Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-02-05
Astron.Astrophys.404:291-300,2003
Astronomy and Astrophysics
Astrophysics
9 pages, 6 figures, accepted for publication in Astronomy & Astrophysics. Also available at http://www-astro.ulb.ac.be/Html/ps
Scientific paper
10.1051/0004-6361:20030447
The standard model for the operation of the s-process in asymptotic giant branch (AGB) stars predicts that low-metallicity ([Fe/H] <= -1) AGB stars should exhibit large overabundances of Pb and Bi as compared to other s-elements. Eight CH stars (with [Fe/H] ranging from -1.5 to -2.5) are studied in the present paper using high-resolution spectra (R = lambda/Delta lambda = 135 000), and five of them appear to be enriched in lead (with [Pb/Ce] ~ 0.7). Abundances of heavy elements in these `lead stars' (defined as stars enriched in s-elements and with [Pb/hs] >= 1, hs being any of Ba, La or Ce) are consistent with the predictions for the s-process operating in low-metallicity AGB stars as a consequence of the `partial mixing' of protons below the convective hydrogen envelope. Two among the studied stars (HD 189711 and V Ari) add to a growing number of low-metallicity stars which do not conform to these predictions, however. Variations on the canonical proton-mixing scenario for the operation of the s-process in low-metallicity stars, that could account for these discrepant stars, are briefly discussed.
Goriely Stephane
Jorissen Alain
Plez Bertrand
Van Eck Sophie
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