FS Lupi: a contact binary in poor thermal contact

The UBV photoelectric lightcurves of the eclipsing binary FS Lupi, observed at ESO, La Silla, during 1982-1984, have been analyzed with a Roche-model-based lightcurve synthesis method. The system, alternatively classified in the past as an EA or EB system, results an A-type contact binary with a relatively large degree of overcontact (33%) and with a large difference in the temperatures of the components (1120 K), which explains the EB-type light curve. The asymmetries and the large scatter of the observed data, when investigated in terms of deviations from the (synthetic) mean light curve, show a systematic trend which has been studied with three different methods, search- ing for periodicity.