Assigned ID: 2 ----- Submission 1 (Tue Dec 21 15:51:07 GMT 2004) ----- Over its 10 years of Costar-enabled lifetime, HST has accumulated a rich legacy of resolved stellar photometry in nearby galaxies. The resulting color-magnitude diagrams of the massive stellar populations rival those obtained from the ground for the Magellanic Clouds. We propose to analyze multiband imagery of 19 nearby galaxies to derive densely populated upper color-magnitude and Hertzsprung Russell diagrams (HRD). This study generalizes previous attempts done for the Magellanic Clouds to lower metallicities. Our primary scientific goal is a comparison with stellar evolution and evolutionary synthesis models, identification of mismatches, and an empirical recalibration. All major models are known to fail to reproduce both the colors and the population densities of metal-poor red supergiants in the HRD. We intend to use average HRDs at low metallicity for a recalibration of the stellar temperatures and lifetimes in stellar evolution models of red supergiants. Lacking such a recalibration, current synthesis models are inadequate for modeling metal-poor star-forming and starburst regions containing cool, evolved stars.

HOT STARS 12 58172 false 0.0 false false false false false SUPPORTED