59 research outputs found
Multiple Gaps in the Disk of the Class I Protostar GY 91
We present the highest spatial resolution ALMA observations to date of the
Class I protostar GY 91 in the Ophiuchus L1688 molecular cloud complex.
Our 870 m and 3 mm dust continuum maps show that the GY 91 disk has a
radius of 80 AU, and an inclination of 40, but most
interestingly that the disk has three dark lanes located at 10 AU, 40 AU, and
70 AU. We model these features assuming they are gaps in the disk surface
density profile and find that their widths are 7 AU, 30 AU, and 10 AU. These
gaps bear a striking resemblance to the gaps seen in the HL Tau disk,
suggesting that there may be Saturn-mass planets hiding in the disk. To
constrain the relative ages of GY 91 and HL Tau, we also model the disk and
envelope of HL Tau and find that they are of similar ages, although GY 91 may
be younger. Although snow lines and magnetic dead zones can also produce dark
lanes, if planets are indeed carving these gaps then Saturn-mass planets must
form within the first 0.5 Myr of the lifetime of protoplanetary disks.Comment: 9 pages, 6 figures, 2 tables. Accepted for publication in Ap
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
Protoplanetary Disks in the Orion Nebula Cluster: Gas Disk Morphologies and Kinematics as seen with ALMA
We present Atacama Large Millimeter Array CO(32) and HCO(43)
observations covering the central region of
the Orion Nebula Cluster (ONC). The unprecedented level of sensitivity
(0.1 mJy beam) and angular resolution ( AU) of these line observations enable us to search for gas-disk
detections towards the known positions of submillimeter-detected dust disks in
this region. We detect 23 disks in gas: 17 in CO(32), 17 in HCO(43),
and 11 in both lines. Depending on where the sources are located in the ONC, we
see the line detections in emission, in absorption against the warm background,
or in both emission and absorption. We spectrally resolve the gas with km
s channels, and find that the kinematics of most sources are consistent
with Keplerian rotation. We measure the distribution of gas-disk sizes and find
typical radii of 50-200 AU. As such, gas disks in the ONC are compact in
comparison with the gas disks seen in low-density star-forming regions. Gas
sizes are universally larger than the dust sizes. However, the gas and dust
sizes are not strongly correlated. We find a positive correlation between gas
size and distance from the massive star Ori C, indicating that disks
in the ONC are influenced by photoionization. Finally, we use the observed
kinematics of the detected gas lines to model Keplerian rotation and infer the
masses of the central pre-main-sequence stars. Our dynamically-derived stellar
masses are not consistent with the spectroscopically-derived masses, and we
discuss possible reasons for this discrepancy.Comment: 42 pages, 31 figure
Protoplanetary Disk Masses from Radiative Transfer Modeling: A Case Study in Taurus
Measuring the masses of protoplanetary disks is crucial for understanding
their planet-forming potential. Typically, dust masses are derived from
(sub-)millimeter flux density measurements plus assumptions for the opacity,
temperature, and optical depth of the dust. Here we use radiative transfer
models to quantify the validity of these assumptions with the aim of improving
the accuracy of disk dust mass measurements. We first carry out a controlled
exploration of disk parameter space. We find that the disk temperature is a
strong function of disk size, while the optical depth depends on both disk size
and dust mass. The millimeter-wavelength spectral index can be significantly
shallower than the naive expectation due to a combination of optical depth and
deviations from the Rayleigh-Jeans regime. We fit radiative transfer models to
the spectral energy distributions (SEDs) of 132 disks in the Taurus-Auriga
region using a Markov chain Monte Carlo approach. We used all available data to
produce the most complete SEDs used in any extant modeling study. We perform
the fitting twice: first with unconstrained disk sizes and again imposing the
disk size--brightness relation inferred for sources in Taurus. This constraint
generally forces the disks to be smaller, warmer, and more optically thick.
From both sets of fits, we find disks to be 1--5 times more massive than
when derived using (sub-)millimeter measurements and common assumptions. With
the uncertainties derived from our model fitting, the previously measured dust
mass--stellar mass correlation is present in our study but only significant at
the 2 level.Comment: 28 pages, 13 figures, accepted for publication in A
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
Systematic Multi-Epoch Monitoring of LkCa 15: Dynamic Dust Structures on Solar-System Scales
We present the highest angular resolution infrared monitoring of LkCa 15, a
young solar analog hosting a transition disk. This system has been the subject
of a number of direct imaging studies from the millimeter through the optical,
which have revealed multiple protoplanetary disk rings as well as three
orbiting protoplanet candidates detected in infrared continuum (one of which
was simultaneously seen at H). We use high-angular-resolution infrared
imaging from 2014-2020 to systematically monitor these infrared signals and
determine their physical origin. We find that three self-luminous protoplanets
cannot explain the positional evolution of the infrared sources, since the
longer time baseline images lack the coherent orbital motion that would be
expected for companions. However, the data still strongly prefer a
time-variable morphology that cannot be reproduced by static scattered-light
disk models. The multi-epoch observations suggest the presence of complex and
dynamic substructures moving through the forward-scattering side of the disk at
AU, or quickly-varying shadowing by closer-in material. We explore
whether the previous H detection of one candidate would be inconsistent
with this scenario, and in the process develop an analytical signal-to-noise
penalty for H excesses detected near forward-scattered light. Under
these new noise considerations, the H detection is not strongly
inconsistent with forward scattering, making the dynamic LkCa 15 disk a natural
explanation for both the infrared and H data.Comment: 24 pages, 11 figures, accepted for publication in Ap
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]
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