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 have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust. © 2010 ESO.
CITATION STYLE
Lis, D. C., Phillips, T. G., Goldsmith, P. F., Neufeld, D. A., Herbst, E., Comito, C., … Zaal, P. (2010). Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C. Astronomy and Astrophysics, 521(1). https://doi.org/10.1051/0004-6361/201015072
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