Abstract
The $J=2{-}1$ and $3{-}2$ rotational lines of the rare isotopomer C36S and the $J=5{-}4$ and $6{-}5$ transitions of Si36S were detected in the carbon star IRC+10216 (CW Leo). These are the first detections of 36S-bearing molecules in a star and the first spectroscopic detection of Si36S. From a comparison of 34S- and 36S-bearing isotopomers, the 34S/36S isotopic ratio is 107($\pm 15$). This value is comparable to values in the interstellar medium of the inner Galactic disk (115) but is smaller than the solar value of 288 (Ding et al. [CITE]). The increase of the 36S abundance relative to 34S only qualitatively follows model predictions of a low mass AGB star. Quantitative agreement of the observed 34S/36S ratio with the stellar models can be reached if the age of IRC+10216 and Galactic chemical evolution are taken into account. Other less likely possibilities are the presence of considerable inhomogeneities in the interstellar medium and either IRC+10216 or the Sun started with a peculiar 36S abundance. Other production mechanisms potentially capable of enhancing the Galactic interstellar medium are discussed. From the observed line density toward IRC+10216 and toward Galactic star forming regions, we estimate the confusion limit toward those sources.