2002MNRAS.333..791Z

We present the results of our monitoring of the halo black hole soft X-ray transient (SXT) XTE J1118+480 during its decline to quiescence. The system has decayed 0.5mag from 2000 December to its present near-quiescent level at R ≃18.65 (2001 June). The ellipsoidal light curve is distorted by an additional modulation that we interpret as a superhump of P_sh=0.17049(1)d i.e. 0.3 per cent longer than the orbital period. This implies a disc precession period P_prec ∼ 52d. After correcting the average phase-folded light curve for veiling, the amplitude difference between the minima suggests that the binary inclination angle lies in the range i =71-82°. However, we urge caution in the interpretation of these values because of residual systematic contamination of the ellipsoidal light curve by the complex form of the superhump modulation. The orbital-mean Hα profiles exhibit clear velocity variations with ∼500km.s^–1 amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc.