A CORAVEL radial-velocity monitoring of giant Ba and S stars: Spectroscopic orbits and intrinsic variations. I.

Abstract

With the aim of deriving the binary frequency among Ba and S stars, 56 new spectroscopic orbits (46 and 10, respectively) have been derived for these chemically- peculiar red giants monitored with the CORAVEL spec- trometers. These orbits are presented in this paper (38 or- bits) and in a companion paper (Udry et al. 1998, Paper II; 18 orbits). The results for 12 additional long-period binary stars (6 and 6, respectively), for which only minimum pe- riods (generally exceeding 10 y) can be derived, are also presented here (10) and in Paper II (2). The global analy- sis of this material, with a few supplementary orbits from the literature, is presented in Jorissen et al. (1998). For the subsample of Mira S, SC and (Tc-poor) C stars showing intrinsic radial-velocity variations due to at- mospheric phenomena, orbital solutions (when available) have been retained if the velocity and photometric pe- riods are dierent (3 stars). However, it is emphasized that these orbit determinations are still tentative. Three stars have been found with radial-velocity variations syn- chronous with the light variations. Pseudo-orbital solu- tions have been derived for those stars. In the case of RZ Peg, a line-doubling phenomenon is observed near maxi- mum light, and probably reflects the shock wave propa- gating through the photosphere.