Internal kinematics and binarity of X-ray stars in the Pleiades open cluster
Copenhagen University Observatory, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
2 DASGAL, Observatoire de Paris-Meudon, bât. 11, 5 place Jansen, 92195 Meudon Cedex, France
Corresponding author: V. V. Makarov, firstname.lastname@example.org
Accepted: 10 January 2001
The classical convergent point analysis is implemented for the Pleiades stars with proper motions in the Tycho-2 Catalogue and X-ray fluxes measured by the ROSAT satellite. It is demonstrated that, with the standard astrometric errors as given in Tycho-2, strong X-ray sources in the cluster (, where LX is in erg s-1) exhibit a velocity dispersion in one component of only 0.20 km s-1, while the distributions of velocity components of moderate () sources and stars not detected by ROSAT at all are consistent with a velocity dispersion of 0.64 km s-1. The difference is statistically significant at the level of , or 0.95 confidence limit. This result is a clue to the kinematics/X-ray luminosity segregation, 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 of the member stars. The occurrence of high X-ray luminosities is found to correlate very well with visual binarity and multiplicity (separations AU).
Key words: open clusters and associations: individual: Pleiades / stars: kinematics / astrometry
© ESO, 2001