Irradiation of the secondary star in X-ray Nova Scorpii 1994 (=GRO J1655-40)

We have obtained intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in 1996 June, when the source was in an X-ray/optic al active state (R similar to 15.05). We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of 279 +/- 10 km s(-1); a value which is 30 per cent larger than the value obtained when the source is in quiescence. Our large value for K-2 is consistent with 60(-7)(+9) per cent of the secondary star's surface being heated, compared with 35 per ce nt, which is what one would expect if only the inner face of the secondary star were irradiated. Effects such as irradiation-induced flows on the seco ndary star may be important in explaining the observed large value for K-2.