Details

Autor(en) / Beteiligte

• MOHANTY, SUBHANJOY
• Greaves, Jane
• Mortlock, Daniel
• Pascucci, Ilaria
• Scholz, Aleks
• Thompson, Mark
• Apai, Daniel
• Lodato, Giuseppe
• Looper, Dagny

Titel

PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

Ist Teil von

• The Astrophysical journal, 2013-08, Vol.773 (2), p.1-33

Ort / Verlag

United States

Erscheinungsjahr

2013

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• We present SCUBA-2 850 mu m 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 3[sigma] limits correspond to a dust mass of 1.2 M sub([+ in circle]) in Taurus and a mere 0.2 M sub([+ in circle]) in the TWA (3-10x deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, [rho] 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[low *] 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 [rho] Oph intermediate-mass and solar-type stars evince an opacity index of beta ~ 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 mu m 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 log sub(10)[M sub(disk)/M[low *]] [approx =] -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 ([> or =, slanted]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.