A plausible explanation would be that the shifts are due to distorted line profiles. Such asymetric lines are observed in dwarf novae when the disk becomes eccentric and the system shows superhumps (Warner 1995). There is evidence for such superhumps in XTE J1118+480 (see discussion in §4.3).

Constraint on the EUV flux
--------------------------

The He[ii]{} emission may be used to obtain a crude estimate of the extreme ultraviolet (EUV) flux from the source (e.g. Patterson & Raymond 1985) [ if one assumes]{} the $\lambda$4686 line stems from the recombination of He[i]{} photoionized in the disk by photons with energies between 55-280 eV. [ On the other hand, the doppler map discussed below in §3.5 shows most of the He[ii]{} emission is localized and in all likelihood associated with stream-disk interaction. In this case the $\lambda$4686 line would be pumped by collisional excitation rather than photoionization. The following estimate therefore only yields an upper limit on the EUV flux. This is still of interest since the upper limit is independent of the column density to the source.]{}

We derive from our observations $F_{\lambda4686}\approx
7\cdot10^{-14}$ erg s$^{-1}$ cm$^{-2}$ and, from the values given by Haswell et al. (2000b), $F_{\lambda1640}\approx 7\cdot10^{-13}$ erg s$^{-1}$ 