J.-L. Halbwachs

Multiplicity among solar-type stars. III. Statistical properties of the F7-K binaries with periods up to 10 years

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 eects 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: 2t oq 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 dierence 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%. The extension of the distribution of mass ratios in

Statistical properties of exoplanets IV. The period-eccentricity relations of exoplanets and of binary stars

A sample of spectroscopic binaries and a sample of single planetary systems, both having main-sequence solar-type primary components, are selected in order to compare their eccentricities. The positions of the objects in the (P.(1 − e 2 ) 3/2 , e) plane is used to determine parts in the period-eccentricity diagram that are not affected by tidal circularization. The original eccentricities of binaries and planets are derived and compared. They seem to be weakly or not at all correlated with period in both samples, but two major differences are found: (1) The tidal circularization of planetary orbits is almost complete for periods shorter than 5 days, but it is not visible when P.(1 − e 2 ) 3/2 is longer than this limit. This suggests that the circularization occurs rapidly after the end of the migration process and is probably simultaneous with the end of the formation of the planet. By contrast, we confirm that the circularization of the binary orbits is a process still progressing a long time after the formation of the systems. (2) Beyond the circularization limit, the eccentricities of the orbits of the planets are significantly smaller than those of binary orbits, and this discrepancy cannot be due to a selection effect. Moreover, the eccentricities of binaries with small mass ratios are quite similar to those of all binaries with q < 0.8. This suggests that the low eccentricities of exoplanet orbits are not a consequence of low-mass secondaries in a universal process. These remarks are in favor of the idea that binaries and exoplanets are two different classes of object from the point of view of their formation.

Variable stars in the Tycho photometric observations I. Detection

We present an original way to detect variable stars in the Tycho photometric observations. A modied Kolmogorov-Smirnov statistical test has been constructed, based on a model of most of the satellites parameters, leading to the dispersion in the measurements. This allows us to build a treatment taking into account truncated detections and censored measurements, and to search for variability in the faint part of the catalogue. The selection threshold of variable stars has been calibrated to minimize false alarm rate. Reliable results were thus obtained for stars as faint as 11 mag. One thousand and ninety-one suspected variable stars have been listed, 407 of which are already known in Hipparcos, GCVS or NSV, and 684 of which are suspected variable stars to be identied soon.

Masses of the components of SB2 binaries observed with Gaia - I. Selection of the sample and mass ratios of 20 new SB2s discovered with Sophie

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the Sophie spectrograph at the Haute-Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient finally to obtain the masses of the components with relative errors as small as 1 per cent when the astrometric measurements of Gaia are taken into account. Simultaneously, the luminosities of the components in the Gaia photometric band G will also be obtained. Our observation program started with 200 SBs, including 152 systems that were only known as single-lined. Thanks to the high efficiency of the Sophie spectrograph, an additional component was found for 25 SBs. After rejection of five multiple systems, 20 new SB2s were retained, including eight binaries with an evolved primary, and their mass ratios were derived. Our final sample contains 68 SB2s, including two late-type giants and 10 other evolved stars.

Masses of the components of SB2 binaries observed with Gaia – IV. Accurate SB2 orbits for 14 binaries and masses of three binaries

ABSTRACT In anticipation of the Gaia astrometric mission, a large sample of spectroscopic bina-ries is being observed since 2010 with the Sophie spectrograph at the Haute–ProvenceObservatory. Our aim is to derive the orbital elements of double-lined spectroscopicbinaries (SB2s) with an accuracy sufficient to finally obtain the masses of the com-ponents with relative errors as small as 1 % when the astrometric measurements ofGaia are taken into account. Simultaneously, the luminosities of the components inthe Gaia photometric band Gwill also be obtained. Our observation program startedwith 200 SBs, including 152 systems that were only known as single-lined. Thanks tothe high efficiency of the Sophie spectrograph, an additional component was found for25 SBs. After rejection of 5 multiple systems, 20 new SB2s were retained, including8 binaries with evolved primary, and their mass ratios were derived. Our final samplecontains 68 SB2s, including 2 late-type giants and 10 other evolved stars.Key words: binaries: spectroscopic

