Sulphur chemistry in the envelopes of massive young stars

The sulphur chemistry in nine regions in the earliest stages of high-mass star formation is studied through single- dish submillimeter spectroscopy. The line profiles indicate that 10-50% of the SO and SO2 emission arises in high-velocity gas, either infalling or outflowing. For the low-velocity gas, excitation temperatures are 25 K for H2S, 50 K for SO, H2CS, NS and HCS + , and 100 K for OCS and SO2, indicating that most observed emission traces the outer parts (T 100 K) of six sources, the SO2 abundance is enhanced by a factor of ∼100-1000. This region of hot, abundant SO2 has been seen before in infrared absorption, and must be small, 100 K) gas, sulphur-bearing molecules cannot be used as evolutionary tracers during star