P Cygni stars and mass loss

The Sobolev approximation is used to compute line profiles formed in rapidly expanding atmospheres. Twelve levels of hydrogen are used in determining the level populations in the envelope under statistical equilibrium. The results are compared to the observed hydrogen Balmer series profiles of P Cygni and other stars of similar type. It is found that a decelerating envelope can most adequately account for the observed profiles. Mass loss rates and mechanical momentum fluxes are determined for these stars and correlated with infrared excesses. It is found that low momentum flux favors the presence of dust in the envelope, as indicated by the presence of large infrared excess, whereas high momentum fluxes are found for stars having a free-free infrared emission spectrum. (auth)