10 research outputs found
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
The evolution of dust-disk sizes from a homogeneous analysis of 1-10 Myr-old stars
We utilize ALMA archival data to estimate the dust disk size of 152
protoplanetary disks in Lupus (1-3 Myr), Chamaeleon I (2-3 Myr), and Upper-Sco
(5-11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust
disk radii were estimated, as here, through fitting radial profile models to
visibility data. We use these 199 homogeneously derived disk sizes to identify
empirical disk-disk and disk-host property relations as well as to search for
evolutionary trends. In agreement with previous studies, we find that dust disk
sizes and millimeter luminosities are correlated, but show for the first time
that the relationship is not universal between regions. We find that disks in
the 2-3 Myr-old Cha I are not smaller than disks in other regions of similar
age, and confirm the Barenfeld et al. (2017) finding that the 5-10 Myr USco
disks are smaller than disks belonging to younger regions. Finally, we find
that the outer edge of the Solar System, as defined by the Kuiper Belt, is
consistent with a population of dust disk sizes which have not experienced
significant truncation.Comment: ApJ accepted, 38 pages, 16 figures, 68k compatibl
Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs
The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O I] 63 ÎŒm line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O I] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O I] 63 ÎŒm nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMAâto establish if and how disk radii scale with stellar massâshould be pursued further. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA
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Evolution of Protoplanetary Dust-Disk Sizes
The planets of our Solar System formed within a disk of dust and gas 4.5 billion
years ago. While the Solar Systemâs primordial protoplanetary disk is now gone, we
can begin to understand its possible properties by looking out to the disks within
nearby star-forming regions. To understand planet formation, dust observations are
used to constrain the mechanics and evolution of planet formation. The properties
of disks around brown dwarfs and very-low mass stars (hereafter VLMOs) provide
important boundary conditions on the process of planet formation and inform us
about the numbers and masses of planets than can form in this regime. Radiative
transfer models are fit to the spectral energy distributions of 11 VLMOs with known
disks and find that these VLMOs do not follow previously derived disk temperature-
stellar luminosity relationships if the disk outer radius scales with stellar mass. The
3 mm continuum observation of the highly inclined transition disk around the star
T Cha reveals multiple dust structures: an inner disk, a spatially resolved dust gap,
and an outer ring. When compared with previously published 1.6”m VLT/SPHERE
imagery, it is found that the location of the outer ring is wavelength dependent. More
specifically, the peak emission of the 3 mm ring is at a larger radial distance than
that of the 1.6 ”m ring, suggesting that millimeter-sized grains in the outer disk
are located further away from the central star than micron-sized grains. The most
likely origin of the dust gap is from an embedded planet or planets. The dust disk
size of 152 protoplanetary disks is estimated from archival ALMA observations. This
sample is combined with 47 disks from Tau/Aur and Oph whose dust disk radii were
estimated, as here, through fitting radial profile models to visibility data. These 199
homogeneously derived disk sizes are used to identify empirical disk-disk and disk-
host property relations as well as to search for evolutionary trends. In agreement
with previous studies, we find that dust disk sizes and millimeter luminosities are
correlated, but show for the first time that the relationship is not universal between
regions. We find that disks in the 2-3 Myr-old are not smaller than disks in other
regions of similar age, and confirm the Barenfeld et al. (2017) finding that the 5-
10 Myr USco disks are smaller than disks belonging to younger regions. Finally,
we find that the outer edge of the Solar System, as defined by the Kuiper Belt, is
consistent with a population of dust disk sizes which have not experienced significant
truncation
Herschel spectra of 11 very low mass stars
VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'Hints for small disks around very low mass stars and brown dwarfs.' (bibcode: 2017ApJ...841..116H
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PhytoOracle: Scalable, modular phenomics data processing pipelines
As phenomics data volume and dimensionality increase due to advancements in sensor technology, there is an urgent need to develop and implement scalable data processing pipelines. Current phenomics data processing pipelines lack modularity, extensibility, and processing distribution across sensor modalities and phenotyping platforms. To address these challenges, we developed PhytoOracle (PO), a suite of modular, scalable pipelines for processing large volumes of field phenomics RGB, thermal, PSII chlorophyll fluorescence 2D images, and 3D point clouds. PhytoOracle aims to (i) improve data processing efficiency; (ii) provide an extensible, reproducible computing framework; and (iii) enable data fusion of multi-modal phenomics data. PhytoOracle integrates open-source distributed computing frameworks for parallel processing on high-performance computing, cloud, and local computing environments. Each pipeline component is available as a standalone container, providing transferability, extensibility, and reproducibility. The PO pipeline extracts and associates individual plant traits across sensor modalities and collection time points, representing a unique multi-system approach to addressing the genotype-phenotype gap. To date, PO supports lettuce and sorghum phenotypic trait extraction, with a goal of widening the range of supported species in the future. At the maximum number of cores tested in this study (1,024 cores), PO processing times were: 235 minutes for 9,270 RGB images (140.7 GB), 235 minutes for 9,270 thermal images (5.4 GB), and 13 minutes for 39,678 PSII images (86.2 GB). These processing times represent end-to-end processing, from raw data to fully processed numerical phenotypic trait data. Repeatability values of 0.39-0.95 (bounding area), 0.81-0.95 (axis-aligned bounding volume), 0.79-0.94 (oriented bounding volume), 0.83-0.95 (plant height), and 0.81-0.95 (number of points) were observed in Field Scanalyzer data. We also show the ability of PO to process drone data with a repeatability of 0.55-0.95 (bounding area)