MULTIFREQUENCY OBSERVATIONS OF K3-9 - A NEW RADIO-LUMINOUS SYMBIOTIC MIRA

K3-9 ranks among the most intense symbiotic radio sources, and most of those that are brighter have experienced very slow nova outbursts wit hin the last century. The intriguing combination of extreme visual fai ntness and high radio flux density led us to obtain multi-frequency co verage in order to determine physical parameters of the source. We rep ort measurements of K3-9 covering the five orders of magnitude in wave length, including the first IR, millimetre and radio data. Near-IR spe ctra and photometry clearly demonstrate that the system contains a lat e-type giant (a Mira or OH/IR star such as those found in D-type symbi otics) which is probably shrouded in a dusty circumbinary envelope. Th is reconciles the level of radio and IR emission with the visual magni tude and the high Balmer decrement. The radio spectrum is similar to t hat of other symbiotic Miras and is best represented by a single power law with spectral index alpha = 0.81 +/- 0.02; it flattens at a frequ ency of approximately 8 GHz, before steepening again beyond 90 GHz. Th is submillimetre flux excess is probably due to emission from dust (po ssibly material lost by the hot star, or by one or more symbiotic nova outbursts) and it is reminiscent of R Aqr which also has its spectral turnover hidden by dust emission. The implied dust mass is 0.01-0.15 M. for 30 < T(d) < 300 K, respectively. The ionized region in K3-9 has been slightly resolved (FWHM approximately 0.1 arcsec approximately 7 50 au) by the A configuration of the Very Large Array at 8.44 GHz and by the BnA configuration at 22.5 GHz. We have determined the systemic distance and made model-dependent estimates of the Mira's mass-loss ra te, the binary separation and the Lyman continuum luminosity.