THE FREQUENCY OF T-TAURI COMPANION STARS

We present the results of a magnitude-limited (K double line arrow pointing left 8.5 mag) multiplicity survey of T Tauri stars in two nearby star-forming regions, Taurus-Auriga and Ophiuchus-Scorpius. Each of the 69 stars in the sample was observed at K (2.2 mum) with an infrared array camera on the Hale 5-m Telescope at Palomar Observatory and imaged using two-dimensional speckle imaging techniques. Thirty-three companion stars were found of which 15 were new detections. One of the main results of this survey indicates that the binary star frequency in the projected linear separation range 14 to 225 AU for T Tauri stars (59 +/- 16%) is a factor of 3.5 greater than that of the solar-type main-sequence stars (17 +/- 3%). Given the limited angular separation range of this survey, i.e., both the spectroscopic and wide binaries are missed, the rate at which binaries are detected suggests that most, if not all T Tauri stars have companions. We propose that the observed overabundance of companions to T Tauri stars relative to their older counterparts on the main sequence is an evolutionary effect; in this scheme triple and higher order T Tauri star systems, which are observed at higher frequencies than for the solar-type main-sequence stars, are disrupted by close encounters with another star or system of stars.