available for public use through the NASA/IPAC Infrared Science Archive (IRSA) and have typical dispersions of 30% or less. We discuss the validity and range of applicability for our SFR indicators in the context of unveiling the formation and evolution of galaxies. Additionally, in the era of the James Webb Space Telescope this will become a flexible tool, applicable to any SFG up to z ∼ 3.

THE JCMT GOULD BELT SURVEY: EVIDENCE FOR DUST GRAIN EVOLUTION IN PERSEUS STAR-FORMING CLUMPS

Energy Technology Data Exchange (ETDEWEB)

Chen, Michael Chun-Yuan; Francesco, J. Di; Johnstone, D.; Broekhoven-Fiene, H. [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Sadavoy, S. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Hatchell, J. [Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Mottram, J. C.; Hogerheijde, M. R. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Kirk, H. [NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Buckle, J.; Salji, C. [Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE (United Kingdom); Berry, D. S.; Currie, M. J.; Jenness, T. [Joint Astronomy Centre, 660 North A‘ohōkū Place, University Park, Hilo, HI-96720 (United States); Fich, M.; Tisi, S. [Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Nutter, D.; Quinn, C. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA (United Kingdom); Pattle, K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE (United Kingdom); Pineda, J. E. [European Southern Observatory (ESO), Garching (Germany); and others

2016-07-20

The dust emissivity spectral index, β , is a critical parameter for deriving the mass and temperature of star-forming structures and, consequently, their gravitational stability. The β value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present β , dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting spectral energy distributions to combined Herschel and JCMT observations in the 160, 250, 350, 500, and 850 μ m bands. Most of the derived β and dust temperature values fall within the ranges of 1.0–2.7 and 8–20 K, respectively. In Perseus, we find the β distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant localized β variations within individual clumps and find low- β regions correlate with local temperature peaks, hinting at the possible origins of low- β grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.

TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

Energy Technology Data Exchange (ETDEWEB)

Liu Tie; Wu Yuefang; Zhang Huawei [Department of Astronomy, Peking University, 100871 Beijing (China); Qin Shengli, E-mail: liutiepku@gmail.com [I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln (Germany)

2012-05-20

The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

International Nuclear Information System (INIS)

Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

2012-01-01

The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10 3 cm –3 and kinematic temperature ∼20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

The L1495-B218 filaments in Taurus seen in NH3 & CCS and Dynamical Stability of Filaments and Dense Cores

Science.gov (United States)

Seo, Youngmin

2016-01-01

We present deep NH3 map of L1495-B218 filaments and the dense cores embedded within the filaments in Taurus. The L1495-B218 filaments form an interconnected, nearby, large complex extending 8 pc. We observed the filaments in NH3 (1,1) & (2,2) and CCS 21-10 with spectral resolution of 0.038 km/s and spatial resolution of 31". The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithm, identifies 39 leaves and 16 branches in NH3 (1,1). Applying a virial analysis for the 39 NH3 leaves, we find only 9 out of 39 leaves are gravitationally bound, and 12 out of 30 gravitationally unbound leaves are pressure-confined. Our analysis suggests that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and then undergo collapse to form a protostar (Seo et al. 2015).We also present more realistic dynamic stability conditions for dense cores with converging motions and under the influence of radiation pressure. The critical Bonnor-Ebert sphere and the isothermal cylinder have been widely used to test stability of dense cores and filaments; however, these assume a quiescent environment while actual star forming regions are turbulent and illuminated by radiation. In a new analysis of stability conditions we account for converging motions which have been modeled toward starless cores (Seo et al. 2011) and the effect of radiation fields into account. We find that the critical size of a dense core having a homologous converging motion with its peak speed being the sound speed is roughly half of the critical size of the Bonnor-Ebert sphere (Seo et al. 2013). We also find that the critical mass/line density of a dense core/filament irradiated by radiation are considerably smaller than that of the Bonnor-Ebert sphere/isothermal cylinder when the radiation pressure is stronger than the central gas pressure of dense core/isothermal cylinder. For inner Galactic regions and regions near OB associations, the critical

GEOMETRY OF STAR-FORMING GALAXIES FROM SDSS, 3D-HST, AND CANDELS

International Nuclear Information System (INIS)

Van der Wel, A.; Chang, Yu-Yen; Rix, H.-W.; Martig, M.; Bell, E. F.; Holden, B. P.; Koo, D. C.; Mozena, M.; Faber, S. M.; Ferguson, H. C.; Brammer, G.; Kassin, S. A.; Giavalisco, M.; Skelton, R.; Whitaker, K.; Momcheva, I.; Van Dokkum, P. G.; Dekel, A.; Ceverino, D.; Franx, M.

2014-01-01

We determine the intrinsic, three-dimensional shape distribution of star-forming galaxies at 0 < z < 2.5, as inferred from their observed projected axis ratios. In the present-day universe, star-forming galaxies of all masses 10 9 -10 11 M ☉ are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M * > 10 10 M ☉ ) disks are the most common geometric shape at all z ≲ 2. Lower-mass galaxies at z > 1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 10 9 M ☉ (10 10 M ☉ ) are a mix of roughly equal numbers of elongated and disk galaxies at z ∼ 1 (z ∼ 2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z ∼ 1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks

Variations of the ISM conditions accross the Main Sequence of star forming galaxies: observations and simulations.

Science.gov (United States)

Martinez Galarza, Juan R.; Smith, Howard Alan; Lanz, Lauranne; Hayward, Christopher C.; Zezas, Andreas; Hung, Chao-Ling; Rosenthal, Lee; Weiner, Aaron

2015-01-01

A significant amount of evidence has been gathered that leads to the existence of a main sequence (MS) of star formation in galaxies. This MS is expressed in terms of a correlation between the SFR and the stellar mass of the form SFR ∝ M* and spans a few orders of magnitude in both quantities. Several ideas have been suggested to explain fundamental properties of the MS, such as its slope, its dispersion, and its evolution with redshift, but no consensus has been reached regarding its true nature, and whether the membership or not of particular galaxies to this MS underlies the existence of two different modes of star formation. In order to advance in the understanding of the MS, here we use a statistically robust Bayesian SED analysis method (CHIBURST) to consistently analyze the star-forming properties of a set of hydro-dynamical simulations of mergers, as well as observations of real mergers, both local and at intermediate redshift. We find a remarkable, very tight correlation between the specific star formation rate (sSFR) of galaxies, and the typical ISM conditions near their inernal star-forming regions, parametrized via a novel quantity: the compactness parameter (C). The evolution of mergers along this correlation explains the spread of the MS, and implies that the physical conditions of the ISM smoothly evolve between on-MS (secular) conditions and off-MS (coalescence/starburst) conditions. Furthermore, we show that the slope of the correlation can be interpreted in terms of the efficiency in the conversion of gas into stars, and that this efficiency remains unchanged along and across the MS. Finally, we discuss differences in the normalization of the correlation as a function of merger mass and redshift, and conclude that these differences imply the existence of two different modes of star formation, unrelated to the smooth evolution across the MS: a disk-like, low pressure mode and a compact nuclear-starburst mode.

STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

Energy Technology Data Exchange (ETDEWEB)

Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara, E-mail: petri@saao.ac.za [South African Astronomical Observatory, P.O. Box 9 Observatory, Cape Town (South Africa)

2014-12-20

An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems.

STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

International Nuclear Information System (INIS)

Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara

2014-01-01

An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems

Gamma-ray emission from star-forming complexes observed by MAGIC: The cases of W51 and HESS J1857+026

Directory of Open Access Journals (Sweden)

Reichardt I.

2015-01-01

Full Text Available Massive star-forming regions assemble a large number of young stars with remnants of stellar evolution and a very dense environment. Therefore, particles accelerated in supernova remnants and pulsar wind nebulae encounter optimal conditions for interacting with target material and photon fields, and thus produce gamma-ray emission. However, observations are challenging because multiple phenomena may appear entangled within the resolution of current gamma-ray telescopes. We report on MAGIC observations aimed to understand the nature of the emission from the star-forming region W51 and the unidentified source HESS J1857+026. While gamma-ray emission from W51 is dominated by the interaction of the supernova remnant W51C with dense molecular clouds, HESS J1857+026 is associated to the pulsar wind nebula from PSR J1856+0245. However, an additional source is resolved north of HESSJ1857+026, with sufficient separation to determine that it cannot be powered by the same pulsar. We search for multiwavelength data to determine the origin of the new source.

Optical region elemental abundance analyses of B and A stars

International Nuclear Information System (INIS)

Adelman, S.J.; Young, J.M.; Baldwin, H.E.

1984-01-01

Abundance analyses using optical region data and fully line blanketed model atmospheres have been performed for two sharp-lined hot Am stars o Pegasi and σ Aquarii and for the sharp-lined marginally peculiar A star v Cancri. The derived abundances exhibit definite anomalies compared with those of normal B-type stars and the Sun. (author)

The difficult births of sunlike stars

International Nuclear Information System (INIS)

Stahler, S.; Comins, N.

1988-01-01

Over 4.5 billion years ago a small region deep inside an enormous cloud of interstellar gas and dust, located in an outer spiral arm of the Milky Way, gradually contracted until it became gravitationally unstable. When the density in this region of the cloud became great enough to allow gravity to overcome all other forces acting on it, the region collapsed. Materials swirled inward, condensed, heated up, radiated energy, and eventually settled down to form the Sun and our solar system. What properties did that original unstable region have when it began to shrink? Astronomers know it rotated, because its angular momentum manifests itself today mostly in the orbital motions of the planets. But that alone cannot help us answer even the most fundamental questions we have about how stars like the Sun form. To find out more, astronomers are studying similar collapsing regions of interstellar gas and dust in the Milky Way known as cold cores, which are even now in the process of becoming solar-type stars. Astronomers want to answer three specific questions: What qualities do these cold cores have that allow stars like the Sun to form from them? What exactly happens during the collapse process? And how do newly formed stars evolve?

High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

Science.gov (United States)

Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

2010-02-11

Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars

Science.gov (United States)

Linsky, J. L.; Bornmann, P. L.; Carpenter, K. G.; Hege, E. K.; Wing, R. F.; Giampapa, M. S.; Worden, S. P.

1982-01-01

Quantitative information is obtained on the chromospheres and transition regions of M dwarf stars, in order to determine how the outer atmospheres of dMe stars differ from dM stars and how they compare with the outer atmospheres of quiet and active G and K type dwarfs. IUE spectra of six dMe and four dM stars, together with ground-based photometry and spectroscopy of the Balmer and Ca II H and K lines, show no evidence of flares. It is concluded, regarding the quiescent behavior of these stars, that emission-line spectra resemble that of the sun and contain emission lines formed in regions with 4000-20,000 K temperatures that are presumably analogous to the solar chromosphere, as well as regions with temperatures of 20,000-200,000 K that are presumably analogous to the solar transition region. Emission-line surface fluxes are proportional to the emission measure over the range of temperatures at which the lines are formed.

High-energy emission from star-forming galaxies

International Nuclear Information System (INIS)

Persic, M.; Rephaeli, Y.

2011-01-01

Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for al lthe relevant hadronic and leptonic processes, the steady-state energy distributions of these particles in the starburst galaxies M 82 and NGC 253 can be determined with a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radioemission from the central starburst region; a commonly expected theoretical relationis then used to normalize the proton spectrum in thisr egion, and a radial profile is assumed for the magnetic field. The resulting radiative yields of electrons and protons are calculated: thepredicted > 100MeV and > 100GeV fluxes are in agreement with the corresponding quantities measured with the orbiting Fermite lescope and the ground-based VERITAS and HESS Cherenkov telescopes. The cosmic-rayenergy densities in central regions of starburst galaxies, as inferred from the radioand γ-ray measurements of (respectively) non-thermal synchrotron and π 0 -decay emission, are U p = O(100)eVcm -3 , i.e. at least an order of magnitude larger than near the Galactic center and in other non-very-actively star-forming galaxies. These very different energy density levelsr eflect a similar disparity in the respective supernova rates in the two environments. A L γ proper to SFR 1.4 relationship is then predicted, in agreement with preliminary observational evidence.

