Doppler tomography of the transient X-ray binary Centaurus X-4 in quiescence

We present ESO-NTT low resolution spectroscopy of the neutron star X-ray transient Cen X-4 in quiescence over a complete orbital cycle. Our data reveal the presence of a K3–7 V companion which contributes 63% to the 5600–6900 A flux and orbits the neutron star with a velocity semi-amplitude of K2 = 145.8 ± 1. 0k m s −1 . This, combined with a previous determination of the inclination angle and mass ratio, yields a –