Rotational Velocities in Short-Period A-Type Binaries

Although a low rotational velocity is a necessary condition for a star to have a metallicAine (Am) spectrum, is it a sufficient condition? This study of rotational velocities of stars in binaries with periods less than 5 days shows that (1) most, but not all, late A-type stars rotate synchronously, and the remainder rotate too rapidly; (2) there is an overlap in equatorial rotational velocities of normal and Am stars which indicates that a given rotational velocity is sometimes insufficient to determine whether a star should have a normal or an abnormal spectrum. The additional distinguishing parameter does not appear to be the star's age, the angle at which the star is viewed, or previous history of mass exchange, although it could be a combination of these.