A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

Energy Technology Data Exchange (ETDEWEB)

Silverman, J. D.; Rujopakarn, W. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Daddi, E.; Liu, D. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay (France); Rodighiero, G. [Dipartimento di Fisica e Astronomia, Universita di Padova, vicolo Osservatorio, 3, I-35122 Padova (Italy); Sargent, M. [Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom); Renzini, A. [Instituto Nazionale de Astrofisica, Osservatorio Astronomico di Padova, v.co dell’Osservatorio 5, I-35122 Padova (Italy); Feruglio, C. [IRAM—Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d’Hères (France); Kashino, D. [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya 464-8602 (Japan); Sanders, D. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Kartaltepe, J. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Nagao, T. [Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan); Arimoto, N. [Subaru Telescope, 650 North A’ohoku Place, Hilo, HI-96720 (United States); Berta, S.; Lutz, D. [Max-Planck-Institut für extraterrestrische Physik, D-84571 Garching (Germany); Béthermin, M. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Koekemoer, A., E-mail: john.silverman@ipmu.jp [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); and others

2015-10-20

Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300–800 M{sub ⊙} yr{sup −1}) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%–50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

NEAR-INFRARED IMAGING AND SPECTROSCOPIC SURVEY OF THE SOUTHERN REGION OF THE YOUNG OPEN CLUSTER NGC 2264

Energy Technology Data Exchange (ETDEWEB)

Marinas, Naibi; Lada, Elizabeth A. [Astronomy Department, University of Florida, Gainesville, FL 32611 (United States); Teixiera, Paula S. [Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180 Vienna (Austria); Lada, Charles J. [Harvard-Smithsonian CFA, Cambridge, MA (United States)

2013-08-01

We have obtained JHK near-IR images and JH band low-resolution spectra of candidate members of the southern region of the young open cluster NGC 2264. We have determined spectral types from H-band spectra for 54 sources, 25 of which are classified for the first time. The stars in our sample cover a large range of spectral types (A8-M8). Using a cluster distance of 780 pc, we determined a median age of 1 Myr for this region of NGC 2264, with 90% of the stars being 5 Myr or younger. To improve the statistical significance of our sample, we included 66 additional cluster members within our field of view with optical spectral classification in the literature. We derived infrared excesses using stellar properties to model the photospheric emission for each source and the extinction to correct FLAMINGOS near-IR and Spitzer mid-IR photometry, and obtained a disk fraction of 51% {+-} 5% for the region. Binning the stars by stellar mass, we find a disk fraction of 38% {+-} 9% for the 0.1-0.3 solar mass group, 55% {+-} 6% for 0.3-1 solar masses, and 58% {+-} 10% for the higher than 1 solar mass group. The lower disk fraction for the lower mass stars is similar to the results found in non-cluster regions like Taurus and Chamaeleon, but differs from the older 3 Myr cluster IC 348 in which the disk fraction is lower for the higher mass stars. This mass-dependent disk fraction is accentuated in the sample with isochrone ages younger than 2 Myr. Here, we find that 45% {+-} 11% of the 0.1-0.3 solar mass stars have disks, 60% {+-} 7% of the 0.3-1 solar mass stars have disks, and all 1-3 solar mass stars have disks. Stellar masses might be an important factor in the ability of a system to form or retain a disk early on. However, regardless of the stellar mass, the large infrared excesses expected from optically thick disks disappear within the first 2 Myr for all stars in our study and small excesses from optically thin disks are found mostly in sources younger than 4 Myr.

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.

On the star-forming ability of Molecular Clouds

Science.gov (United States)

Anathpindika, S.; Burkert, A.; Kuiper, R.

2018-02-01

The star-forming ability of a molecular cloud depends on the fraction of gas it can cycle into the dense-phase. Consequently, one of the crucial questions in reconciling star formation in clouds is to understand the factors that control this process. While it is widely accepted that the variation in ambient conditions can alter significantly the ability of a cloud to spawn stars, the observed variation in the star-formation rate in nearby clouds that experience similar ambient conditions, presents an interesting question. In this work, we attempted to reconcile this variation within the paradigm of colliding flows. To this end we develop self-gravitating, hydrodynamic realizations of identical flows, but allowed to collide off-centre. Typical observational diagnostics such as the gas-velocity dispersion, the fraction of dense-gas, the column density distribution (N-PDF), the distribution of gas mass as a function of K-band extinction and the strength of compressional/solenoidal modes in the post-collision cloud were deduced for different choices of the impact parameter of collision. We find that a strongly sheared cloud is terribly inefficient in cycling gas into the dense phase and that such a cloud can possibly reconcile the sluggish nature of star formation reported for some clouds. Within the paradigm of cloud formation via colliding flows this is possible in case of flows colliding with a relatively large impact parameter. We conclude that compressional modes - though probably essential - are insufficient to ensure a relatively higher star-formation efficiency in a cloud.

Modeling tracers of young stellar population age in star-forming galaxies

Energy Technology Data Exchange (ETDEWEB)

Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Leitherer, Claus, E-mail: Emily.Levesque@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2013-12-20

The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

Investigating nearby star-forming galaxies in the ultraviolet with HST/COS spectroscopy. I. Spectral analysis and interstellar abundance determinations

International Nuclear Information System (INIS)

James, B. L.; Aloisi, A.; Sohn, S. T.; Wolfe, M. A.; Heckman, T.

2014-01-01

This is the first in a series of three papers describing a project with the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure abundances of the neutral interstellar medium (ISM) in a sample of nine nearby star-forming galaxies. The goal is to assess the (in)homogeneities of the multiphase ISM in galaxies where the bulk of metals can be hidden in the neutral phase, yet the metallicity is inferred from the ionized gas in the H II regions. The sample, spanning a wide range in physical properties, is to date the best suited to investigate the metallicity behavior of the neutral gas at redshift z = 0. ISM absorption lines were detected against the far-ultraviolet spectra of the brightest star-forming region(s) within each galaxy. Here we report on the observations, data reduction, and analysis of these spectra. Column densities were measured by a multicomponent line-profile fitting technique, and neutral-gas abundances were obtained for a wide range of elements. Several caveats were considered, including line saturation, ionization corrections, and dust depletion. Ionization effects were quantified with ad hoc CLOUDY models reproducing the complex photoionization structure of the ionized and neutral gas surrounding the UV-bright sources. An 'average spectrum of a redshift z = 0 star-forming galaxy' was obtained from the average column densities of unsaturated profiles of neutral-gas species. This template can be used as a powerful tool for studies of the neutral ISM at both low and high redshift.

Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies

Science.gov (United States)

Vidal-García, A.; Charlot, S.; Bruzual, G.; Hubeny, I.

2017-09-01

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (∼10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.

DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Ohyama, Youichi; Hota, Ananda [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China)

2013-04-20

IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES

International Nuclear Information System (INIS)

Ohyama, Youichi; Hota, Ananda

2013-01-01

IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

International Nuclear Information System (INIS)

Matzner, Christopher D.; Jumper, Peter H.

2015-01-01

During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive

COLLISIONAL DEBRIS AS LABORATORIES TO STUDY STAR FORMATION

International Nuclear Information System (INIS)

Boquien, M.; Duc, P.-A.; Wu, Y.; Charmandaris, V.; Lisenfeld, U.; Braine, J.; Brinks, E.; Iglesias-Paramo, J.; Xu, C. K.

2009-01-01

In this paper we address the question of whether star formation (SF) is driven by local processes or the large-scale environment. To do so, we investigate SF in collisional debris where the gravitational potential well and velocity gradients are shallower and compare our results with previous work on SF in noninteracting spiral and dwarf galaxies. We have performed multiwavelength spectroscopic and imaging observations (from the far-ultraviolet to the mid-infrared) of six interacting systems, identifying a total of 60 star-forming regions in their collision debris. Our analysis indicates that in these regions (1) the emission of the dust is at the expected level for their luminosity and metallicity, (2) the usual tracers of SFR display the typical trend and scatter found in classical star-forming regions, and (3) the extinction and metallicity are not the main parameters governing the scatter in the properties of intergalactic star-forming regions; age effects and variations in the number of stellar populations seem to play an important role. Our work suggests that local properties such as column density and dust content, rather than the large-scale environment seem to drive SF. This means that intergalactic star-forming regions can be used as a reliable tool to study SF.

Baby Solar System

Science.gov (United States)

Currie, Thayne; Grady, Carol

2012-01-01

What did our solar system look like in its infancy,...... when the planets were forming? We cannot travel back in time to take an image of the early solar system, but in principle we can have the next best thing: images of infant planetary systems around Sun-like stars with ages of 1 to 5 million years, the time we think it took for the giant planets to form. Infant exoplanetary systems are critically important because they can help us understand how our solar system fits within the context of planet formation in general. More than 80% of stars are born with gas- and dust-rich disks, and thus have the potential to form planets. Through many methods we have identified more than 760 planetary systems around middle-aged stars like the Sun, but many of these have architectures that look nothing like our solar system. Young planetary systems are important missing links between various endpoints and may help us understand how and when these differences emerge. Well-known star-forming regions in Taurus, Scorpius. and Orion contain stars that could have infant planetary systems. But these stars are much more distant than our nearest neighbors such as Alpha Centauri or Sirius, making it extremely challenging to produce clear images of systems that can reveal signs of recent planet formation, let alone reveal the planets themselves. Recently, a star with the unassuming name LkCa 15 may have given us our first detailed "baby picture" of a young planetary system similar to our solar system. Located about 450 light-years away in the Taurus starforming region. LkCa 15 has a mass comparable to the Sun (0.97 solar mass) and an age of l to 5 million years, comparable to the time at which Saturn and perhaps Jupiter formed. The star is surrounded by a gas-rich disk similar in structure to the one in our solar system from which the planets formed. With new technologies and observing strategies, we have confirmed suspicions that LkCa 15's disk harbors a young planetary system.

Not all stars form in clusters - measuring the kinematics of OB associations with Gaia

Science.gov (United States)

Ward, Jacob L.; Kruijssen, J. M. Diederik

2018-04-01

It is often stated that star clusters are the fundamental units of star formation and that most (if not all) stars form in dense stellar clusters. In this monolithic formation scenario, low-density OB associations are formed from the expansion of gravitationally bound clusters following gas expulsion due to stellar feedback. N-body simulations of this process show that OB associations formed this way retain signs of expansion and elevated radial anisotropy over tens of Myr. However, recent theoretical and observational studies suggest that star formation is a hierarchical process, following the fractal nature of natal molecular clouds and allowing the formation of large-scale associations in situ. We distinguish between these two scenarios by characterizing the kinematics of OB associations using the Tycho-Gaia Astrometric Solution catalogue. To this end, we quantify four key kinematic diagnostics: the number ratio of stars with positive radial velocities to those with negative radial velocities, the median radial velocity, the median radial velocity normalized by the tangential velocity, and the radial anisotropy parameter. Each quantity presents a useful diagnostic of whether the association was more compact in the past. We compare these diagnostics to models representing random motion and the expanding products of monolithic cluster formation. None of these diagnostics show evidence of expansion, either from a single cluster or multiple clusters, and the observed kinematics are better represented by a random velocity distribution. This result favours the hierarchical star formation model in which a minority of stars forms in bound clusters and large-scale, hierarchically structured associations are formed in situ.

Statistical investigation of flare stars. III. Flare stars in the general galactic star field

International Nuclear Information System (INIS)

Mirzoyan, L.V.; Ambaryan, V.V.; Garibdzhanyan, A.T.; Mirzoyan, A.L.

1989-01-01

Some questions relating to the existence of a large number of flare stars in the general star field of the Galaxy are discussed. It is shown that only a small proportion of them can be found by photographic observations, and the fraction of field flare stars among such stars found in the regions of star clusters and associations does not exceed 10%. The ratio of the numbers of flare stars of the foreground and the background for a particular system depends on its distance, reaching zero at a distance of about 500 pc. The spatial density of flare stars in the Pleiades is at least two orders of magnitude greater than in the general galactic field. A lower limit for the number of flare stars in the Galaxy is estimated at 4.2 ·10 9 , and the number of nonflare red dwarfs at 2.1·10 10 . There are grounds for believing that they were all formed in star clusters and associations

The HNC/HCN ratio in star-forming regions

International Nuclear Information System (INIS)

Graninger, Dawn M.; Öberg, Karin I.; Herbst, Eric; Vasyunin, Anton I.

