Stellar Populations and Mass Loss in M15: A Spitzer Space Telescope Detection of Dust in the Intracluster Medium

We present Spitzer Space Telescope IRAC and MIPS observations of the Galactic globular cluster M15 (NGC 7078), one of the most metal-poor clusters, with a [Fe/H] = -2.4. Our Spitzer images reveal a population of dusty red giants near the cluster center, a previously detected planetary nebula designated K648, and a possible detection of the intracluster medium arising from mass-loss episodes from the evolved stellar population. Our analysis suggests that (9 ± 2) × 10-4 M⊙ of dust is present in the core of M15, and that this material has accumulated over a period of ≈106 yr, a timescale 10 times shorter than the last Galactic plane crossing event. We also present Spitzer IRS follow-up observations of K648, including the detection of the [Ne II] 12.81 μm line, and discuss abundances derived from infrared fine-structure lines.