Herschel observations of EXtra-Ordinary Sources (HEXOS): Observations of H2O and its isotopologues towards Orion KL

• Published in: Astronomy and astrophysics (Berlin) 2010-10, Vol.521
• Main Authors: Melnick, G. J., Tolls, V., Neufeld, D. A., Bergin, E. A., Phillips, T. G., Wang, S., Crockett, N. R., Bell, T. A., Blake, G. A., Cabrit, S., Caux, E., Ceccarelli, C., Cernicharo, J., Comito, C., Daniel, F., Dubernet, M.-L., Emprechtinger, M., Encrenaz, P., Falgarone, E., Gerin, M., Giesen, T. F., Goicoechea, J. R., Goldsmith, P. F., Herbst, E., Joblin, C., Johnstone, D., Langer, W. D., Latter, W. D., Lis, D. C., Lord, S. D., Maret, S., Martin, P. G., Menten, K. M., Morris, P., Müller, H. S. P., Murphy, J. A., Ossenkopf, V., Pagani, L., Pearson, J. C., Pérault, M., Plume, R., Qin, S.-L., Salez, M., Schilke, P., Schlemmer, S., Stutzki, J., Trappe, N., van der Tak, F. F. S., Vastel, C., Yorke, H. W., Yu, S., Zmuidzinas, J.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; ISM: abundances; ISM: molecules
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201015085

We report the detection of more than 48 velocity-resolved ground rotational state transitions of H216O, H218O, and H217O – most for the first time – in both emission and absorption toward Orion KL using Herschel/HIFI. We show that a simple fit, constrained to match the known emission and absorption components along the line of sight, is in excellent agreement with the spectral profiles of all the water lines. Using the measured H218O line fluxes, which are less affected by line opacity than their H216O counterparts, and an escape probability method, the column densities of H218O associated with each emission component are derived. We infer total water abundances of 7.4 × 10-5, 1.0 × 10-5, and 1.6 × 10-5 for the plateau, hot core, and extended warm gas, respectively. In the case of the plateau, this value is consistent with previous measures of the Orion-KL water abundance as well as those of other molecular outflows. In the case of the hot core and extended warm gas, these values are somewhat higher than water abundances derived for other quiescent clouds, suggesting that these regions are likely experiencing enhanced water-ice sublimation from (and reduced freeze-out onto) grain surfaces due to the warmer dust in these sources.