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86 GHz SiO masers in Galactic Centre OH/IR stars

We present results on a search for 86.243 GHz SiO (J = 2 -- 1, v = 1) maser emission toward 67 OH/IR stars located near the Galactic Centre. We detected 32 spectral peaks, of which 28 correspond to SiO maser lines arising from the envelopes of these OH/IR stars. In OH/IR stars, we obtained an SiO maser detection rate of about 40%. We serendipitously detected two other lines from OH/IR stars at 86.18 GHz, which could be due to a CCS-molecule transition at 86.181 GHz or probably to an highly excited OH molecular transition at 86.178 GHz. The detection rate of 86 GHz maser emission is found to be about 60% for sources with The Midcourse Space Experiment (MSX) A - E < 2.5 mag; but it drops to 25% for the reddest OH/IR stars with MSX A - E > 2.5 mag. This supports the hypothesis by Messineo et al. (2002) that the SiO masers are primarily found in relatively thinner circumstellar material.