Spectroscopic binaries among Hipparcos M giants
III. The eccentricity – period diagram and mass-transfer signaturesA. Jorissen, A. Frankowski, B. Famaey, and S. Van Eck
Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP. 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
Received 29 July 2008 / Accepted 20 December 2008
Context. This paper is the third one in a series devoted to studying the properties of binaries involving M giants.
Aims. We use a new set of orbits to construct the first (e - log P) diagram of an extensive sample of M giant binaries, to obtain their mass-function distribution, and to derive evolutionary constraints for this class of binaries and related systems.
Methods. The orbital properties of binaries involving M giants were analysed and compared with those of related families of binaries (K giants, post-AGB stars, barium stars, Tc-poor S stars).
Results. The orbital elements of post-AGB stars and M giants are not very different, which may indicate that, for the considered sample of post-AGB binaries, the post-AGB star left the AGB at quite an early stage (M4 or so). Neither are the orbital elements of post-mass-transfer binaries like barium stars very different from those of M giants, suggesting that the mass transfer did not alter the orbital elements much, contrary to current belief. Finally, we show that binary systems with e < 0.4 log P - 1 (with periods expressed in days) are predominantly post-mass-transfer systems, because (i) the vast majority of barium and S systems match this condition; and (ii) these systems have companion masses peaking around 0.6 , as expected for white dwarfs. The latter property has been shown to hold as well for open-cluster binaries involving K giants, for which a lower bound on the companion mass may easily be set.
Key words: stars: binaries: spectroscopic -- stars: AGB and post-AGB -- stars: late-type -- stars: binaries: symbiotic
© ESO 2009