Excitation of he II in Wolf-Rayet Envelopes

Abstract

view Abstract Citations (102) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation of he II in Wolf-Rayet Envelopes Castor, John I. ; van Blerkom, David Abstract We investigate the conditions of excitation which determine the strengths of the many He ii emission lines in the spectra of Wolf-Rayet stars. The observed line intensities from the WN 6 stars HD 192163 and HD 191765 are used to infer the level populations of He ii ions in their envelopes. Then, an ab initio calculation of the populations of the first thirty levels of He II is performed in which the equations of statistical equilibrium are solved with all radiative and collisional transitions included. The calculation of line transfer is based on the radial-expansion model of Wolf-Rayet envelopes, for which simplification of the transfer problem is achieved by means of an escape-probability method. The continua are treated in a similar manner, and the level populations are obtained at one representative point in the envelope. For plausihle combinations of temperature and density there is good agreement between the computed populations and those inferred from the observed line intensities. We conclude that the radialexpansion model is a valid description of the region in which He ii lines are formed. Publication: The Astrophysical Journal Pub Date: August 1970 DOI: 10.1086/150554 Bibcode: 1970ApJ...161..485C full text sources ADS |