Martha Boyer
Space Telescope Science Institute
& Gemini South Visiting Astronomer
 

"Dust Production and Mass Loss at Low Metallicity: A Survey of AGB Stars with the Spitzer Space Telescope"
 

In the last five years, the Spitzer Space Telescope has provided new images and spectra with unprecedented sensitivity in the infrared, allowing for the most detailed studies of astronomical dust to date. Using these data, astronomers have begun to piece together a complete picture of dust production and processing, especially in distant, low metallicity environments akin to the early Universe. We conducted infrared (IR) imaging surveys of ten Galactic globular clusters (GCs) and eight Local Group dwarf irregular galaxies using Spitzer. In GCs, we investigate the stars with IR excesses, attributed to dust, and the intracluster medium.  The GC M15 is the most metal-poor Galactic GC, and is ideal for studying dust production at metallicity less than 1% solar. The most massive Galactic GC, omega Centauri, harbors three distinct populations of differing metal content, providing the opportunity to study dust production at three metallicities within the same environment. The large population of dusty Asymptotic Giant Branch (AGB) stars present in the eight observed Local Group dwarf galaxies allows a statistically significant study of dusty stellar mass loss at a broad range of metallicities (2%-19% solar).  In all observed systems, we find large populations of dust enshrouded stars and, in some cases, a surplus of dusty interstellar medium. Our results suggest that dust production is not prohibited at very low metallicity, although it may be forming in smaller quantities.