150 research outputs found
The Mass Distributions of Starless and Protostellar Cores in Gould Belt Clouds
Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space
Telescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus,
Perseus, Serpens, and Orion molecular clouds. We develop a new method to
discriminate submillimeter cores found by SCUBA as starless or protostellar,
using point source photometry from Spitzer wide field surveys. First, we
identify infrared sources with red colors associated with embedded young
stellar objects (YSOs). Second, we compare the positions of these
YSO-candidates to our submillimeter cores. With these identifications, we
construct new, self-consistent starless and protostellar core mass functions
(CMFs) for the five clouds. We find best fit slopes to the high-mass end of the
CMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for
Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are
each consistent with the -1.35 power-law slope of the Salpeter IMF at higher
masses, but suggest some differences. We examine a variety of trends between
these CMF shapes and their parent cloud properties, potentially finding a
correlation between the high-mass slope and core temperature. We also find a
trend between core mass and effective size, but we are very limited by
sensitivity. We make similar comparisons between core mass and size with visual
extinction (for A_V >= 3) and find no obvious trends. We also predict the
numbers and mass distributions of cores that future surveys with SCUBA-2 may
detect in each of these clouds.Comment: 56 pages, 18 figures, fixed typo in Eq 1, results in paper remain
unchange
An ALMA Search for Substructure, Fragmentation, and Hidden Protostars in Starless Cores in Chamaeleon I
We present an Atacama Large Millimeter/submillimeter Array (ALMA) 106 GHz
(Band 3) continuum survey of the complete population of dense cores in the
Chamaeleon I molecular cloud. We detect a total of 24 continuum sources in 19
different target fields. All previously known Class 0 and Class I protostars in
Chamaeleon I are detected, whereas all of the 56 starless cores in our sample
are undetected. We show that the Spitzer+Herschel census of protostars in
Chamaeleon I is complete, with the rate at which protostellar cores have been
misclassified as starless cores calculated as <1/56, or < 2%. We use synthetic
observations to show that starless cores collapsing following the turbulent
fragmentation scenario are detectable by our ALMA observations when their
central densities exceed ~10^8 cm^-3, with the exact density dependent on the
viewing geometry. Bonnor-Ebert spheres, on the other hand, remain undetected to
central densities at least as high as 10^10 cm^-3. Our starless core
non-detections are used to infer that either the star formation rate is
declining in Chamaeleon I and most of the starless cores are not collapsing,
matching the findings of previous studies, or that the evolution of starless
cores are more accurately described by models that develop less substructure
than predicted by the turbulent fragmentation scenario, such as Bonnor-Ebert
spheres. We outline future work necessary to distinguish between these two
possibilities.Comment: Accepted by Ap
The JCMT Gould Belt Survey: A First Look at the Auriga–California Molecular Cloud with SCUBA-2
We present 850 and 450 μm observations of the dense regions within the Auriga–California molecular cloud using SCUBA-2 as part of the JCMT Gould Belt Legacy Survey to identify candidate protostellar objects, measure the masses of their circumstellar material (disk and envelope), and compare the star formation to that in the Orion A molecular cloud. We identify 59 candidate protostars based on the presence of compact submillimeter emission, complementing these observations with existing Herschel/SPIRE maps. Of our candidate protostars, 24 are associated with young stellar objects (YSOs) in the Spitzer and Herschel/PACS catalogs of 166 and 60 YSOs, respectively (177 unique), confirming their protostellar nature. The remaining 35 candidate protostars are in regions, particularly around LkHα 101, where the background cloud emission is too bright to verify or rule out the presence of the compact 70 μm emission that is expected for a protostellar source. We keep these candidate protostars in our sample but note that they may indeed be prestellar in nature. Our observations are sensitive to the high end of the mass distribution in Auriga–Cal. We find that the disparity between the richness of infrared star-forming objects in Orion A and the sparsity in Auriga–Cal extends to the submillimeter, suggesting that the relative star formation rates have not varied over the Class II lifetime and that Auriga–Cal will maintain a lower star formation efficiency
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A triple protostar system formed via fragmentation of a gravitationally unstable disk