2014-01-01

HNC and HCN, typically used as dense gas tracers in molecular clouds, are a pair of isomers that have great potential as a temperature probe because of temperature dependent, isomer-specific formation and destruction pathways. Previous observations of the HNC/HCN abundance ratio show that the ratio decreases with increasing temperature, something that standard astrochemical models cannot reproduce. We have undertaken a detailed parameter study on which environmental characteristics and chemical reactions affect the HNC/HCN ratio and can thus contribute to the observed dependence. Using existing gas and gas-grain models updated with new reactions and reaction barriers, we find that in static models the H + HNC gas-phase reaction regulates the HNC/HCN ratio under all conditions, except for very early times. We quantitatively constrain the combinations of H abundance and H + HNC reaction barrier that can explain the observed HNC/HCN temperature dependence and discuss the implications in light of new quantum chemical calculations. In warm-up models, gas-grain chemistry contributes significantly to the predicted HNC/HCN ratio and understanding the dynamics of star formation is therefore key to model the HNC/HCN system.

An optical spectroscopic study of T Tauri stars. I. Photospheric properties

Energy Technology Data Exchange (ETDEWEB)

Herczeg, Gregory J. [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, Beijing 100871 (China); Hillenbrand, Lynne A. [Caltech, MC105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

2014-05-10

Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to

Symbiotic stars

International Nuclear Information System (INIS)

Kafatos, M.; Michalitsianos, A.G.

1984-01-01

Among the several hundred million binary systems estimated to lie within 3000 light years of the solar system, a tiny fraction, no more than a few hundred, belong to a curious subclass whose radiation has a wavelength distribution so peculiar that it long defied explanation. Such systems radiate strongly in the visible region of the spectrum, but some of them do so even more strongly at both shorter and longer wavelengths: in the ultraviolet region and in the infrared and radio regions. This odd distribution of radiation is best explained by the pairing of a cool red giant star and an intensely hot small star that is virtually in contact with its larger companion. Such objects have become known as symbiotic stars. On photographic plate only the giant star can be discerned, but evidence for the existence of the hot companion has been supplied by satellite-born instruments capable of detecting ultraviolet radiation. The spectra of symbiotic stars indicate that the cool red giant is surrounded by a very hot ionized gas. Symbiotic stars also flared up in outbursts indicating the ejection of material in the form of a shell or a ring. Symbiotic stars may therefore represent a transitory phase in the evolution of certain types of binary systems in which there is substantial transfer of matter from the larger partner to the smaller

Star formations rates in the Galaxy

International Nuclear Information System (INIS)

Smith, L.F.; Mezger, P.G.; Biermann, P.

1978-01-01

Data relevant to giant HII regions in the Galaxy are collected. The production rate for Lyman continuum photons by O stars in giant HII regions is 4.7 10 52 s -1 in the whole Galaxy. The corresponding present rate of star formation is M (sun)/yr, of which 74% occurs in main spiral arms, 13% in the interarm region and 13% in the galactic center. The star formation rates, the observed heavy element and deuterium abundances in the solar neighbourhood are compared to model predictions based on star formation proportional to a power (k) of the gas surface density. The mass function is terminated at Msub(u)=100 M (sun) above and M 1 below. Msub(u)=50 M (sun) is also considered. Comparing with data derived from observations a) the star formation rate, b) metal abundances, c) deuterium abundances, and d) colors of the stellar population, we find that models of k=1/2 to 1, and M 1 1 M (sun) are formed together with O and B stars, but under rather special conditions of the interstellar gas, while lower mass stars form wherever dense molecular clouds exist. The high rate of star formation in the galactic center may represent a burst. (orig.) [de

How astronomers watch the birth of stars

International Nuclear Information System (INIS)

Little, L.

1984-01-01

The paper describes the recent progress in stellar evolution, due to the new techniques in infrared and radio astronomy. The latter techniques have revealed where the stars are born, and the way the stars actually form. The nature of the molecular clouds where the stars form, star formation regions, collapse in molecular clouds, gas flows within clouds and cores of clouds have also been investigated using the new techniques and new telescopes. (U.K.)

THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

International Nuclear Information System (INIS)

Torres-Papaqui, J. P.; Coziol, R.; Ortega-Minakata, R. A.; Neri-Larios, D. M.

2012-01-01

We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z ≤ 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more

Diagnostics for mechanical heating in star-forming galaxies

NARCIS (Netherlands)

Kazandjian, Mher V.

2015-01-01

In this thesis the molecular emission of species such as CO, HCN and HNC and HCO+ are used to probe and quantify mechanical heating in star-forming galaxies. In the first part of the thesis photo-dissociation models are used to find a diagnostic of mechanical heating at the level of molecular

FORMING AN O STAR VIA DISK ACCRETION?

International Nuclear Information System (INIS)

Qiu Keping; Zhang Qizhou; Beuther, Henrik; Fallscheer, Cassandra

2012-01-01

We present a study of outflow, infall, and rotation in a ∼10 5 L ☉ star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of ∼80 M ☉ and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 ± 50 K and a mass of ∼13 M ☉ . The outflow has a gas mass of 54 M ☉ and a dynamical timescale of 8 × 10 3 yr. The kinematics of the HMC are probed by high-excitation CH 3 OH and CH 3 CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 × 10 –3 M ☉ yr –1 , is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the 13 CO and C 18 O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass ∼10 M ☉ embedded within MM1 will develop into an O star via disk accretion and envelope infall.

Hα emission stars in the region of Lynds 1228

International Nuclear Information System (INIS)

Ogura, Katsuo; Sato, Fumio.

1990-01-01

The dark cloud L1228 and its surrounding region have been surveyed for candidate pre-main-sequence stars by use of the Kiso Schmidt telescope with an objective prism. 69 Hα emission stars and 49 suspects have been found. Their celestial coordinates and rough estimates of their magnitude and color have been derived from the positions and image diameters on Palomar Sky Survey prints. Nine of them cluster in a small area near the central part of L1228, suggesting active star formation there in the near past. A star with a large color index lying in the northern part has been identified with an IRAS point source having a far-infrared spectrum of moderately low temperature. Preliminary 13 CO (J=1-0) line observations show that the star is embedded in the core of the molecular cloud. (author)

Red Misfits in the Sloan Digital Sky Survey: properties of star-forming red galaxies

Science.gov (United States)

Evans, Fraser A.; Parker, Laura C.; Roberts, Ian D.

2018-06-01

We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies (˜11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly inclined blue cloud galaxies or quiescent red galaxies with poorly constrained star formation. The proportion of Red Misfits is nearly independent of environment, and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an active galactic nucleus. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0s, red spirals, and green valley galaxies.

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.

Radio stars

International Nuclear Information System (INIS)

Hjellming, R.M.; Gibson, D.M.

1985-01-01

Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

Resolved star formation on sub-galactic scales in a merger at z = 1.7

International Nuclear Information System (INIS)

Whitaker, Katherine E.; Rigby, Jane R.; Teng, Stacy H.; Brammer, Gabriel B.; Gladders, Michael D.; Sharon, Keren; Wuyts, Eva

2014-01-01

We present a detailed analysis of Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704. We measure the spatial variations of the extinction in RCS0327 through the observed Hγ/Hβ emission line ratios, finding a constant average extinction of E(B – V) gas = 0.40 ± 0.07. We infer that the star formation is enhanced as a result of an ongoing interaction, with measured star formation rates derived from demagnified, extinction-corrected Hβ line fluxes for the individual star-forming clumps falling >1-2 dex above the star formation sequence. When combining the HST/WFC3 [O III] λ5007/Hβ emission line ratio measurements with [N II]/Hα line ratios from Wuyts et al., we find that the majority of the individual star-forming regions fall along the local 'normal' abundance sequence. With the first detections of the He I λ5876 and He II λ4686 recombination lines in a distant galaxy, we probe the massive-star content of the star-forming regions in RCS0327. The majority of the star-forming regions have a He I λ5876 to Hβ ratio consistent with the saturated maximum value, which is only possible if they still contain hot O-stars. Two regions have lower ratios, implying that their last burst of new star formation ended ∼5 Myr ago. Together, the He I λ5876 and He II λ4686 to Hβ line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high-redshift merger. We place the spatial variations of the extinction, star formation rate and ionization conditions in the context of the star formation history of RCS0327.

Preferential Pathway for Glycine Formation in Star-Forming Regions

Science.gov (United States)

Pilling, S.; Boechat-Roberty, H. M.; Baptista, L.; Santos A. C., F.

Interstellar clouds, similar to that from which the solar system was formed, contain many organic molecules including aldehydes, acids, ketones, and sugars Ehrenfreund & Charnley (2000). Those organic compounds have important functions in terrestrial biochemistry and could also have been important in prebiotic synthesis. The simplest amino acid, glycine (NH2CH2COOH), was recently detected in the hot molecular cores Sgr B2(N-LMH), Orion KL, and W51 e1/e2 Kuan et al. (2003). The formic acid (HCOOH) and acetic acid(CH3COOH) have also been detected in those regions Liu et al. (2002), Remijan et al. (2004). The goal of this work is to study experimentally photoionization and photodissociation processes of glycine precursor molecules, acetic acid and formic acid to elucidate a possible preferentially in the glycine synthesis between ice and gas phase. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a toroidal grating monochromator TGM) beamline (100 - 310 eV). The experimental set up consists of a high vacuum chamber with a Time-Of-Flight Mass Spectrometer (TOF-MS). Mass spectra were obtained using PhotoElectron PhotoIon Coincidence (PEPICO) technique. Kinetic energy distributions and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Dissociative and non-dissociative photoionization cross sections for both molecules were also determined Boechat-Roberty, Pilling & Santos (2005). Due to the high photodissociation cross section of formic acid it is possible that in PDRs regions, just after molecules evaporation from the grains surface, it is almost destructed by soft X-rays, justifying the observed low abundance of HCOOH in gaseous phase Ehrenfreund et al. (2001). Acetic acid have shown to be more stable to the ionizing field, and its main outcomes from dissociation process were the reactive ionic fragments COOH+ and CH3CO+. To

Probing Disk Stratification by Combining X-ray and Disk Inclination Data for Taurus-Auriga

Science.gov (United States)

Arraki, Kenza S.; Daly, B.; Harding, M.; McCleary, J.; Cox, A. W.; Grady, C. A.; Woodgate, B. E.; Hamaguchi, K.; Wisniewski, J. P.; Brakken-Thal, S.; Hilton, G.; Bonfield, D.; Williger, G. M.

2010-01-01

Photoelectric neutral Hydrogen absorption, N(H), is a probe of the gas and dust column towards the star. Kastner et al. (2005) found a correlation between N(H) and proplyd aspect ratio in the Orion nebula cluster. We extend this study to Taurus-Auriga by combining publicly available N(H) data from the XMM-Newton Extended Survey of the Taurus molecular cloud (XEST), with published disk inclination data obtained from HST coronagraphic imagery and mm interferometry. Additional inclinations were derived from jet proper motion and radial velocity data obtained from archival HST imagery and the Apache Point Observatory 3.5m telescope's Goddard Fabry-Perot and DIS long-slit spectrograph. Both N(H) and extinction have linear relations with system inclination, where the extinction has a smaller slope than the N(H) trend. Correlations with system inclination demonstrate that the bulk of both N(H) and extinction arise in the disk rather than in remnant envelopes, nearby molecular cloud material, or foreground material. The deficit in extinction compared with predictions for ISM-like gas to dust ratios is consistent with grain growth and settling toward the disk midplane and stratification in disks occurring by 2 Myr. However, the disks remain gas-rich, indicating that giant planet formation is still feasible. We gratefully acknowledge the support of the NASA Motivating Undergraduates in Science and Technology (MUST) Project and of NASA's APRA program under WBS#399131.02.06.02.32. A grant of Director's Discretionary Time funded observing time at the Apache Point Observatory.

