3,589 research outputs found
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks
We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ~0.β1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ~0 08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are 44.9^(+5.8)_(β3.4), 37.0^(+4.9)_(β3.0), and 28.5^(+3.7)_(β2.3) au, respectively, and the mean protostellar dust disk masses are 25.9^(+7.7)_(β4.0), 14.9^(+3.8)_(β2.2), 1.6^(+3.5)_(β1.9) Mβ, respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase
Constraining the Envelope Structure of L1527 IRS: Infrared Scattered Light Modeling
We model Spitzer Space Telescope observations of the Taurus Class 0 protostar
L1527 IRS (IRAS 04368+2557) to provide constraints on its protostellar envelope
structure. The nearly edge-on inclination of L1527 IRS, coupled with the highly
spatially-resolved near to mid-infrared images of this object and the detailed
IRS spectrum, enable us to constrain the outflow cavity geometry quite well,
reducing uncertainties in the other derived parameters. The mid-infrared
scattered light image shows a bright central source within a dark lane; the
aspect ratio of this dark lane is such that it appears highly unlikely to be a
disk shadow. In modeling this dark lane, we conclude that L1527 IRS is probably
not described by a standard TSC envelope with simple bipolar cavities. We find
it necessary to model the dark lane and central source as a modified inner
envelope structure. This structure may be due either to a complex wind-envelope
interaction or induced by the central binary. To fit the overall SED, we
require the central source to have a large near to mid-infrared excess,
suggesting substantial disk accretion. Our model reproduces the overall
morphology and surface brightness distribution of L1527 IRS fairly well, given
the limitations of using axisymmetric models to fit the non-axisymmetric real
object, and the derived envelope infall rates are in reasonable agreement with
some other investigations. IRAC observations of L1527 IRS taken 12 months apart
show variability in total flux and variability in the opposing bipolar
cavities, suggesting asymmetric variations in accretion. We also provide model
images at high resolution for comparison to future observations with current
ground-based instrumentation and future space-based telescopes.Comment: 50 pages, 14 figures 2 tables, accepted by the Astrophysical Journal.
The manuscript with full resolution figures can be downloaded from
http://astro.lsa.umich.edu/~jjtobin/L1527.pd
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks
We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ~0.β1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ~0 08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are 44.9^(+5.8)_(β3.4), 37.0^(+4.9)_(β3.0), and 28.5^(+3.7)_(β2.3) au, respectively, and the mean protostellar dust disk masses are 25.9^(+7.7)_(β4.0), 14.9^(+3.8)_(β2.2), 1.6^(+3.5)_(β1.9) Mβ, respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions
We present Atacama Large Millimeter/submillimeter Array (0.87 mm) and Very Large Array (9 mm) observations toward OMC-2 FIR4 and OMC-2 FIR3 within the Orion integral-shaped filament, thought to be two of the nearest regions of intermediate-mass star formation. We characterize the continuum sources within these regions on ~40 au (0."1) scales and associated molecular line emission at a factor of ~30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC-2 FIR4, four in OMC-2 FIR3, and one additional source just outside OMC-2 FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100 au scales. HOPS-108 is the only protostar in OMC-2 FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC-2 FIR3, with L ~ 360 Lβ, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate it from icy dust grains; overall, these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in ΒΉΒ²CO, but we find evidence of interaction between the outflow/jet from HOPS-370 and the OMC-2 FIR4 region. A multitude of observational constraints indicate that HOPS-108 is likely a low- to intermediate-mass protostar in its main mass accretion phase and is the most luminous protostar in OMC-2 FIR4. The high-resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them
Kinematic and Spatial Substructure in NGC 2264
We present an expanded kinematic study of the young cluster NGC 2264 based
upon optical radial velocities measured using multi-fiber echelle spectroscopy
at the 6.5 meter MMT and Magellan telescopes. We report radial velocities for
695 stars, of which approximately 407 stars are confirmed or very likely
members. Our results more than double the number of members with radial
velocities from F{\H u}r{\'e}sz et al., resulting in a much better defined
kinematic relationship between the stellar population and the associated
molecular gas.
In particular, we find that there is a significant subset of stars that are
systematically blueshifted with respect to the molecular (CO) gas. The
detection of Lithium absorption and/or infrared excesses in this blue-shifted
population suggests that at least some of these stars are cluster members; we
suggest some speculative scenarios to explain their kinematics. Our results
also more clearly define the redshifted population of stars in the northern end
of the cluster; we suggest that the stellar and gas kinematics of this region
are the result of a bubble driven by the wind from O7 star S Mon. Our results
emphasize the complexity of the spatial and kinematic structure of NGC 2264,
important for eventually building up a comprehensive picture of cluster
formation.Comment: Accepted to AJ. 38 pages, 5 Figures 3 Table
A Flattened Protostellar Envelope in Absorption around L1157
Deep Spitzer IRAC images of L1157 reveal many of the details of the outflow
and the circumstellar environment of this Class 0 protostar. In IRAC band 4, 8
microns, there is a flattened structure seen in absorption against the
background emission. The structure is perpendicular to the outflow and is
extended to a diameter of 2 arcminutes. This structure is the first clear
detection of a flattened circumstellar envelope or pseudo-disk around a Class 0
protostar. Such a flattened morphology is an expected outcome for many collapse
theories that include magnetic fields or rotation. We construct an extinction
model for a power-law density profile, but we do not constrain the density
power-law index.Comment: ApJL accepte
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