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Herschel/Hifi Measurements Of The Ortho/Para Ratio In Water Towards Sagittarius B2(M) And W31c*, Dc Lis, Nr Erickson, Et. Al.

Astronomy Department Faculty Publication Series

We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H₂¹⁶O and H₂¹⁸O in absorption towards Sagittarius B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of 2.35 ± 0.35, corresponding to a spin temperature of ~27 K, towards Sagittarius B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to …