We present new dynamical parameters of the AR Pav binary system .
Our observations consist of a series of high resolution optical/NIR spectra from which we derive the radial velocity curve of the red giant as well as its rotation velocity .
Assuming co-rotation , we determine the stellar radius ( 130 R _ { \odot } ) of the red giant .
Based on this we derive the red giant ’ s luminosity and mass ( 2.0 M _ { \odot } ) as well as the distance of the system ( 4.9 kpc ) .
The binary mass function finally yields the companion ’ s mass ( 0.75 M _ { \odot } ) and the binary separation ( 1.95 AU ) .
We find that the red giant does not fill its Roche lobe .
We review the radial velocity data of Thackeray and 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 with the red giant , and that the forbidden emission lines are shifted by a quarter of a period .
The blue absorptions and the permitted emission lines are associated with the hot companion but not in a straightforward way .
The blue absorption system only tracks the hot component ’ s orbital motion whilst 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 continuum at all wavelengths .
The eclipse light curves are unusual in that they show a slow and gradual decline prior to eclipse which is followed by a sharp increase after eclipse .