AAS 201st Meeting, January, 2003
Session 81. Extragalactic Star Clusters
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[81.07] Starburst Anatomy: Surprising Results from HST Photometry of Ionizing Stellar Populations in M33

W. H. Waller (Tufts University), M. G. Lee (Seoul National University and DTM/CIW), H. S. Park, S. C. Kim (Seoul National University)

We present multi-band HST photometry of the stellar populations that underlie and power six giant H II regions in the nearby galaxy, M33. We find that the stellar luminosity functions (LFs) and derived initial mass functions (IMFs) both show strong dependences on the galactocentric radius and corresponding metal abundance. The sense of the dependence is surprising, in that the most metal-rich H II regions play host to the greatest preponderance of the most massive and luminous stars -- contrary to predictions based on metallicity-dependent accretion and cooling/fragmentation processes. The slope of the IMF (\Gamma) is seen to flatten with increasing metallicity [O/H] by ~1/dex. This variation in the IMF represents the first strong evidence for a systematic environmental effect on stellar population at the high-mass end. Photo-ablation of proto-stellar cores by neighboring hot stars and the mediation of this process by metallicity-dependent dust may help to explain this surprising result.

The author(s) of this abstract have provided an email address for comments about the abstract: waller@cosmos.phy.tufts.edu

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.