Parameters of Wolf-Rayet Stars

Wolf-Rayet (W-R) stars are objects with strong emission lines in the optical region due to a substantial stellar wind. They are found among the extreme Population I stars which are the topic of this Symposium and also this talk, and as central stars of planetary nebulae which I will not discuss here. The mass loss rates, Ṁ, are typically several 10−5 solar masses per year. W-R stars come in two major subtypes, the WN, in which strong lines of helium and nitrogen are seen, and the WC, in which strong lines of carbon and oxygen are found, along with the helium ions. In a few WN stars hydrogen appears to be present but the spectra of W-R stars are notable for the absence of this element. Absorption lines are generally not found in W-R stars, except in some instances due to a binary companion, or a more distant companion, or as a P-Cygni profile associated with certain emission features. An absorption spectrum appears to be an intrinsic feature in a very few WN stars.