THE MULTIPLICITY OF T-TAURI STARS IN THE STAR-FORMING REGIONS TAURUS AURIGA AND OPHIUCHUS SCORPIUS - A 2.2 MICRON SPECKLE IMAGING SURVEY

We present the results of a magnitude limited (K < = 8.5 mag) speckle imaging survey of 69 T Tauri stars in the star forming regions Taurus- Auriga and Ophiuchus-Scorpius. Thirty-three companion stars were found with separations ranging from 0.07'' to 2.5''; nine are new detection s. This survey reveals a distinction between the classical T Tauri sta rs (CTTS) and the weak-lined T Tauri stars (WTTS) based on the binary star frequency as a function of separation: the WTTS binary star distr ibution is enhanced at the closer separations (< 50 AU) relative to th e CTTS binary star distribution. We suggest that the nearby companion stars shorten the accretion time scale in multiple star systems, there by accounting for the presence of WTTS that are coeval with many CTTS. The binary star frequency in the projected linear separation range 16 to 252 AU for T Tauri stars (60[+/- 17]%) is a factor of 4 greater th an that of the solar-type main-sequence stars (16[+/- 3]%). Given the limited separation range of this survey, the rate at which binaries ar e detected suggests that most, if not all, T Tauri stars have companio ns. We propose that the observed overabundance of companions of T Taur i stars is an evolutionary effect, in which triple and higher order T Tauri stars are disrupted by close encounters with another star or sys tem of stars.