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

Abstract

We have carried out a new determination of abundances in the very metal-poor CH/CN strong stars CS 29497-34 and CS 22948-27, using high-resolution spectra obtained with the HARPS spectrograph at the 3.6m telescope of ESO, La Silla, that covers the range 400 - 690 nm 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 all 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.