Astronomy and Astrophysics, volume 368, 873-879 (2001/3-4)
Internal kinematics and binarity of X-ray stars in the Pleiades open cluster.
MAKAROV V.V. and ROBICHON N.
Abstract (from CDS):
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 (logLX>29.1, where LX is in erg/s) exhibit a velocity dispersion in one component of only 0.20km/s, while the distributions of velocity components of moderate (logLX<29.1) sources and stars not detected by ROSAT at all are consistent with a velocity dispersion of 0.64km/s. The difference is statistically significant at the level of 1.6σ, 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 >10AU).
open clusters and associations: individual: Pleiades - stars: kinematics - astrometry