THE FREQUENCY OF T-TAURI COMPANION STARS

We present the results of a magnitude-limited (K double line arrow poi nting left 8.5 mag) multiplicity survey of T Tauri stars in two nearby star-forming regions, Taurus-Auriga and Ophiuchus-Scorpius. Each of t he 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 ima ged using two-dimensional speckle imaging techniques. Thirty-three com panion stars were found of which 15 were new detections. One of the ma in 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 mai n-sequence stars (17 +/- 3%). Given the limited angular separation ran ge 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 o verabundance of companions to T Tauri stars relative to their older co unterparts on the main sequence is an evolutionary effect; in this sch eme triple and higher order T Tauri star systems, which are observed a t higher frequencies than for the solar-type main-sequence stars, are disrupted by close encounters with another star or system of stars.