High-frequency SiO masers in long-period variable stars

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Abstract
Gray et al. reported the first detection of 300-GHz SiO maser emission from the v = 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 supergiant stars, showing that excitation of this line does not depend upon the presence of a close binary companion. The first detection of the SiO v = 1, 7=8−7 line and a 3σ detection of the v = 2,7 = 8−7 line towards the supergiant VY CMa are also reported. Successful simultaneous detections of the v = 1 and 2, J=5−4, 6−5 and 7−6 lines towards three sources have been made. Detections of v = 1 and 2, J=7-6 maser emission in VY CMa followed earlier unsuccessful observations of this object at 300 GHz. In R Hya, J=7−6 emission was detected in the absence of corresponding emission in J=6−5 for both v = 1 and 2 states. The presence of J=7−6 emission is almost certainly an indication of the presence of shock-heated material with a kinetic temperature above 3000 K.

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