Protoplanetary disk masses from stars to brown dwarfs

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Title: Protoplanetary disk masses from stars to brown dwarfs
Authors: Mohanty, S
Greaves, J
Mortlock, D
Pascucci, I
Scholz, A
Thompson, M
Apai, D
Lodato, G
Looper, D
Item Type: Journal Article
Abstract: We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ~100 AU for intermediate-mass stars, solar types, and VLMS, and ~20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ~ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly constant mean of log10[M disk/M *] ≈ –2.4 all the way from intermediate-mass stars to VLMS/BDs, supporting previous qualitative suggestions that the ratio is ~1% throughout the stellar/BD domain. (6) Similar analysis shows that the disk mass in close solar-type Taurus binaries (sep <100 AU) is significantly lower than in singles (by a factor of 10), while that in wide solar-type Taurus binaries (≥100 AU) is closer to that in singles (lower by a factor of three). (7) We discuss the implications of these results for planet formation around VLMS/BDs, and for the observed dependence of accretion rate on stellar mass.We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ~100 AU for intermediate-mass stars, solar types, and VLMS, and ~20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ~ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly constant mean of log10[M disk/M *] ≈ –2.4 all the way from intermediate-mass stars to VLMS/BDs, supporting previous qualitative suggestions that the ratio is ~1% throughout the stellar/BD domain. (6) Similar analysis shows that the disk mass in close solar-type Taurus binaries (sep <100 AU) is significantly lower than in singles (by a factor of 10), while that in wide solar-type Taurus binaries (≥100 AU) is closer to that in singles (lower by a factor of three). (7) We discuss the implications of these results for planet formation around VLMS/BDs, and for the observed dependence of accretion rate on stellar mass.
Issue Date: 20-Aug-2013
Date of Acceptance: 28-May-2013
URI: http://hdl.handle.net/10044/1/73474
DOI: https://doi.org/10.1088/0004-637X/773/2/168
ISSN: 0004-637X
Publisher: American Astronomical Society
Journal / Book Title: The Astrophysical Journal: an international review of astronomy and astronomical physics
Volume: 773
Issue: 2
Copyright Statement: © 2013 IOP Publishing Ltd. This is an author-created, un-copyedited version of an article accepted for publication in Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at https://doi.org/10.1088/0004-637X/773/2/168.
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council [2006-2012]
Funder's Grant Number: ST/K001051/1
ST/K001051/1
Keywords: Science & Technology
Physical Sciences
Astronomy & Astrophysics
brown dwarfs
protoplanetary disks
stars: formation
stars: pre-main sequence
stars: variables: T Tauri, Herbig Ae/Be
submillimeter: stars
T-TAURI STARS
MAIN-SEQUENCE STARS
SPECTRAL ENERGY-DISTRIBUTIONS
CIRCUMSTELLAR DUST DISKS
2MASSW J1207334-393254
HYDRAE ASSOCIATION
PLANET FORMATION
EVOLUTIONARY MODELS
ACCRETION DISKS
MOLECULAR CLOUD
Science & Technology
Physical Sciences
Astronomy & Astrophysics
brown dwarfs
protoplanetary disks
stars: formation
stars: pre-main sequence
stars: variables: T Tauri, Herbig Ae/Be
submillimeter: stars
T-TAURI STARS
MAIN-SEQUENCE STARS
SPECTRAL ENERGY-DISTRIBUTIONS
CIRCUMSTELLAR DUST DISKS
2MASSW J1207334-393254
HYDRAE ASSOCIATION
PLANET FORMATION
EVOLUTIONARY MODELS
ACCRETION DISKS
MOLECULAR CLOUD
astro-ph.SR
astro-ph.SR
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
0306 Physical Chemistry (incl. Structural)
Publication Status: Published
Article Number: 168
Online Publication Date: 2013-08-06
Appears in Collections:Physics
Astrophysics



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