Volume 558, October 2013
|Number of page(s)||12|
|Published online||01 October 2013|
The Hamburg/ESO R-process Enhanced Star survey (HERES)⋆
VIII. The r+s star HE 1405−0822⋆⋆
1 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: firstname.lastname@example.org; N.Christlieb@lsw.uni-heidelberg.de
2 Department of Physics, Hebei Normal University, Nanerhuan dong Road 20, 050024 Shijiazhuang, PR China
3 Indian Institute of Astrophysics, 560 034 Bangalore, India
Received: 29 March 2013
Accepted: 13 August 2013
Aims. The aim of this study is a detailed abundance analysis of the newly discovered r-rich star HE 1405−0822, which has [Fe/H] = −2.40. This star shows enhancements of both r- and s-elements, [Ba/Fe] = + 1.95 and [Eu/Fe] = 1.54, for which reason it is called r+s star.
Methods. Stellar parameters and element abundances were determined by analyzing high-quality VLT/UVES spectra. We used Fe I line excitation equilibria to derive the effective temperature. The surface gravity was calculated from the Fe i/Fe ii and Ti i/Ti ii equilibria.
Results. We determined accurate abundances for 39 elements, including 19 neutron-capture elements. HE 1405−0822 is a red giant. Its strong enhancements of C, N, and s-elements are the consequence of enrichment by a former AGB companion with an initial mass of less than 3 M⊙. The heavy n-capture element abundances (including Eu, Yb, and Hf) seen in HE 1405−0822 do not agree with the r-process pattern seen in strongly r-process-enhanced stars. We discuss possible enrichment scenarios for this star. The enhanced α elements can be explained as the result of enrichment by supernovae of type II. Na and Mg may have partly been synthesized in a former AGB companion, when the primary 22Ne acted as a neutron poison in the 13C-pocket.
Key words: stars: abundances / stars: AGB and post-AGB / stars: atmospheres / stars: chemically peculiar
Based on observations collected at the European Southern Observatory, Paranal, Chile (Proposal numbers 170.D-0010G, and 170.D-0010J).
Tables 5, 6 are available in electronic form at http://www.aanda.org
© ESO, 2013
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