Interstellar ${}^{36}$S: a probe of s-process nucleosynthesis

The first detection of a ${}^{36}$S-bearing molecule in interstellar space is reported. The $J$=$2-1$ and $3-2$ transitions of C${}^{36}$S have been observed toward eight Galactic molecular hot cores. From a comparison with other optically thin isotopic species of CS, the abundance ratio of ${}^{34}$S/${}^{36}$S is 115$(\pm 17)$. This is smaller than the solar system ratio of 200 and supports the idea that ${}^{36}$S is, unlike the other stable sulfur isotopes, a purely secondary nucleus that is produced by s-process nucleosynthesis in massive stars.