Analysis of a high-excitation transition of SO in the Orion molecular core

Observations have been made of the 56-45 high excitation rotational transition of sulphur monoxide in the Orion -KL region. The central 4 arcmin have been mapped and single point detections have been made in six other galactic sources. Chemical kinetic models have been used to investigate the chemistry of sulfur in particular on how the SO/SO2 ratio varies as a function of sulfur depletion and on the initial C/O ratio. A link has been found between SO/SO2 and C/O and the data is consistent with a depletion of gas-phase oxygen. In the Orion plateau source, however, enhanced abundances of both SO and SO2 may be caused by an oxygen-rich molecular outflow but are certainly not explained by cold cloud chemistry or by shock chemistry. In addition, a methanol line and an unidentified line appear in the Orion data