Schilke, P. and Comito, C. and Muller, H.S.P. and Bergin, E.A. and Herbst, E. and Lis, D.C. and Neufeld, D.A. and Phillips , T.G. and Bell, T.A. and Blake, G.A. and Cabrit, S. and Caux, E. and Ceccarelli, C. and Cernicharo, J. and Crockett, N.R. and Daniel, F. and Dubernet, M.-L. and Emprechtinger, M. and Encrenaz, P. and Falgarone, E. and Gerin, M. and Giesen, T.F. and Goicoechea, J.R. and Goldsmith, P.F. and Gupta, H. and Joblin, C. and Johnstone, D. and Langer, W.D. and Latter, W.B. and Lord, S.D. and Maret, S. and Martin, P.G. and Melnick, G.J. and Menten, K.M. and Morris, P. and Murphy, J.A. and Ossenkopf, V. and Pagini, L. and Pearson, J.C. and Perault, M. and Plume, R. and Qin, S.-L. and Salez, M. and Schlemmer, S. and Stutzki, J. and Trappe, N. and van der Tak, F.F.S. and Vastel, C. and Wang, S. and Yorke, H.W. and Yu, S. and Erickson, N. and Maiwald, F.W. and Kooi, J. and Karpov, A. and Zmuidzinas, J. and Boogert, A. and Schieder, R. and Zaal, P.
Herschel observations of ortho- and para-oxidaniumyl (H2O+)
in spiral arm clouds toward Sagittarius B2(M).
Astronomy & Astrophysics, 521 (L11).
H2O+ has been observed in its ortho- and para- states toward the massive star forming core Sgr B2(M), located close to the Galactic center. The
observations show absorption in all spiral arm clouds between the Sun and Sgr B2. The average o/p ratio of H2O+ in most velocity intervals
is 4.8, which corresponds to a nuclear spin temperature of 21 K. The relationship of this spin temperature to the formation temperature and current
physical temperature of the gas hosting H2O+ is discussed, but no firm conclusion is reached. In the velocity interval 0–60 km s−1, an ortho/para
ratio of below unity is found, but if this is due to an artifact of contamination by other species or real is not clear.
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