DETECTION OF (SIO)-SI-29 NU=3 J=8-]7 MASER EMISSION - A NEW IR SIO OVERLAP

We have performed detailed radiative transfer calculations which show that, in circumstellar envelopes of late-type stars, some submillimete r rotational transitions of (SiO)-Si-29 and (SiO)-Si-30 can be inverte d with amplification high enough to be detected. The pumping mechanism is due to overlaps between re-vibrational lines of the three stable S iO isotopomers. We present the detection of one of these lines, the v= 3 J=8-7 transition of (SiO)-Si-29, in four circumstellar sources. This is the highest frequency SiO maser detected up to date, and provides a strong confirmation of infrared SiO overlaps as efficient pumping ag ents of SiO masers.