Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532

Abstract

We report spectroscopic observations for bright stars in the open cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial velocities by cross-correlations and determine spectral types and rotational velocities. Using 21 stars identified as certain members, we derive a mean cluster velocity of +3.4 ± 0.3 km s-1. From radial velocities and angular distances to the cluster center, we compute membership probabilities for all but two stars that are radial velocity variables. Only one out of 34 program stars is a clear kinematic nonmember. Three spectroscopic binaries and three additional possible radial velocity variables are detected among the 23 stars measured more than once. We report the star HD 96609 as a double-lined spectroscopic binary. Using the two-dimensional cross-correlation technique TODCOR developed by Zucker & Mazeh, we derive the radial velocity curves for both components and obtain the orbital parameters with errors of 0.3% and 0.7% for the projected orbital semiaxis and masses, respectively. This system is composed of two main-sequence stars in a circular orbit, with a period of 8.19 days.