Extended Gamma-Ray Emission from the G25.0+0.0 Region: A Star-forming Region Powered by the Newly Found OB Association?

Energy Technology Data Exchange (ETDEWEB)

Katsuta, J. [Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Uchiyama, Y. [Rikkyo University, Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501 (Japan); Funk, S., E-mail: katsuta@hep01.hepl.hiroshima-u.ac.jp [Erlangen Centre for Astroparticle Physics, D-91058 Erlangen (Germany)

2017-04-20

We report a study of extended γ -ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope , which is likely to be the second case of a γ -ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1.°7 × 2.°1 around ( l , b ) = (25.°0, 0.°0). The γ -ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1.°4 × 0.°6. An ∼0.°4 diameter subregion of one has a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837−069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ -ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ -ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ -ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton , we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. We propose that the extended γ -ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.

The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

Energy Technology Data Exchange (ETDEWEB)

Grasha, K.; Calzetti, D. [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States); Adamo, A.; Messa, M. [Dept. of Astronomy, The Oskar Klein Centre, Stockholm University, Stockholm (Sweden); Kim, H. [Gemini Observatory, La Serena (Chile); Elmegreen, B. G. [IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY (United States); Gouliermis, D. A. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Dale, D. A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY (United States); Fumagalli, M. [Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Durham University, Durham (United Kingdom); Grebel, E. K.; Shabani, F. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Johnson, K. E. [Dept. of Astronomy, University of Virginia, Charlottesville, VA (United States); Kahre, L. [Dept. of Astronomy, New Mexico State University, Las Cruces, NM (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Cambridge (United Kingdom); Pellerin, A. [Dept. of Physics and Astronomy, State University of New York at Geneseo, Geneseo NY (United States); Ryon, J. E.; Ubeda, L. [Space Telescope Science Institute, Baltimore, MD (United States); Smith, L. J. [European Space Agency/Space Telescope Science Institute, Baltimore, MD (United States); Thilker, D., E-mail: kgrasha@astro.umass.edu [Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)

2017-05-10

We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

Science.gov (United States)

Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Messa, M.; Pellerin, A.; Ryon, J. E.; Smith, L. J.; Shabani, F.; Thilker, D.; Ubeda, L.

2017-05-01

We present a study of the hierarchical clustering of the young stellar clusters in six local (3-15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ˜40-60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

International Nuclear Information System (INIS)

Grasha, K.; Calzetti, D.; Adamo, A.; Messa, M.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Shabani, F.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Pellerin, A.; Ryon, J. E.; Ubeda, L.; Smith, L. J.; Thilker, D.

2017-01-01

We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

On the Formation of the C{sub 2}H{sub 6}O Isomers Ethanol (C{sub 2}H{sub 5}OH) and Dimethyl Ether (CH{sub 3}OCH{sub 3}) in Star-forming Regions

Energy Technology Data Exchange (ETDEWEB)

Bergantini, Alexandre; Maksyutenko, Pavlo; Kaiser, Ralf I., E-mail: ralfk@hawaii.edu [Department of Chemistry, University of Hawaii at Mānoa, Honolulu, HI 96822 (United States)

2017-06-01

The structural isomers ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}) were detected in several low-, intermediate-, and high-mass star-forming regions, including Sgr B2, Orion, and W33A, with the relative abundance ratios of ethanol/dimethyl ether varying from about 0.03 to 3.4. Until now, no experimental data regarding the formation mechanisms and branching ratios of these two species in laboratory simulation experiments could be provided. Here, we exploit tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) to detect and analyze the production of complex organic molecules (COMs) resulting from the exposure of water/methane (H{sub 2}O/CH{sub 4}) ices to energetic electrons. The main goal is to understand the formation mechanisms in star-forming regions of two C{sub 2}H{sub 6}O isomers: ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}). The results show that the experimental branching ratios favor the synthesis of ethanol versus dimethyl ether (31 ± 11:1). This finding diverges from the abundances observed toward most star-forming regions, suggesting that production routes on interstellar grains to form dimethyl ether might be missing; alternatively, ethanol can be overproduced in the present simulation experiments, such as via radical–radical recombination pathways involving ethyl and hydroxyl radicals. Finally, the PI-ReTOF-MS data suggest the formation of methylacetylene (C{sub 3}H{sub 4}), ketene (CH{sub 2}CO), propene (C{sub 3}H{sub 6}), vinyl alcohol (CH{sub 2}CHOH), acetaldehyde (CH{sub 3}CHO), and methyl hydroperoxide (CH{sub 3}OOH), in addition to ethane (C{sub 2}H{sub 6}), methanol (CH{sub 3}OH), and CO{sub 2} detected from infrared spectroscopy. The yield of all the confirmed species is also determined.

Parameters of oscillation generation regions in open star cluster models

Science.gov (United States)

Danilov, V. M.; Putkov, S. I.

2017-07-01

We determine the masses and radii of central regions of open star cluster (OCL) models with small or zero entropy production and estimate the masses of oscillation generation regions in clustermodels based on the data of the phase-space coordinates of stars. The radii of such regions are close to the core radii of the OCL models. We develop a new method for estimating the total OCL masses based on the cluster core mass, the cluster and cluster core radii, and radial distribution of stars. This method yields estimates of dynamical masses of Pleiades, Praesepe, and M67, which agree well with the estimates of the total masses of the corresponding clusters based on proper motions and spectroscopic data for cluster stars.We construct the spectra and dispersion curves of the oscillations of the field of azimuthal velocities v φ in OCL models. Weak, low-amplitude unstable oscillations of v φ develop in cluster models near the cluster core boundary, and weak damped oscillations of v φ often develop at frequencies close to the frequencies of more powerful oscillations, which may reduce the non-stationarity degree in OCL models. We determine the number and parameters of such oscillations near the cores boundaries of cluster models. Such oscillations points to the possible role that gradient instability near the core of cluster models plays in the decrease of the mass of the oscillation generation regions and production of entropy in the cores of OCL models with massive extended cores.

NEAR-ULTRAVIOLET SPECTROSCOPY OF STAR-FORMING GALAXIES FROM eBOSS: SIGNATURES OF UBIQUITOUS GALACTIC-SCALE OUTFLOWS

International Nuclear Information System (INIS)

Zhu, Guangtun Ben; Comparat, Johan; Kneib, Jean-Paul; Delubac, Timothée; Raichoor, Anand; Yèche, Christophe; Dawson, Kyle S.; Newman, Jeffrey; Zhou, Xu; Schneider, Donald P.

2015-01-01

We present rest-frame near-ultraviolet (NUV) spectroscopy of star-forming galaxies (SFGs) at 0.6 < z < 1.2 from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) in SDSS-IV. One of the eBOSS programs is to obtain 2″ (about 15 kpc) fiber spectra of about 200,000 emission-line galaxies (ELGs) at redshift z ≳ 0.6. We use the data from the pilot observations of this program, including 8620 spectra of SFGs at 0.6 < z < 1.2. The median composite spectra of these SFGs at 2200 Å < λ < 4000 Å feature asymmetric, preferentially blueshifted non-resonant emission, Fe ii*, and blueshifted resonant absorption, e.g., Fe ii and Mg ii, indicating ubiquitous outflows driven by star formation at these redshifts. For the absorption lines, we find a variety of velocity profiles with different degrees of blueshift. Comparing our new observations with the literature, we do not observe the non-resonant emission in the small-aperture (<40 pc) spectra of local star-forming regions with the Hubble Space Telescope, and find the observed line ratios in the SFG spectra to be different from those in the spectra of local star-forming regions, as well as those of quasar absorption-line systems in the same redshift range. We introduce an outflow model that can simultaneously explain the multiple observed properties and suggest that the variety of absorption velocity profiles and the line ratio differences are caused by scattered fluorescent emission filling in on top of the absorption in the large-aperture eBOSS spectra. We develop an observation-driven, model-independent method to correct the emission infill to reveal the true absorption profiles. Finally, we show that the strengths of both the non-resonant emission and the emission-corrected resonant absorption increase with [O ii] λλ3727, 3730 rest equivalent width and luminosity, with a slightly larger dependence on the former. Our results show that the eBOSS and future dark-energy surveys (e.g., Dark Energy Spectroscopic

CSO BOLOCAM 1.1 mm CONTINUUM MAPPING OF THE BRAID NEBULA STAR FORMATION REGION IN CYGNUS OB7

International Nuclear Information System (INIS)

Aspin, Colin; Beck, Tracy L.; Davis, Chris J.

2011-01-01

We present a 1.1 mm map of the Braid Nebula star formation region in Cygnus OB7 taken using Bolocam on the Caltech Submillimeter Observatory. Within the 1 deg 2 covered by the map, we have detected 55 cold dust clumps all of which are new detections. A number of these clumps are coincident with IRAS point sources although the majority are not. Some of the previously studied optical/near-IR sources are detected at 1.1 mm. We estimate total dust/gas masses for the 55 clumps together with peak visual extinctions. We conclude that over the whole region, approximately 20% of the clumps are associated with IRAS sources suggesting that these are protostellar objects. The remaining 80% are classed as starless clumps. In addition, both FU Orionis (FUor) like objects in the field, the Braid Star and HH 381 IRS, are associated with strong millimeter emission. This implies that FUor eruptions can occur at very early stages of pre-main-sequence life. Finally, we determine that the cumulative clump mass function for the region is very similar to that found in both the Perseus and ρ Ophiuchus star-forming regions.

THE 'TRUE' COLUMN DENSITY DISTRIBUTION IN STAR-FORMING MOLECULAR CLOUDS

International Nuclear Information System (INIS)

Goodman, Alyssa A.; Pineda, Jaime E.; Schnee, Scott L.

2009-01-01

We use the COMPLETE Survey's observations of the Perseus star-forming region to assess and intercompare the three methods used for measuring column density in molecular clouds: near-infrared (NIR) extinction mapping; thermal emission mapping in the far-IR; and mapping the intensity of CO isotopologues. Overall, the structures shown by all three tracers are morphologically similar, but important differences exist among the tracers. We find that the dust-based measures (NIR extinction and thermal emission) give similar, log-normal, distributions for the full (∼20 pc scale) Perseus region, once careful calibration corrections are made. We also compare dust- and gas-based column density distributions for physically meaningful subregions of Perseus, and we find significant variations in the distributions for those (smaller, ∼few pc scale) regions. Even though we have used 12 CO data to estimate excitation temperatures, and we have corrected for opacity, the 13 CO maps seem unable to give column distributions that consistently resemble those from dust measures. We have edited out the effects of the shell around the B-star HD 278942 from the column density distribution comparisons. In that shell's interior and in the parts where it overlaps the molecular cloud, there appears to be a dearth of 13 CO, which is likely due either to 13 CO not yet having had time to form in this young structure and/or destruction of 13 CO in the molecular cloud by the HD 278942's wind and/or radiation. We conclude that the use of either dust or gas measures of column density without extreme attention to calibration (e.g., of thermal emission zero-levels) and artifacts (e.g., the shell) is more perilous than even experts might normally admit. And, the use of 13 CO data to trace total column density in detail, even after proper calibration, is unavoidably limited in utility due to threshold, depletion, and opacity effects. If one's main aim is to map column density (rather than temperature

The structural evolution of Milky-Way-like star-forming galaxies since z ∼ 1.3

International Nuclear Information System (INIS)

Patel, Shannon G.; Fumagalli, Mattia; Franx, Marijn; Labbé, Ivo; Muzzin, Adam; Van Dokkum, Pieter G.; Leja, Joel; Skelton, Rosalind E.; Momcheva, Ivelina; Nelson, Erica June; Van der Wel, Arjen; Rix, Hans-Walter; Brammer, Gabriel; Whitaker, Katherine E.; Lundgren, Britt; Wake, David A.; Quadri, Ryan F.

