INVESTIGATION OF THE PLEIADES CLUSTER .2. BINARY STARS IN THE F5-K0 SPECTRAL REGION

Coravel observations of 100 F5-K0 stars in the Pleiades cluster yielded 13 spectroscopic binary stars, and 11 orbits were determined. All 11 periods are shorter than 1000 days and the longest circular period is 7.05 days. One single-lined spectroscopic binary belongs to a triple system, the orbital motion of which has been detected. Based on a complete sample in the colour range 0.40 < B - V < 0.90 (88 stars), the percentage of spectroscopic binaries with P < 1000 days is 13% (11/88). The combined photometric and spectroscopic analysis showed that six among eight single-lined spectroscopic binaries are located within the "single" star sequence in the (V, B - V) diagram and cannot be detected by the photometric analysis in the UBV system. In addition, 13 photometrically analysed binaries were not detected with the radial velocity observations, but are confirmed members. The number of single:binary:triple stars is 56:30:2 . The mass ratio distribution is flat for 0.4 < q < 1.0 and does not show a peak at q almost-equal-to 1.