FT Lupi: UBV photometry and synthetic solution

We present 1423 UBV observations of the eclipsing binary FT Lupi observed over 6yr at Bosque Alegre Station of Córdoba Observatory. A period study based on 32 photoelectric minima and on 181 previous photographic and visual minima covering a time base of 80 yr gives a period change of $$\dot P=-0.0016\text { s yr}^{-1}$$. The Wilson–Devinney analysis leads to a solution of a semi-detached configuration. The primary component is a ‘normal’ F2 V star filling its Roche lobe. The secondary one is a K5–K7 object overluminous and oversized as compared with a main-sequence star, but fractionally smaller than its lobe. A hot area on the following hemisphere of the secondary component could account for the observed asymmetries in the light curve. These facts are consistent with the Thermal Relaxation Oscillations (TRO) theory in the sense that the primary is transferring mass to the secondary component in the broken-contact phase. The conservative mass transfer as inferred from the observed $$\dot P/P\enspace\text {is}\enspace \dot M=-1.3\times10^{-7}\enspace M_\odot\text{ yr}^{-1}$$ FT Lupi may be evolving in the final stage of the B-type W UMa configuration towards a contact W UMa system, as described by the TRO theory.