Multiplicity among solar-type stars IV. The CORAVEL radial velocities and the spectroscopic orbits of 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.


Introduction
The spectrovelocimeter CORAVEL (COrrelation RAdial VE-Locities, Baranne et al. 1979) was installed on the Swiss 1-m telescope at the Observatory of Haute-Provence (OHP) from the late 1970s until its decommissioning in 2000. Amongst other programmes, it provided the radial-velocity (RV) measurements exploited in two statistical studies of binarity among the stars in the solar neighbourhood: the study of solar-type stars until G8, and its extension towards the K-type stars. A series of articles has been devoted to these programmes. The first (Duquennoy et al. 1991, Paper I hereafter) presented the radial-velocity measurements of the sample of F-G type stars; these data led to the orbital elements of several spectroscopic binaries (SBs), and to the statistical properties of solar-type binaries (Duquennoy & Mayor 1991, DM91 hereafter). Later, Halbwachs et al. (2003, Paper III hereafter) extended the statistical investigations to the K-type binaries with periods shorter than ten years, again on the basis of CORAVEL observations. This paper presented the parameters relevant for statistics, namely the periods, the semi-amplitudes, the mass ratios, and the orbital eccentricities of the spectroscopic binaries, excluding the other orbital elements. The long period K-type binaries were eventually studied by Eggenberger et al. (2004).
The present paper completes the series by presenting the radial velocity measurements and the full set of orbital elements ⋆ Based on photoelectric radial-velocity measurements collected at Haute-Provence Observatory. that gave rise to Paper III. It will give the orbits we have discovered all the visibility they deserve, so that they are henceforth taken into account in statistical studies, such as that of Raghavan et al. (2010). Moreover, they will be available for the validation of the spectroscopic orbits derived from the Radial Velocity Spectrometer of the Gaia satellite (Gaia Collaboration et al. 2016). The CORAVEL programme is presented in Sect. 2, the RV catalogue is in Sect. 3, and the spectroscopic orbital elements are in Sect. 4. Section 5 is the conclusion.

The CORAVEL survey of nearby K-type stars
The CORAVEL survey for nearby SBs was initiated in the early 1980s, although some stars (especially among the F-G types) had been measured before. The stars were taken from the second edition of the "Catalogue of Nearby Stars" (CNS Gliese 1969) and from its supplement (Gliese & Jahreiss 1979). The stars discarded from the preliminary third version of the CNS (CNS3 Gliese & Jahreiss 1991) were kept in the observing runs. All stars were observed with CORAVEL from the Haute-Provence Observatory. Due to the location of the instrument and to its characteristics, only the stars as late as F7 and northern to −15 • in declination were observed. Some stars with declination below −15 • were observed, but they were not taken into account in Paper III. The programme was split according to the spectral types of the stars: the search for SBs amongst 288 F-G stars ended in December 1989, but the detection of SBs amongst the K-type stars was intensively performed until July 1993. After this date, A&A proofs: manuscript no. Halbwachs the SBs were observed until 2000; at the same time, the RV of a few stars were still measured in order to confirm that it was constant.

CORAVEL individual measurements
The catalogue of the RV measurements provides 5413 measurements for 269 stars: 261 K-type stars and eight stars from the sample of DM91. These eight G-type stars were already in Paper I or another paper quoted in DM91, but they fulfil two conditions: they received enough additional RV measurements between 1991 and 2000 to significantly improve their spectroscopic orbit, and this new CORAVEL orbit was not published elsewhere. Moreover, the reduction of the CORAVEL observations was slightly improved, and the RV measurements are not exactly the same as in Paper I.
The format of the catalogue is presented in Table 1. Each record consists in the following data: -The number of the star in the CNS, followed by a letter designating the component, if any. -The epoch of the observation, given as a date with the year, the month, and the day, and also as barycentric Julian Day (BJD). -The RV, in km s −1 .
-The uncertainty of the RV.
-The index of component ("1" for the primary, "2" for the secondary). -A flag "R" indicates the measurement was discarded from the calculation of the orbital elements.
The records are sorted by stars (from the smallest to the largest right ascension), and then by observation epochs.

Elodie individual measurements
The CORAVEL observations were not sufficiently accurate to derive valuable SB orbital elements for two stars of the sample, GJ 1069 and GJ 554. The latter of these two stars is even a constant velocity star when only the CORAVEL RVs are considered. Fortunately, RV measurements were performed thanks to the spectrograph Elodie of the 193 cm telescope at the Haute-Provence Observatory, and they are provided by the Elodie archive (http://atlas.obs-hp.fr/elodie/). Fifteen Elodie RVs of GJ 1069 and 58 RVs of GJ 554 are presented in a separate file, with a slightly different format due to their accuracy. The uncertainties of the Elodie RVs were estimated as explained in Sect. 4.1. Sample records are presented at the end of Table 1.

