Fundamental Evolutionary Parameters of B-Supergiants in the POST Main Sequence Gap of the HR Diagram: CYCLE4 Medium

Details Fundamental Evolutionary Parameters of B-Supergiants in the POST Main Sequence Gap of the HR Diagram: CYCLE4 Medium Fundamental Evolutionary Parameters of B-Supergiants in the POST Main Sequence Gap of the HR Diagram: CYCLE4 Medium

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5346l&link_type=abstract

HST Proposal ID #5346

Computer Science

Hst Proposal Id #5346 Hot Stars Massive Stars

Scientific paper

All stellar evolution calculations to date predict, for massive stars, the existence of a post main sequence gap in the Hertzsprung-Russell diagram. This gap is not observed, on the contrary the relevant region of the HR diagram is populated by early B supergiants. Consequently, the evolutionary status of these stars is uncertain, various attempts at explaining them range from post red supergiant evolution, diffusion processes in their main sequence progenitors or enhanced mass loss near the Humphreys-Davidson limit. These scenarios predict altered H/He ratios and CNO abundances as well as reduced masses in comparison to 'normal' stars, and this information is the key to understanding their evolutionary status. We propose to use FOS to obtain high S/N spectral data for four LMC early-B supergiants covering the wavelength range 1150-2300 A which will be analysed together with existing high resolution optical data to provide reliable values of the effective temperature, surface gravity, chemical composition, mass loss rate and stellar mass of each object. Highly sophisticated model atmosphere, stellar wind and 'unified' model atmosphere codes will be used in this analysis. The resulting information will be used to discriminate between various evolutionary scenarios and to constrain new stellar evolution calculations. A comparison with a parallel project for the Milky Way will yield valuable information on the importance of metallicity.

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