Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008pasp..120..361w&link_type=abstract
The Publications of the Astronomical Society of the Pacific, Volume 120, Issue 866, pp. 361-366.
Astronomy and Astrophysics
Astronomy
2
Stars
Scientific paper
High-dispersion spectra were obtained to derive the radial velocity and chemical composition of the distant Cepheid QQ Per. Its location at ℓ = 141°, b = -6.5° allows it to be either a very distant classical Cepheid at 31 kpc from the Galactic center or a type II Cepheid at roughly half that distance. Five spectra at various phases were analyzed for abundances and an additional four spectra were useful for radial velocity. Effective temperatures ranging from 5100 to 5700 K were derived from the five spectra by requiring that there be no dependence of the iron abundance as derived from lines arising from a range of excitation potentials. The metallicity from the mean of five spectra is [Fe/H] = -0.6 ± 0.1. While this allows membership in either the thick disk or the distant thin disk, the presence of H emission at almost all phases indicates that QQ Per is a type II Cepheid of the thick disk. Relative to iron we find a small excess of oxygen, as often seen in metal-poor stars, and a surprising excess of C and N, as derived from high excitation lines. We show that the excess remains so long as no temperature error remains greater than about 200 K. Small deficiencies of the s-process elements appear to be present in common with many metal-poor stars.
Andrievsky Sergei. M.
Kovtyukh Valery V.
Wallerstein George
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