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[50.02] First detection of CO in Uranus

T. Encrenaz, E. Lellouch, P. Drossart (LESIA, Paris Observatory, F), H. Feuchtgruber (Max-Planck Inst. f. Extr. Physik, Garching, D), G. S. Orton (JPL, Pasadena, USA), S. K. Atreya (U. of Michigan, Ann Arbor, USA)

The spectrum of Uranus has been recorded between 4.6 and 5.0 microns, using the ISAAC imaging spectrometer at the VLT-UT1(ANTU) 8-m telescope of ESO. We used a 2-arcsec slit, corresponding to a resolving power of 1500. The 4.60-4.82 micron range was recorded on October 15-16, 2002, with a total integration time of 360 minutes, and the 4.77-5.00 micron range was recorded on Nov.20, 2002 with an integration time of 80 minutes.

In addition to a few H3+ emission lines, the spectrum of Uranus distinctly shows emission lines corresponding to the CO(1-0) band between P6 and R7, and also possibly to the CO(2-1) band between R0 and R4 (which almost coincide with the P6 to P2 lines of the CO(1-0) band). The relative intensity distribution of the observed CO emission is not compatible with a thermal distribution of the CO(1-0) band only, for any value of the rotational temperature, which suggests that fluorescence is probably responsible for the stratospheric emission of CO. A full modelling of the fluorescence mechanism is required before the CO stratospheric abundance can be inferred. These data provide the first evidence for the presence of CO in Uranus' atmosphere.

T.E., E.L. and P.D. acknowledge support from the Centre National de la Recherche Scientifique (CNRS).

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.