A MULTIFREQUENCY STUDY OF SYMBIOTIC STARS .2. SUBMILLIMETER MILLIMETER OBSERVATIONS

It has been suggested that free-free emission from symbiotic stars should become optically thin at submillimetre and millimetre wavelengths. We present 0.45-2.0 mm continuum measurements for a selected sample of symbiotic stars, H2-38, HM Sagittae, V1016 Cygni, AG Pegasi and R Aquarii. These observations clearly confirm that the D-type symbiotic stars HM Sge and V1016 Cyg exhibit a spectral turnover at a wavelength of approximately 3 cm. The 1.1-2.0 min spectral indices for these sources agree well with that expected for optically thin free-free emission. Contemporaneous optical H-beta intensities are combined with submillimetre free-free flux densities to determine the extinction due to circumstellar and interstellar dust. In addition, the 0.45-0.8 mm data for HM Sge and V1016 Cyg tentatively suggest that an extra emission component may be contributing to the observed flux densities at shorter wavelengths. This may be interpreted as either cold dust emitting at a temperature of approximately 10-20 K or as emission from an optically thick, ionized stellar wind within the cavity evacuated by the last outburst. If the former interpretation is accepted then estimated dust masses (M(d) approximately 0.01 M.) suggest that this additional component may be the first evidence of material ejected during an earlier evolutionary phase of these systems.