2005A&A...429.1031B

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 3.6m telescope of ESO, La Silla, that covers the range λλ4000-6900Å at a resolution of R=100000. Both stars are found to be long period binaries. It is confirmed that the abundance patterns show an enhancement of the α-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.