Optical Studies of the X-ray Transient Xte J2123–058 – Ii. Phase Resolved Spectroscopy

We present time-resolved spectroscopy of the soft X-ray transient XTEJ2123–058 in outburst. A useful spectral coverage of 3700–6700Å was achieved spanning two orbits of the binary, with single epoch coverage extending to ∼ 9000 Å. The optical spectrum approximates a steep blue power-law, consistent with emission on the Rayleigh-Jeans tail of a hot black body spectrum. The strongest spectral lines are He ii 4686 Å and C iii/N iii 4640 Å (Bowen blend) in emission. Their relative strengths suggest that XTEJ2123–058 was formed in the Galactic plane, not in the halo. Other weak emission lines of He ii and C iv are present and Balmer lines show a complex structure, blended with He ii. He ii 4686 Å profiles show a complex multiple S-wave structure with the strongest component appearing at low velocities in the lower-left quadrant of a Doppler tomogram. Hα shows transient absorption between phases 0.35–0.55. Both of these effects appear to be analogous to similar behaviour in SW Sex type cataclysmic variables. We therefore consider whether the spectral line behaviour of XTEJ2123–058 can be explained by the same models invoked for those systems.