Multiplicity of X-ray selected T Tauri stars in the Scorpius-Centaurus OB association

We report the results of a search for binarity among young stars, performed in the Scorpius-Centaurus OB association on a sample of 118 X-ray selected T Tauri stars. We use speckle interferometry and direct-imaging observatio ns to find companions in the separation range 0.13" - 6". After corrections to account for confusion with background stars and for the bias induced by the X-ray selection, we find a multiplicity (number of binaries or multipl es divided by number of systems) of (32.6 +/- 6.1) %, and a number of compa nions per system of (35.2 +/- 6.3) %. This is higher by a factor of 1.59 +/ - 0.34 compared to main-sequence stars, but slightly lower than in a sample in the Taurus-Auriga star-forming region that was selected and studied sim ilary. In Scorpius-Centaurus, we find fewer binaries with nearly equal brig htness than in Taurus-Auriga. There are significant differences between the period distributions in the two subgroups Upper Scorpius A and B: The peak of the distribution of stars in US-A is at about 10(5) days, while that of stars in US-B is around 10(6.5) days. We compared our results with the opt ical multiplicity survey of Brandner et al. (1996), whose sample contains 4 9 stars that were also observed by us, and find no infrared companions. The flux ratio distributions of close and wide binaries in our sample show no significant difference.