PI: Phil Massey, Lowell Observatory, Phil.Massey@lowell.edu
Address: 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA
CoI: Shadrian Holmes, Univ of Texas
Title: Evolved Massive Stars in the Local Group: Spectroscopy of Wolf-Rayets and Red Supergiants Candidates
Abstract: The most massive stars spend their He-burning years as red supergiants (RSGs) and Wolf-Rayet stars (WRs). The relative number of RSGs and WRs, and the relative numbers of WC-type to WN-type WRs, are expected to be a very sensitive function of the initial metallicity of the gas out of which these stars formed. Previous studies of the WR and RSG populations of Local Group galaxies have shown that these ratios do indeed vary with metallicity, but none of the current evolutionary models reproduce the trend. It may be that the models are simply inadequate. Alternatively, it could be that the small regions previously surveyed among the Local Group are either incomplete for WN- type WRs (which are much harder to find), or else that we have not surveyed large enough regions to have a good mix of ages in our sample, which will bias the number ratios, as WRs are typically older than RSGs. We have conducted powerful new photometric surveys for WRs using on-band and off-band emission-line imaging using the KPNO 4-m, and are asking time for spectroscopic confirmation with GEMINI. We have also identified RSG candidates in the same regions using the \it BVR data from the Local Group survey. For this, we are asking for WIYN Hydra time to distinquish bona-fide RSGs from the numerous foreground dwarfs. With these two spectroscopic samples we will have the excellent observational data base needed for testing the new and improved generation of stellar evolutionary models (which include the effects of rotation, an important mixing mechanism) which our collaborator Maeder and his colleagues are producing.
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