HIGH-FREQUENCY SIO MASERS IN LONG-PERIOD VARIABLE-STARS

Gray et al. reported the first detection of 300-GHz SiO maser emission from the upsilon = 1 and 2, J = 7-6 transitions towards the symbiotic Mira system R Aquarii. We report the widespread detection of 300-GHz SiO maser emission towards long-period variable red giant and supergia nt stars, showing that excitation of this line does not depend upon th e presence of a close binary companion. The first detection of the SiO upsilon = 1, J = 8-7 line and a 3 sigma detection of the upsilon = 2, J = 8-7 line towards the supergiant VY CMa are also reported. Success ful simultaneous detections of the upsilon = 1 and 2, J = 5-4, 6-5 and 7-6 lines towards three sources have been made. Detections of upsilon = 1 and 2, J = 7-6 maser emission in VY CMa followed earlier unsucces sful observations of this object at 300 GHz. In R Hya, J = 7-6 emissio n was detected in the absence of corresponding emission in J = 6-5 for both upsilon = 1 and 2 states. The presence of J = 7-6 emission is al most certainly an indication of the presence of shock-heated material with a kinetic temperature above 3000 K.