Adam Frankowski

Spectroscopic binaries among Hipparcos M giants - III. The eccentricity – period diagram and mass-transfer signatures

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 − logP) 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. 4l ogP − 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 M� , 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.

Spectroscopic binaries among Hipparcos M giants , I. Data, orbits, and intrinsic variations

Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars belonging to the Hipparcos survey. Aims. We aim at extending the orbital data available for binaries with M giant primaries. The data presented in this paper will be used in the companion papers of this series to (i) derive the binar y frequency among M giants and compare it to that of K giants (Paper II) and (ii) analyse the eccentricity ‐ period diagram and the mass-function distribution (Paper III). Methods. Keplerian solutions are fitted to radial-velocity data. How ever, for several stars, no satisfactory solution could be f ound, even though the radial-velocity standard deviation is grea ter than the instrumental error, because M giants suffer fro m intrinsic radialvelocity variations due to pulsations. We show that these intrinsic radial-velocity variations can be linked with both the average spectral-line width and the photometric variability. Results. We present an extensive collection of spectroscopic orbits for M giants with 12 new orbits, plus 17 from the literature. On top of these, 1 preliminary orbit yielded an approximate value for the eccentricity and the orbital period. Moreover, to illustrate how the large radial-velocity jitter present in Mira and semi-regular variables may easily be confused with orbital variations, we also present examples of pseudo-orbital variations (in S UMa, X Cnc, and possibly in HD 115521, a former IAU radial-velocity standard). Because of this difficulty, M giants involving Mira variable s were excluded from our monitored sample. We finally show tha t the majority of M giants detected as X-ray sources are actually binaries. Conclusions. The data presented in this paper considerably increase the orbital data set for M giants, and will allow us to conduct a detailed analysis of the eccentricity ‐ period diagram in a c ompanion paper (Paper III).

Spectroscopic binaries among Hipparcos M giants - II. Binary frequency

Context. This paper is the second in a series devoted to studying the properties of binaries with M giant primaries. Aims. The binary frequency of field M giants is derived and compared with the binary fraction of K giants. Methods. Diagrams of the CORAVEL spectroscopic parameterSb (measuring the average line width) vs. radial-velocity sta ndard deviation for our samples were used to define appropriate bin arity criteria. These then served to extract the binarity fr action among the M giants. Comparison is made to earlier data on K giant binarity frequency. The Sb parameter is discussed in relation to global stellar parameters, and the Sb vs. stellar radius relation is used to identify fast rotator s. Results. We find that the spectroscopic binary detection rate among fie ld M giants, in a sample with few velocity measurements (� 2), unbiased toward earlier known binaries, is 6.3%. This is less than half of the analogous rate for field K giants. This dif ference originates in the greater difficulty of finding binaries amon g M giants because of their smaller orbital velocity amplitudes and larger intrinsic jitter and in the different distributions of K and M giants in the eccentricity ‐ period diagram. A higher detection rate was obtained in a smaller M giant sample with more radial velocity measurements per object: 11.1% confirmed plus 2.7% poss ible binaries. The CORAVEL spectroscopic parameterSb was found to correlate better with the stellar radius than wi th either luminosity or effective temperature separately. Two outliers of the Sb vs. stellar radius relation, HD 190658 and HD 219654, have been recognised as fast rotators. The rotation is companion-induced, as bot h objects turn out to be spectroscopic binaries.

Detection methods of binary stars with low‐ and intermediate‐mass components

This paper reviews methods which can be used to detect binaries involving low‐ and intermediate‐mass stars, with special emphasis on evolved systems. Besides the traditional methods involving radial‐velocity or photometric monitoring, the paper discusses as well less known methods involving astrometry or maser (non‐)detection. An extensive list of internet resources (mostly catalogues/databases of orbits and individual measurements) for the study of binary stars is provided at the end of the paper.

Binary CSPN and PN abundances

Bipolar planetary nebulae (PNe) are often associated with high mass objects because of their metallicity, but there are numerous exceptions (including as many as 1/3 of all bipolars). On the other hand, it seems that the main requirement for this morphology is a binary companion. In this paper a possible connection of the exceptional cases to a specific binary evolution path is considered.