Definitions, Summary, and Some Issues

Extract

This Joint Discussion has been titled Massive Star Birth. Perhaps it is appropriate here to define what we mean by a massive star. The very word massive suggests we consider a minimum mass M below which one would speak of low (or intermediate) mass evolution, and above which is the realm of massive stars. It is natural to take this mass limit as that in which a (single) star will end its life as a supernova: 8M_⊙. This corresponds to a (minimum) luminosity L of a few × 10³L_⊙, a (minimum) Teff of 20000 K, and a ZAMS spectral type of about B1.5V. Note that this mass division refers to the final evolution of a star, and might well have nothing to do with difference in physical processes between massive and low mass star birth. For example, the minimum Teff for a star to produce an UCHII region, a readily observable quantity, corresponds to a T_eff closer to 30000 K and a mass of 15M_⊙.