The mean RV and the detection of SBs
The RV measurements were used to derive statistical information to decide whether a star is binary or not. These data are provided in Table A The content is the following: -The identification of the star is the CNS number (GJ), as in the RV catalogue, and another identification, which is HD when it exists, otherwise BD, or HIP, or AG (Astronomische Gesellschaft catalogue). Three stars are designated only by the GJ identification; these stars are all visual secondary components, as indicated by letter "B" following their GJ number: GJ 57.1B, GJ 615.1B, and GJ 764.1B. Histogram of the number of observations. The shaded area refers to the stars that were not considered as variable and the white area to the spectroscopic binaries. The last bin represents all the stars with at least 21 observations; for the spectroscopic binaries, the count in this bin is 72.
-The B − V colour index used to derive the CORAVEL RVs of the star. For the eight stars from the G-type sample, B − V = 0.63 was assumed. -The mean RV, RV. When the star is a binary with known orbital elements, the RV of the barycentre is provided, as it is in Table A σ RV is the standard deviation of the RV measurements.
-E/I is the ratio of external to internal errors.
-P(χ 2 ) is the probability to obtain the χ 2 of the RVs of the star, assuming that the RV is constant in reality. -N 1 is the number of observations of the star.
-N tot is the number of RV measurements of the primary and of the secondary components. -∆T is the time span of the observation.
-The spectroscopic status is "CST" (ConStanT) when P(χ 2 ) is more than 1%. Otherwise, it is SB1, or SB2 when the RV of the secondary component was measured. An "O" indicates that the orbital elements were derived, as explained in Sect. 4 hereafter. One star, GJ 554, has a constant CORAVEL RV, but an SB orbit derived by adding Elodie RV; this star is flagged "CSTO". The status of two stars (GJ 893.2B and GJ 907.1) is "?" since only one RV measurement was obtained; these stars have both declinations around −10 • , and are too faint to be easily observable. However, they were only in the so-called "extended sample" of Paper III, and they were not relevant in the statistical investigations. -A flag indicates that the SB orbital elements of the star are in Table A.2, "*" when they are derived for the first time, and "+" otherwise. The velocity curves of the flagged stars are in Figs. 3, 4, and 5.
The efficiency of the detection of the SBs depends on the time spans of the RV survey and on the numbers of RV measurements per star. The histograms of N 1 and of ∆T are presented in Figs. 1 and 2, respectively. The stars with variable RV are counted apart from the others, since they received more observations when their variability was detected.
It appears from Fig. 1 that a few stars received much less observations than the others. In addition to the two stars with only one observation already mentioned above, two stars have  three observations, although one of them have a variable RV. This star is GJ 142, which was not taken into account in the binarity statistics because its declination is close to −20 • . The other star is GJ 764.1B; it is difficult to observe since it is 5 arcsec away from its brighter companion GJ 764.1A, and it is only in the "extended" sample.
Half of the 209 constant RV stars received 11 observations or less. For the 269 stars in Table A.1, the median number of observations is 12.
The distribution of the time span, Fig. 2, also indicates that a few stars seem to have been less well observed than others. In addition to the two stars with one measurement and ∆T = 0, 3 stars were observed during less than 1500 days, although their RVs were variable. In fact, these stars are GJ 1124, GJ 343.1, and GJ 870, three short-period binaries, and their observations were completed in a few years; they received enough RV measurements to derive their orbital elements, which are listed in The accuracy of the CORAVEL RVs precludes the derivation of relevant orbital elements for GJ 1069 and GJ 554, and it was necessary to take into account RVs provided by the Elodie archive. For that purpose, the uncertainty of the Elodie RVs must be estimated in order to assign them a reliable weight with respect to the CORAVEL RVs. For each star, the same weight was assigned to all the Elodie RV measurements and the SB orbital elements were derived from Elodie alone. The residuals of the RVs were calculated and the uncertainty of the RVs was then chosen so that the F 2 estimator of the goodness-of-fit is zero. According to Stuart & Ord (1994), F 2 is derived from the formula where ν is the number of degrees of freedom and χ 2 is the weighted sum of the squares of the differences between the predicted and the observed RVs, normalised with respect to their uncertainties. It was thus found that the uncertainty is 44 m s −1 for GJ 1069 and 14 m s −1 for GJ 554. The final elements were then derived taking into account simultaneously the RVs from Elodie and those of CORAVEL. A systematic offset between the two sets of measurements was derived with the SB solution. It is worth noticing that, although the CORAVEL RVs have weights much smaller than those of Elodie, they slightly improve the accuracy of the solution terms.

