59 research outputs found
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of multiple protostar systems in the Perseus molecular cloud previously
detected by the Karl G. Jansky Very Large Array (VLA). We observed 17 close
(600~AU separation) multiple systems at 1.3~mm in continuum and five
molecular lines (i.e., \twco, \cateo, \thco, HCO, SO) to characterize the
circum-multiple environments in which these systems are forming. We detect at
least one component in the continuum for the 17 multiple systems. In three
systems, one companion is not detected, and for two systems the companions are
unresolved at our observed resolution. We also detect circum-multiple dust
emission toward 8 out of 9 Class 0 multiples. Circum-multiple dust emission is
not detected toward any of the 8 Class I multiples. Twelve systems are detected
in the dense gas tracers toward their disks/inner envelopes. For these 12
systems, we use the dense gas observations to characterize their formation
mechanism. The velocity gradients in the circum-multiple gas are clearly
orthogonal to the outflow directions in 8 out of the 12 systems, consistent
with disk fragmentation. Moreover, only two systems with separations 200~AU
are \textit{inconsistent} with disk fragmentation, in addition to the two
widest systems (500~AU). Our results suggest that disk fragmentation via
gravitational instability is an important formation mechanism for close
multiple systems, but further statistics are needed to better determine the
relative fraction formed via this method.Comment: 48 Pages, 26 Figures, 7 Tables, Accepted by Ap
High Resolution 8 mm and 1 cm Polarization of IRAS 4A from the VLA Nascent Disk and Multiplicity (VANDAM) Survey
Magnetic fields can regulate disk formation, accretion and jet launching.
Until recently, it has been difficult to obtain high resolution observations of
the magnetic fields of the youngest protostars in the critical region near the
protostar. The VANDAM survey is observing all known protostars in the Perseus
Molecular Cloud. Here we present the polarization data of IRAS 4A. We find that
with ~ 0.2'' (50 AU) resolution at {\lambda} = 8.1 and 10.3 mm, the inferred
magnetic field is consistent with a circular morphology, in marked contrast
with the hourglass morphology seen on larger scales. This morphology is
consistent with frozen-in field lines that were dragged in by rotating material
entering the infall region. The field morphology is reminiscent of rotating
circumstellar material near the protostar. This is the first polarization
detection of a protostar at these wavelengths. We conclude from our
observations that the dust emission is optically thin with {\beta} ~ 1.3,
suggesting that mm/cm-sized grains have grown and survived in the short
lifetime of the protostar.Comment: Accepted to ApJL. 13 pages, 4 figure
Kinematic Analysis of a Protostellar Multiple System: Measuring the Protostar Masses and Assessing Gravitational Instability in the Disks of L1448 IRS3B and L1448 IRS3A
We present new Atacama Large Millimeter/submillimeter Array (ALMA)
observations towards a compact (230~au separation) triple protostar system,
L1448 IRS3B, at 879~\micron with \contbeam~resolution. Spiral arm structure
within the circum-multiple disk is well resolved in dust continuum toward
IRS3B, and we detect the known wide (2300~au) companion, IRS3A, also resolving
possible spiral substructure. Using dense gas tracers, C17O, H13CO, and
H13CN, we resolve the Keplerian rotation for both the circum-triple disk in
IRS3B and the disk around IRS3A. Furthermore, we use the molecular line
kinematic data and radiative transfer modeling of the molecular line emission
to confirm that the disks are in Keplerian rotation with fitted masses of
for IRS3B-ab, ~Msun for IRS3A, and
place an upper limit on the central protostar mass for the tertiary IRS3B-c of
0.2~Msun. We measure the mass of the fragmenting disk of IRS3B to be 0.29~Msun
from the dust continuum emission of the circum-multiple disk and estimate the
mass of the clump surrounding IRS3B-c to be 0.07~Msun. We also find that the
disk around IRS3A has a mass of 0.04~Msun. By analyzing the Toomre~Q parameter,
we find the IRS3A circumstellar disk is gravitationally stable (Q5), while
the IRS3B disk is consistent with a gravitationally unstable disk (Q1)
between the radii 200-500~au. This coincides with the location of the spiral
arms and the tertiary companion IRS3B-c, supporting the hypothesis that IRS3B-c
was formed in situ via fragmentation of a gravitationally unstable disk
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
The VLA Nascent Disk And Multiplicity (VANDAM) Survey of Perseus Protostars. Resolving the Sub-Arcsecond Binary System in NGC 1333 IRAS2A
We are conducting a Jansky VLA Ka-band (8 mm and 1 cm) and C-band (4 cm and
6.4 cm) survey of all known protostars in the Perseus Molecular Cloud,
providing resolution down to 0.06'' and 0.35" in Ka-band and
C-band, respectively. Here we present first results from this survey that
enable us to examine the source NGC 1333 IRAS2A in unprecedented detail and
resolve it into a proto-binary system separated by 0.621"0.006" (143
AU) at 8 mm, 1 cm, and 4 cm. These 2 sources (IRAS2A VLA1 and VLA2) are likely
driving the two orthogonal outflows known to originate from IRAS2A. The
brighter source IRAS2A VLA1 is extended perpendicular to its outflow in the VLA
data, with a deconvolved size of 0.055" (13 AU), possibly tracing a
protostellar disk. The recently reported candidate companions (IRAS2A MM2 and
MM3) are not detected in either our VLA data, CARMA 1.3 mm data, or SMA 850
m data. SMA CO (), CARMA CO (), and
lower resolution CARMA CO () observations are used to examine
the outflow origins and the nature of the candidate companions to IRAS2A VLA1.
The CO () and () data show that IRAS2A MM2 is
coincident with a bright CO emission spot in the east-west outflow, and IRAS2A
MM3 is within the north-south outflow. In contrast, IRAS2A VLA2 lies at the
east-west outflow symmetry point. We propose that IRAS2A VLA2 is the driving
source of the East-West outflow and a true companion to IRAS2A VLA1, whereas
IRAS2A MM2 and MM3 may not be protostellar.Comment: Accepted to ApJ, 27 pages, 6 Figures, 2 Table
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