New binary asteroid 809 Lundia

CCD photometry of 809 Lundia obtained between September?2005 and January?2006 at Borowiec and Pic du Midi Observatories demonstrates that this object is a synchronous binary system with an orbital period of 15.418?? 0.001?h. In this paper, we present the results of photometric observations of Lundia from two oppositions in 2005/2006 and?2007, as well as the first modelling of the system. For simplicity we assumed a fluid-like nature for each component with a modified Roche model and a triaxial ellipsoid shape in kinematic models. Our models provided similar results. Poles of the orbit in ecliptic coordinates are ? = 119 ? 2?, ? = 28 ? 4??(modified Roche) or ? = 120 ? 5?, ? = 18 ? 12?? (kinematic). Triaxial ellipsoid shape solutions and a separation between components of 15.8?km are given after taking an equivalent diameter of 9.1?km from H?= 11.8?mag and assuming an albedo of?0.4. The orbital period of the Lundia system obtained from modelling is the same as from the lightcurve analysis i.e., 15.418?? 0.001?h. The bulk density of both components is?1.64 or 1.71?? 0.01?g/cm3. The double system of Lundia probably originates from the fission process of a single body that could have been spun up by the YORP?effect. The predicted lightcurves for future oppositions are also presented.