Computer Science
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........2v&link_type=abstract
Ph.D. Thesis Colorado Univ., Boulder.
Computer Science
5
Emission Spectra, Magellanic Clouds, Massive Stars, Milky Way Galaxy, Starburst Galaxies, Wolf-Rayet Stars, Abundance, Extinction, H Ii Regions, Line Spectra, Luminosity, O Stars, Star Distribution, Stellar Color, Stellar Models
Scientific paper
Wolf-Rayet (W-R) stars are the short-lived endpoints of massive star evolution. Recent studies have identified a set of blue emission-line 'starburst' galaxies whose integrated spectra reveal broad emission features due to the presence of 102-105 such stars. We have performed a systematic study of the properties of a sample of such 'W-R galaxies'. The properties of W-R stars in the Galaxy and the Large Magellanic Cloud (LMC) provide the foundation for this analysis. Using a relation between the size of continuum discontinuities and the intrinsic (b - v)0 color found from model atmospheres of WN stars, we derive a formula for calculating the color excesses of such stars. We then calculate color excesses for nearly all WN stars in the Galaxy and the LMC. Our results are in good agreement with previous determinations of the color excesses for WN stars. Next, we derive average intrinsic He II 4686 and C IV 5808 emission line luminosities from the spectra of LMC WN and WC stars, respectively. Models of WN atmospheres are used to calculate effective temperatures, radii, luminosities, and Lyman continuum fluxes of LMC WNL stars. We have obtained a spatially integrated spectrum of the central 8 x 8 min. region of the giant H II region 30 Doradus in the LMC. From the observed line strengths and our average emission line and Lyman continuum luminosities we estimate the numbers of W-R and O stars present. Our results are in excellent agreement with direct star counts in the region. Finally we have obtained moderate resolution optical spectra of ten W-R galaxies and four comparison starburst galaxies. From the strong nebular emission lines, we determine the internal extinctions, densities, temperatures, oxygen abundances, and the Lyman continuum luminosity in these galaxies. From the strength of the broad He II 4686 feature, the number of W-R stars and the ratio of the number of W-R to O stars present are determined. Contrary to model predictions, we find no correlation of the number of W-R stars or the W-R/O number ratio with oxygen abundance. We calculate W-R/O number ratios that are an order of magnitude larger than predicted by current models of starburst regions.
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