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M. L. Boyer, C. E. Woodward (University of Minnesota), J. T. van Loon (Keele University), E. F. Polomski, R. D. Gehrz (University of Minnesota), A. Evans (Keele University), K. Gordon (University of Arizona)
Globular clusters (GCs), believed to have formed during the assemblage of the Galaxy, are coeval samples of stars at a common, well-determined distance with nearly uniform initial composition. GCs enable study of the chemical enrichment of the interstellar medium arising from mass ejection during the post-main sequence evolution of stars. During post-main sequence evolution, especially ascending the Asymptotic Giant Branch, Red Giant stars are expected to develop winds that inject processed material into the intra-cluster medium (ICM). These winds contain gas and solid phase materials, the latter in the form of dust grains that condense from the metals. However, detection of thermal emission arising from ICM dust has been elusive, suggesting that the ICM is 100 to 1000 times less massive than expected from current stellar evolution theory and from observations of mass losing stars in clusters and the solar neighborhood. Here we discuss Spitzer Space Telescope IRAC and MIPS observations of the galactic GC M15. Our images reveal several possibly spatially extended red sources near the cluster center, a previously detected planetary nebula, and a possible detection of the ICM. The integrated Spitzer 70 micron flux, primarily arising from the ICM, is approximately 700 mJy, comparable to that derived by Evans et al. (A&A 408, L9, 2003) using lower spatial resolution ISOPHOT observations.
This work supported in part by NASA/JPL contracts 1256406 and 1215746 awarded to the University of Minnesota, as well as a grant from the NSF AST02-05814.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.