Stellar Winds of Hot Massive Stars Nearby and Beyond the Local Group

Photospheric radiation momentum is efficiently transferred by absorption through metal lines to the gaseous matter in the atmospheres of massive stars, sustaining strong winds and mass loss rates. Not only is this critical for the evolution of such stars, it also provides us with diagnostic UV/optical spectral lines for the determination of mass loss rates, chemical abundances and absolute stellar luminosities. We review the mechanisms which render the wind parameters sensitive to the chemical composition, through the statistics of the wind-driving lines. Observational evidence in support of the radiation driven wind theory is presented, with special regard to the Wind Momentum-Luminosity Relationship and the blue supergiant work carried out by our team in galaxies outside of the Local Group.
Comment: To appear in Carnegie Observatories Astrophysics Series, Vol. 4: `Origin and Evolution of the Elements', ed. A. McWilliam and M. Rauch (Cambridge: Cambridge Univ. Press)