Spectroscopic study of the open cluster Blanco 1

Aims. As a part of our program on binaries in open clusters, we present a spectroscopic study of the bright stars of Blanco 1 aimed at detecting and characterizing spectroscopic binaries. Methods. Forty five stars previously mentioned as cluster candidates, plus another 24 stars in a wider region around the cluster were observed repeatedly during 6 years, with a spectral resolving power 13 300. Radial velocities were measured by cross-correlations. Results. We obtained a mean cluster velocity of 6.2 ± 0.3 km s-1 and determined kinematic membership. Eleven spectroscopic binaries were detected, and orbital solutions are presented for eight of them. Six binaries are confirmed to be members of the cluster. All of them are single-lined spectroscopic systems with periods in the range 1.9-1380 days. Considering all suspected binaries, the cluster binary frequency amounts to about 50%