Stephane Udry

Red giants in open clusters - XIV. Mean radial velocities for 1309 stars and 166 open clusters

Context. Radial velocities have proved to be an efficient method for membership determination if there are at least 2 or 3 red giants in a cluster. They are necessary for galactic studies, but are still missing for many open clusters. Aims. We present the final catalogues of a long-term observing programme performed with the two coravel spectrovelocimeters for red giants in open clusters. The main aims were to detect spectroscopic binaries and determine their orbital parameters, determine the membership, and compute mean velocities for the stars and open clusters. Methods. We computed weighted mean radial velocities for 1309 stars from 10 517 individual observations, including the systemic radial velocities from spectroscopic orbits and for cepheids. Results. The final results are contained in three catalogues collecting 10 517 individual radial velocities, mean radial velocities for 1309 red giants, and mean radial velocities for 166 open clusters among which there are 57 new determinations. We identified 891 members and 418 non-members. We discovered a total of 288 spectroscopic binaries, among which 57 are classified as nonmembers. In addition 27 stars were judged to be variable in radial velocities and they are all red supergiants. Conclusions. The present material, combined with recent absolute proper motions, will permit various investigation of the galactic distribution and space motions of a large sample of open clusters. However, the distance estimates still remain the weakest part of the necessary data. This paper is the last one in this series devoted to the study of red giants in open clusters based on radial velocities obtained with the coravel instruments.

Multiplicity among chemically peculiar stars - II. Cool magnetic Ap stars

We present new orbits for sixteen Ap spectroscopic binaries, four of which might in fact be Am stars, and give their orbital elements. Four of them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. The twelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339, HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD 216533. Rough estimates of the individual masses of the components of HD 65339 (53 Cam) are given, combining our radial velocities with the results of speckle interferometry and with Hipparcos parallaxes. Considering the mass functions of 74 spectroscopic binaries from this work and from the literature, we conclude that the distribution of the mass ratio is the same for cool Ap stars and for normal G dwarfs. Therefore, the only differences between binaries with normal stars and those hosting an Ap star lie in the period distribution: except for the case of HD 200405, all orbital periods are longer than (or equal to) 3 days. A consequence of this peculiar distribution is a deficit of null eccentricities. There is no indication that the secondary has a special nature, like e.g. a white dwarf.

Catalogues of radial and rotational velocities of 1253 F-K dwarfs in 13 nearby open clusters

Context. We conducted a long-term monitoring of solar-type dwarfs in 13 nearby open clusters, d < 500 pc, over 19 years, but most individual radial velocities were never published, apart from a small number of spectroscopic binaries. Aims. Our program was designed to study membership and duplicity, and to search for new cluster members.

Multiplicity among peculiar A stars - I. The Ap stars HD 8441 and HD 137909, and the Am stars HD 43478 and HD 96391

We present the rst results of a radial-velocity survey of cool Ap and Am stars. HD 8441 is not only a double system with P = 106:357 days, but is a triple one, the third companion having an orbital period larger than 5000 days. Improved orbital elements are given for the classical Ap star HD 137909 = CrB by combining our radial velocities with published ones. We yield new orbital elements of the two Am, SB2 binaries HD 43478 and HD 96391. Good estimates of the individual masses of the components of HD 43478 can be given thanks to the eclipses of this system, for which an approximate pho- tometric solution is also proposed.

The Diversity of Extrasolar Planets Around Solar Type Stars

An important step in the search for an environment favorable to the development of exobiologicallife was accomplished in 1995 with the discovery by Mayor and Queloz [1] of the first extrasolar planet orbiting a star similar to the Sun, 51 Pegasi. As the proximity of the planet to the star and the large luminosity contrast between the star and the planet prevent the planet to be seen directly, its presence was inferred from the induced modulation of the observed stellar radial velocity. This method provides interesting information on the orbital characteristics of the system, although giving only access to the minimum mass of the planetary companion (projection effect due to the non-alignment of the orbital plane with the line of sight). Nevertheless, the radialvelocity technique, whose precision allows giant-planet detections, has proven since then to be very efficient. During the past 6 years an impressive series of new enthusiastic results in the domain were announced. New candidates are regularly pointed out by the teams of «planet hunters« monitoring high-precision radial velocities. Also a number of various approaches to the field are explored aiming to better understand and constrain planetary formation.

Analysis of a

CQ Lyn is a new double-lined spectroscopic binary, composed of an Am Scuti and a solar-like star, with an orbital period of 12.50736 d and a zero-eccentricity. Physical parameters of both stars are well constrained. The characteristics of the primary are the following: M = 1:714 M, Te = 6760 K, log L=L = 1:097 and logg = 3:85 dex. Power spectra of Hipparcos photometry and Coravel radial velocities show multi-period pulsation behaviour. Three frequencies are identified: f1 = 8:86725, f2 = 8:81150 and f3 = 8:91007 c/d and are assumed to be l = 2 f -modes split by rotation, considering their pulsation constants Q1= 0:0356, Q2= 0:0359 and Q3= 0:0355 d. Two combination oscillations are also present in the power spectrum at frequency f1+f2 and f2+f3.

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We report high-precision interferometric and radial velocity (RV) observations of the M-dwarf binary Gl 268. Combining measurements conducted using the IOTA interferometer and the ELODIE and Harvard Center for As- trophysics RV instruments leads to a mass of 0.22596 ± 0.00084 Mfor component A and 0.19230 ± 0.00071 M� for component B. The system parallax as determined by these observations is 0.1560 ± 0.0030 arcsec—a mea- surement with 1.9% uncertainty in excellent agreement with Hipparcos (0.1572 ± 0.0033). The absolute H-band magnitudes of the component stars are not well constrained by these measurements; however, we can place an approximate upper limit of 7.95 and 8.1 for Gl 268A and B, respectively. We test these physical parameters against the predictions of theoretical models that combine stellar evolution with high fidelity, non-gray atmospheric mod- els. Measured and predicted values are compatible within 2σ . These results are among the most precise masses measured for visual binaries and compete with the best adaptive optics and eclipsing binary results.

Scuti spectroscopic binary: CQ Lyncis

We present recent X-ray and optical observations of five M-type giants which were detected as strong X-ray sources. One of these stars, HR 5512, shows short-term variations in both X-ray flux as well as in the shape of the Hα and Ca ii H+K lines, and it rotates much faster than M-type giants usually do. No indication of binarity has been found for this star. We propose that the X-ray emission of HR 5512 is related to a large degree of stellar activity. For two other stars (15 Tri, HR 7547) radial velocity observations seem to indicate spectroscopic binarity.