2008AJ....135.1395B

We present a Spitzer Space Telescope imaging survey of the most massive Galactic globular cluster, ω Centauri, and investigate stellar mass loss at low metallicity and the intracluster medium (ICM). The survey covers approximately 3.2x the cluster half-mass radius at 3.6, 4.5, 5.8, 8, and 24 µm, resulting in a catalog of over 40,000 point sources in the cluster. Approximately 140 cluster members ranging 1.5 dex in metallicity show a red excess at 24 µm, indicative of circumstellar dust. If all of the dusty sources experience mass loss, the cumulative rate of loss is estimated at 2.9-4.2 x10^–7 M_☉.yr^–1, 63%-66% of which is supplied by three asymptotic giant branch stars at the tip of the red giant branch (RGB). There is little evidence for strong mass loss lower on the RGB. If this material had remained in the cluster center, its dust component (≳1x10^–4M_☉) would be detectable in our 24 and 70 µm images. While no dust cloud located at the center of ω Cen is apparent, we do see four regions of very faint, diffuse emission beyond two half-mass radii at 24 µm. It is unclear whether these dust clouds are foreground emission or are associated with ω Cen. In the latter case, these clouds may be the ICM in the process of escaping from the cluster.