The SED in the hot continuum of the symbiotic binary AR Pavonis. I. Tests with the current models

We present the spectral energy distribution (SED) in the continuum of the eclipsing symbiotic binary AR Pav between 0.12 and 3.4 microns. This revealed a high luminosity of the hot object in the binary, L(hot) = 2200(d/4.9 kpc)**2 L(Sun). We introduce a method of disentangling the total continuum spectrum into its individual components of radiation for current models of symbiotic binaries. Applying a standard ionization model we show that the configuration of AR Pav differs significantly from that typical for symbiotic binaries during their quiescent phases. The best fit of the observed SED is provided by radiation of a simple blackbody accretion disk with L(AD)=1700(d/4.9 kpc)**2 L(Sun), which is embedded in an extended hot corona with Te=40000+/-5000K and L(neb)=500 (d/4.9 kpc)**2 L(Sun). This basic configuration of the hot object explains also the observed wavelength-dependent depth and width of the eclipse profile. The standard thin disk model requires a high accretion rate dot M(acc) > 2x1E-4M(Sun)/yr onto the central star with a radius R(acc) > 2R(Sun) to balance the observed luminosity. Irrespectively to the disk model, the accretion process limits R(acc) > 0.1R(Sun) for dot M(acc) > 1.7x1E-5 M(Sun)/yr and M(acc)=0.75 - 1.0M(Sun), which precludes a white dwarf to be the accreting star. Application of models with the disk and the boundary layer shows that the far-UV spectrum is not consistent with a large amount of a hot radiation from the boundary layer.