EDP Sciences
Free Access
Volume 395, Number 2, November IV 2002
Page(s) 657 - 662
Section Diffuse matter in space
DOI https://doi.org/10.1051/0004-6361:20021303
Published online 14 November 2002

A&A 395, 657-662 (2002)
DOI: 10.1051/0004-6361:20021303

Comparing SWAS and ISO observations of water in outflows

M. Benedettini1, S. Viti2, T. Giannini3, B. Nisini3, P. F. Goldsmith4 and P. Saraceno1

1  CNR-Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via del Fosso del Cavaliere 100, 00133 Roma, Italy
2  Department of Physics and Astronomy, UCL, Gower St., London WC1E 6BT, UK
3  INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio, Italy
4  National Astronomy and Ionosphere Center, Department of Astronomy, Cornell University, Space Sciences Building, Ithaca, NY 14853-6801, USA

(Received 24 April 2002 / Accepted 27 August 2002)

We present a detailed comparison of SWAS and ISO observations of H 2O emission in a sample of outflows. By taking into consideration the different methods used to derive the fractional water abundance, we find that, despite the initial apparent discrepancies, there is satisfactory agreement between ISO and SWAS results for the outflows observed by both satellites. Such an agreement is reached by assuming that most of the detected water comes from a single region smaller than both the ISO and SWAS beam apertures and considering temperatures higher ( T > 100 K) and density lower ( n(H 2)  < 2  $\times$ 10 6 cm -3) than previously adopted. The ratio between the integrated flux of the ortho-H 2O 2 12-1 01 line at 179.5  $\mu$m observed by ISO and the fundamental ortho-H 2O 1 10-1 01 line at 538.3  $\mu$m observed by SWAS is always smaller (never by more than a factor of 7) than the expected ratio. We propose that the fundamental ortho-H 2O transition has a contribution from a cooler gas component to which SWAS is sensitive but which is not traced by ISO. We conclude that, while ISO and SWAS observations are consistent with chemical models predicting a significant enhancement of water vapor abundance in outflow regions, the explanation for the low water abundance derived from SWAS observations of the cold ISM is still unclear.

Key words: ISM: jets and outflows -- ISM: abundances -- ISM: molecules

Offprint request: M. Benedettini, milena@ifsi.rm.cnr.it

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