A multi-frequency study of symbiotic stars. I. Near-simultaneous optical and radio observations.

The relationship between optical line flux and 5 GHz radio flux is investigated for a sample of 17 northern sky symbiotic stars. Data were obtained near-simultaneously with the Manchester Echelle Spectrograph mounted on the Isaac Newton Telescope, La Palma and the Broad Band Interferometer at Jodrell Bank. Colour excesses, calculated from Balmer hydrogen line fluxes assuming Case B recombination ratios, are compared with other reddening estimates and also combined with extinction maps to provide improved distance estimates. Optical line fluxes are used in combination with radio fluxes to estimate physical parameters of these objects, including mass-loss rates. The suggestion that the ionized regions of D-type symbiotics are much more extensive than those in S-type is confirmed. This in turn strengthens the hypothesis that S-type symbiotics are more likely to be undergoing Roche-lobe overflow than their D-type counterparts.