Optically-Thick Stellar Winds and Photospheres of Hot Stars

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The investigators will continue theoretical modeling of stellar atmospheres with mass loss. The emphasis rests on very luminous and massive stars, typically over 40 solar masses. Accurate line spectra are needed to obtain effective temperatures. Such detailed understanding of the spectra yields information not only about the causes of the winds but also about properties of stellar evolution, such as convection; ways to identify the luminosities of such stars in distant galaxies; and the effects on the interstellar medium. The hottest observable stars provide important tests of our understanding of stellar evolution, they energize the interstellar medium; and they may become accurate indicators of distances of distant galaxies. However, observations of hot stars can be interpreted reliably only after a detailed model of their atmospheres has been constructed. The model must include information on both the velocities of the winds leaving the stars and on the atoms in the winds that absorb and re-emit the stellar radiation. Such a computation has only recently become possible. The investigators are at the forefront of this research. This grant will allow them to model the stellar atmospheres so that the spectra of the hottest stars can indeed become effective tools for astronomical research.