On the kinematics of the neutron star low mass X-ray binary Cen X-4

Abstract

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 ($e\simeq 0.85\pm 0.1$) orbit with an inclination of $\simeq 110^{\circ }$ 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 $\sim$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.

arXiv comment6 pages, 4 figures, accepted for publication in A&A

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• Kinematics of Black Hole X-ray Binary GRS 1915+105
• The Radiative Efficiency of a Radiatively Inefficient Accretion Flow
• The donor of Aquila X-1 revealed by high angular resolution near-infrared spectroscopy
• Restless quiescence: thermonuclear flashes between transient X-ray outbursts
• Chemical Abundances of the Secondary Star in the Black Hole X-Ray Binary V404 Cygni
• Chemical Abundances in the Secondary Star of the Neutron Star Binary Centaurus X-4
• An Observationally-Derived Kick Distribution for Neutron Stars in Binary Systems
• Identification of twenty-three accreting binaries in the Galactic Bulge Survey
• Dynamical confirmation of a stellar-mass black hole in the transient X-ray dipping binary MAXI J1305-704
• The isotopic 6Li/7Li ratio in Cen X-4 and the origin of Li in X-ray binaries
• Chemical abundances of the secondary star in the Neutron star X-ray binary Cygnus X-2
• Constraining the inclination of the Low-Mass X-ray Binary Cen X-4
• High-resolution radio observations of X-ray binaries