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Published November 1, 2006 | Published
Journal Article Open

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


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 M_☉ 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 (~0.1–1.2M_☉) appear surrounded by primordial optically thick disks based on, the excess emission characteristics. Starsmoremassive than ~1.8M_☉ 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 M_☉) in our sample have an infrared excess at wavelengths ≤16 µm. These results indicate that the mechanisms for, dispersing primordial optically thick disks operate less efficiently, on average, for low-mass stars, and that longer timescales are available for the buildup of planetary systems in the terrestrial zone for stars with masses ≾1 M_☉.

Additional Information

© 2006 The American Astronomical Society. Received 2006 August 13; accepted 2006 September 13; published 2006 October 16. J. M. C. would like to thank the Spitzer Science Center staff for patiently answering numerous questions regarding Spitzer data. E. E. M. is supported by a Clay Postdoctoral Fellowship through the Smithsonian Astrophysical Observatory. M. R. M. acknowledges support by NASA through the NASA Astrobiology Institute under cooperative agreement CAN-02-OSS-02 issued through the Office of Space Science. This work is based on observations made with the Spitzer Space Telescope, which is operated by JPL/Caltech under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

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