Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986a%26a...162..171h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 162, no. 1-2, July 1986, p. 171-179.
Astronomy and Astrophysics
Astronomy
52
B Stars, Globular Clusters, Horizontal Branch Stars, Stellar Spectra, Subdwarf Stars, Atmospheric Models, Helium, Stellar Temperature, Ultraviolet Astronomy, Visible Spectrum
Scientific paper
Ultraviolet and visual spectra of 9 horizontal branch stars in the globular cluster NGC 6752 are analyzed for effective temperatures, gravities and helium abundances. Effective temperatures range from 9700K to 40000K. Helium is deficient and its abundance varies from less than 0.2% to 3%, by number, which can be explained by gravitational settling (diffusion). The bluest stars are found to have atmospheric parameters strikingly similar to those of field sdB and sdOB stars, and are, therefore, regarded as their natural population II counterparts. The sdB stars in NGC 6752 are identified with evolutionary models for the extended horizontal branch. The authors regard the spectroscopic results as direct observational evidence that the stellar masses are of the order 0.5 M_sun; as predicted by theory.
Caloi Vittoria
Castellani Vittorio
Danziger John
Heber Uli
Kudritzki Rolf Peter
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