Bibcode
González Hernández, J. I.; Rebolo, R.; Peñarrubia, J.; Casares, J.; Israelian, G.
Bibliographical reference
Astronomy and Astrophysics, Volume 435, Issue 3, June I 2005, pp.1185-1190
Advertised on:
6
2005
Journal
Citations
21
Refereed citations
18
Description
We present the first determination of the proper motion of the neutron
star low mass X-ray binary Cen X-4 measured from relative astrometry of
the secondary star using optical images at different epochs. We
determine the Galactic space velocity components of the system and find
them to be significantly different from the mean values that
characterize the kinematics of stars belonging to the halo, and the thin
and the thick disc of the Galaxy. The high metallicity of the secondary
star of the system rules out a halo origin and indicates that the system
probably originated in the Galactic disc. A statistical analysis of the
galactocentric motion revealed that this binary moves in a highly
eccentric (e≃ 0.85±0.1) orbit with an inclination of
≃110° to the Galactic plane. The large Galactic space velocity
components strongly support that a high natal kick as a result of a
supernova explosion could have propelled the system into such an orbit
from a birth place in the Galactic disc. The high Li abundance in the
secondary, comparable to that of stars in star forming regions and young
stellar clusters like the Pleiades, may suggest a relatively recent
formation of the system. Following the orbit backwards in time, we found
that the system could have been in the inner regions of the Galactic
disc ~100-200 Myr ago. The neutron star might have formed at that
moment. However, we cannot rule out the possibility that the system
formed at a much earlier time if a Li production mechanism exists in
this LMXB.