Journal or Book Title
Astronomy and Astrophysics
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.
Lis, DC; Phillips, TG; Goldsmith, PF; Neufeld, Da; Herbst, E; Comito, C; Schilke, P; Muller, HSP; Bergin, EA; Gerin, M; Bell, TA; Emprechtinger, M; Black, JH; Blake, GA; Boulanger, F; Caux, E; Ceccarelli, C; Cernicharo, J; Coutens, A; Crockett, NR; Daniel, F; Dartois, E; De Luca, M; Dubernet, ML; Encrenaz, P; Falgarone, E; Geballe, TR; Godard, B; Giesen, TF; Goicoechea, JR; Gry, C; Gupta, H; Hennebelle, P; Hily-Blant, P; Kolos, R; Krelowski, J; Joblin, C; Johnstone, D; Kazmierczak, M; Lord, SD; Maret, S; Martin, PG; Martin-Pintado, J; Melnick, GJ; Menten, KM; Monje, R; Mookerjea, B; Morris, P; Murphy, JA; Ossenkopf, V; Pearson, JC; Perault, M; Persson, C; Plume, R; Qin, SL; Salez, M; Schlemmer, S; Schmidt, M; Sonnentrucker, P; Stutzski, J; Teyssier, D; Trappe, N; van der Tak, FFS; Vastel, C; Wang, S; Yorke, HW; Yu, S; Zmuidzinas, J; Boogert, A; Erickson, NR; Karpov, A; Kooi, J; Maiwald, FW; Schieder, R; and Zaal, P, "Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C*" (2010). Astronomy and Astrophysics. 1162.