206 research outputs found
An ALMA Dynamical Mass Estimate of the Proposed Planetary-mass Companion FW Tau C
Dynamical mass estimates down to the planet-mass regime can help to
understand planet formation. We present Atacama Large Millimeter/submillimeter
Array (ALMA) 1.3 mm observations of FW Tau C, a proposed ~10
planet-mass companion at ~330 au from the host binary FW Tau AB. We spatially
and spectrally resolve the accretion disk of FW Tau C in CO (2-1). By
modeling the Keplerian rotation of gas, we derive a dynamical mass of ~0.1
. Therefore, FW Tau C is unlikely a planet, but rather a low-mass star
with a highly inclined disk. This also suggests that FW Tau is a triple system
consisting of three ~0.1 stars.Comment: Accepted for publication in ApJ
WL 17: A Young Embedded Transition Disk
We present the highest spatial resolution ALMA observations to date of the
Class I protostar WL 17 in the Ophiuchus L1688 molecular cloud complex,
which show that it has a 12 AU hole in the center of its disk. We consider
whether WL 17 is actually a Class II disk being extincted by foreground
material, but find that such models do not provide a good fit to the broadband
SED and also require such high extinction that it would presumably arise from
dense material close to the source such as a remnant envelope. Self-consistent
models of a disk embedded in a rotating collapsing envelope can nicely
reproduce both the ALMA 3 mm observations and the broadband SED of WL 17. This
suggests that WL 17 is a disk in the early stages of its formation, and yet
even at this young age the inner disk has been depleted. Although there are
multiple pathways for such a hole to be created in a disk, if this hole were
produced by the formation of planets it could place constraints on the
timescale for the growth of planetesimals in protoplanetary disks.Comment: 7 pages, 3 figures, 2 tables, accepted for publication in ApJ
A VLA Survey For Faint Compact Radio Sources in the Orion Nebula Cluster
We present Karl G. Janksy Very Large Array (VLA) 1.3 cm, 3.6 cm, and 6 cm
continuum maps of compact radio sources in the Orion Nebular Cluster. We
mosaicked 34 square arcminutes at 1.3 cm, 70 square arcminutes at 3.6 cm and
109 square arcminutes at 6 cm, containing 778 near-infrared detected YSOs and
190 HST-identified proplyds (with significant overlap between those
characterizations). We detected radio emission from 175 compact radio sources
in the ONC, including 26 sources that were detected for the first time at these
wavelengths. For each detected source we fit a simple free-free and dust
emission model to characterize the radio emission. We extrapolate the free-free
emission spectrum model for each source to ALMA bands to illustrate how these
measurements could be used to correctly measure protoplanetary disk dust masses
from sub-millimeter flux measurements. Finally, we compare the fluxes measured
in this survey with previously measured fluxes for our targets, as well as four
separate epochs of 1.3 cm data, to search for and quantify variability of our
sources.Comment: 13 pages, 6 figures, 4 tables, ApJ, in pres
Anomalous CO2 Ice Toward HOPS-68: A Tracer of Protostellar Feedback
We report the detection of a unique CO2 ice band toward the deeply embedded,
low-mass protostar HOPS-68. Our spectrum, obtained with the Infrared
Spectrograph onboard the Spitzer Space Telescope, reveals a 15.2 micron CO2 ice
bending mode profile that cannot modeled with the same ice structure typically
found toward other protostars. We develop a modified CO2 ice profile
decomposition, including the addition of new high-quality laboratory spectra of
pure, crystalline CO2 ice. Using this model, we find that 87-92% of the CO2 is
sequestered as spherical, CO2-rich mantles, while typical interstellar ices
show evidence of irregularly-shaped, hydrogen-rich mantles. We propose that (1)
the nearly complete absence of unprocessed ices along the line-of-sight is due
to the flattened envelope structure of HOPS-68, which lacks cold absorbing
material in its outer envelope, and possesses an extreme concentration of
material within its inner (10 AU) envelope region and (2) an energetic event
led to the evaporation of inner envelope ices, followed by cooling and
re-condensation, explaining the sequestration of spherical, CO2 ice mantles in
a hydrogen-poor mixture. The mechanism responsible for the sublimation could be
either a transient accretion event or shocks in the interaction region between
the protostellar outflow and envelope. The proposed scenario is consistent with
the rarity of the observed CO2 ice profile, the formation of nearly pure CO2
ice, and the production of spherical ice mantles. HOPS-68 may therefore provide
a unique window into the protostellar feedback process, as outflows and heating
shape the physical and chemical structure of protostellar envelopes and
molecular clouds.Comment: Accepted to the Astrophysical Journal, 2013 February 15: 14 pages, 9
figures, 3 table
High-precision Dynamical Masses of Pre-main-sequence Stars with ALMA and Gaia
The Keplerian rotation in protoplanetary disks can be used to robustly measure stellar masses at very high precision if the source distance is known. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of spatially and spectrally resolved (CO)-C-12 (2-1) emission toward the disks around 2MASS J16262774-2527247 (the tertiary companion to ROXs 12 at 5100 au), CT Cha, and DH Tau. We employ detailed modeling of the Keplerian rotation profile, coupled with accurate distances from Gaia, to directly measure the stellar masses with similar to 2% precision. We also compare these direct mass measurements with the masses inferred from evolutionary models, determined in a statistically rigorous way. We find that 2MASS J16262774-2527247 has a mass of 0.535(-)(0.007)(+0.006) M-circle dot and CT Cha has a mass of 0.796(-0.014)(+0.015) M-circle dot, broadly consistent with evolutionary models, although potentially significant differences remain. DH Tau has a mass of 0.101(-0.003)(+0.004) M-circle dot, but it suffers from strong foreground absorption that may affect our mass estimate. The combination of ALMA, Gaia, and codes like pdspy, presented here, can be used to infer the dynamical masses for large samples of young stars and substellar objects, and place constraints on evolutionary models.Heising-Simons Foundation; Homer L. Dodge Endowed Chair; National Science Foundation Graduate Research Fellowship [2012115762]; NSF AAG grant [1311910]; NASA's Science Mission DirectorateThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Evolution of Mass Outflow in Protostars
We have surveyed 84 Class 0, Class I, and flat-spectrum protostars in
mid-infrared [Si II], [Fe II] and [S I] line emission, and 11 of these in
far-infrared [O I] emission. We use the results to derive their mass outflow
rates. Thereby we observe a strong correlation of mass outflow rates with
bolometric luminosity, and with the inferred mass accretion rates of the
central objects, which continues through the Class 0 range the trend observed
in Class II young stellar objects. Along this trend from large to small
mass-flow rates, the different classes of young stellar objects lie in the
sequence Class 0 -- Class I/flat-spectrum -- Class II, indicating that the
trend is an evolutionary sequence in which mass outflow and accretion rates
decrease together with increasing age, while maintaining rough proportionality.
The survey results include two which are key tests of magnetocentrifugal
outflow-acceleration mechanisms: the distribution of the outflow/accretion
branching ratio b, and limits on the distribution of outflow speeds. Neither
rule out any of the three leading outflow-acceleration,
angular-momentum-ejection mechanisms, but they provide some evidence that disk
winds and accretion-powered stellar winds (APSWs) operate in many protostars.
An upper edge observed in the branching-ratio distribution is consistent with
the upper bound of b = 0.6 found in models of APSWs, and a large fraction
(0.31) of the sample have branching ratio sufficiently small that only disk
winds, launched on scales as large as several AU, have been demonstrated to
account for them.Comment: Version submitted to ApJ: 36 pages, 3 tables, 8 figure
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