New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34: Binarity and neutron capture elements

We have carried out a new determination of abundances in the very metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34, using high-resolution spectra obtained with the HARPS spectrograph at the 3.6 m telescope of ESO, La Silla, that covers the range lambdalambda 4000-6900 Angstrom at a resolution of R = 100 000. Both stars are found to be long period binaries. It is confirmed that the abundance patterns show an enhancement of the alpha-elements (like Mg, Ca), of the proton capture elements (like Na and Al) and a strong enrichment in r and s process elements, where the s-enrichment is probably due to a mass transfer episode from a companion in its AGB phase. The possible origins of the abundance pattern and especially of the strong enhancement of both s and r elements are discussed.