The Rotation of Binary Systems with Evolved Components

In the present study we analyze the behavior of the rotational velocity, v sin i, for a large sample of 134 spectroscopic binary systems with a giant star component of luminosity class III, along the spectral region from middle F to middle K. The distribution of v sin i as a function of color index B-V seems to follow the same behavior as their single counterparts, with a sudden decline around G0 III. Blueward of this spectral type, namely, for binary systems with a giant F-type component, one sees a trend for a large spread in the rotational velocities, from a few to at least 40 km s-1. Along the G and K spectral regions there are a considerable number of binary systems with moderate to moderately high rotation rates. This reflects the effects of synchronization between rotation and orbital motions. These rotators have orbital periods shorter than about 250 days and circular or nearly circular orbits. Except for these synchronized systems, the large majority of binary systems with a giant component of spectral type later than G0 III are composed of slow rotators.