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 as 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.Comment: 31 pages, 15 figures, A&A accepte

KINEMATICS OF DISK STARS IN THE SOLAR NEIGHBOURHOOD A.E. G'omez

Using Hipparcos parallaxes and proper motions together with radial velocity complementary data (Coravel for late type stars and new ground-based data for early type stars) for several thousand B-F type stars, the velocity ellipsoid has been determined as a function of age. The variations with age of the ratio of the velocity dispersions, of the vertex deviation and the age-velocity dispersion relation (AVR) have been estimated. Our results confirm that mixing is not complete at about 0:8 \Gamma 1 Gyr. The shape of the velocity ellipsoid changes with time, getting rounder from oe U /oe V /oe W = 1=0:63=0:42 \Sigma 0:04 at about 1 Gyr to 1=0:7=0:62 \Sigma 0:04 at 4 \Gamma 5 Gyr. The AVR rises to a maximum, thereafter remaining roughly constant; there is no dynamically significant evolution of the disk after about 4 \Gamma 5 Gyr. The velocity dispersion in the direction perpendicular to the galactic plane saturates at about 15 \Gamma 17 km s \Gamma1 for thin disk stars. The vertex devi..

New CORAVEL spectroscopic-binary orbits of giant barium stars. II

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