A CORAVEL radial - velocity monitoring of giant Ba and S stars : spectroscopic orbits and intrinsic variations ( I ) ⋆

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 chemicallypeculiar red giants monitored with the CORAVEL spectrometers. These orbits are presented in this paper (38 orbits) 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 periods (generally exceeding 10 y) can be derived, are also presented here (10) and in Paper II (2). The global analysis 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 atmospheric phenomena, orbital solutions (when available) have been retained if the velocity and photometric periods are different (3 stars). However, it is emphasized that these orbit determinations are still tentative. Three stars have been found with radial-velocity variations synchronous with the light variations. Pseudo-orbital solutions have been derived for those stars. In the case of RZ Peg, a line-doubling phenomenon is observed near maximum light, and probably reflects the shock wave propagating through the photosphere.