2013-01-01

We follow the structural evolution of star-forming galaxies (SFGs) like the Milky Way by selecting progenitors to z ∼ 1.3 based on the stellar mass growth inferred from the evolution of the star-forming sequence. We select our sample from the 3D-HST survey, which utilizes spectroscopy from the HST/WFC3 G141 near-IR grism and enables precise redshift measurements for our sample of SFGs. Structural properties are obtained from Sérsic profile fits to CANDELS WFC3 imaging. The progenitors of z = 0 SFGs with stellar mass M = 10 10.5 M ☉ are typically half as massive at z ∼ 1. This late-time stellar mass growth is consistent with recent studies that employ abundance matching techniques. The descendant SFGs at z ∼ 0 have grown in half-light radius by a factor of ∼1.4 since z ∼ 1. The half-light radius grows with stellar mass as r e ∝M 0.29 . While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudobulges are common features in present day late-type galaxies. Some portion of this growth in the central regions is due to star formation as recent observations of Hα maps for SFGs at z ∼ 1 are found to be extended but centrally peaked. Connecting our lookback study with galactic archeology, we find the stellar mass surface density at R = 8 kpc to have increased by a factor of ∼2 since z ∼ 1, in good agreement with measurements derived for the solar neighborhood of the Milky Way.

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

Energy Technology Data Exchange (ETDEWEB)

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

2017-09-20

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

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

International Nuclear Information System (INIS)

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

2017-01-01

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

General Relativity and Compact Stars

International Nuclear Information System (INIS)

Glendenning, Norman K.

2005-01-01

Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10 14 times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed

The possible nature of socket stars in H II regions

International Nuclear Information System (INIS)

Castelaz, M.W.

1990-01-01

Close inspection of faint stars (V of about 14 mag) in H II regions show that they appear to be surrounded by circumstellar envelopes of about 10 arcsecs in diameter (as reported by Feibelman in 1989). The present premise is that the sockets are envelopes of obscuring dust which should emit a measurable amount of infrared radiation based on a simple thermal equilibrium model. A search of literature shows that, of 36 socket stars listed by Feibelman, 17 have been measured in the infrared. Of the 17, 14 show excess IR emission. This is very strong evidence that the socket stars are really stars with circumstellar envelopes. Socket stars may be a new type of astronomical object or well-known astronomical objects in environments or evolutionary states not previously seen. 22 refs

FORMALDEHYDE MASERS: EXCLUSIVE TRACERS OF HIGH-MASS STAR FORMATION

Energy Technology Data Exchange (ETDEWEB)

Araya, E. D.; Brown, J. E. [Western Illinois University, Physics Department, 1 University Circle, Macomb, IL 61455 (United States); Olmi, L. [INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Ortiz, J. Morales [University of Puerto Rico, Río Piedras Campus, Physical Sciences Department, P.O. Box 23323, San Juan, PR 00931 (United States); Hofner, P.; Creech-Eakman, M. J. [New Mexico Institute of Mining and Technology, Physics Department, 801 Leroy Place, Socorro, NM 87801 (United States); Kurtz, S. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, 58089 Morelia, Michoacán (Mexico); Linz, H. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)

2015-11-15

The detection of four formaldehyde (H{sub 2}CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H{sub 2}CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H{sub 2}CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H{sub 2}CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H{sub 2}CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH{sub 3}OH masers. We detected a new 6 cm H{sub 2}CO emission line in G32.74−0.07. This work provides further evidence that supports an exclusive association between H{sub 2}CO masers and young regions of high-mass star formation. Furthermore, we detected H{sub 2}CO absorption toward all Hi-GAL sources, and toward 24 low-mass star-forming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH{sub 3}OH (5005 MHz), and CH{sub 2}NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.

GOODS-HERSCHEL: SEPARATING HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI AND STAR-FORMING GALAXIES USING INFRARED COLOR DIAGNOSTICS

Energy Technology Data Exchange (ETDEWEB)

Kirkpatrick, Allison; Pope, Alexandra [Department of Astronomy, University of Massachusetts, Amherst, MA 01002 (United States); Charmandaris, Vassilis [Department of Physics and Institute of Theoretical and Computational Physics, University of Crete, GR-71003, Heraklion (Greece); Daddi, Emmanuele; Elbaz, David; Pannella, Maurilio; Aussel, Herve; Dasyra, Kalliopi; Leiton, Roger [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Hwang, Ho Seong [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Scott, Douglas; Magnelli, Benjamin; Popesso, Paola [Max-Planck-Institut fuer Extraterrestrische Physik (MPE), Postfach 1312, D-85741, Garching (Germany); Altieri, Bruno; Coia, Daniela; Valtchanov, Ivan [Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Canada, E-28691 Madrid (Spain); Dannerbauer, Helmut [Universitaet Wien, Institut fuer Astrophysik, Tuerkenschanzstrasse 17, A-1180 Wien (Austria); Dickinson, Mark; Kartaltepe, Jeyhan [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Magdis, Georgios [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom)

2013-02-15

We have compiled a large sample of 151 high-redshift (z = 0.5-4) galaxies selected at 24 {mu}m (S {sub 24} > 100 {mu}Jy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-infrared spectrum into contributions from star formation and activity in the galactic nuclei. In addition, we have a wealth of photometric data from Spitzer IRAC/MIPS and Herschel PACS/SPIRE. We explore how effective different infrared color combinations are at separating our mid-IR spectroscopically determined active galactic nuclei from our star-forming galaxies. We look in depth at existing IRAC color diagnostics, and we explore new color-color diagnostics combining mid-IR, far-IR, and near-IR photometry, since these combinations provide the most detail about the shape of a source's IR spectrum. An added benefit of using a color that combines far-IR and mid-IR photometry is that it is indicative of the power source driving the IR luminosity. For our data set, the optimal color selections are S {sub 250}/S {sub 24} versus S {sub 8}/S {sub 3.6} and S {sub 100}/S {sub 24} versus S {sub 8}/S {sub 3.6}; both diagnostics have {approx}10% contamination rate in the regions occupied primarily by star-forming galaxies and active galactic nuclei, respectively. Based on the low contamination rate, these two new IR color-color diagnostics are ideal for estimating both the mid-IR power source of a galaxy when spectroscopy is unavailable and the dominant power source contributing to the IR luminosity. In the absence of far-IR data, we present color diagnostics using the Wide-field Infrared Survey Explorer mid-IR bands which can efficiently select out high-z (z {approx} 2) star-forming galaxies.

MAGNETIC FIELD MEASUREMENTS OF T TAURI STARS IN THE ORION NEBULA CLUSTER

International Nuclear Information System (INIS)

Hao Yang; Johns-Krull, Christopher M.

2011-01-01

We present an analysis of high-resolution (R ∼ 50, 000) infrared K-band echelle spectra of 14 T Tauri stars (TTSs) in the Orion Nebula Cluster. We model Zeeman broadening in three magnetically sensitive Ti I lines near 2.2 μm and consistently detect kilogauss-level magnetic fields in the stellar photospheres. The data are consistent in each case with the entire stellar surface being covered with magnetic fields, suggesting that magnetic pressure likely dominates over gas pressure in the photospheres of these stars. These very strong magnetic fields might themselves be responsible for the underproduction of X-ray emission of TTSs relative to what is expected based on main-sequence star calibrations. We combine these results with previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae association to study the potential variation of magnetic field properties during the first 10 million years of stellar evolution, finding a steady decline in total magnetic flux with age.

Relations between stellar mass and electron temperature-based metallicity for star-forming galaxies in a wide mass range

International Nuclear Information System (INIS)

Shi Wei-Bin; Zhao Gang; Ruan Gui-Ping; Zhou Li; Liang Yan-Chun; Shao Xu; Liu Xiao-Wei; Hammer Francois; Flores Hector; Zhang Yong

2014-01-01

We select 947 star-forming galaxies from SDSS-DR7 with [O III]λ4363 emission lines detected at a signal-to-noise ratio larger than 5σ. Their electron temperatures and direct oxygen abundances are then determined. We compare the results from different methods. t 2 , the electron temperature in the low ionization region, estimated from t 3 , that in the high ionization region, is compared using three analysis relations between t 2 – t 3 . These show obvious differences, which result in some different ionic oxygen abundances. The results of t 3 , t 2 , O ++ /H + and O + /H + derived by using methods from IRAF and literature are also compared. The ionic abundances O ++ /H + are higher than O + /H + for most cases. The different oxygen abundances derived from T e and the strong-line ratios show a clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio R 23 . The sample of galaxies from SDSS with detected [O III]λ4363 have lower metallicites and higher star formation rates, so they may not be typical representatives of the whole population of galaxies. Adopting data objects from Andrews and Martini, Liang et al. and Lee et al. data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from 10 6 M ⊙ to 10 11 M ⊙ . (research papers)

DECIPHERING THE IONIZED GAS CONTENT IN THE MASSIVE STAR-FORMING COMPLEX G75.78+0.34

Energy Technology Data Exchange (ETDEWEB)

Sanchez-Monge, Alvaro [Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, I-50125 Firenze (Italy); Kurtz, Stan; Lizano, Susana [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Apdo. Postal 3-72, 58090, Morelia, Michoacan (Mexico); Palau, Aina [Institut de Ciencies de l' Espai (CSIC-IEEC), Campus UAB-Facultat de Ciencies, Torre C5p 2, E-08193 Bellaterra, Catalunya (Spain); Estalella, Robert [Dpt d' Astronomia i Meteorologia (IEEC-UB), Institut de Ciencies del Cosmos, Universitat de Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain); Shepherd, Debra [NRAO, P.O. Box O, Socorro, NM 87801-0387 (United States); Franco, Jose [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Apdo. Postal 70-264, 04510 Mexico, D.F. (Mexico); Garay, Guido, E-mail: asanchez@arcetri.astro.it [Departamento de Astronomia, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago (Chile)

2013-04-01

We present subarcsecond observations toward the massive star-forming region G75.78+0.34. We used the Very Large Array to study the centimeter continuum and H{sub 2}O and CH{sub 3}OH maser emission, and the Owens Valley Radio Observatory and Submillimeter Array to study the millimeter continuum and recombination lines (H40{alpha} and H30{alpha}). We found radio continuum emission at all wavelengths, coming from three components: (1) a cometary ultracompact (UC) H II region with an electron density {approx}3.7 Multiplication-Sign 10{sup 4} cm{sup -3}, excited by a B0 type star, and with no associated dust emission; (2) an almost unresolved UCH II region (EAST), located {approx}6'' to the east of the cometary UCH II region, with an electron density {approx}1.3 Multiplication-Sign 10{sup 5} cm{sup -3}, and associated with a compact dust clump detected at millimeter and mid-infrared wavelengths; and (3) a compact source (CORE), located {approx}2'' to the southwest of the cometary arc, with a flux density increasing with frequency, and embedded in a dust condensation of 30 M{sub Sun }. The CORE source is resolved into two compact and unresolved sources which can be well fit by two homogeneous hypercompact H II regions each one photoionized by a B0.5 zero-age main sequence star, or by free-free radiation from shock-ionized gas resulting from the interaction of a jet/outflow system with the surrounding environment. The spatial distribution and kinematics of water masers close to the CORE-N and S sources, together with excess emission at 4.5 {mu}m and the detected dust emission, suggest that the CORE source is a massive protostar driving a jet/outflow.

DECIPHERING THE IONIZED GAS CONTENT IN THE MASSIVE STAR-FORMING COMPLEX G75.78+0.34

International Nuclear Information System (INIS)

Sánchez-Monge, Álvaro; Kurtz, Stan; Lizano, Susana; Palau, Aina; Estalella, Robert; Shepherd, Debra; Franco, José; Garay, Guido

2013-01-01

We present subarcsecond observations toward the massive star-forming region G75.78+0.34. We used the Very Large Array to study the centimeter continuum and H 2 O and CH 3 OH maser emission, and the Owens Valley Radio Observatory and Submillimeter Array to study the millimeter continuum and recombination lines (H40α and H30α). We found radio continuum emission at all wavelengths, coming from three components: (1) a cometary ultracompact (UC) H II region with an electron density ∼3.7 × 10 4 cm –3 , excited by a B0 type star, and with no associated dust emission; (2) an almost unresolved UCH II region (EAST), located ∼6'' to the east of the cometary UCH II region, with an electron density ∼1.3 × 10 5 cm –3 , and associated with a compact dust clump detected at millimeter and mid-infrared wavelengths; and (3) a compact source (CORE), located ∼2'' to the southwest of the cometary arc, with a flux density increasing with frequency, and embedded in a dust condensation of 30 M ☉ . The CORE source is resolved into two compact and unresolved sources which can be well fit by two homogeneous hypercompact H II regions each one photoionized by a B0.5 zero-age main sequence star, or by free-free radiation from shock-ionized gas resulting from the interaction of a jet/outflow system with the surrounding environment. The spatial distribution and kinematics of water masers close to the CORE-N and S sources, together with excess emission at 4.5 μm and the detected dust emission, suggest that the CORE source is a massive protostar driving a jet/outflow.

