NEW LIGHT ON UU SAGITTAE

New V- and I-band CCD photometry and medium-resolution spectroscopy ar e used to derive the masses and radii accurate to < 10 per cent for th e individual components of the eclipsing central star of the planetary nebula Abell 63 - UU Sge (M1 = 0.63 +/- 0.06 M., R1 = 0.33 +/- 0.01 R ., M2 = 0.29 +/- 0.04 M. and R2 = 0.53 +/- 0.02 R.). Emission lines fr om the secondary component and He II and N V absorption features from the primary component are used to determine the first radial velocity curves for the system. Ultraviolet and optical spectra show that the t emperature of the primary component is much larger than previously sus pected. As the techniques used are essentially model-independent, this is probably the most accurately known mass for a planetary nebula cen tral star and therefore allows meaningful comparison to be made with e volutionary tracks for these objects.