H and He II spectra of Of stars

Previously developed dynamical models of Of stars are used as the basis of a set of statistical equilibrium calculations for hydrogen and ionized helium, on the hypothesis of radiative equilibrium in the stellar envelope. A number of spectral lines of these species are observed in the expanding envelopes of Of stars, and thus they provide diagnostic information about the stellar wind. It is found that the H-alpha line has a strength that is quite sensitive to the rate of mass loss by the star, and comparison with observation indicates loss rates as high as 0.00001 solar mass/yr. The ratio H-alpha/He II 4686-A as observed is in agreement with one of the two sets of theoretical values that are computed; the choice is allowed by uncertainties in the treatment of He II 304-A. Other lines of He II, for which the data are more fragmentary, give only factor-of-2 agreement with theory. The computed profiles of H-alpha and 4686-A are in qualitative agreement with observation, but certain systematic differences exist; the effect of absorption on the violet side of the emission profile is generally more marked in the theoretical profile. The effect of assuming a higher electron temperature in the stellar wind is considered. The primary change would be an upward adjustment in the inferred rates of mass loss, with some worsening of agreement between theory and observation of the H-alpha/4686-A ratio in the later subclasses.