Investigation of the Praesepe cluster - III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars

Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24 spectroscopic binaries (3 are non-members), and 20 orbits were determined, with periods from 4 to 7400 days. Based on a complete sample in the colour range 0.40 less than or equal to B - V greater than or equal to 0.80 (80 st ars, including KW 244 = TX Cnc), the companion star fraction CSF = 0.45. Th e percentage of spectroscopic binaries with P < 1000.(d) is 20% (16/80). Th e combined photometric and spectroscopic analysis showed that 12 among is s ingle-lined spectroscopic binaries are located within the "single" star seq uence in the (V, B - V) diagram and cannot be detected by the photometric a nalysis in the UBV system. In addition, seven photometrically analysed bina ries were not detected with the radial velocity observations, but are confi rmed members. The number of single:binary:triple stars is 47:30:3.