87 research outputs found
A revised estimate of the distance to the clouds in the Chamaeleon complex using the Tycho-Gaia Astrometric Solution
The determination of the distance to dark star-forming clouds is a key
parameter to derive the properties of the cloud itself, and of its stellar
content. This parameter is still loosely constrained even in nearby
star-forming regions. We want to determine the distances to the clouds in the
Chamaeleon-Musca complex and to explore the connection between these clouds and
the large scale cloud structures in the galaxy. We use the newly estimated
distances obtained from the parallaxes measured by the Gaia satellite and
included in the Tycho-Gaia Astrometric Solution catalog. When known members of
a region are included in this catalog we use their parallaxes to infer the
distance to the cloud. Otherwise, we analyze the dependence of the color excess
on the distance of the stars and look for a turn-on of this excess, which is a
proxy of the position of the front-edge of the star-forming cloud. We are able
to measure the distance to the three Chamaeleon clouds. The distance to
Chamaeleon I is 179 pc, 20 pc further away than previously assumed. The
Chamaeleon II cloud is located at the distance of 181 pc, which agrees with
previous estimates. We are able to measure for the first time a distance to the
Chamaeleon III cloud of 199 pc. Finally, the distance of the Musca cloud is
smaller than 603 pc. These estimates do not allow us to distinguish between the
possibility that the Chamaeleon clouds are part of a sheet of clouds parallel
to the galactic plane, or perpendicular to it. Gaia Data Release 2 will allow
us to put more stringent constraints on the distances to these clouds by giving
us access to parallax measurements for a larger number of members of these
regions.Comment: Accepted for publication on A&A. Abstract shortened for arxiv
constraint
Stellar masses and disk properties of Lupus young stellar objects traced by velocity-aligned stacked ALMA 13CO and C18O spectra
In recent ALMA surveys, the gas distributions and velocity structures of most
of the protoplanetary disks can still not be imaged at high S/N due to the
short integration time. In this work, we re-analyzed the ALMA 13CO (3-2) and
C18O (3-2) data of 88 young stellar objects in Lupus with the velocity-aligned
stacking method to enhance S/N and to study the kinematics and disk properties
traced by molecular lines. This method aligns spectra at different positions in
a disk based on the projected Keplerian velocities at their positions and then
stacks them. This method enhances the S/N ratios of molecular-line data and
allows us to obtain better detections and to constrain dynamical stellar masses
and disk orientations. We obtain 13CO detections in 41 disks and C18O
detections in 18 disks with 11 new detections in 13CO and 9 new detections in
C18O after applying the method. We estimate the disk orientations and the
dynamical stellar masses from the 13CO data. Our estimated dynamical stellar
masses correlate with the spectroscopic stellar masses, and in a subsample of
16 sources, where the inclination angles are better constrained, the two masses
are in a good agreement within the uncertainties and with a mean difference of
0.15 Msun. With more detections of fainter disks, our results show that high
gas masses derived from the 13CO and C18O lines tend to be associated with high
dust masses estimated from the continuum emission. Nevertheless, the scatter is
large (0.9 dex), implying large uncertainties in deriving the disk gas mass
from the line fluxes. We find that with such large uncertainties it is expected
that there is no correlation between the disk gas mass and the mass accretion
rate with the current data. Deeper observations to detect disks with gas masses
<1E-5 Msun in molecular lines are needed to investigate the correlation between
the disk gas mass and the mass accretion rate.Comment: Submitted to A&
An ALMA Survey of Protoplanetary Disks in the Orionis Cluster
The Orionis cluster is important for studying protoplanetary disk
evolution, as its intermediate age (3-5 Myr) is comparable to the median
disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas
in 92 protoplanetary disks around Orionis members with
. Our observations cover the 1.33 mm continuum
and several CO lines: out of 92 sources, we detect 37 in the mm
continuum and six in CO, three in CO, and none in CO.
Using the continuum emission to estimate dust mass, we find only 11 disks with
, indicating that after only a few Myr of
evolution most disks lack sufficient dust to form giant planet cores. Stacking
the individually undetected continuum sources limits their average dust mass to
5 lower than that of the faintest detected disk, supporting theoretical
models that indicate rapid dissipation once disk clearing begins. Comparing the
protoplanetary disk population in Orionis to those of other
star-forming regions supports the steady decline in average dust mass and the
steepening of the - relation with age; studying these
evolutionary trends can inform the relative importance of different disk
processes during key eras of planet formation. External photoevaporation from
the central O9 star is influencing disk evolution throughout the region: dust
masses clearly decline with decreasing separation from the photoionizing
source, and the handful of CO detections exist at projected separations
pc. Collectively, our findings indicate that giant planet formation is
inherently rare and/or well underway by a few Myr of age.Comment: 16 pages, 9 figures; published in AJ; The full machine readable
tables can be obtained by downloading and extracting the gzipped tar source
file listed under "Other formats.
