Sum of the 17 WHT spectra from 2010 after correcting for the orbital velocity. The S/N in this mean spectrum peaks at ~350, and many weak metal lines can be distinguished in addition to the Balmer lines and He i lines at 4472 and 4026 Å. The slope of the observed spectrum was corrected by dividing with an instrument response function derived from a flux standard to put it on a F_λ grid. The absolute units are arbitrary. Shifted down by 0.2 is the model fit computed with Tlusty/XTgrid. The final parameters for this model fit are given in Table 5.