A photometric study of the eclipsing symbiotic binary ARPavonis

In this study we present and re-analyse the historical, 1889-1998, light curve (LC) of the eclipsing symbiotic binary ARPav. For the first time, we show that the timing of mid-points of eclipses observed during a quiescent phase obeys a quadratic ephemeris, with an initial orbital period P₀=605.18d and a rate of period change Pdot=-3.5+/-0.8x10^-5. We determined a distance to the system of 5.8+/-1.5kpc, the mass ratio of the giant to the hot star, M_gM_h=0.4+/-0.1, the mass of the giant, M_g=1.8+1/-0.5M_solar and its radius, R_g=167+/-15R_solar. During quiescence, the LC has characteristic features similar to those observed in cataclysmic variables (CVs). It can be well reproduced by a model of 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 accretor in ARPav is different from that of CVs. During active phases the shape of the LC changes considerably. A complex wave-like variation developed as a function of the orbital phase with an amplitude of ~1mag. It is interpreted in terms of a collisionally heated emission region located on the giant surface and arising from the hot star eruption.