Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...219..543s&link_type=abstract
Astrophysical Journal, Part 1, vol. 219, Jan. 15, 1978, p. 543-549.
Astronomy and Astrophysics
Astrophysics
8
Cepheid Variables, Helium, Hot Stars, Stellar Evolution, Stellar Spectra, A Stars, Abundance, B Stars, M Stars, Star Clusters, Stellar Envelopes, Stellar Gravitation, Stellar Luminosity, Stellar Spectrophotometry, Ubv Spectra
Scientific paper
A study is made of the stellar pulsation and helium abundance of clusters containing Cepheid-strip stars. Specifically, spectra are obtained of the main-sequence B stars in the NGC 129 cluster (containing a nonvariable Cepheid-strip star), and the M25 cluster (containing a relatively hot Cepheid). It is suggested that the intrinsic helium abundances are not the source of the appearance of nonvariables in the Cepheid strip. And, if helium abundance is involved, a diffusion mechanism in the driving regions of the envelopes of Cepheid-strip stars must be present. In NGC 129, two stars are observed to yield a normal helium abundance, whereas in M25, all of the stars observed have abnormally low abundances. The significance of these low abundances is not clear.
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