Letter to the Editor

Observations of water in comets with Odin^*

¹ Observatoire de Paris, FRE 2461 du CNRS, Place Jules Janssen, 92195 Meudon, France e-mail: [alain.lecacheux; nicolas.biver; jacques.crovisier@obspm.fr; dominique.bockelee]@obspm.fr
² ESA-ESTEC, Keplerlaan 1, 2200 AG, Noordwijk, The Netherlands
³ Noveltis, Parc Technologique du canal, 2 avenue de l'Europe, 31520 Ramonville Saint Agne, France
⁴ Onsala Space Observatory, 439 92 Onsala, Sweden
⁵ Observatoire de Paris, FRE 2460 du CNRS, 61 Av. de l'Observatoire, 75014 Paris, France
⁶ Stockholm Observatory, SCFAB-Albanova, 106 91 Stockholm, Sweden
⁷ Swedish Space Corporation, Box 4207, 171 04 Solna, Sweden
⁸ Dept. of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada
⁹ Observatory, PO Box 14, Tähtitorninmäki, University of Helsinki, 00014 Helsinki, Finland
¹⁰ Swedish National Space Board, Box 4006, 171 04 Solna, Sweden
¹¹ Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
¹² CESR, 9 Avenue du Colonel Roche, BP 4346, 31029 Toulouse, France
¹³ Canadian Space Agency, St-Hubert, Québec J3Y 8Y9, Canada

Corresponding author: J. Crovisier, jacques.crovisier@obspm.fr

Received: 29 November 2002
Accepted: 25 January 2003

Abstract

The Odin satellite, which can observe the 1₁₀–1₀₁ rotational line at 557 GHz of ortho water with a high spectral resolution (80 m s^-1) and a spatial resolution of 2.1´, is well suited for cometary studies. The intensity of this line provides an estimate of the water production rate. The line width gives a direct measure of the coma expansion velocity. The line centre position and shape are affected by the anisotropy of the outgassing and by optical depth effects. Comets observed with Odin up to now are C/2001 A2 (LINEAR) during the commissioning phase of the satellite, 19P/Borrelly at the time of the Deep Space 1 flyby, C/2000 WM₁ (LINEAR), and 153P/2002 C1 (Ikeya-Zhang). For this last comet, thorough observations were made at the moment of its closest approach to Earth at the end of April 2002. A deep integration resulted in the detection of the 1₁₀–1₀₁ line of HO at 548 GHz. No ¹⁶O/¹⁸O isotopic anomaly is found.