A photometric study of the eclipsing symbiotic binary AR Pavonis

In this study we present and re-analyse the historical, 1889-1998, light cu rve (LC) of the eclipsing symbiotic binary AR Pav. For the first time, we s how that the timing of mid-points of eclipses observed during a quiescent p hase obeys a quadratic ephemeris, with an initial orbital period P-0 = 605. 18 d and a rate of period change (P) over dot = -3.5 +/- 0.8 x 10(-5). We determined a distance to the system of 5.8 +/- 1.5 kpc, the mass ratio o f the giant to the hot star, M-g/M-h = 0.4 +/- 0.1, the mass of the giant, M-g = 1.8 + 1/ -0.5 M-circle dot and its radius, R-g = 167 +/- 15 R-circle dot. During quiescence, the LC has characteristic features similar to those obse rved in cataclysmic variables (CVs). It can be well reproduced by a model o f a large accretion disc surrounding the hot star. However, it is probable that the geometry of the transferred material in the Roche lobe of the accr etor in AR Pav is different from that of CVs. During active phases the shape of the LC changes considerably. A complex wa ve-like variation developed as a function of the orbital phase with an ampl itude of similar to 1 mag. It is interpreted in terms of a collisionally he ated emission region located on the giant surface and arising from the hot star eruption.