Contact and near-contact binary systems

Reticon spectroscopy and BVRI photometry are presented for the short-period eclipsing binary system Ft Lup. Analysis of the V light curve, the radial velocity curves and the BVRI colours shows that the system comprises a normal F2 V primary component and an intrinsically variable K2-5 V secondary component whose radius is of the order of 65 per cent larger than expected for its mass. The two stars are in marginal contact, but clearly without a common convective envelope. (author)