[Previous] | [Session 23] | [Next]
C. Goukenleuque, B. B\'ezard, E. Lellouch (DESPA)
We have developed a radiative equilibrium model for jovian-type extrasolar planets. Opacity from H2O, CO and CH4 roto-vibrational molecular bands as well as H2-H2 and H2-He collision-induced absorption are included. The model atmosphere is limited at the bottom by an opaque silicate cloud (SiO2,MgSiO3 or Mg2SiO4). Cooling and heating rates, averaged over the whole planet, are calculated through a line-by-line multilayer radiative transfer code. Temperature profiles from 10-5 to 10 bars are derived under the assumption of level-by-level radiative equilibrium.\\ \indent Simulations are made for various masses and orbital distances of the planet, although we essentially focused on the 51 Peg system. In all cases, a major result is that the profiles do not show any stratosphere. Especially for 51 Peg B, whose mass is close to Jupiter's and which orbits its star at 0.05 AU, the temperature above the 0.1-bar level is in the range 700-1200 K. This is higher than predicted by Burrows et al's (1997) non-gray model for isolated planets, but much lower than a Jupiter-scaled model as assumed in Wiedemann's (1997) spectral calculations. Also, we find that the CO/CH4 ratio is larger than 1 at all atmospheric levels, in contrast to Burrows et al's calculations. The cloud single scattering albedos are derived from Mie theory assuming particle size in the range 1-100 \mum .\\ \indent We also synthetized emission and reflection spectra. They are mainly dominated by the water bands and show a window at 4 \mum. High resolution spectra in the methane band at 3.3 \mum and carbon monoxide band at 4.7 \mum have been calculated in order to investigate the detectability of spectral signatures from such planets.\\ \indent Finally, Bond albedos and effective temperature are calculated. In the case of 51 Peg B, \rm T\rm eff=1100-1300 K is found.