2016MNRAS.458.1859M

The nature of the main sulphur reservoir in star-forming regions is a long standing mystery. The observed abundance of sulphur-bearing species in dense clouds is only about 0.1 per cent of the same quantity in diffuse clouds. Therefore, the main sulphur species in star-forming regions of the interstellar medium are still unknown. IRAS 16293-2422 is one of the regions where production of S-bearing species is favourable due to its conditions which allows the evaporation of ice mantles. We carried out observations in the 3 mm band towards the solar type protostar IRAS 16293-2422 with the IRAM 30 m telescope. We observed a single frequency setup with the EMIR heterodyne 3 mm receiver with an Lower Inner tuning frequency of 89.98 GHz. Several lines of the complex sulphur species CH₃SH were detected. Observed abundances are compared with simulations using the nautilus gas-grain chemical model. Modelling results suggest that CH₃SH has the constant abundance of 4 x 10^–9 (compared to H₂) for radii lower than 200 au and is mostly formed on the surfaces. Detection of CH₃SH indicates that there may be several new families of S-bearing molecules (which could form starting from CH₃SH) which have not been detected or looked for yet.