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Astron. Astrophys. 315, L389-L392 (1996)

First detection of the 56 img2.gifm rotational line of HD
in Saturn's atmosphere*

M.J. Griffin1, D.A. Naylor2, G.R. Davis3, P.A.R. Ade1, P.G. Oldham1, B.M. Swinyard4, D. Gautier5, E. Lellouch5, G.S. Orton6, Th. Encrenaz5, T. de Graauw7, I. Furniss8, H. Smith9, C. Armand10, M. Burgdorf10, A. Di Giorgio10, D. Ewart10, C. Gry10, K.J. King10, T. Lim10, S. Molinari10, M. Price10, S. Sidher10, A. Smith10, D. Texier10, N. Trams10, S.J. Unger4, and A. Salama11

1 Dept. of Physics, Queen Mary and Westfield College, Mile End Road, London, E1 4NS, UK
2 Dept. of Physics, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, T1K 3M4, Canada
3 Institute of Space and Atmospheric Studies, University of Saskatchewan, 116 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada
4 Rutherford Appleton Laboratory, Chilton, Didcot, Oxon., OX11 0QX, UK
5 Observatoire de Paris-Meudon, 5 Place Janssen, F-92195 Meudon Cedex, Paris, France
6 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, Ca 91109, USA
7 SRON, PO Box 800, Groningen, The Netherlands
8 Dept. of Physics and Astronomy, University College, Gower St., London, WC1E 6BT, UK
9 National Air and Space Museum, Smithsonian Institute, Lab. Astrophysics, Washington, DC 20560, USA
10 LWS Instrument Dedicated Team, P.O. Box 50727, E-28080 Madrid, Spain
11 ISO Science Operations Centre, P.O. Box 50727, E-28080 Madrid, Spain

Received 3 July 1996 / Accepted 2 August 1996

Abstract. The R(1) rotational line of HD at 56.23 microns has been detected for the first time on Saturn using the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The measurements were made using the LWS in Fabry-Perot mode in January 1996 during the ISO performance verification phase. The measured spectrum has been compared with atmospheric models to determine the img1.gif abundance ratio. The best model fit to the measured spectrum was obtained with a D/H ratio in hydrogen of img2.gif ; D/H values between img3.gif and img4.gif are however also compatible with the data. This result is intermediate between the saturnian value derived from ground-based observations of methane and its deuterated isotope, and the preliminary determination of the jovian D/H ratio measured by the mass spectrometer in the Galileo probe. The initial Saturn measurements reported here will be repeated to improve the signal-to-noise ratio, and LWS observations of HD on Jupiter, Uranus and Neptune will also be made.

Key words: planets and satellites: individual: Saturn - infrared: solar system

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

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