Rotational and radial velocities of T Tauri stars

Abstract

The authors report rotational and radial velocities for 50 T Tauri stars in the Taurus-Auriga and Orion complexes. They confirm and extend the finding of Vogel and Kuhi that most T Tauri stars are slow rotators, with rotation an order of magnitude or more below breakup velocity. About 30% of the 0.5 - 1.0 M_sun; stars in Taurus-Auriga have rotational velocities at or below the detection limit of 10 km s<SUP>-1</SUP>; half have v sin i values between 10 and 15 km s<SUP>-1</SUP>. These observed low rotation rates show that low-mass stars have lost most of the angular momentum of their parent interstellar clouds by the time they first appear optically. This substantial loss must occur either during protostellar collapse or within ≡10<SUP>5</SUP>yr after its cessation. There is no correlation between Hα emission and rotation among low-mass T Tauri stars, suggesting that T Tauri activity may not be driven by a solar-type magnetic dynamo.