Massive Star Evolution as a Function of Metallicity: Closing the Loop in the Local Group

Details Massive Star Evolution as a Function of Metallicity: Closing the Loop in the Local Group Massive Star Evolution as a Function of Metallicity: Closing the Loop in the Local Group

Aug 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009noao.prop..149m&link_type=abstract

NOAO Proposal ID #2009B-0149

Physics

Scientific paper

The NOAO Local Group Galaxy Survey (LGGS) obtained photometry of half a million stars in M31 and M33 (Massey et al. 2006, 2007a). We are applying here for the spectroscopic followup needed to construct physical (T_eff, log L/L_&sun;) H-R diagrams for the unevolved (core H-burning) massive stars in these two galaxies. These will be compared to the number of evolved massive stars in these system (Wolf-Rayets, red supergiants, and luminous blue variables), providing critical tests of stellar evolutionary models as a function of metallicity. This study will be complete for massive stars brighter than M_V<-5.5 (V<19.5), corresponding to masses > 50M_&sun; for zero-age main-sequence stars, and >25M_&sun; for older (5 Myr) stars. This sample consists of 600 stars in M31 and 1700 stars in M33, and our project will lead to a 100-fold increase in the number of main-sequence stars classified in our spiral neighbors. M31 has a (young-age) metallicity that is roughly 2× solar, with only a slight gradient, while M33 has a galactocentric gradient in metallicity from 0.6 to 0.3 solar. This will allow us to test the latest generation of Geneva stellar evolution models at a variety of metallicities, which is important given that rotation plays a dominant role at low metallicity, while radiatively driven stellar winds dominate at high metallicities. The data gathered here will help to refine the stellar evolutionary models, not only improving our knowledge of massive star evolution, but also the interpretation of the integrated spectra of distant galaxies. This proposal was awarded time by the 2008B TAC, but never scheduled.

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