Luminous Stars in Nearby Galaxies

Abstract

Perhaps the greatest uncertainty in all of astrophysics, and especially in stellar structure and evolution, is distance. This is especially true for the most massive, most luminous stars that may be located at incredibly vast distances in our own galaxy. Studies on stellar populations in nearby galaxies thus have the advantage that all the stars of interest are at approximately the same distance, a distance that is relatively well known, especially in comparison with the uncertain distances of individual stars in our own galaxy. Surveys and the subsequent spectroscopy of massive stars in different stages of stellar evolution in relatively nearby resolved galaxies have revealed a complex distribution in the luminosity-temperature plane, that is (the HR diagram). The fundamentals of massive star evolution are mostly understood, but the roles of mass loss, episodic mass loss, rotation, and binarity are still in question. Moreover, the final stages of these stars of different masses and their possible relation to each other are not understood. The purpose of this volume is to provide a current review of the different populations of evolved massive stars. The emphasis is on massive stars in the Local Group, the Magellanic Clouds, and the nearby spirals M31 and M33.