A spectroscopic investigation of four O-type subdwarfs

Citation

Peterson, Arsine Victoria (1970) A spectroscopic investigation of four O-type subdwarfs. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9AF4-BY55. https://resolver.caltech.edu/CaltechETD:etd-05092008-145009

Abstract

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The spectra of four O-type subdwarfs, of the class with strong nitrogen lines and very weak carbon and oxygen lines, have been studied in some detail. Model atmospheres have been constructed for the stars HZ 44, +25°4655, and HD 127493, and the computed profiles of selected hydrogen and helium lines have been compared with the observed profiles. The effective temperatures of the model atmospheres are [...] 40 000 °K and the surface gravities are g [...] 5 x [...] (cgs). A mass of approximately [...] and an absolute visual magnitude of about +4 for the stars HZ 44 and HD 127493 is found to be consistent with the available data. The star +25°4655 is probably less luminous.

High helium abundances have been inferred for these stars -- from Y [...] 0.4 for HZ 44 to Y [...] 0.9 for +25°4655. Chemical abundances have been derived for heavier elements in a fine analysis. The nitrogen to carbon, and nitrogen to oxygen ratios derived for these stars are two orders of magnitude greater than is observed in the sun and in other main sequence stars. The high helium abundance and the observed CNO ratios are consistent with abundances predicted for material which has undergone hydrogen-burning in the CNO cycle.

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