AAS 197, January 2001
Session 97. Evolved Stars
Oral, Wednesday, January 10, 2001, 1:30-3:00pm, Pacific One

## [97.06] Infrared Studies of Wolf-Rayet Stars and Stellar Populations

J.D.T. Smith, J.R. Houck (Cornell Dept. of Astronomy)

Wolf-Rayet (WR) stars represent an evolved phase of the most massive stellar population, and are characterized by high mass loss rates (10-5--10-4 M\odot yr-1) from fast, dense stellar winds. Short lifetimes (few\times105 yr) and high luminosities make them excellent tracers of active and recent star formation.

WR stars are increasingly recognized as an important constituent of young and massive star formation regions. They have a substantial impact on observational properties of these regions and significantly affect the process of ISM enrichment. Among the most exciting outcomes of the recent detailed investigations of the WR phenomenon, both theoretically and observationally, has been the pioneering development of techniques using the relatively unambiguous spectral signatures of WR stars to diagnose the source of energy in a variety of sources, including AGN, and Blue Compact Dwarf galaxies. The direct detection enabled by these techniques promises to help resolve controversies surrounding the powering mechanisms of ultra-luminous infrared and other luminous early-epoch galaxies.

We have undertaken a mid-infrared spectral survey of northern galactic WR stars, and have obtained near-infrared spectra in support of detailed analysis of the numerous infrared wind lines they emit, using the latest non-LTE line-blanketed atmospheric models. We also studied the warm dust surrounding some WR stars, especially of the late carbon (WC) subtype, and investigated the possibility of substantial cool circumstellar silicate implied by anomalous 10\micron\ absorption. A synthesis model of young starbursts with large numbers of WR stars was constructed to place the infrared WR emission in context, and analyze the potential detectability of these stars in the integrated infrared emission of such regions.