SiS maser emission from IRC + 10 deg 216

IRC + 10 deg 216 (CW Leo, GL 1381), a late-type carbon star, is one of the brightest objects in the sky at 5 microns. Its distance is estimated to be between 200 and 300 pc, and its circumstellar envelope allows detection of many molecules typical of a carbon-rich environment. SiS was found for the first time by Morris et al. (1975) in the circumstellar envelope. With the objective to obtain much better data, observations were conducted of the J equals 1 to 0 transition of SiS with a 43 m telescope. For the first time a strong molecular maser was detected in the envelope of a late-type carbon star. The SiS J equals 1 to 0 profile shows spikes of different intensity at the redshifted and blueshifted sides of the profile. It is proposed that the J equals 1 to 0 line is inverted. The SiS maser emission mechanism is comparable to the process of OH maser emission in late-type stars.