137 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
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
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 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
The VLA Nascent Disk And Multiplicity Survey of Perseus Protostars (VANDAM). IV. Free-Free Emission from Protostars: Links to Infrared Properties, Outflow Tracers, and Protostellar Disk Masses
Emission from protostars at centimeter radio wavelengths has been shown to
trace the free-free emission arising from ionizing shocks as a result of jets
and outflows driven by protostars. Therefore, measuring properties of
protostars at radio frequencies can provide valuable insights into the nature
of their outflows and jets. We present a C-band (4.1 cm and 6.4 cm) survey of
all known protostars (Class 0 and Class I) in Perseus as part of the VLA
Nascent Disk and Multiplicity (VANDAM) Survey. We examine the known
correlations between radio flux density and protostellar parameters such as
bolometric luminosity and outflow force, for our sample. We also investigate
the relationship between radio flux density and far-infrared line luminosities
from Herschel. We show that free-free emission originates most likely from
J-type shocks; however, the large scatter indicates that those two types of
emission probe different time and spatial scales. Using C-band fluxes, we
removed an estimation of free-free contamination from the corresponding Ka-band
(9 mm) flux densities that primarily probe dust emission from embedded disks.
We find that the compact (~1") dust emission is lower for Class I sources
(median dust mass 96 M) relative to Class 0 (248 M), but
several times higher than in Class II (5-15 M). If this compact dust
emission is tracing primarily the embedded disk, as is likely for many sources,
this result provides evidence for decreasing disk masses with protostellar
evolution, with sufficient mass for forming giant planet cores primarily at
early times.Comment: 90 pages, 21 figures, 10 tables; accepted for publication in ApJ
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