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Abundance analysis for long-period variables II. RGB and AGB stars in the globular duster 47 Tucanae
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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2014 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 567, A143- p.Article in journal (Refereed) Published
Abstract [en]

Context Asymptotic giant branch (AGB) stars play a key role in the enrichment of galaxies with heavy elements. Due to their large amplitude variability, the measurement of elemental abundances is a highly challenging task that has not been solved in a satisfactory V ay yet. Aims. Following our previous work we use hydrostatic and dynamical model atmospheres to simulate observed high-resolution near-infrared spectra of 12 variable and non variable red giants in the globular cluster 47 Tuc. The 47 Tuc red giants are independently well characterized in important parameters (mass, metallicity, luminosity). The principal aim was to compare synthetic spectra based on the dynamical models with observational spectra of 47 Ric variables. Assuming that the abundances are unchanged on the upper giant branch in these low-mass stars, our goal is to estimate the impact of atmospheric dynamics on the abundance determination. Methods. To estimate abundances we measured the equivalent widths of selected features in observed spectra and compared the results with predictions from a set of hydrostatic and dynamical model atmospheres resembling 47 Tun AGB stars in their fundamental parameters. Our study includes lines of (CO)-C-12, (CO)-C-13. OH, and Na. Furthermore, we investigated the variations in line intensities over a pulsation cycle. Results. We present new measurements of the C/O and C-12/C-13 ratio for 5 non variable red giants in 47 Tuc. The equivalent widths measured for our 7 variable star, strongly differ from the non variable stars arid cannot be reproduced by either hydrostatic or dynainical model atmospheres. Nevertheless, the dynamical models fit the observed spectra of long-period variables much better than any hydrostatic model. For some spectral features. the variations in the line intensities predicted by dynamical models over a pulsation cycle give similar values as a sequence of hydrostatic models with varying temperature and constant surface gravity. Conclusions. Our study of the dynamical effects on abundance determination visible in these well characterized cluster stars prepares the ground for the long-term goal of deriving abundarices for variable AGB stars in general.

Place, publisher, year, edition, pages
2014. Vol. 567, A143- p.
Keyword [en]
stars: AGB and post-AGB, stars: late-type, stars: atmospheres, stars: abundances, line: profiles
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-234211DOI: 10.1051/0004-6361/201424078ISI: 000341185300148OAI: oai:DiVA.org:uu-234211DiVA: diva2:755931
Available from: 2014-10-15 Created: 2014-10-15 Last updated: 2014-10-15Bibliographically approved

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Höfner, SusanneAringer, Bernhard
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