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

Abstract

We have detected the companion star in X1822 -371 from the behaviour of the He I λ5876 in absorption around phase 0.5 and find a lower limit for the radial velocity of Kc > 225±23 kms-1. The irradiation-induced dominant component within the He I λ5876 absorption profile is the only detected spectral signature of the companion star. Hα 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 Hα emission distribution is centred towards the disc bulge at phase 0.8 rather than towards the compact object. Detection of Fe II λ6516, 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 ∼20 ±8(T/104 K) for the absorbing gas. © 1997 RAS.