THE LATE STAGES OF PROTOPLANETARY DISK EVOLUTION: A MILLIMETER SURVEY OF UPPER SCORPIUS

We present deep 1.2 mm photometry of 37 stars in the young (5 Myr) Upper Scorpius OB association, sensitive to ∼4 × 10–3 MJup of cool millimeter dust. Disks around four low- and solar-mass stars are detected, as well as one debris disk around an intermediate-mass star, with dust masses ranging from 3.6 × 10–3 to 1.0 × 10–1 MJup. The source with the most massive disk exhibits a transition-disk spectral energy distribution. Combining our results with previous studies, we find that the millimeter-detection fraction of Class II sources has significantly decreased from younger ages, and comparison with near-infrared and Hα measurements indicates that the present disks have undergone significant evolution in composition or structure at all radii. The disks of Upper Scorpius represent the tail-end of the depletion of primordial disks; while a few near-solar-mass stars may still sustain giant planet formation, this process has finished around higher mass stars.