Unified NLTE model atmospheres including spherical extension and stellar winds. III - The EUV fluxes of hot massive stars and He II emission in extragalactic giant H II regions

Details Unified NLTE model atmospheres including spherical extension and stellar winds. III - The EUV fluxes of hot massive stars and He II emission in extragalactic giant H II regions Unified NLTE model atmospheres including spherical extension and stellar winds. III - The EUV fluxes of hot massive stars and He II emission in extragalactic giant H II regions

Nov 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...265..656g&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 265, no. 2, p. 656-662.

Astronomy and Astrophysics

Astrophysics

28

Massive Stars, Nonequilibrium Thermodynamics, O Stars, Stellar Atmospheres, Stellar Models, Stellar Winds, Electron Density (Concentration), H Ii Regions, Helium, Wolf-Rayet Stars

Scientific paper

We demonstrate that massive O stars sufficiently close to the Eddington limit, and with effective temperatures only slightly higher than 50,000 K, can provide enough flux shortward of 228 A to reproduce the strength of the observed He II 4686 narrow nebular emission in the few known cases of high-excitation extragalactic H II regions. We present the results of calculations made using 'unified' model atmospheres, describe the models which are able to produce the required amount of He(+) ionizing photons, and show their predicted stellar H and He optical line profiles. The spectral characteristics of these models are similar to those observed in stars classified as extreme Of supergiants or 'slash' stars. We conclude that the detection of a Wolf-Rayet spectrum within a high-excitation H II region may not necessarily be a definitive proof that a WR star is the source of He(+) ionizing photons.

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