AHerschelPACS survey of the dust and gas in Upper Scorpius disks

Geoffrey S Mathews,Christophe Pinte,François Ménard,Jonathan P Williams,Gaspard Duchêne

doi:10.1051/0004-6361/201321228

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 micron 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 micron and CII 157 micron 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 micron 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.

Highlights

Circumstellar disks of gas and dust are the sites of planet formation
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
After merging WISE photometry and Spitzer spectroscopy with the previously studied spectral energy distributions (SEDs), we find the presence of an excess at all wavelengths from 3.4 μm to 16 μm

Summary

Introduction

Circumstellar disks of gas and dust are the sites of planet formation They are most readily detected from continuum emission of cool dust at wavelengths from the (near-)infrared to millimeter wavelengths. The dust only accounts for 1% of the disk mass, and a more complete understanding of disk structure, chemistry, evolution, and – not least – the formation of giant planets, requires that we measure and accurately interpret the line emission from disks. The interpretation of line data requires a complete understanding of the dust, which establishes the temperature baseline for gas models. Ground based observations have been restricted to (sub-)millimeter molecular rotational lines in the cold outer disk, where depletion of molecules (i.e. freezeout onto dust grains) is important and in the near-infrared (NIR) from the hot, central few AU, regions of disks (van Dishoeck 2006)

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