Mathematics
Scientific paper
Sep 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986phdt.........5d&link_type=abstract
Ph.D. Thesis Wisconsin Univ., Madison.
Mathematics
2
Carbon, Halos, Interstellar Gas, Ionizing Radiation, Milky Way Galaxy, Nebulae, Nitrogen, O Stars, Photoionization, Radiation Sources, Silicon, White Dwarf Stars, H Ii Regions, Hydrogen, Mathematical Models
Scientific paper
Photoionization models are constructed for studying the ability of hot (40,000 K less than or equal to T(eff) less than or equal to 100,000 K) white dwarfs to produce the highly ionized species (C IV, Si IV, and N V) seen toward stars at high z distances. To study the maximum effect white dwarfs can have on the halo gas, these stars are assumed to be surrounded by an H II region produced by dilute ionizing radiation from O stars (T(eff) = 40,000 K). The observed column density of C IV, Si IV, and N V seen towards hot individual white dwarfs can be reproduced. However, white dwarfs produce such small Stroemgren spheres of C IV, Si IV, and N V that they contribute about 1 percent to the C IV column density observed in the halo gas and less than 1 percent to the Si IV and N V colum densities. This result holds even with probable overestimates of the space density of white dwarfs. Photoionization models of nebulae surrounding O stars (T(eff) = 40,000 and 35,000 K) show that O stars are an important source of Si IV. The O type stars of spectral type O6 and earlier can produce or at least contribute to the observed C IV column density, while production of N V by these stars is negligible. Possible ionizing sources of the halo gas are discussed.
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