Constraints from Dust Mass and Mass Accretion Rate Measurements on Angular Momentum Transport in Protoplanetary Disks
We investigate the relation between disk mass and mass accretion rate to
constrain the mechanism of angular momentum transport in protoplanetary disks.
Dust mass and mass accretion rate in Chamaeleon I are correlated with a slope
close to linear, similar to the one recently identified in Lupus. We
investigate the effect of stellar mass and find that the intrinsic scatter
around the best-fit Mdust-Mstar and Macc-Mstar relations is uncorrelated. Disks
with a constant alpha viscosity can fit the observed relations between dust
mass, mass accretion rate, and stellar mass, but over-predict the strength of
the correlation between disk mass and mass accretion rate when using standard
initial conditions. We find two possible solutions. 1) The observed scatter in
Mdust and Macc is not primoridal, but arises from additional physical processes
or uncertainties in estimating the disk gas mass. Most likely grain growth and
radial drift affect the observable dust mass, while variability on large time
scales affects the mass accretion rates. 2) The observed scatter is primordial,
but disks have not evolved substantially at the age of Lupus and Chamaeleon I
due to a low viscosity or a large initial disk radius. More accurate estimates
of the disk mass and gas disk sizes in a large sample of protoplanetary disks,
either through direct observations of the gas or spatially resolved
multi-wavelength observations of the dust with ALMA, are needed to discriminate
between both scenarios or to constrain alternative angular momentum transport
mechanisms such as MHD disk winds.Comment: See also the paper by Lodato et a
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, Nâ). Semi-forbidden C II] λ2325 and UV-fluorescent Hâ emission were also measured to constrain inner disk populations of Câș and vibrationally excited H2. We find a significant positive correlation between 14 ÎŒm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring Nâ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-Hâ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
An ALMA Survey of faint disks in the Chamaeleon I star-forming region: Why are some Class II disks so faint?
ALMA surveys of nearby star-forming regions have shown that the dust mass in
the disk is correlated with the stellar mass, but with a large scatter. This
scatter could indicate either different evolutionary paths of disks or
different initial conditions within a single cluster. We present ALMA Cycle 3
follow-up observations for 14 Class II disks that were low S/N detections or
non-detections in our Cycle 2 survey of the Myr-old Chamaeleon I
star-forming region. With 5 times better sensitivity, we detect millimeter dust
continuum emission from six more sources and increase the detection rate to
94\% (51/54) for Chamaeleon I disks around stars earlier than M3. The
stellar-disk mass scaling relation reported in \citet{pascucci2016} is
confirmed with these updated measurements. Faint outliers in the
-- plane include three non-detections (CHXR71, CHXR30A, and T54)
with dust mass upper limits of 0.2 M and three very faint disks
(CHXR20, ISO91, and T51) with dust masses M. By
investigating the SED morphology, accretion property and stellar multiplicity,
we suggest for the three millimeter non-detections that tidal interaction by a
close companion (100 AU) and internal photoevaporation may play a role in
hastening the overall disk evolution. The presence of a disk around only the
secondary star in a binary system may explain the observed stellar SEDs and low
disk masses for some systems.Comment: ApJ accepte
When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster
The high-quality OmegaCAM photometry of the 3x3 deg around the Orion Nebula
Cluster (ONC) in r, and i filters by Beccari et al.(2017) revealed three
well-separated pre-main sequences in the color-magnitude diagram (CMD). The
objects belonging to the individual sequences are concentrated towards the
center of the ONC. The authors concluded that there are two competitive
scenarios: a population of unresolved binaries and triples with an exotic mass
ratio distribution, or three stellar populations with different ages. We use
Gaia DR2 in combination with the photometric OmegaCAM catalog to test and
confirm the presence of the putative three stellar populations. We also study
multiple stellar systems in the ONC for the first time using Gaia DR2. We
confirm that the second and third sequence members are more centrally
concentrated towards the center of the ONC. In addition we find an indication
that the parallax and proper motion distributions are different among the
members of the stellar sequences. The age difference among stellar populations
is estimated to be 1-2 Myr. We use Gaia measurements to identify and remove as
many unresolved multiple system candidates as possible. Nevertheless we are
still able to recover two well-separated sequences with evidence for the third
one, supporting the existence of the three stellar populations. We were able to
identify a substantial number of wide binary objects (separation between
1000-3000 au). This challenges previously inferred values that suggested no
wide binary stars exist in the ONC. Our inferred wide-binary fraction is approx
5%. We confirm the three populations correspond to three separated episodes of
star formation. Based on this result, we conclude that star formation is not
happening in a single burst in this region. (abridged)Comment: Astronomy and Astrophysics (A&A) accepted. 12 pages, 9 figures +
appendix. New version with language corrections and new ID values in Tab.A.
- âŠ