Saturday, December 3, 2016



Andsell et al


We present the first high-resolution sub-millimeter 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 the Atacama Large Millimeter/Submillimeter Array (ALMA) to survey 89 protoplanetary disks around stars with ${M}_{* }\gt 0.1\,{M}_{\odot }$ 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-millimeter continuum to constrain ${M}_{{\rm{dust}}}$ to a few Martian masses (0.2–0.4 M ⊕) and the CO isotopologue lines to constrain ${M}_{{\rm{gas}}}$ to roughly a Jupiter mass (assuming an interstellar medium (ISM)-like $[\mathrm{CO}]/[{{\rm{H}}}_{2}]$ abundance). Of 89 sources, we detect 62 in continuum, 36 in 13CO, and 11 in C18O at $\gt 3\sigma $ significance. Stacking individually undetected sources limits their average dust mass to $\lesssim 6$ Lunar masses (0.03 M ⊕), indicating rapid evolution once disk clearing begins. We find a positive correlation between ${M}_{{\rm{dust}}}$ and M *, and present the first evidence for a positive correlation between ${M}_{{\rm{gas}}}$ and M *, which may explain the dependence of giant planet frequency on host star mass. 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. Most detected disks have ${M}_{{\rm{gas}}}\lesssim 1\,{M}_{{\rm{Jup}}}$ and gas-to-dust ratios $\lt 100$, assuming an ISM-like $[\mathrm{CO}]/[{{\rm{H}}}_{2}]$ abundance; unless CO is very depleted, the inferred gas depletion indicates that planet formation is well underway by a few Myr and may explain the unexpected prevalence of super-Earths in the exoplanet population.

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