The Infrared-Radio Correlation of Dusty Star Forming Galaxies at High Redshift

Science.gov (United States)

Lower, Sidney; Vieira, Joaquin Daniel; Jarugula, Sreevani

2018-01-01

Far-infrared (FIR) and radio continuum emission in galaxies are related by a common origin: massive stars and the processes triggered during their birth, lifetime, and death. FIR emission is produced by cool dust, heated by the absorption of UV emission from massive stars, which is then re-emitted in the FIR. Thermal free-free radiation emitted from HII regions dominates the spectral energy density (SED) of galaxies at roughly 30 GHz, while non-thermal synchrotron radiation dominates at lower frequencies. At low redshift, the infrared radio correlation (IRC, or qIR) holds as a tight empirical relation for many star forming galaxy types, but until recently, there has not been sensitive enough radio observations to extend this relation to higher redshifts. Many selection biases cloud the results of these analyses, leaving the evolution of the IRC with redshift ambiguous. In this poster, I present CIGALE fitted spectral energy distributions (SEDs) for 24 gravitationally-lensed sources selected in the mm-wave from the South Pole Telescope (SPT) survey. I fit the IRC from infrared and submillimeter fluxes obtained with Herschel, Atacama Pathfinder Experiment (APEX), and SPT and radio fluxes obtained with ATCA at 2.1, 5.5, 9, and 30 GHz. This sample of SPT sources has a spectroscopic redshift range of 2.1poster, I will present the results of this study and compare our results to various results in the literature.

PHOTOIONIZATION MODELS FOR THE SEMI-FORBIDDEN C iii] 1909 EMISSION IN STAR-FORMING GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Jaskot, A. E. [Department of Astronomy, Smith College, Northampton, MA 01063 (United States); Ravindranath, S. [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2016-12-20

The increasing neutrality of the intergalactic medium at z  > 6 suppresses Ly α emission, and spectroscopic confirmation of galaxy redshifts requires the detection of alternative ultraviolet lines. The strong [C iii]  λ 1907+C iii]  λ 1909 doublet frequently observed in low-metallicity, actively star-forming galaxies is a promising emission feature. We present CLOUDY photoionization model predictions for C iii] equivalent widths (EWs) and line ratios as a function of starburst age, metallicity, and ionization parameter. Our models include a range of C/O abundances, dust content, and gas density. We also examine the effects of varying the nebular geometry and optical depth. Only the stellar models that incorporate binary interaction effects reproduce the highest observed C iii] EWs. The spectral energy distributions from the binary stellar population models also generate observable C iii] over a longer timescale relative to single-star models. We show that diagnostics using C iii] and nebular He ii  λ 1640 can separate star-forming regions from shock-ionized gas. We also find that density-bounded systems should exhibit weaker C iii] EWs at a given ionization parameter, and C iii] EWs could, therefore, select candidate Lyman continuum-leaking systems. In almost all models, C iii] is the next strongest line at <2700 Å after Ly α , and C iii] reaches detectable levels for a wide range of conditions at low metallicity. C iii] may therefore serve as an important diagnostic for characterizing galaxies at z  > 6.

PHOTOIONIZATION MODELS FOR THE SEMI-FORBIDDEN C iii] 1909 EMISSION IN STAR-FORMING GALAXIES

International Nuclear Information System (INIS)

Jaskot, A. E.; Ravindranath, S.

2016-01-01

The increasing neutrality of the intergalactic medium at z  > 6 suppresses Ly α emission, and spectroscopic confirmation of galaxy redshifts requires the detection of alternative ultraviolet lines. The strong [C iii]  λ 1907+C iii]  λ 1909 doublet frequently observed in low-metallicity, actively star-forming galaxies is a promising emission feature. We present CLOUDY photoionization model predictions for C iii] equivalent widths (EWs) and line ratios as a function of starburst age, metallicity, and ionization parameter. Our models include a range of C/O abundances, dust content, and gas density. We also examine the effects of varying the nebular geometry and optical depth. Only the stellar models that incorporate binary interaction effects reproduce the highest observed C iii] EWs. The spectral energy distributions from the binary stellar population models also generate observable C iii] over a longer timescale relative to single-star models. We show that diagnostics using C iii] and nebular He ii  λ 1640 can separate star-forming regions from shock-ionized gas. We also find that density-bounded systems should exhibit weaker C iii] EWs at a given ionization parameter, and C iii] EWs could, therefore, select candidate Lyman continuum-leaking systems. In almost all models, C iii] is the next strongest line at <2700 Å after Ly α , and C iii] reaches detectable levels for a wide range of conditions at low metallicity. C iii] may therefore serve as an important diagnostic for characterizing galaxies at z  > 6.

MASSIVE INFANT STARS ROCK THEIR CRADLE

Science.gov (United States)

2002-01-01

Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

Peculiar A star HD 43819 - A photographic region line-identification study

International Nuclear Information System (INIS)

Adelman, S.J.; The Citadel, Charleston, SC)

1985-01-01

A line identification study of the sharp-lined silicon star HD 43819 has been performed for the photographic region 3759-4924 A. Comparison of this star's spectrum with those of other silicon stars shows that it shares many of their apparent abundance anomalies. The TiII, CrII, FeI, and FeII spectra are well represented while the singly ionized rare earths are represented by at best a few lines per species. 21 references

H2O sources in regions of star formation

International Nuclear Information System (INIS)

Lo, K.Y.; Burke, B.F.; Haschick, A.D.

1975-01-01

Regions and objects believed to be in early stages of stellar formation have been searched for H 2 O 22-GHz line emission with the Haystack 120-foot (37 m) telescope. The objects include radio condensations, infrared objects in H ii regions, and Herbig-Haro objects. Nine new H 2 O sources were detected in the vicinity of such objects, including the Sharpless H ii regions S152, S235, S255, S269, G45.1+0.1, G45.5+0.1, AFCRL infrared object No. 809--2992, and Herbig-Haro objects 1 and 9. The new H 2 O sources detected in H ii regions are associated, but not coincident, with the the radio condensations. Water vapor line emission was detected in approx.25 percent of the regions searched. The association of H 2 O sources with regions of star formation is taken to be real. The spatial relationship of H 2 O sources to infrared objects, radio condensations, class I OH sources, and molecular clouds are discussed. The suggestion is made that an H 2 O source may be excited by a highly obscured star of extreme youth

MAXIMALLY STAR-FORMING GALACTIC DISKS. II. VERTICALLY RESOLVED HYDRODYNAMIC SIMULATIONS OF STARBURST REGULATION

Energy Technology Data Exchange (ETDEWEB)

Shetty, Rahul [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); Ostriker, Eve C., E-mail: R.Shetty@.uni-heidelberg.de, E-mail: ostriker@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2012-07-20

We explore the self-regulation of star formation using a large suite of high-resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium, the total midplane pressure, dominated by turbulence, must balance the vertical weight of the interstellar medium. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a wide range of parameters, including surface density {Sigma}, momentum injected per stellar mass formed (p{sub *}/m{sub *}), and angular velocity. The simulations are two-dimensional radial-vertical slices, and include both self-gravity and an external potential that helps to confine gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate {Sigma}{sub SFR}, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with p{sub *}/m{sub *}. The efficiency of star formation per free-fall time at the midplane density, {epsilon}{sub ff}(n{sub 0}), is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure {epsilon}{sub ff}(n{sub 0}) {approx} 0.004-0.01, consistent with low and approximately constant efficiencies inferred from observations. For {Sigma} in (100-1000) M{sub Sun} pc{sup -2}, we find {Sigma}{sub SFR} in (0.1-4) M{sub Sun} kpc{sup -2} yr{sup -1}, generally following a {Sigma}{sub SFR} {proportional_to} {Sigma}{sup 2} relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed {Sigma}-{Sigma}{sub SFR} relation in high

Ethnoveterinary survey of tradomedical importance of Bos taurus L ...

African Journals Online (AJOL)

ethnoveterinary uses of B. taurus by-products by traditional practitioners in Nigeria and South Africa. Conclusion: There ... Moreover, there are over 60 species of bacteria, about 100 species ..... bioremediation of pharmaceutical, pesticides and.

Halo Histories vs. Galaxy Properties at z=0, III: The Properties of Star-Forming Galaxies

Science.gov (United States)

Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.

2018-05-01

We measure how the properties of star-forming central galaxies correlate with large-scale environment, δ, measured on 10 h-1Mpc scales. We use galaxy group catalogs to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disk scale length Rexp, and Sersic index of the galaxy light profile, nS. We find that, at all stellar masses, there is an inverse correlation between SFR and δ, meaning that above-average star forming centrals live in underdense regions. For nS and Rexp, there is no correlation with δ at M_\\ast ≲ 10^{10.5} M⊙, but at higher masses there are positive correlations; a weak correlation with Rexp and a strong correlation with nS. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, \\dot{M}_h. In this model, galaxies are assigned to halos using the abundance matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but \\dot{M}_h is used to map onto SFR. The best-fit model requires some scatter in the \\dot{M}_h-SFR relation. The Rexp and nS measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, λ. Halo spin does not correlate with δ at low halo masses, but for higher mass halos, high-spin halos live in higher density environments at fixed Mh. Put together with the earlier installments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

STAR FORMATION ACTIVITY IN THE GALACTIC H II REGION Sh2-297

International Nuclear Information System (INIS)

Mallick, K. K.; Ojha, D. K.; Dewangan, L. K.; Samal, M. R.; Pandey, A. K.; Bhatt, B. C.; Ghosh, S. K.; Tamura, M.

2012-01-01

We present a multiwavelength study of the Galactic H II region Sh2-297, located in the Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756 cm –3 and 9.15 × 10 5 cm –6 pc using the radio continuum observations at 610 and 1280 MHz, and Very Large Array archival data at 1420 MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area ∼7.'5 × 7.'5 centered on Sh2-297 using grism slitless spectroscopy (to identify the Hα emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color and color-magnitude (CM) diagrams, giving 50 red sources (H – K > 0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be ∼0.1-2 M ☉ and 0.5-2 Myr using optical (V/V–I) and NIR (J/J–H) CM diagrams. The mean age of the YSOs is found to be ∼1 Myr, which is of the order of dynamical age of 1.07 Myr of the H II region. Using the estimated range of visual extinction (1.1-25 mag) from literature and NIR data for the region, spectral energy distribution models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star toward the cold dark cloud LDN1657A located west of Sh2-297.

Star Formation Activity in the Galactic H II Region Sh2-297

Science.gov (United States)

Mallick, K. K.; Ojha, D. K.; Samal, M. R.; Pandey, A. K.; Bhatt, B. C.; Ghosh, S. K.; Dewangan, L. K.; Tamura, M.

2012-11-01

We present a multiwavelength study of the Galactic H II region Sh2-297, located in the Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756 cm-3 and 9.15 × 105 cm-6 pc using the radio continuum observations at 610 and 1280 MHz, and Very Large Array archival data at 1420 MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area ~7farcm5 × 7farcm5 centered on Sh2-297 using grism slitless spectroscopy (to identify the Hα emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color and color-magnitude (CM) diagrams, giving 50 red sources (H - K > 0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be ~0.1-2 M ⊙ and 0.5-2 Myr using optical (V/V-I) and NIR (J/J-H) CM diagrams. The mean age of the YSOs is found to be ~1 Myr, which is of the order of dynamical age of 1.07 Myr of the H II region. Using the estimated range of visual extinction (1.1-25 mag) from literature and NIR data for the region, spectral energy distribution models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star toward the cold dark cloud LDN1657A located west of Sh2-297.

