Orbital elements of S stars : revisiting the evolutionary status of S stars.

Abstract

The hypothesis of an evolutionary link between barium stars and the non-Mira S stars is discussed. The hypothesis of an evolutionary link between the barium stars and the non-Mira S stars is confirmed. The mass function distribution of S stars, indicating that the companions are likely white dwarfs, as is the case for barium stars, supports this hypothesis. However, systems with periods shorter than 600 d appear to be lacking among S stars, although they are present among barium stars. Moreover, S stars appear to be less massive on the average than barium stars. It is suggested that these differences between the two families can be naturally explained by assuming that non-Mira S stars (without Tc) populate the first giant branch instead of the asymptotic branch. A synoptic view of the evolutionary paths followed by low- and intermediate-mass binary systems is presented, with special emphasis on the relationships between the families of peculiar red giants.