AN ALMA CONTINUUM SURVEY OF CIRCUMSTELLAR DISKS IN THE UPPER SCORPIUS OB ASSOCIATION

We present ALMA 880 mu m continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M-circle dot) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 mu m dust continuum at >= 3 sigma with inferred dust masses between 0.3 and 52 M-circle plus. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p approximate to 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around similar to 1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3 sigma. For stellar masses between 0.49 M-circle dot and 1.6 M-circle dot, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Delta log M-dust = 0.44 +/- 0.26.