Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association

Abstract

We present 4.5, 8, and 16 μm photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB association. The data are used to investigate the frequency and properties of circumstellar disks around stars with masses between ~0.1 and 20 Msolar at an age of ~5 Myr. We identify 35 stars that have emission at 8 or 16 μm in excess of the stellar photosphere. The lower mass stars (~0.1-1.2 Msolar) appear surrounded by primordial optically thick disks based on the excess emission characteristics. Stars more massive than ~1.8 Msolar have lower fractional excess luminosities suggesting that the inner ~10 AU of the disk has been largely depleted of primordial material. None of the G and F stars (~1.2-1.8 Msolar) in our sample have an infrared excess at wavelengths