Binary and multiple star systems are a frequent outcome of the star formation process(1,2) and as a result almost half of all stars with masses similar to that of the Sun have at least one companion star(3). Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large-scale fragmentation of turbulent gas cores and filaments(4,5) or smaller-scale fragmentation of a massive protostellar disk due to gravitational instability(6,7). Observational evidence for turbulent fragmentation on scales of more than 1,000 astronomical units has recently emerged(8,9). Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems(10-13). The triple protostar system L1448 IRS3B is an ideal system with which to search for evidence of disk fragmentation as it is in an early phase of the star formation process, it is likely to be less than 150,000 years old(14) and all of the protostars in the system are separated by less than 200 astronomical units. Here we report observations of dust and molecular gas emission that reveal a disk with a spiral structure surrounding the three protostars. Two protostars near the centre of the disk are separated by 61 astronomical units and a tertiary protostar is coincident with a spiral arm in the outer disk at a separation of 183 astronomical units(13). The inferred mass of the central pair of protostellar objects is approximately one solar mass, while the disk surrounding the three protostars has a total mass of around 0.30 solar masses. The tertiary protostar itself has a minimum mass of about 0.085 solar masses. We demonstrate that the disk around L1448 IRS3B appears susceptible to disk fragmentation at radii between 150 and 320 astronomical units, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning one or two companion stars
The Mass Distribution of Starless and Protostellar Cores in Gould Belt Clouds
Using data from the SCUBA Legacy Catalogue (850 μm) and Spitzer Space Telescope (3.6-70 μm), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. We develop a new method to discriminate submillimeter cores found by Submillimeter Common-User Bolometer Array (SCUBA) as starless or protostellar, using point source photometry from Spitzer wide field surveys. First, we identify infrared sources with red colors associated with embedded young stellar objects (YSOs). Second, we compare the positions of these YSO candidates to our submillimeter cores. With these identifications, we construct new, self-consistent starless and protostellar core mass functions (CMFs) for the five clouds. We find best-fit slopes to the high-mass end of the CMFs of –1.26 ± 0.20, –1.22 ± 0.06, –0.95 ± 0.20, and –1.67 ± 0.72 for Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are each consistent with the –1.35 power-law slope of the Salpeter initial mass function at higher masses, but suggest some differences. We examine a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and core temperature. We also find a trend between core mass and effective size, but we are very limited by sensitivity. We make similar comparisons between core mass and size with visual extinction (for A_V ≥ 3) and find no obvious trends. We also predict the numbers and mass distributions of cores that future surveys with SCUBA-2 may detect in each of these clouds
Mass Assembly of Stellar Systems and Their Evolution with the SMA (MASSES)-Full Data Release
We present and release the full dataset for the Mass Assembly of Stellar
Systems and their Evolution with the SMA (MASSES) survey. This survey used the
Submillimeter Array (SMA) to image the 74 known protostars within the Perseus
molecular cloud. The SMA was used in two array configurations to capture
outflows for scales 30 (9000 au) and to probe scales
down to 1 (300 au). The protostars were observed
with the 1.3 mm and 850 m receivers simultaneously to detect continuum at
both wavelengths and molecular line emission from CO(2-1), CO(2-1),
CO(2-1), ND(3-2), CO(3-2), HCO(4-3), and
HCO(4-3). Some of the observations also used the SMA's recently
upgraded correlator, SWARM, whose broader bandwidth allowed for several more
spectral lines to be observed (e.g., SO, HCO, DCO, DCN, CS, CN). Of the
main continuum and spectral tracers observed, 84% of the images and cubes had
emission detected. The median CO(2-1) linewidth is 1.0 km
s, which is slightly higher than those measured with single-dish
telescopes at scales of 3000-20000 au. Of the 74 targets, six are suggested to
be first hydrostatic core candidates, and we suggest that L1451-mm is the best
candidate. We question a previous continuum detection toward L1448 IRS2E. In
the SVS13 system, SVS13A certainly appears to be the most evolved source, while
SVS13C appears to be hotter and more evolved than SVS13B. The MASSES survey is
the largest publicly available interferometric continuum and spectral line
protostellar survey to date, and is largely unbiased as it only targets
protostars in Perseus. All visibility () data and imaged data are publicly
available at https://dataverse.harvard.edu/dataverse/full_MASSES/.Comment: Accepted to ApJ
A Triple Protostar System Formed via Fragmentation of a Gravitationally Unstable Disk
Binary and multiple star systems are a frequent outcome of the star formation
process, and as a result, almost half of all sun-like stars have at least one
companion star. Theoretical studies indicate that there are two main pathways
that can operate concurrently to form binary/multiple star systems: large scale
fragmentation of turbulent gas cores and filaments or smaller scale
fragmentation of a massive protostellar disk due to gravitational instability.
