Detection of the X-ray-heated companion of X1822-371

We have detected the companion star in X1822 - 371 from the behaviour of the He I lambda 5876 in absorption around phase 0.5 and find a lower limit for the radial velocity of K-c > 225+/-23 km s(-1). The irradiation-induced dominant component within the He I lambda 5876 absorption profile is the only detected spectral signature of the companion star. H alpha shows a narrow double-peaked emission profile embedded in a wider absorption profile. There is no evidence of any binary motion (i.e., rotational disturbance during eclipse) probably implying a vertically extended region obscuring the inner disc. The H alpha emission distribution is centred towards the disc bulge at phase 0.8 rather than towards the compact object. Detection of Fe II lambda 6516, in the region of phase 0.8, suggests an 'iron-curtain' related to the impact region of the gas stream with supersonic velocities of Mach similar to 20 +/- 8(T/10(4) K) for the absorbing gas.