Radial Velocities Monitoring of a Sample of Barium and S Stars Using Coravel: Towards an Evolutionary Link Between Barium and S Stars

摘要

A sample of 27 southern BaII and nine northern S stars was observed with the radial velocity spectrometer CORAVEL during three seasons. A high proportion (89 percent) of stars with variable (either well above or just at the three sigma level) radial velocities is found in both samples. Concerning BaII stars, there is no doubt about the orbital origin of the observed radial velocity variations. At least five S stars show velocity variations originating in orbital motions, while Mira-type pulsations of small amplitude cannot be firmly excluded for more S stars displaying velocity variations with dispersions in the interval 1.0 to 1.5 km sec. Observations support the BaII-S evolutionary scheme, although a review of other observational data shows that it is probably not possible to totally rule out the M-S-C sequence. A binary scenario involving mass transfer and accounting for this dual origin of S stars is proposed. This scenario could also account for the rather wide range of stellar populations in which S stars are found.