The metal abundance of M28 and the occurrence of Cepheids in globular clusters

Details The metal abundance of M28 and the occurrence of Cepheids in globular clusters The metal abundance of M28 and the occurrence of Cepheids in globular clusters

Nov 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...298..572s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 298, Nov. 15, 1985, p. 572-580. NSERC-supported research.

Astronomy and Astrophysics

Astrophysics

27

Cepheid Variables, Globular Clusters, Metallicity, Red Giant Stars, Stellar Spectra, Histograms, Horizontal Branch Stars, Star Distribution, Stellar Evolution

Scientific paper

The metal abundance of the globular cluster M28 has been determined from low-resolution SIT-Vidicon spectra of red giants and RR Lyrae stars. The CN, Ca II H and K, and Ca I λ4226 features in the red giant spectra indicate [M/H] = -1.0 ± 0.2. Delta-S measures of the RR Lyrae star spectra give [Fe/H] = -1.16 ± 0.2, in good agreement. Spectra of the variable star V7 show that it is probably not a U Geminorum star; it may not be a member of M28. The spectrum of the RV Tauri star V17 is briefly discussed. M28 is confirmed as one of the most metal-rich globular clusters known to contain type II Cepheid variable stars. The properties of the Cepheid-producing globular clusters are discussed. W Virginis-type Cepheids are most common among the most metal-rich globular clusters which also have blue horizontal branches. This predilection can be qualitatively explained by stellar evolution theory. There are 22 globular clusters with [Fe/H] > -1.8 which also have predominantly blue horizontal branches. Fourteen of these are known to contain type II Cepheids. These 14 clusters tend to have higher total visual luminosities, and hence larger stellar populations, than the eight clusters in which no Cepheids have been found. This is probably a result of the relatively brief lifetimes of globular cluster Cepheids: they are only represented in large stellar populations.

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