On the radio spectrum of CI Cygni: a test of popular models for symbiotic stars

We have determined the spectral energy distribution at wavelengths between 6 cm and 850 mum for the prototypical S(stellar)-type symbiotic star, CI Cy gni, during quiescence. Data were obtained simultaneously with the Very Lar ge Array and the SCUBA submillimetre (sub-mm) camera on the James Clerk Max well Telescope. The data have allowed us to determine the free-free turnove r frequency of the ionized component, facilitating a model-dependent estima te of the binary separation to compare with the known orbital parameters of CI Cyg and to critically test the known models for radio emission from sym biotic stars. In particular, our data rule out the two most popular models: ionization of the giant wind by Lyman continuum photons from its hot compa nion, and emission resulting from the interaction of winds from the two bin ary components.