SPECKLE IMAGING MEASUREMENTS OF THE RELATIVE TANGENTIAL VELOCITIES OFTHE COMPONENTS OF T-TAURI BINARY STARS

Over a five year period, we have used speckle imaging to monitor 20 T Tauri binary stars with separations ranging from 0 '' 09 to 1 '' (13-1 40 AU). This project is aimed at detecting the relative motion of the component stars to ascertain whether or not the observed companions (1 ) are stellar in nature, as opposed to being HH objects, and (2) are g ravitationally bound to the primary stars. These observations demonstr ate that speckle imaging measurements of close binary stars' separatio ns can be made with an accuracy of a few milliarcseconds. The majority of the observed systems show significant relative velocities which (1 ) are not consistent with the motion expected for HH objects, (2) are greater than the velocity dispersion of these star-forming regions and thus are not the result of differential proper motion, and (3) are co nsistent with orbital motion. This is the first demonstration that the se systems are physically bound. Furthermore, these relative velocity measurements provide dynamical evidence that the average total mass of these T Tauri binary star systems is similar to 1.7 M(o). (C) 1995 Am erican Astronomical Society.