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Temperatures and luminosities

A major advance in obtaining reliable temperatures of the optically thick, stratified W-R stars has been through the Standard Model, since standard methods are insensistive for hot stars (e.g. Hummer et al. 1988). Stellar temperatures for extended atmospheres are related to the inner boundary of the model atmosphere (generally around Rosseland optical depth 20), which often deviates significantly from the effective temperature, related to =2/3 (see Hamann 1994). For WN stars, stellar temperatures lie in the approximate range 30--100kK, while effective temperatures are typically 25--40kK (Hamann et al. 1995). HD104994 (WN3pec, Crowther et al. 1995d) is amongst the hottest W-R stars known, while the LMC star R84 (WN9, Crowther et al. 1995a) is one of the coolest (see Table 1), supporting the anticipated relation between temperature and spectral type. Although most WC stars have still to be analysed in detail, they show a similar range (Koesterke & Hamann 1995). Luminosities of W-R stars span a wide range =10, with the most luminous stars exclusively WNL stars, and the least luminous generally WNE and WCE. The presence of low luminosity WNE stars containing surface hydrogen is difficult to reconcile with standard evolutionary theory, without resorting to unrealistic mass-loss prior to the W-R phase (Crowther et al. 1995d).

Table 1: Comparison of properties of early--type, emission line stars. The parameters for AG Car relate to its WN11 visual minimum phase. Abundances are by mass

Paul Crowther
Mon Feb 12 13:51:35 GMT 1996