Tidal Effects in Binaries of Various Periods

We found in the published literature the rotational velocities for 162 B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V or IV, that are in spectroscopic or visual binaries with known orbital elements. The data show that stars in binaries with periods of less than about 4 days have synchronized rotational and orbital motions. Stars in binaries with periods of more than about 500 days have the same rotational velocities as single stars. However, the primaries in binaries with periods of between 4 and 500 days have substantially smaller rotational velocities than single stars, implying that they have lost one-third to two-thirds of their angular momentum, presumably because of tidal interactions. The angular momentum losses increase with decreasing binary separations or periods and increase with increasing age or decreasing mass.