NOAO >   Observing Info >   Approved Programs >   2011B-0083

# Proposal Information for 2011B-0083

PI: Philip Massey, Lowell Observatory, phil.massey@lowell.edu

CoI: Kathryn Neugent, Lowell Observatory
CoI: Georges Meynet, Geneva Observatory

Title: The Wolf-Rayet Content of M31

Abstract: Wolf-Rayet stars (WRs) are the evolved descendants of massive O-type stars, and the relative number of WC-type to WN-type WRs is known" to vary by large factors with metallicity. Current evolutionary models do well at predicting the WC/WN ratio for lower metallicity galaxies but fail to predict the ratio at higher metallicities. Two theoretical explanations have been advanced to explain the deficiency in the models. Nevertheless, it is not clear how real this problem is. WN stars have much weaker emission lines than do WC stars, and thus are harder to detect. We have completed a very sensitive survey for WRs in M31 using Mosaic and the KPNO 4-m, and found 180 new WR candidates, about 4\times the currently known number. We are now proposing for the follow-up spectroscopy needed to confirm these candidates, and to determine which are WCs and which are WNs. The result will be a reliable value for the WC/WN ratio in the highest metallicity galaxy studied, against which the models can be compared and, if necessary, refined.

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 NOAO >   Observing Info >   Approved Programs >   2011B-0083