Presentation of the orbital elements
We used the RV measurements to derive the SB orbital elements for all stars sufficiently observed. The number of these stars is 45; they are flagged "O" in Table A.1. An SB orbit based on our CORAVEL RV measurements has already been published for three of them: GJ 1064B, GJ 692.1, and GJ 765.2; the orbits of the last two stars are even SB+VB orbits, since interferometric observations were also taken into account; the references of these three orbits are given in the footnotes of   The footnotes of Table A.2 indicate that 23 of these orbits were previously published on the basis of a part of our measurements or from RVs measured with a different instrument than CORAVEL. The 21 other orbits refer to new SBs.
The orbits of eight G-type stars mentioned in DM91 are included in Table A.2. DM91 provided a preliminary orbit for six of these stars, but the orbital elements are significantly improved there, thanks to additional RV measurements. The 44 SB orbits in Table A.2 are presented in Figs. 3, 4, and 5.

Conclusion
We have drawn up a catalogue of 5413 RV measurements obtained with CORAVEL for 269 stars, 261 K-type dwarfs, and  eight G-type dwarfs of the solar neighbourhood. These measurements were used to detect the SBs on which were based the statistical investigations of Paper III. We calculated the elements of 44 SB orbits, corresponding to 42 stellar systems. Twenty-one orbits, corresponding to 20 stellar systems, are the first orbits ever published for these stars.
All these data will be available through the VizieR service of the Centre de Donnée astronomique de Strasbourg (CDS). The SB orbits and the corresponding RV measurements will also be included in the on-line SB9 catalogue (http://sb9.astro.ulb.ac.be/, Pourbaix et al. 2004).
A&A proofs: manuscript no. Halbwachs  Table A.2; the circles refer to the non-rejected CORAVEL RV measurements.  Table A.2; it is "*" when the orbital elements are derived for the first time, and "+" otherwise.      Orbital elements of the SBs. The G-type stars with an orbit in DM91 are included in this table when their elements are significantly improved thanks to additional observations; they are indicated by "(G)" following the GJ identification HD/BD P T 0 (JD) e V 0 ω 1 K 1,2 m 1,2 sin 3 i or a 1,2 sin i  Griffin (1987); other orbit by Scarfe (1988). 9 Preliminary orbit in DM91; first orbit with ∆T longer than the period. 10 Triple system. 11 First orbit by Griffin et al. (1985). 12 Preliminary orbit by Latham et al. (2002). 13 We improve the orbit of DM91. 14 First SB orbit; the star was already a VB with known orbital elements (Al-Wardat et al. 2014 Tokovinin et al. (1994); other orbit by Latham et al. (2002). 17 First orbit by Griffin et al. (1985); other orbit by Tokovinin (1990). 18 First orbit by Griffin & Emerson (1975). 19 First orbit by Griffin & Griffin (1982); combined VB+SB2 orbits by Mason et al. (1996) and by Pourbaix (2000). 20 We improve the orbit of DM91; high precision orbit by Sahlmann et al. (2011). Article number, page 15 of 18 A&A proofs: manuscript no. Halbwachs  21 We improve the CORAVEL orbit of Jasniewicz & Mayor (1988). 22 We improve the preliminary orbit of DM91; first orbit with ∆T longer than the period. 23 The period of the interferometric orbit by Tokovinin et al. (2015) is assumed. 24 The orbital elements were derived taking into account Elodie RV measurements; the offset of the Elodie RVs is −0.028 km s −1 . 25 First orbit by Kamper & Lyons (1981); other orbit by Beavers & Salzer (1983); high precision orbits by Nidever et al. (2002) and by Katoh et al. (2013Katoh et al. ( , 2016. 26 First orbit by Tokovinin (1991); we improve the orbit of Duquennoy et al. (1992).   27 We improve the orbit of Duquennoy & Mayor (1988). 28 First orbit by Tokovinin (1991); high precision orbit by Katoh et al. (2013). 29 The BY Dra variable star; first orbit by Bopp & Evans (1973); other orbit by Vogt & Fekel (1979). 30 First orbit by Tokovinin (1991); high precision orbit by Kiefer et al. (2018). 31 First orbit by McClure (1983); combined VB+SB2 orbit by Pourbaix (2000). A high precision VB+SB2 orbit was derived by Kiefer et al. (2018). 32 Triple system; first orbit by Duquennoy (1987). 33 The period and the semi-amplitude were fixed to the results of the SB+VB solution derived by Tokovinin & Latham (2017). Article number, page 17 of 18