Astron. Astrophys. 333, L43-L46 (1998)

Letter to the Editor

ISO observations of Uranus: The stratospheric distribution of C₂ H₂ and the eddy diffusion coefficient

Th. Encrenaz ¹, H. , Feuchtgruber ², S.K. , Atreya ³, B. , Bézard ¹, E. , Lellouch ¹, J. , Bishop ⁴, S. , Edgington ³, Th. , de , Graauw ⁵, M. , Griffin ⁶, M.F. and Kessler <sup>7

1</sup> DESPA, Observatoire de Paris, F-92195 Meudon, France
² Max-Planck-Institut für Extraterrestrische Physik, D-85748 Garching, Germany
³ The University of Michigan, Ann Arbor, MI 48109-2143, USA
⁴ Computational Physics Inc., Virginia, USA
⁵ SRON, P.O. Box 800, 9700 AV Groningen, The Netherlands
⁶ Queen Mary and Westfield College, Miles End Road, London E1 4NS, UK
⁷ ISO Science Operation Center, ESA, P.O. Box 50727, E-28080 Madrid, Spain

Received 16 February 1998 / Accepted 6 March 1998

Abstract

The infrared spectrum of Uranus has been recorded between 7 and 16.5 µm with the grating mode of the Short-Wavelength Spectrometer of ISO, with a resolving power of 1500. The 6-12 µm spectrum of Uranus has also been recorded at lower resolution (R=90) by the PHOT instrument in spectroscopic mode. The spectra show no signatures other than the C₂ H₂ band centered at 13.7 µm. From the absence of emission in the region of the CH₄ 7.7 µm band, and by fitting the C₂ H₂ data on the basis of a photochemical model, the eddy diffusion coefficient is retrieved (in the range 5 10³ -10⁴ cm² s^-1 at the homopause). This result is consistent with the values previously derived from the Voyager UV occultation experiments.

Key words: planets and satellites Uranus infrared: solar system

Send offprint requests to: Th. Encrenaz

Contents

• 1. Introduction
• 2. Observations
• 3. Modelling and interpretation
  • 3.1. The C₂ H_{2 5} emission band
  • 3.2. The CH_{4 4} emission band
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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