A Herschel PACS survey of the dust and gas in Upper Scorpius disks

Abstract

We present results of far-infrared photometric observations with Herschel PACS of a sample of Upper Scorpius stars, with a detection rate of previously known disk-bearing K and M stars at 70, 100, and 160 μm of 71%, 56%, and 50%, respectively. We fit power-law disk models to the spectral energy distributions of K & M stars with infrared excesses, and have found that while many disks extend in to the sublimation radius, the dust has settled to lower scale heights than in disks of the less evolved Taurus-Auriga population, and have much reduced dust masses.We also conducted Herschel PACS observations for far-infrared line emission and JCMT observations for millimeter CO lines. Among B and A stars, 0 of 5 debris disk hosts exhibit gas line emission, and among K and M stars, only 2 of 14 dusty disk hosts are detected. The OI 63 μm and CII 157 μm lines are detected toward [PZ99] J160421.7-213028 and [PBB2002] J161420.3-190648, which were found in millimeter photometry to host two of the most massive dust disks remaining in the region. Comparison of the OI line emission and 63 μm continuum to that of Taurus sources suggests the emission in the former source is dominated by the disk, while in the other there is a significant contribution from a jet. The low dust masses found by disk modeling and low number of gas line detections suggest that few stars in Upper Scorpius retain sufficient quantities of material for giant planet formation. By the age of Upper Scorpius, giant planet formation is essentially complete.