High resolution spectroscopy of symbiotic stars VI. Orbital and stellar parameters for AR Pavonis

We present new dynamical parameters of the AR Pav binary system. Our observ ations consist of a series of high resolution optical/NIR spectra from whic h we derive the radial velocity curve of the red giant as well as its rotat ion velocity. Assuming co-rotation, we determine the stellar radius (130 R. ) of the red giant. Based on this we derive the red giant's luminosity and mass (2.0 M.) as well as the distance of the system (4.9 kpc). The binary m ass function finally yields the companion's mass (0.75 M.) and the binary s eparation (1.95 AU). We find that the red giant does not fill its Roche lob e. We review the radial velocity data of Thackeray & Hutchings (1974), and compare it with our red giant's orbit. We find that their RV curves of the blue absorption system and the permitted emission lines are in anti-phase w ith the red giant, and that the forbidden emission lines are shifted by a q uarter of a period. The blue absorptions and the permitted emission lines a re associated with the hot companion but not in a straightforward way. The blue absorption system only tracks the hot component's orbital motion whils t it is in front of the red giant, whereas at other phases line blanketing by interbinary material leads to perturbations. We finally present UV light curves based on IUE archive spectra. We clearly detect eclipses in the con tinuum at all wavelengths. The eclipse light curves are unusual in that the y show a slow and gradual decline prior to eclipse which is followed by a s harp increase after eclipse.