EXTRAGALACTIC X-RAY BINARY-SYSTEMS .1. SMC X1 = SK 160

The properties of the extragalactic X-ray binary system SMC Xi-Sk 160 are discussed using constraints provided by X-ray and optical data, SMC membership and X-ray heating effects. Three different optical light curves are solved and the existence of multiple sets of solutions demonstrated. The analysis of X-ray heating properties shows that the X-ray intensity in the direction of the Earth may not be the same as the intensity in the direction of Sk 160. Variable X-ray heating can, by itself, account for the different observed optical light curves only if observational difficulties and circumstellar effects are allowed for; otherwise there may be difficulties for the ' standard ' model. An explanation is given for the different sets of system parameters found by previous authors. Even with the imposed constraints there are large uncertainties in the system parameters; formal derived quantities are: i2G 2 0 0 , 45i_ 1) © Royal Astronomical Society.