AAS 207th Meeting, 8-12 January 2006
Session 10 Circumstellar Disks II
Poster, Monday, 9:20am-7:00pm, January 9, 2006, Exhibit Hall

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[10.01] Spitzer Mid-Infrared Emission From Circumstellar Clouds

S.B. Fajardo-Acosta (SSC/Caltech), M.W. Werner (JPL), C.A. Beichman, R.M. Cutri (IPAC/Caltech), G. Bryden (JPL), K.Y.L. Su (U. Arizona)

Using the Spitzer Space Telescope, we discovered mid-infrared excess emission from three stellar systems. These excesses were initially suggested by a survey of IRAS 12 \mum excesses with respect to photospheric baselines estimated from 2MASS. Our initial goal was to search for warm circumstellar dust, at terrestrial material temperatures, primarily in main-sequence stars. To corroborate the excesses, we conducted Spitzer IRAC 3.6, 4.5, 5.8, 8 \mum, MIPS 24, 70 \mum imaging photometry, and IRS low-resolution 5--22 \mum spectroscopy. The star HD 179419 (B8/9 V) has excess emission increasing with wavelength, starting at ~ 5 \mum. The excess cannot be adequately fit by free-free (plasma) emission, although a small contribution is possible, because the system has circumstellar gas. The excess spectrum is well modeled by a 430 K dust continuum. The spectrum also shows emission lines from HI. The star HD 93331 (B9.5 V) shows excess emission from a neighboring source, of color temperature 82 K, as measured in IRAS 25--60 \mum and MIPS 24--70 \mum data. The MIPS data show the source to be located ~ 15 arcsec from the star. We fortuitously discovered a proto-planetary nebula (PPN) around the star HD 59509 (F5, previously unknown luminosity class). The continuum can be fit by a combination of hot (550 K) and cold (90 K) dust continua. The IRS spectrum shows PAH emission features, HI, NeII, NeIII, and SiIII emission lines. The PPN is spatially resolved in MIPS 24 and 70 \mum images.

This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through an award issued by JPL/Caltech.

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