Observational evidence for turbulent fragmentation on scales of 1000~AU has
recently emerged. Previous evidence for disk fragmentation was limited to
inferences based on the separations of more-evolved pre-main sequence and
protostellar multiple systems. The triple protostar system L1448 IRS3B is an
ideal candidate to search for evidence of disk fragmentation. L1448 IRS3B is in
an early phase of the star formation process, likely less than 150,000 years in
age, and all protostars in the system are separated by 200~AU. Here we
report observations of dust and molecular gas emission that reveal a disk with
spiral structure surrounding the three protostars. Two protostars near the
center of the disk are separated by 61 AU, and a tertiary protostar is
coincident with a spiral arm in the outer disk at a 183 AU separation. The
inferred mass of the central pair of protostellar objects is 1 M,
while the disk surrounding the three protostars has a total mass of 0.30
M_{\sun}. The tertiary protostar itself has a minimum mass of 0.085
M. We demonstrate that the disk around L1448 IRS3B appears susceptible
to disk fragmentation at radii between 150~AU and 320~AU, overlapping with the
location of the tertiary protostar. This is consistent with models for a
protostellar disk that has recently undergone gravitational instability,
spawning one or two companion stars.Comment: Published in Nature on Oct. 27th. 24 pages, 8 figure
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. IV. Unveiling the Embedded Intermediate-Mass Protostar and Disk within OMC2-FIR3/HOPS-370
We present ALMA (0.87 and 1.3 mm) and VLA (9 mm) observations toward the candidate intermediate-mass protostar OMC2-FIR3 (HOPS-370; L_(bol) ~ 314 L_⊙) at ~0."1 (40 au) resolution for the continuum emission and ~0."25 (100 au) resolution of nine molecular lines. The dust continuum observed with ALMA at 0.87 and 1.3 mm resolves a near edge-on disk toward HOPS-370 with an apparent radius of ~100 au. The VLA observations detect both the disk in dust continuum and free–free emission extended along the jet direction. The ALMA observations of molecular lines (H₂CO, SO, CH₃OH, ¹³CO, C¹⁸O, NS, and H¹³CN) reveal rotation of the apparent disk surrounding HOPS-370 orthogonal to the jet/outflow direction. We fit radiative transfer models to both the dust continuum structure of the disk and molecular line kinematics of the inner envelope and disk for the H₂CO, CH₃OH, NS, and SO lines. The central protostar mass is determined to be ~2.5 M_⊙ with a disk radius of ~94 au, when fit using combinations of the H₂CO, CH₃OH, NS, and SO lines, consistent with an intermediate-mass protostar. Modeling of the dust continuum and spectral energy distribution yields a disk mass of 0.035 M_⊙ (inferred dust+gas) and a dust disk radius of 62 au; thus, the dust disk may have a smaller radius than the gas disk, similar to Class II disks. In order to explain the observed luminosity with the measured protostar mass, HOPS-370 must be accreting at a rate of (1.7−3.2) × 10⁻⁵ M_⊙ yr⁻¹
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