Résumé
Asymptotic giant branch (AGB) stars are the most important galactic providers of s-elements. The standard model for the operation of the s-process in AGB stars is the partial mixing of protons (PMP) operating in the intershell zone shortly after a thermal pulse episode. This model predicts that low-metallicity (Z less than or equal to 0.002) AGB stars should exhibit large overabundances of Pb and Bi as compared to other s-elements [1]. The discovery of the first three such 'lead stars' (which are enriched in s-elements and have [Pb/hs] greater than or similar to 1, hs being any of Ba, La or Ce) has been reported in [2]. We present here lead abundances for five more CH stars. The abundances of two of these stars (HD 198269 and HD 201626) are consistent with the predictions of PMP operating in low-metallicity AGB stars; they are therefore classified as 'lead stars'. The three other stars (HD 26, V Ari and HD 189711) add to the growing number of low-metallicity stars which do not conform to these predictions, however.