Sunday, August 7, 2016

ALMA Survey of Lupus Protoplanetary Disks I: Dust and Gas Masses

ALMA Survey of Lupus Protoplanetary Disks I: Dust and Gas Masses


Andsell et al


We present the first high-resolution sub-mm survey of both dust and gas for a large population of protoplanetary disks. Characterizing fundamental properties of protoplanetary disks on a statistical level is critical to understanding how disks evolve into the diverse exoplanet population. We use ALMA to survey 89 protoplanetary disks around stars with M∗ greater than 0.1 M⊙ in the young (∼1-3 Myr), nearby (∼150-200 pc) Lupus complex. Our observations cover the 890 μm continuum and the 13CO and C18O 3-2 lines. We use the sub-mm continuum to constrain Mdust to a few Martian masses (0.2-0.4 M⊕) and the CO isotopologue lines to constrain Mgas to roughly a Jupiter mass (assuming ISM-like [CO]/[H2] abundance). Of 89 sources, we detect 62 in the continuum, 36 in 13CO, and 11 in C18O at greater than 3σ significance. Several new "transition disks" are found with relatively bright continuum and CO isotopologue emission. Stacking the individually undetected sources limits their average dust mass to ≲6 Lunar masses (0.03 M⊕), indicating rapid evolution once disk clearing begins. We find a positive but non-linear correlation between Mdust and M∗, and also demonstrate for the first time a tentative positive correlation between Mgas and M∗. The mean dust mass in Lupus is 3× higher than in Upper Sco, while the dust mass distributions in Lupus and Taurus are statistically indistinguishable from each other. Most detected disks have Mgas≲1 MJup and gas-to-dust ratios less than 100 when using our parameterized model framework; if confirmed, the inferred rapid gas depletion indicates that planet formation is largely complete by a few Myr, and may also explain the unexpected prevalence of super-Earths in the exoplanet population.

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