July 11-15, 2011
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Massive Evolved Stars with Circumstellar Shells

Stefanie Wachter (IPAC / Caltech)

J. Mauerhan, S. Van Dyk, D. W. Hoard (IPAC/Caltech), M. Cohen (MIRA), D. Leisawitz (GSFC)

We have recently discovered a large number of circular shells at 24 microns around luminous central sources with the MIPS instrument on-board the Spitzer Space Telescope. While the majority of the shells is only seen at 24 microns, the central stars are generally detected at multiple wavelengths from the mid- to the near-IR regime. Our initial IR spectroscopic follow-up of the central sources of these shells has revealed several new Wolf-Rayet (WR) stars, as well as a large number of candidate Luminous Blue Variables (LBVs). We will report on our ongoing efforts to characterize the complete sample of these shells sources. We will also present a survey of the known Galactic population of Wolf-Rayet stars with WISE. The WISE all-sky data allow for a homogenous look at their mid-IR photometric properties and large scale environment. We compare the frequency of circumstellar shells between LBVs and WRs, highlight the differences between optically detected shells and those seen at mid-IR wavelengths, and discuss the implications for evolution of mass loss in the final stages of the lives of massive stars.
(to be confirmed by the SOC)