Abstract

Searching for Wolf-Rayet stars in M101 using the Hubble Space Telescope

Joanne Bibby (American Museum of Natural History)

J. Bibby (AMNH), M.Shara (AMNH), P.Crowther (Sheffield), A.Moffat (Montreal)

Ground-based, narrow-band imaging and spectroscopic surveys of nearby star-forming galaxies have been successful in identifying evolved massive stars called Wolf-Rayet (WR) stars in Local Group galaxies. However, stellar population searches in more distant galaxies have proven to be more difficult, with lower WR numbers found than expected. This is a result of the WR emission lines being diluted by surrounding massive stars in unresolved regions; the size of these regions is similar to that of giant HII regions which can host many luminous main-sequence O stars. Here we present initial results of our M101 WR survey using the Hubble Space Telescope (HST). The increased spatial resolution reveals the fainter WR population, which is impossible using ground-based imaging at the distance of M101. We can use this information to quantify the percentage of WR stars that are undetected in ground-based imaging of similar star-forming galaxies. WR stars are predicted to be the progenitors of Type Ibc core-collapse supernova, however to date no direct detection has confirmed this. If we hope to directly confirm the WR-supernova connection, on a reasonable time-scale, then we require complete WR surveys of a sample of galaxies.