Multiplicity among solar–type stars

Abstract

Abstract. Two CORAVEL radial velocity surveys -one among stars in the solar neighbourhood, the other in the Pleiades and in Praesepe -are merged to derive the statistical properties of main-sequence binaries with spectral types F7 to K and with periods up to 10 years. A sample of 89 spectroscopic orbits was finally obtained. Among them, 52 relate to a free-of-bias selection of 405 stars (240 field stars and 165 cluster stars). The statistics corrected for selection effects yield the following results: (1) No discrepancy is found between the binaries among field stars and the binaries in open cluster. The distributions of mass ratios, of periods, the period-eccentricity diagram and the binary frequencies are all within the same error intervals. (2) The distribution of mass ratios presents two maxima: a broad peak from q ≈ 0.2 to q ≈ 0.7, and a sharp peak for q > 0.8 (twins). Both are present among the early-type as well as among the late-type part of the sample, indicating a scale-free formation process. The peak for q > 0.8 gradually decreases when long-period binaries are considered. Whatever their periods, the twins have eccentricities significantly lower than the other binaries, confirming a difference in the formation processes. Twins could be generated by in situ formation followed by accretion from a gaseous envelope, whereas binaries with intermediate mass ratios could be formed at wide separations, but they are made closer by migration led by interactions with a circumbinary disk. (3) The frequency of binaries with P < 10 years is about 14%. (4) About 0.3% of binaries are expected to appear as false positives in a planet search. Therefore, the frequency of planetary systems among stars is presently 7 +4 −2 %. The extension of the distribution of mass ratios in the planetary range would result in a very sharp and very high peak, well separated from the binary stars with low mass ratios.

Precession and accretion in circumbinary discs: the case of HD 104237

“…However, moving towards higher eccentricity can change this, and Roedig et al (2011) found that for high eccentricity, the binary components can accrete at comparable rates with a mass ratio of q b = 1/3. This should affect the mass ratio of the final binary, and Halbwachs et al (2003) indeed found that for stellar 'twins', there is a small preference towards lower eccentricities, indicating that more eccentric binaries have less equal mass ratios. However, this has not been studied in detail to date.…”

A possible dividing line between massive planets and brown-dwarf companions

“…Radial-velocity (RV) studies show that close-in (< 10 AU) brown-dwarf companions to Sun-like stars are rare compared to planets and stars (Marcy & Butler 2000;Halbwachs et al 2003;Grether & Lineweaver 2006). Precision-RV surveys have found ∼ 50 of these objects with M 2 sin i = 13 − 80 M J , which we adopt as working-definition of the brown-dwarf mass range, regardless of the object's formation history, composition, and membership in a multiple system (Sozzetti & Desidera 2010;Sahlmann et al 2010, henceforth SA10).…”

Gaia's potential for the discovery of circumbinary planets

“…We examined the sample of 89 spectroscopic binaries studied by Halbwachs et al (2003). An analysis of the Kepler results shows a tendency for circumbinary planets to exist in orbits near the inner stability limit, with an over-density at ∼6 P bin .…”

“…These stars are made the primary stars in binaries constructed using the results from radial velocity surveys. The secondary masses come from the mass ratio distribution in Halbwachs et al (2003). The binary periods are drawn from the log-normal distribution calculated in Duquennoy & Mayor (1991), and restricted to be within 1 day and 10 years, to correspond to the Halbwachs survey.…”