Modeling the extended atmospheres of WN stars

A detailed study of WN stars with particular reference to HD 50896 is initiated. Using radiative transfer calculations in the comoving frame, the author examines the behavior of the He II, He I, and H departure coefficients in a dense extended atmosphere. The models indicate that in HD 50896 (WN5) the helium ionization decreases strongly with radius, so that helium is predominantly singly ionized in the radio emitting region. This will necessitate the revision of mass loss rates for Wolf-Rayet (W-R) stars similar to HD 50896, which have been derived from radio data. It is shown that a star with a small core (2. 5 Rₛun;) and a dense stellar wind (M≈ 5×10-5Mₛun;yr-1) can explain the observed energy distribution of W-R stars similar to HD 50896.