Wolf-Rayet stars in IC 10: probing the nearest starburst.
MASSEY P. and HOLMES S.
Abstract (from CDS):
IC 10 is the nearest starburst galaxy, as revealed both by its Hα surface brightness and by the large number of Wolf-Rayet (W-R) stars per unit area. The relative number of known WC- to WN-type W-R stars has been thought to be unusually high (approximately two), which is unexpected for IC 10's metallicity. In this Letter, we report the first results of a new and deeper survey for W-R stars in IC 10. We successfully detected all of the spectroscopically known W-R stars, and based on comparisons with a neighboring control field, we estimate that the total number of W-R stars in IC 10 is about 100. We present spectroscopic confirmation of two of our W-R candidates, both of which are of WN type. Our photometric survey predicts that the actual WC/WN ratio is ∼0.3. This makes the WC/WN ratio of IC 10 consistent with that expected for its metallicity but greatly increases the already unusually high number of W-R stars, resulting in a surface density that is about 20 times higher than in the LMC. If the majority of these candidates are spectroscopically confirmed, IC 10 must have an exceptional population of high-mass stars.