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D. Luz (Observatoire de Paris-Meudon and Lisbon Observatory, Portugal), R. Courtin, D. Gautier (Observatoire de Paris-Meudon), J.-P. Lebreton, T. Approuchaux (ESA-ESTEC), F. Ferri (Universitá di Padova), L. Lara (Instituto de Astrofísica de Andalucía, Spain), A. Kaufer (ESO), F. Hourdin (Laboratoire de Météorologie Dynamique, France)
We will report on recent efforts to characterize the zonal wind flow in Titan's stratosphere. We have used the UVES echelle spectrometer mounted at ESO's VLT-UT2 to obtain high-resolution solar spectra reflected off Titan. The purpose of the observations has been to detect the differential Doppler shift induced by the zonal wind flow in the back-scattered solar radiation from the East and West limbs of Titan. Since the wind speed should not exceed 200 m/s, an absolute detection of the shift on single solar lines is not feasible due to the limited spectral resolution of UVES. This is why we apply a retrieval scheme developed for stellar accelerometry (Connes 1985, ApSS 110, 211; Martyc et al. 1999, A&A 351, 993) which makes use of the full spectral range (~4200 to 6200 Angstroms for the red arm of the instrument) and takes into account all the lines present in the spectrum. Our results strongly suggest that the wind is prograde, which will allow to reduce the error ellipse of the Huygens probe by one half.
DL acknowledges financial support from the Portuguese Foundation for Science and Technology (grant SFRH/BPD/3630/2000) and from Observatoire de Paris.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.