HII regions in symbiotic binaries and their radio emission

The slow and dense wind from a symbiotic red giant (RG) can be significantly deflected toward the orbital plane by the gravitational pull of the companion star. In such an environment, the ionizing radiation from the companion creates a highly asymmetric H II region. We present three-dimensional models of H II regions in symbiotic S-type systems, for which we calculate radio maps and radio spectra. We show that the standard assumption of spherically symmetric RG wind results in wrong shapes, sizes and spectra of ionized regions, which in turn affects the observational estimates of orbital separation and mass loss rate. A sample of radio maps and radio spectra of our models is presented and the results are discussed in relation to observational data.