The theory of mass loss from hot stars

Abstract

Although some evidence had been available earlier, it was the work of Morton (1967) that proved that the OB Supergiants are losing mass. He obtained spectra with a rocket borne spectrograph of the three stars in Orion's belt, δ, ε and ζ Orionis. These stars are all supergiants of spectral type 09.5 or BO. The spectra showed resonance lines of ions such as C III, C IV, Si IV, N V with P-Cygni type profiles. The deepest part of the absorption profile corresponded to a velocity away from the star of 1400 km s−1, and the absorption profile extended out to wavelengths corresponding to velocities of 2000 km s−1 away from the star. Since these velocities are much greater than the escape velocities from the surface of these stars, it is clear that matter is escaping from them. With a number of simplifying assumptions Morton deduced that the rate of mass loss is about 10−6 M⊙ yr−1. This order of magnitude has remained unchanged by the many high quality observations made since that time.