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E. M. Levesque (Lowell Obs/MIT), P. Massey (Lowell Obs), K. A. G. Olsen (CTIO/NOAO), B. Plez, E. Josselin (U. MontpellierII), A. Maeder, G. Meynet (Geneva Obs), N. White (Lowell Obs)
The red supergiant (RSG) stage of massive star evolution is poorly matched by available evolutionary tracks. This is partly due to uncertainties in the derived physical properties (effective temperatures and bolometric luminosities) from observed quantities, which result in questionable placement of RSGs in the Hertzsprung-Russell diagram. The new generation of MARCS stellar atmosphere models includes a more rigorous treatment of molecular absorption, and we have used these models to make a far more robust determination of Teff and Mbol for a sample of Galactic RSGs. We obtained moderate-resolution (5Å) spectrophotometry of sixty-seven Galactic RSGs during two runs at the KPNO 2.1-m telescope and one at the CTIO 1.5-m. We reclassified the spectral types, and by comparing the depth of titanium oxide bands in the observed spectral energy distributions to those predicted by model atmospheres of various temperatures, we determined the Teff and E(B-V)'s of the observed RSGs. Here we will present our new effective temperature scale for Galactic RSGs. Our scale is warmer than those proposed in the past (Massey & Olsen 2003, Humphreys & McElroy 1983), by 60 K for the late K-type supergiants, and by 450 K for the latest M supergiants. The new scale shifts the RSGs closer to the predictions of current evolutionary theory. This work has been supported by the National Science Foundation through grant AST 00-93060 and the Research Experience for Undergraduates program at Northern Arizona University.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.