Spitzer 24 μm Excesses for Bright Galactic Stars in Boötes and First Look Survey Fields

Abstract

Optically bright Galactic stars (V ≾ 13 mag) having f_ν(24 μm) > 1 mJy are identified in Spitzer mid-infrared surveys within 8.2 deg^2 for the Boötes field of the NOAO Deep Wide-Field Survey and within 5.5 deg^2 for the First Look Survey (FLS). One hundred and twenty-eight stars are identified in Boötes and 140 in the FLS, and their photometry is given. (K – [24]) colors are determined using K magnitudes from the Two Micron All Sky Survey for all stars in order to search for excess 24 μm luminosity compared to that arising from the stellar photosphere. Of the combined sample of 268 stars, 141 are of spectral types F, G, or K, and 17 of these 141 stars have 24 μm excesses with (K – [24]) > 0.2 mag. Using limits on absolute magnitude derived from proper motions, at least eight of the FGK stars with excesses are main-sequence stars, and estimates derived from the distribution of apparent magnitudes indicate that all 17 are main-sequence stars. These estimates lead to the conclusion that between 9% and 17% of the main-sequence FGK field stars in these samples have 24 μm infrared excesses. This result is statistically similar to the fraction of stars with debris disks found among previous Spitzer targeted observations of much brighter, main-sequence field stars.

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