2002MNRAS.332..928H

We compare ultraviolet (UV) spectra of the recent soft X-ray transients XTE J1118+480 and XTE J1859+226. The emission line strengths in XTE J1118+480 strongly suggest that the accreting material has been CNO processed. We show that this system must have come into contact with a secondary star of about 1.5M_☉, and an orbital period ∼15h, very close to the bifurcation value at which the nuclear and angular momentum loss time-scales are similar. Subsequent evolution to the current period of 4.1h was driven by angular momentum loss. In passing through a period of 7.75h the secondary star would have shown essentially normal surface abundances. XTE J1118+480 could thus represent a slightly later evolutionary stage of A0620-00. We briefly discuss the broad Lyα absorption wings in XTE J1118+480.