SIMBAD references

A method is presented to model light variation caused by spots in binary systems with two spotted components. The reference light level of the binary is divided between the two components by their fractional luminosities. Spot models of the two stars were separately performed and the results combined. Spot temperatures can be determined on both components separately. We tested our method modelling light curves of BY Dra from the years 1965, 1988 and 1991. Using this method the problem of modelling the large amplitude light variation at the lowest system brightness in 1965 was solved.