Wolf-Rayet Phenomena

Abstract

I have been asked to review in broad terms the concept of Wolf-Rayet (W-R) phenomena, that is, to outline what we currently know about the properties of stars showing such phenomena and to indicate the directions in which future work is leading. I thought I would begin by listing the characteristics of W-R spectra to which probably all the participants at this Symposium will be able to agree. These can readily be adapted from Thomas (1968) who discussed them at the Boulder W-R Symposium. The characteristics of W-R spectra are as follows: (1)They are primarily an emission line spectrum superimposed on a “hot” continuous spectrum.(2)P Cygni absorption components are observed for some lines in some stars; a fact not realized in 1968 was that a very few W-R stars have intrinsic absorption lines (e.g. The Balmer series in HD 92740 — Niemela (1973).(3)The emission lines represent a wide range of excitation and ionization. This level is often higher than indicated by simple modeling of the continuous spectrum.(4)The emission lines are broad, corresponding to widths of hundreds to thousands of kilometers per second; widths often differ among various ions in the same star.(5)The W-R stars can be divided into two subtypes: These are the WN types, in which the ions of nitrogen dominate, and the WC types, in which the ions of carbon (and oxygen) dominate. Both sub-types have strong lines of helium; in a few cases, hydrogen lines, in emission, are also observed (Underbill 1968).