2002MNRAS.334..233T

We present high- and intermediate-resolution spectroscopy of the X-ray nova Centaurus X-4 during its quiescent phase. Our analysis of the absorption features supports a K3-K5 V spectral classification for the companion star, which contributes ≃75 per cent of the total flux at Hα. Using the high-resolution spectra we have measured the rotational broadening of the secondary star to be v sini =43±6km.s^–1 and determined a binary mass ratio of q =0.17±0.06. Combining our results for K₂ and q with the published limits for the binary inclination, we constrain the mass of the compact object and the secondary star to the ranges 0.49<M₁<2.49M_☉ and 0.04<M₂<0.58M_☉. A Doppler image of the Hα line shows emission coming from the secondary star, but no hotspot is present. We discuss the possible origins of this emission.