Normalised spectrum of 4U 1812−12 after subtraction of the nebular contribution (i.e. using the B-labelled regions from Fig. 1 for background correction). The red vertical lines indicate the position of Hα (solid) and several He emission lines (dashed). The vertical dotted blue lines indicate the approximate location of C and O blends detected in some ultra-compact systems (Nelemans et al. 2004). The grey-shaded bands indicate the spectral regions affected by interstellar or telluric features.