Spitzer IRS Observations of Circumstellar Disk Candidates in the 5 Myr Old Upper Scorpius OB Association

Details Spitzer IRS Observations of Circumstellar Disk Candidates in the 5 Myr Old Upper Scorpius OB Association Spitzer IRS Observations of Circumstellar Disk Candidates in the 5 Myr Old Upper Scorpius OB Association

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...211.6234d&link_type=abstract

American Astronomical Society, AAS Meeting #211, #62.34

Astronomy and Astrophysics

Astrophysics

Scientific paper

We present initial results of a Spitzer Infrared Spectrograph (IRS) low resolution, spectroscopic survey of 29 infrared excess members of the 5 Myr old Upper Scorpius OB Association. The excess stars were identified by the Spitzer 4.5, 8.0, and 16.0 μm photometric survey of Carpenter et al., which examined more than 200 suspected members of the association. The more massive stars (B and A spectral types) in our sample all exhibit mid-infrared excesses that suggest the inner disk (˜10; AU) regions have been effectively cleared of micron-sized dust. The IRS spectra of these early-type excess stars show little evidence for the 10 and 20 μm silicate emission features. Among the low-mass infrared excess stars (K and M spectral types), most exhibit these silicate emission peaks, implying the presence of small dust grains in the atmospheres of their disks. High resolution (R˜33,000), optical (λλ4800-9200) spectra for all excess stars obtained using HIRES on Keck I are also presented. These spectra are examined for the broadened emission line profiles of Hα, He I λ5876, and Ca II λλ8498, 8542, 8662 that are indicative of gaseous accretion. None of the early-type infrared excess stars are found to be accreting while less than half of the low-mass excess stars exhibit signatures of accretion activity. Mass accretion rates are derived for all suspected accretors using established relationships between accretion luminosity and emission line flux. Finally we examine the coupling between hot, micron-sized dust grains and the presence of inner disk gas and the implications for the formation of planetary systems. SED is supported by a NSF Astronomy and Astrophysics Postdoctoral Fellowship under award number AST 05-02381.

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