The Effective Temperatures of Hot Stars

We review the eeective temperature scale of hot (10kK) stars, including results from direct, continuum and ionization equilibrium techniques. We discuss the impact of recent developments in theoretical model atmospheres for OB subdwarfs, dwarfs and supergiants, white dwarfs and Wolf Rayet stars and present a revised T ee scale for OB stars. Direct techniques coupled with Kurucz model atmospheres allow Strr omgren photome-try to be used as a sensitive T ee indicator for normal stars with T ee 25kK. Reliable T ee determinations for hotter, low surface gravity and H-deecient stars require sophisticated ionization equilibrium techniques, generally considering non-LTE and line-blanketing eeects. 1. Continuum techniques 1.1. DIRECT METHODS The eeective temperature of a star { providing the essential link between observed properties and results of theoretical stellar structure and atmosphere models { can be directly obtained from measurements of its angular diameter together with the total absolute ux at the Earth, integrated over the entire spectrum The prime source in this eld remains the seminal work of Code et al. (1976), who combined angular diameters measured by the Narrabri stellar intensity interferometer with UV, visual and IR observations for 32 hot stars, corrected for interstellar extinction. Smalley & Dworetsky (1995) repeated their analysis using more recent observational and theoretical results, and obtained values on average only one percent lower for stars with T ee 25kK.