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A. Coustenis, M. Hirtzig (LESIA, Obs. de Paris-Meudon, France), O. Lai (CFHT, Hawaii, USA and LESIA), M. Combes, E. Gendron (LESIA, Obs. de Meudon, France), Th. Fusco (ONERA/France), P. Rannou (S. A., Univ. Paris 6 - Univ. de Versailles, France), J.-P. Veran (HIA, NRC, Canada), B. Schmitt (Lab. de Planétologie de Grenoble, France), E. Bratsolis (E.N.S.T., France)
In our observations of Titan with the CFHT/PUEO adaptive optics system, besides the well-known Titan smile (or north-south asymmetry observed usually), our 1998 J2 and H2 images (of remarkable quality due to a seeing of 0.35 arcsec) showed a 10-17% brighter western than eastern limb, that we interpreted as a first detection of possible diurnal effects in Titan's atmosphere : something like a fog, observed on the morning limb, after condensation processes have enhanced in condensates the atmospheric levels between 70 and 100 km (Coustenis et al., 2001). The feature observed could not be a phase effect, because the latter was expected on the other side.
We observed Titan again in 2001, on 7-8 March and 4 December, with PUEO, using several new filters besides the narrow-band ones particularly designed for our study (J1, J2, H1, H2). Thus, with our new images we cover many more wavelengths than previously in the near-IR and in the December 2001 images, where the phase effect is small, we find again a suggestion of perhaps a morning fog visible on the Western limb of the stratospheric images FeII, J2 and Jcont. We were not able to confirm the effect more securely because the images were acquired in mediocre condictions (seeing of 0.5-1 arcsec).
The North-South asymmetry appears as previously (with the South brighter than the North) on the images sounding the lower atmosphere, but there is a suggestion of reversal on the images sounding higher atmospheric levels (such as FeII and Kcont: Coustenis et al., 2002), as predicted by seasonal effect models.
After subtracting the atmosphere from the images sounding the CH4 windows, we recover information on the surface of Titan. We find the equatorial spot to be bright again in all the filters investigated from 1 to 2 micron.
References: Coustenis et al. (2001) Icarus 154, 501-515; Coustenis et al. (2002) Paper in preparation.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.