Blue Supergiants as a Tool for Extragalactic Distances - Empirical Diagnostics
arXiv:astro-ph/0301179 · doi:10.1007/978-3-540-39882-0_8
Abstract
Blue supergiant stars can be exceptionally bright objects in the optical, making them prime targets for the determination of extragalactic distances. I describe how their photometric and spectroscopic properties can be calibrated to provide a measurement of their luminosity. I first review two well-known techniques, the luminosity of the brightest blue supergiants and, with the aid of recent spectroscopic data, the equivalent width of the Balmer lines. Next I discuss some recent developments concerning the luminosity dependence of the wind momentum and of the flux-weighted gravity, which can provide, if properly calibrated, powerful diagnostics for the determination of the distance to the parent galaxies.
Invited review at the International Workshop on "Stellar Candles for the Extragalactic Distance Scale", held in Concepcion, Chile, December 9-11, 2002