AAS 203rd Meeting, January 2004
Session 25 Young Stars and Clusters
Oral, Monday, January 5, 2004, 10:00-11:30am, Centennial IV

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[25.02] An HST/WFPC2 Survey for Nearby Companions of Galactic Wolf-Rayet Stars

D. J. Wallace (Georgia State University)

Wolf-Rayet (WR) stars provide key insights about the final evolutionary phase of the most massive stars. I present here the results of a new, high angular resolution, imaging survey of 61 Galactic WR stars, which was designed to detect new companions, clusters, and/or associations surrounding these stars. High resolution observations are essential to provide a true census of the number and astrophysical parameters of massive stars, to understand the effects of nearby companions on their evolutionary paths, and to understand the effects of these companions on the stellar environment.

The survey is based on images of each WR target made with the Planetary Camera of the Hubble Space Telescope WFPC2 instrument (usually through the F336W, F439W, and F555W filters, which are near counterparts of the Johnson UBV filters). I measured astrometric positions and photometric magnitudes on the HST synthetic system for all the stars found within 15 arcsec of each WR star. I present results on new companions for 23 (38%) of the 61 WR stars in the survey sample. Three WR stars (WR 86, WR 146, and WR 147) are resolved as close colliding-wind binary systems. Another three WR stars (WR 98a, WR 104, and WR 112) are dusty WC9 type stars in hierarchical multiple systems. Six WR stars are members of previously unrecognized stellar groups. Finally, for thirteen WR stars, I determine new stellar parameters based on an analysis of the color-color and color-magnitude diagrams of the nearby cluster/association main sequence stars.

My WR sample breaks down into 57% cluster/association members, 33% field stars, and 10% runaways. This agrees reasonably well with the fractions determined by Mason et al. (1998) of 72%, 20%, and 8% for the same categories among the O stars. I find the same trend that the binary fraction decreases from cluster/association to field and to runaway groups in accordance with our expectation that many of the latter were originally binary members that were ejected by supernovae or close gravitational encounters.

The author(s) of this abstract have provided an email address for comments about the abstract: wallace@chara.gsu.edu

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.