Internal kinematics and binarity of X-ray stars in the Pleiades open cluster

The classical convergent point analysis is implemented for the Pleiades sta rs with proper motions in the Tycho-2 Catalogue and X-ray fluxes measured b y the ROSAT satellite. It is demonstrated that, with the standard astrometr ic errors as given in Tycho-2, strong X-ray sources in the cluster (log L-X > 29.1, where L-X is in erg s(-1)) exhibit a velocity dispersion in one co mponent of only 0.20 km s(-1), while the distributions of velocity componen ts of moderate (log L-X < 29.1) sources and stars not detected by ROSAT at all are consistent with a velocity dispersion of 0.64 km s(-1). The differe nce is statistically significant at the level of 1.6<sigma>, or 0.95 confid ence limit. This result is a clue to the kinematics/X-ray luminosity segreg ation, similar to that previously discovered in the Hyades open cluster. It is discussed that the segregation may be caused by a wide spread of ages o f the member stars. The occurrence of high X-ray luminosities is found to c orrelate very well with visual binarity and multiplicity (separations > 10 AU).