AGB nucleosynthesis in the Large Magellanic Cloud
Detailed abundance analysis of the RV Tauri star MACHO 47.2496.8
Instituut voor Sterrenkunde, Departement Natuurkunde en Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: email@example.com
2 Dpto. Física Teórica y del Cosmos, Universidad de Granada, 18 071 Granada, Spain
3 SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland, UK
4 Department of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
5 Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Accepted: 2 October 2006
Context.Abundance analysis of post-AGB objects as probes of AGB nucleosynthesis.
Aims.A detailed photospheric abundance study is performed on the carbon-rich post-AGB candidate MACHO 47.2496.8 in the LMC.
Methods.High-resolution, high signal-to-noise ESO VLT-UVES spectra of MACHO 47.2496.8 are analysed by performing detailed spectrum synthesis modelling using state-of-the-art carbon-rich MARCS atmosphere models.
Results.The spectrum of MACHO 47.2496.8 is not only dominated by bands of carbon bearing molecules, but also by lines of atomic transitions of s-process elements. The metallicity of [Fe/H] = -1.4 is surprisingly low for a field LMC star. The C/O ratio, however difficult to quantify, is greater than 2, and the s-process enrichment is large: the light s-process elements are enhanced by 1.2 dex compared to iron ([ls/Fe] = +1.2), while for the heavy s-process elements an even stronger enrichment is measured: [hs/Fe] = +2.1. The lead abundance is comparable to the [hs/Fe]. With its low intrinsic metallicity and its luminosity at the low end of the carbon star luminosity function, the star represents likely the final stage of a low initial mass star.
Conclusions.The LMC RV Tauri star MACHO 47.2496.8 is highly carbon and s-process enriched, and is most probable a genuine post-C(N-type) AGB star. This is the first detailed abundance analysis of an extragalactic post-AGB star to date.
Key words: stars: AGB and post-AGB / stars: abundances / stars: carbon / stars: individual: MACHO 47.2496.8 / Magellanic Clouds
© ESO, 2006