Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986pasp...98..453s&link_type=abstract
Astronomical Society of the Pacific, Publications (ISSN 0004-6280), vol. 98, April 1986, p. 453-456.
Astronomy and Astrophysics
Astronomy
3
Globular Clusters, Stellar Composition, Stellar Spectra, Variable Stars, Hydrogen, Iron, Metallicity, Radial Velocity
Scientific paper
Rutily and Terzan (1977) identified 14 c-type RR Lyrae variable stars in and near the globular cluster NGC 6638 but only one ab-type was found. Among globular clusters which have more than a few RR Lyrae stars, such a large preponderance of c-type variables is unique. Low-resolution spectra for six of the supposed c-type stars have been obtained. In all six cases, the spectra are consistent with the c-type designation. Radial velocities are determined from the spectra, and metal abundances are measured by the Delta-S method. Variables V37, V38, V42, and V45 are found to be probable members of NGC 6638, while the membership of V40 and V43 is questionable. The Delta-S measures confirm that NGC 6638 is only moderately metal deficient: Fe/H abundance = 0.82 + or - 0.2. The large ratio of c-types to ab-type variables in NGC 6638 can be attributed to a gap in the color distribution of horizontal branch stars
Smith Harold A.
Stryker L. L.
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