STAR-FORMATION ENVIRONMENTS AND THE DISTRIBUTION OF BINARY SEPARATIONS

We have carried out K-band speckle observations of a sample of 114 X-r ay-selected weak-line T Tauri stars in the nearby Scorpius-Centaurus O B association. We find that for binary T Tauri stars closely associate d with the early-type stars in Upper Scorpius, which is the youngest s ubgroup of the OB association, the peak in the distribution of binary separations is at 90 AU. For binary T:T Tauri stars located in the dir ection of an older subgroup but not closely associated with early-type stars, the peak in the distribution is at 215 AU. A Kolmogorov Smirno v test indicates at a significance level of 98% that the two binary po pulations do not result from the same distribution. Apparently, the sa me physical conditions that facilitate the formation of massive stars also facilitate the formation of closer binaries among low-mass stars, whereas physical conditions unfavorable for the formation of massive stars lead to the formation of wider binaries among low-mass stars. Th e outcome of the binary formation process might be related to the inte rnal turbulence and the angular momentum of molecular cloud cores, to the magnetic field, to the initial temperature within a cloud, or-most likely-to a combination of all of these. We conclude that the distrib ution of binary separations is not a universal quantity and that the b road distribution of binary separations observed among main-sequence s tars can be explained by a superposition of more peaked binary distrib utions resulting from various star-forming environments. The overall b inary frequency among pre-main-sequence stars in individual star-formi ng regions is not necessarily higher than that among main-sequence sta rs.