The atmosphere of subluminous B stars. II - Analysis of 10 helium poor subdwarfs and the birthrate of sdB stars

Details The atmosphere of subluminous B stars. II - Analysis of 10 helium poor subdwarfs and the birthrate of sdB stars The atmosphere of subluminous B stars. II - Analysis of 10 helium poor subdwarfs and the birthrate of sdB stars

Jan 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986a%26a...155...33h&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 155, no. 1, Jan. 1986, p. 33-45.

Astronomy and Astrophysics

Astrophysics

262

B Stars, Horizontal Branch Stars, Stellar Atmospheres, Stellar Evolution, Stellar Spectra, Subdwarf Stars, Abundance, Diffusion, Interstellar Extinction, Statistical Analysis, Stellar Gravitation, Stellar Luminosity, Stellar Temperature, Ultraviolet Spectra, White Dwarf Stars

Scientific paper

Ultraviolet and visual spectra of 10 helium-poor hot subluminous subdwarfs are analyzed, and the birthrate of these stars is determined. Effective temperatures range from 25,000 - 75,000 K in the group, which includes three binaries. sdB's occupy a narrow range in gravities and photospheric helium content in contrast to the sdOB ranges of gravities between 5.0 and 6.3 and helium contents from 0.07 to 6 percent. The helium deficiency occurs by diffusion, suggesting that the sdB mass loss rate is twice as small as the sdO mass loss rate. Data suggest that these stars form a single evolutionary group of extended horizon branch (EHB) stars which behave like helium main sequence stars with masses of approximately 0.5 solar mass. The completed survey of EHB stars reveals a birthrate of 2 x 10 to the 14th stars/cu pc/yr, and that their evolution directly into white dwarfs represents only 2 percent of this evolutionary channel; though they contribute significantly to the lowest mass tail of the white dwarf mass distribution.

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