Star Formation Environments and the Distribution of Binary Separations

We have carried out K-band speckle observations of a sample of 114 X-rayselected weak-line T Tauri stars in the nearby Scorpius-Centaurus OBassociation. We find that for binary T Tauri stars closely associated to theearly type stars in Upper Scorpius, the youngest subgroup of the OBassociation, the peak in the distribution of binary separations is at 90 A.U.For binary T Tauri stars located in the direction of an older subgroup, but notclosely associated to early type stars, the peak in the distribution is at 215A.U. A Kolmogorov-Smirnov test indicates that the two binary populations do notresult from the same distibution at a significance level of 98%. Apparently,the same physical conditions which facilitate the formation of massive starsalso facilitate the formation of closer binaries among low-mass stars, whereasphysical conditions unfavorable for the formation of massive stars lead to theformation of wider binaries among low-mass stars. The outcome of the binaryformation process might be related to the internal turbulence and the angularmomentum of molecular cloud cores, magnetic field, the initial temperaturewithin a cloud, or - most likely - a combination of all of these. We concludethat the distribution of binary separations is not a universal quantity, andthat the broad distribution of binary separations observed among main-sequencestars can be explained by a superposition of more peaked binary distributionsresulting from various star forming environments. The overall binary frequencyamong pre-main-sequence stars in individual star forming regions is notnecessarily higher than among main-sequence stars.