Type II Cepheids: Evidence for Na-O anticorrelation for BL Her type stars?
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Fecha
2018-06
Profesor/a Guía
Facultad/escuela
Idioma
en
Título de la revista
ISSN de la revista
Título del volumen
Editor
Oxford University Press
Nombre de Curso
Licencia CC
CC BY 4.0
Licencia CC
Resumen
The chemical composition of 28 Population II Cepheids and one RR Lyrae variable has been studied using high-resolution spectra. The chemical composition of W Vir variable stars (with periods longer than 8 d) is typical for the halo and thick disc stars. However, the chemical composition of BL Her variables (with periods of 0.8-4 d) is drastically different, although it does not differ essentially from that of the stars belonging to globular clusters. In particular, the sodium overabundance ([Na/Fe] ≈ 0.4) is reported for most of these stars, and the Na-O anticorrelation is also possible. The evolutionary tracks for BL Her variables (with a progenitor mass value of 0.8 solar masses) indicate that mostly helium-overabundant stars (Y = 0.30-0.35) can fall into the instability strip region. We suppose that it is the helium overabundance that accounts not only for the existence of BL Her variable stars but also for the observed abnormalities in the chemical composition of this small group of pulsating variables. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
Notas
Indexación Scopus
Palabras clave
Period, Magellanic Clouds, Globular Clusters, Chemical compositions, Anticorrelation, Cepheids
Citación
Monthly Notices of the Royal Astronomical Society Volume 477, Issue 2, Pages 2276 - 228521 June 2018
DOI
10.1093/mnras/sty671