Joint NuSTAR and IRIS observation of a microflaring active region

Science.gov (United States)

Hannah, I. G.; Kleint, L.; Krucker, S.; Glesener, L.; Grefenstette, B.

2017-12-01

We present observations of a weakly microflaring active region observed in X-rays with NuSTAR, UV with IRIS and EUV with SDO/AIA. NuSTAR was pointed at this unnamed active region near the East limb between 23:27UT and 23:37UT 26-July-2016, finding mostly quiescent emission except for a small microflare about 23:35UT. The NuSTAR spectrum for the pre-microflare time (23:27UT to 23:34UT) is well fitted by a single thermal component of about 3MK and combined with SDO/AIA we can determine the differential emission measure (DEM), finding it, as expected, drops very sharply to higher temperatures. During the subsequent microflare, the increase in NuSTAR counts matches a little brightening loop observed with IRIS SJI 1400Å and SDO/AIA. Fortuitously the IRIS slit crosses this microflaring loop and we find an increased emission in Si IV 1394Å, Si IV 1403Å and O IV 1402Å but only average line widths and velocities. The NuSTAR microflare spectrum shows heating to higher temperatures and also allows us to investigate the energetics of this event.

Examining Sites of Recent Star Formation in the Galactic Center: A Closer Look at the Arched Filaments and H HII Regions

Science.gov (United States)

Hankins, Matthew; Herter, Terry; Lau, Ryan; Morris, Mark; Mills, Elisabeth

2018-01-01

In this dissertation presentation, we analyze mid-infrared imaging of the Arched Filaments and H HII regions in the Galactic center taken with the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). Examining these regions are of great interest because they provide insights on star formation in the Galactic center and the interactions massive stars have with the ISM. The Arched Filaments are a collection of molecular cloud ridges which are ionized by the nearby Arches star cluster, and give the appearance of large (~25 pc) arch-like structures. The H HII regions are a collection of HII regions just to the west of the Arches cluster (~5-15 pc). The origin of the stars powering the H HII regions is uncertain, as they may have formed in a nearby molecular cloud or could be ejected members of the Arches cluster. FORCAST observations of these regions were used to study the morphology and heating structure of the HII regions, as well as constrain their luminosities.Color-temperature maps of the Arched Filaments created with the FORCAST data reveals fairly uniform dust temperatures (~70-100 K) across the length filaments. The temperature uniformity of the clouds can be explained if they are heated by the Arches cluster but are located at a larger distance from the cluster than they appear. The density of the Arched Filaments clouds was estimated from the FORCAST data and was found to be below the threshold for tidal shearing, indicating that that the clouds will be destroyed by the strong tidal field near the Galactic center. To the west of the Arched Filaments, there is an interesting collection of HII regions, referred to as the H HII regions. These regions are likely heated by massive O/B type stars, and the morphology of the dust emission associated with these objects indicate a mixture of potential in situ formation mechanisms and interlopers. Interestingly, FORCAST imaging of the H HII regions also reveal several compact sources, which may be young

Galaxy Evolution in the Radio Band: The Role of Star-forming Galaxies and Active Galactic Nuclei

Energy Technology Data Exchange (ETDEWEB)

Mancuso, C.; Prandoni, I. [INAF-IRA, Via P. Gobetti 101, I-40129 Bologna (Italy); Lapi, A.; Obi, I.; Perrotta, F.; Bressan, A.; Celotti, A.; Danese, L. [SISSA, Via Bonomea 265, I-34136 Trieste (Italy); Gonzalez-Nuevo, J. [Departamento de Fisica, Universidad de Oviedo, C. Calvo Sotelo s/n, E-33007 Oviedo (Spain)

2017-06-20

We investigate the astrophysics of radio-emitting star-forming galaxies and active galactic nuclei (AGNs) and elucidate their statistical properties in the radio band, including luminosity functions, redshift distributions, and number counts at sub-mJy flux levels, which will be crucially probed by next-generation radio continuum surveys. Specifically, we exploit the model-independent approach by Mancuso et al. to compute the star formation rate functions, the AGN duty cycles, and the conditional probability of a star-forming galaxy to host an AGN with given bolometric luminosity. Coupling these ingredients with the radio emission properties associated with star formation and nuclear activity, we compute relevant statistics at different radio frequencies and disentangle the relative contribution of star-forming galaxies and AGNs in different radio luminosity, radio flux, and redshift ranges. Finally, we highlight that radio-emitting star-forming galaxies and AGNs are expected to host supermassive black holes accreting with different Eddington ratio distributions and to occupy different loci in the galaxy main-sequence diagrams. These specific predictions are consistent with current data sets but need to be tested with larger statistics via future radio data with multiband coverage on wide areas, as will become routinely achievable with the advent of the Square Kilometre Array and its precursors.

Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies

Science.gov (United States)

Hashimoto, Tetsuya; Goto, Tomotsugu; Momose, Rieko

2018-04-01

Star-forming galaxies display a close relation among stellar mass, metallicity, and star formation rate (or molecular-gas mass). This is known as the fundamental metallicity relation (FMR) (or molecular-gas FMR), and it has a profound implication on models of galaxy evolution. However, there still remains a significant residual scatter around the FMR. We show here that a fourth parameter, the surface density of stellar mass, reduces the dispersion around the molecular-gas FMR. In a principal component analysis of 29 physical parameters of 41 338 star-forming galaxies, the surface density of stellar mass is found to be the fourth most important parameter. The new 4D fundamental relation forms a tighter hypersurface that reduces the metallicity dispersion to 50 per cent of that of the molecular-gas FMR. We suggest that future analyses and models of galaxy evolution should consider the FMR in a 4D space that includes surface density. The dilution time-scale of gas inflow and the star-formation efficiency could explain the observational dependence on surface density of stellar mass.

NuSTAR Search for Hard X-ray Emission from the Star Formation Regions in Sh2-104

Science.gov (United States)

Gotthelf, Eric V.

2016-04-01

We present NuSTAR hard X-ray observations of Sh2-104, a compact Hii region containing several young massive stellar clusters (YMSCs). We have detected distinct hard X-ray sources coincident with localized VERITAS TeV emission recently resolved from the giant gamma-ray complex MGRO J2019+37 in the Cygnus region. Faint, diffuse X-ray emission coincident with the eastern YMSC in Sh2-104 is likely the result of colliding winds of component stars. Just outside the radio shell of Sh2-104 lies 3XMM J201744.7+365045 and nearby nebula NuSTAR J201744.3+364812, whose properties are most consistent with extragalactic objects. The combined XMM-Newton and NuSTAR spectrum of 3XMM J201744.7+365045 is well-fit to an absorbed power-law model with NH = (3.1+/-1.0)E22 1/cm^2 and photon index Gamma = 2.1+/-0.1. Based on possible long-term flux variation and lack of detected pulsations (Sh2-104 will help identify the nature of the X-ray sources and their relation to MGRO J2019+37.

Nebular excitation in z ∼ 2 star-forming galaxies from the SINS and LUCI surveys: The influence of shocks and active galactic nuclei

Energy Technology Data Exchange (ETDEWEB)

Newman, Sarah F.; Genzel, Reinhard [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States); Buschkamp, Peter; Förster Schreiber, Natascha M.; Kurk, Jaron; Rosario, David; Davies, Ric; Eisenhauer, Frank; Lutz, Dieter [Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); Sternberg, Amiel [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Gnat, Orly [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Mancini, Chiara; Renzini, Alvio [Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Lilly, Simon J.; Carollo, C. Marcella [Institute of Astronomy, Department of Physics, Eidgenössische Technische Hochschule, ETH, CH-8093 Zürich (Switzerland); Burkert, Andreas [Universitäts-Sternwarte Ludwig-Maximilians-Universität (USM), Scheinerstr. 1, D-81679 München (Germany); Cresci, Giovanni [Istituto Nazionale di Astrofisica Osservatorio di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Genel, Shy [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Shapiro Griffin, Kristen [Space Sciences Research Group, Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278 (United States); Hicks, Erin K. S., E-mail: sfnewman@berkeley.edu [Department of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580 (United States); and others

2014-01-20

Based on high-resolution, spatially resolved data of 10 z ∼ 2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGNs), shocks, and photoionization. We explore how these spatially resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the 'composite' region of the z ∼ 0 [N II]/Hα versus [O III]/Hβ diagnostic (BPT) diagram, between star-forming galaxies and those with AGNs. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from an enhanced ionization parameter as compared with H II regions in normal, local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [O III]/Hβ versus stellar mass plane, does not properly separate z ∼ 2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z ∼ 2 mass-metallicity relation (i.e., to the mass they would have at z ∼ 0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [N II]/Hα are more biased by shocks and AGNs at high-z than the [O III]/Hβ/[N II]/Hα calibration.

Polymorphism and Mobilization of Rransposons in Bos taurus

DEFF Research Database (Denmark)

Guldbrandtsen, Bernt; Sahana, Goutam; Lund, Mogens Sandø

The bovine genome assembly was explored to detect putative retrotransposon sequences. In total 87,310 such sites were detected. Four breeds of dairy cattle (Bos taurus) were examined with respect to the presence, segregation or complete absence of the putative retrotransposon. A total of 10...

The Light and Dark Face of a Star-Forming Nebula

Science.gov (United States)

2010-03-01

Today, ESO is unveiling an image of the little known Gum 19, a faint nebula that, in the infrared, appears dark on one half and bright on the other. On one side hot hydrogen gas is illuminated by a supergiant blue star called V391 Velorum. New star formation is taking place within the ribbon of luminous and dark material that brackets V391 Velorum's left in this perspective. After many millennia, these fledgling stars, coupled with the explosive demise of V391 Velorum as a supernova, will likely alter Gum 19's present Janus-like appearance. Gum 19 is located in the direction of the constellation Vela (the Sail) at a distance of approximately 22 000 light years. The Gum 19 moniker derives from a 1955 publication by the Australian astrophysicist Colin S. Gum that served as the first significant survey of so-called HII (read "H-two") regions in the southern sky. HII refers to hydrogen gas that is ionised, or energised to the extent that the hydrogen atoms lose their electrons. Such regions emit light at well-defined wavelengths (or colours), thereby giving these cosmic clouds their characteristic glow. And indeed, much like terrestrial clouds, the shapes and textures of these HII regions change as time passes, though over the course of eons rather than before our eyes. For now, Gum 19 has somewhat of a science fiction-esque, "rip in spacetime" look to it in this image, with a narrow, near-vertical bright region slashing across the nebula. Looking at it, you could possibly see a resemblance to a two-toned angelfish or an arrow with a darkened point. This new image of the evocative Gum 19 object was captured by an infrared instrument called SOFI, mounted on ESO's New Technology Telescope (NTT) that operates at the La Silla Observatory in Chile. SOFI stands for Son of ISAAC, after the "father" instrument, ISAAC, that is located at ESO's Very Large Telescope observatory at Paranal to the north of La Silla. Observing this nebula in the infrared allows astronomers to see

Outflows in the star-formation region near R CrA

Science.gov (United States)

Hartigan, Patrick; Graham, J. A.

1987-01-01

Photographs, spectra, and velocities are presented for the Herbig-Haro objects and visible stars associated with the star-formation region near R CrA. The new data are used to discuss the gas outflows in the area. At least two flows are present; one is linked with the bright variable star R CrA, and the second with the IR source near HH 100. Special attention is given to HH 101. The velocity and spatial structures HH 101 are complex, but are consistent with condensations inside an expanding shell of material ejected from HH 100IR.

Star Formation in Merging Galaxies Using FIRE

Science.gov (United States)

Perez, Adrianna; Hung, Chao-Ling; Naiman, Jill; Moreno, Jorge; Hopkins, Philip

2018-01-01

Galaxy interactions and mergers are efficient mechanisms to birth stars at rates that are significantly higher than found in our Milky Way galaxy. The Kennicut-Schmidt (KS) relation is an empirical relationship between the star-forming rate and gas surface densities of galaxies (Schmidt 1959; Kennicutt 1998). Although most galaxies follow the KS relation, the high levels of star formation in galaxy mergers places them outside of this otherwise tight relationship. The goal of this research is to analyze the gas content and star formation of simulated merging galaxies. Our work utilizes the Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high-resolution cosmological simulation that resolves star-forming regions and incorporates stellar feedback in a physically realistic way. In this work, we have noticed a significant increase in the star formation rate at first and second passage, when the two black holes of each galaxy approach one other. Next, we will analyze spatially resolved star-forming regions over the course of the interacting system. Then, we can study when and how the rates that gas converts into stars deviate from the standard KS. These analyses will provide important insights into the physical mechanisms that regulate star formation of normal and merging galaxies and valuable theoretical predictions that can be used to compare with current and future observations from ALMA or the James Webb Space Telescope.

IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

Science.gov (United States)

Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

2017-04-01

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

SUBMILLIMETER ARRAY OBSERVATIONS TOWARD THE MASSIVE STAR-FORMING CORE MM1 OF W75N

International Nuclear Information System (INIS)

Minh, Y. C.; Su, Y.-N.; Liu, S.-Y.; Yan, C.-H.; Chen, H.-R.; Kim, S.-J.

2010-01-01

The massive star-forming core MM1 of W75N was observed using the Submillimeter Array with ∼1'' and 2'' spatial resolutions at 217 and 347 GHz, respectively. From the 217 GHz continuum we found that the MM1 core consists of two sources, separated by about 1'': MM1a (∼0.6 M sun ) and MM1b (∼1.4 M sun ), located near the radio continuum sources VLA 2/VLA 3 and VLA 1, respectively. Within MM1b, two gas clumps were found to be expanding away from VLA 1 at about ±3 km s -1 , as a result of the most recent star formation activity in the region. Observed molecular lines show emission peaks at two positions, MM1a and MM1b: sulfur-bearing species have emission peaks toward MM1a, but methanol and saturated species at MM1b. We identified high-temperature (∼200 K) gas toward MM1a and the hot core in MM1b. This segregation may result from the evolution of the massive star-forming core. In the very early phase of star formation, the hot core is seen through the evaporation of dust ice-mantle species. As the mantle species are consumed via evaporation the high-temperature gas species (such as the sulfur-bearing molecules) become bright. The SiO molecule is unique in having an emission peak exactly at the VLA 2 position, probably tracing a shock powered by VLA 2. The observed sulfur-bearing species show similar abundances both in MM1a and MM1b, whereas the methanol and saturated species show significant abundance enhancement toward MM1b, by about an order of magnitude, compared to MM1a.

The dependence of stellar properties on initial cloud density

Science.gov (United States)

Jones, Michael O.; Bate, Matthew R.

2018-05-01

We investigate the dependence of stellar properties on the initial mean density of the molecular cloud in which stellar clusters form using radiation hydrodynamical simulations that resolve the opacity limit for fragmentation. We have simulated the formation of three star clusters from the gravitational collapse of molecular clouds whose densities vary by a factor of a hundred. As with previous calculations including radiative feedback, we find that the dependence of the characteristic stellar mass, Mc, on the initial mean density of the cloud, ρ, is weaker than the dependence of the thermal Jeans mass. However, unlike previous calculations, which found no statistically significant variation in the median mass with density, we find a weak dependence approximately of the form Mc∝ρ-1/5. The distributions of properties of multiple systems do not vary significantly between the calculations. We compare our results to the result of observational surveys of star-forming regions, and suggest that the similarities between the properties of our lowest density calculation and the nearby Taurus-Auriga region indicate that the apparent excess of solar-type stars observed may be due to the region's low density.

SUPERMASSIVE BLACK HOLES IN A STAR-FORMING GASEOUS CIRCUMNUCLEAR DISK

Energy Technology Data Exchange (ETDEWEB)

Del Valle, L.; Escala, A.; Molina, J. [Departamento de Astronomía, Universidad de Chile (Chile); Maureira-Fredes, C.; Amaro-Seoane, P. [Max Planck Institut fur Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany); Cuadra, J., E-mail: ldelvalleb@gmail.com [Instituto de Astrofísica, Pontificia Universidad Catolica de Chile (Chile)

2015-09-20

Using N-body/smoothed particle hydrodynamics simulations we study the evolution of the separation of a pair of supermassive black holes (SMBHs) embedded in a star-forming circumnuclear disk (CND). This type of disk is expected to be formed in the central kiloparsec of the remnant of gas-rich galaxy mergers. Our simulations indicate that orbital decay of the SMBHs occurs more quickly when the mean density of the CND is higher, due to increased dynamical friction. However, in simulations where the CND is fragmented in high-density gaseous clumps (clumpy CND), the orbits of the SMBHs are erratically perturbed by the gravitational interaction with these clumps, delaying, in some cases, the orbital decay of the SMBHs. The densities of these gaseous clumps in our simulations and in recent studies of clumpy CNDs are two orders of magnitude higher than the observed density of molecular clouds in isolated galaxies or ultraluminous infrared galaxies (ULIRGs), thus, we expect that SMBH orbits are perturbed less in real CNDs than in the simulated CNDs of this study and other recent studies. We also find that the migration timescale has a weak dependence on the star formation rate of the CND. Furthermore, the migration timescale of an SMBH pair in a star-forming clumpy CND is at most a factor of three longer than the migration timescale of a pair of SMBHs in a CND modeled with more simple gas physics. Therefore, we estimate that the migration timescale of the SMBHs in a clumpy CND is on the order of 10{sup 7} years.

GMC Collisions as Triggers of Star Formation. III. Density and Magnetically Regulated Star Formation

Energy Technology Data Exchange (ETDEWEB)

Wu, Benjamin [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tan, Jonathan C. [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Christie, Duncan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Collins, David, E-mail: ben.wu@nao.ac.jp [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

2017-06-01

We study giant molecular cloud (GMC) collisions and their ability to trigger star cluster formation. We further develop our three-dimensional magnetized, turbulent, colliding GMC simulations by implementing star formation subgrid models. Two such models are explored: (1) “Density-Regulated,” i.e., fixed efficiency per free-fall time above a set density threshold and (2) “Magnetically Regulated,” i.e., fixed efficiency per free-fall time in regions that are magnetically supercritical. Variations of parameters associated with these models are also explored. In the non-colliding simulations, the overall level of star formation is sensitive to model parameter choices that relate to effective density thresholds. In the GMC collision simulations, the final star formation rates and efficiencies are relatively independent of these parameters. Between the non-colliding and colliding cases, we compare the morphologies of the resulting star clusters, properties of star-forming gas, time evolution of the star formation rate (SFR), spatial clustering of the stars, and resulting kinematics of the stars in comparison to the natal gas. We find that typical collisions, by creating larger amounts of dense gas, trigger earlier and enhanced star formation, resulting in 10 times higher SFRs and efficiencies. The star clusters formed from GMC collisions show greater spatial substructure and more disturbed kinematics.

Connecting the Cosmic Star Formation Rate with the Local Star Formation

Science.gov (United States)

Gribel, Carolina; Miranda, Oswaldo D.; Williams Vilas-Boas, José

2017-11-01

We present a model that unifies the cosmic star formation rate (CSFR), obtained through the hierarchical structure formation scenario, with the (Galactic) local star formation rate (SFR). It is possible to use the SFR to generate a CSFR mapping through the density probability distribution functions commonly used to study the role of turbulence in the star-forming regions of the Galaxy. We obtain a consistent mapping from redshift z˜ 20 up to the present (z = 0). Our results show that the turbulence exhibits a dual character, providing high values for the star formation efficiency ( ˜ 0.32) in the redshift interval z˜ 3.5{--}20 and reducing its value to =0.021 at z = 0. The value of the Mach number ({{ M }}{crit}), from which rapidly decreases, is dependent on both the polytropic index (Γ) and the minimum density contrast of the gas. We also derive Larson’s first law associated with the velocity dispersion ( ) in the local star formation regions. Our model shows good agreement with Larson’s law in the ˜ 10{--}50 {pc} range, providing typical temperatures {T}0˜ 10{--}80 {{K}} for the gas associated with star formation. As a consequence, dark matter halos of great mass could contain a number of halos of much smaller mass, and be able to form structures similar to globular clusters. Thus, Larson’s law emerges as a result of the very formation of large-scale structures, which in turn would allow the formation of galactic systems, including our Galaxy.

Orphan Stars Found in Long Galaxy Tail

Science.gov (United States)

2007-09-01

Astronomers have found evidence that stars have been forming in a long tail of gas that extends well outside its parent galaxy. This discovery suggests that such "orphan" stars may be much more prevalent than previously thought. The comet-like tail was observed in X-ray light with NASA's Chandra X-ray Observatory and in optical light with the Southern Astrophysical Research (SOAR) telescope in Chile. The feature extends for more than 200,000 light years and was created as gas was stripped from a galaxy called ESO 137-001 that is plunging toward the center of Abell 3627, a giant cluster of galaxies. "This is one of the longest tails like this we have ever seen," said Ming Sun of Michigan State University, who led the study. "And, it turns out that this is a giant wake of creation, not of destruction." Chandra X-ray Image of ESO 137-001 and Tail in Abell 3627 Chandra X-ray Image of ESO 137-001 and Tail in Abell 3627 The observations indicate that the gas in the tail has formed millions of stars. Because the large amounts of gas and dust needed to form stars are typically found only within galaxies, astronomers have previously thought it unlikely that large numbers of stars would form outside a galaxy. "This isn't the first time that stars have been seen to form between galaxies," said team member Megan Donahue, also of MSU. "But the number of stars forming here is unprecedented." The evidence for star formation in this tail includes 29 regions of ionized hydrogen glowing in optical light, thought to be from newly formed stars. These regions are all downstream of the galaxy, located in or near the tail. Two Chandra X-ray sources are near these regions, another indication of star formation activity. The researchers believe the orphan stars formed within the last 10 million years or so. The stars in the tail of this fast-moving galaxy, which is some 220 million light years away, would be much more isolated than the vast majority of stars in galaxies. H-alpha Image of

Dinâmica folicular e taxa de prenhez em novilhas receptoras de embrião (Bos taurus indicus x Bos taurus taurus tratadas com o protocolo "Ovsynch" para inovulação em tempo fixo

Directory of Open Access Journals (Sweden)

Pietro Sampaio Baruselli

2003-01-01

Full Text Available Objetivou-se avaliar a eficiência da sincronização da ovulação para inovulação em tempo fixo em novilhas Bos taurus indicus x Bos taurus taurus receptoras de embrião. No Experimento 1, a dinâmica folicular foi acompanhada durante o protocolo "Ovsynch" (G1; n=35 e após a aplicação de PGF2alfa (G2; n=34. No Experimento 2, os mesmos tratamentos foram realizados a campo em 168 (G1 e 177 (G2 novilhas. No D6, colheu-se sangue para dosagem de P4 e se realizaram exames ultra-sonográficos. No D7, realizou-se a inovulação. No Experimento 1, 45,7% dos animais ovularam após o 1º GnRH (P;0,05. Ao final, a taxa de prenhez no Gl foi de 35,7% e no G2 de 25,4% (P<0,05. Foram detectadas em estro 53,7% das novilhas do G2 e 33,3% do Gl (P<0,05. Os corpos lúteos com maior área determinaram maiores concentrações de P4 e taxa de concepção (P<0,05. A sincronização da ovulação para inovulação em tempo fixo aumentou as taxas de ovulação, de aproveitamento e de prenhez em novilhas receptoras de embrião.

Star formation and its relation to free-free emission from ionized gas and far-infrared emission from dust

International Nuclear Information System (INIS)

Mezger, P.G.

1985-01-01

The author reviews the physical state of the galactic disk and especially of the thin layer of interstellar matter (ISM) out of which stars form today. The characteristics of OB stars and the HII regions which these stars form are summarized. Dust emission characteristics are also summarized. The author shows how the Lyc photon production rate of all O stars, and the total IR luminosity of all dust grains in the galactic disk can be estimated from radio and FIR surveys of the galactic plane. Star formation rates are derived for a constant initial mass function. The concept of bimodal star formation, where about equal fractions of O stars form in spiral arms and interarm region but low mass stars form only in the interarm region, is introduced. The relation between the 2.4 μm emission from M giants and supergiants is discussed qualitatively, lending support to the process of bimodal star formation. (Auth.)