Multiplicity among solar-type stars. IV. The CORAVEL radial velocities and the spectroscopc orbits of the nearby K dwarfs

Context. The statistical properties of binary stars are clues for understanding their formation process. A radial velocity survey was carried on amongst nearby G-type stars and the results were published in 1991. Aims. The survey of radial velocity measurements was extended towards K-type stars. Methods. A sample of 261 K-type stars was observed with the spectrovelocimeter CORAVEL (COrrelation RAdial VELocities). Those stars with a variable radial velocity were detected on the basis of the P(chi^2) test. The orbital elements of the spectroscopic binaries were then derived. Results. The statistical properties of binary stars were derived from these observations and published in 2003. We present the catalogue of the radial velocity measurements obtained with CORAVEL for all the K stars of the survey and the orbital elements derived for 34 spectroscopic systems. In addition, the catalogue contains eight G-type spectroscopic binaries that have received additional measurements since 1991 and for which the orbital elements are revised or derived for the first time.

Binaries and distances

Gaia s five-year observation baseline might naively lead to the expectation that it will be possible to fit the parallax of any sufficiently nearby object with the default five-parameter model (position at a reference epoch, parallax and proper motion). However, simulated Gaia observations of a ‘model Universe’ composed of nearly 10 7 objects, 50% of which turn out to be multiple stars, show that the single-star hypothesis can severely affect parallax estimation and that more sophisticated models must be adopted. In principle, screening these spurious single-star solutions is rather straightforward, for example by evaluating the quality of the fits. However, the simulated Gaia observations also reveal that some seemingly acceptable single-star solutions can nonetheless lead to erroneous distances. These solutions turn out to be binaries with an orbital period close to one year. Without auxiliary (e.g., spectroscopic) data, they will remain unnoticed.

Binaries at the Bottom of the Main Sequence and below

Long-term radial-velocity surveys of G, K and M dwarfs of the solar neighbourhood are presented. The inferred orbital elements are discussed, focusing on the (e; log P) diagram, the mass-ratio and secondary mass distributions, and on the binary frequency of the studied samples. The proportion of companions to M dwarfs is found to be not signiicantly diierent from the binary frequency among G-and K-dwarf primaries. The mass function of stellar and planetary companions to solar-type stars strongly suggests diierent formation and evolution mechanisms for the two populations. Finally, beautiful mass-luminosity relations are obtained from low-mass binaries with high-precision radial-velocity measurements and adaptive optics visual data.

On derivation of masses of the SB2 components with Gaia astrometry

Apart from the case of the visual binaries for which the mass ratios can be found dynamically, the Hipparcos astrometric data can also provide masses from the photocentric orbits of double-lined spectroscopic binaries (SB2s). This method is applied to HIP 111170 with the following results: Mi = 1.89±0.40 M© and M2 = 1.04±0.20 MQ. It is estimated that the number of SB2s from the 8th catalogue of orbital elements of SB systems, for which the masses of the components could be derived with the Gaia astrometric observations, is about 80. Taking into account the evolution of the number of SB2s, the final estimate is about 160 systems at the end of the Gaia project. This number could be easily exceeded later, if particular efforts were dedicated to the ground-based observations of SBs, discovered from the Gaia radial velocity measurements.

OVERVIEW OF THE TYCHO CATALOGUE

The final Tycho Catalogue (ESA 1997b) has been derived from 37 months of observations with the star mapper of the astrometric satellite Hipparcos. The Hipparcos Catalogue (ESA 1997a) with about 120,000 stars is the result of the main Hipparcos mission and has, e.g., been described by Kovalevsky et al. (1995). Both catalogues will be published in 1997.