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J.J. Fortney, W.B. Hubbard, A. Burrows, J.I. Lunine, D. Sudarsky (U Ariz), M.S. Marley (NMSU)
The transit of planet HD 209458b around its G class parent star has been observed numerous times in the past year. In order to better understand the compositional and structural properties of this planet, we have created theoretical transits, using a simple limb darkened model of radiation from the parent star, and a planetary model based on past and current work. The star and planet are both assumed to be two dimensional in this introductory study. Here we report our theoretical predictions for light curves and (as yet unobservable) images of the transit at a number of wavelengths, including 0.45, 0.65, and 2.0 \mum. Key factors affecting the amount of light passing through the atmosphere of HD 209458b, now known to be a gas giant planet, are Rayleigh scattering, refraction, and absorption. Perhaps the most interesting effect is that of flux due to an atmospheric halo of light around the planet, that begins before ingress and persists past the egress of the transit. The effect is due to Rayleigh scattering in the planet's atmosphere, and has an extreme wavelength dependence. The ``transit radius'' of the planet will be a function of the wavelength of observation and its wavelength dependence may be observationally detectable for a variety of plausible atmospheric structures. Measurement of the transit radius will help to constrain the interior and atmospheric structure and composition of HD 209458b.
Supported in part by NASA Grants NAG5-4214, NAG5-7499, NAG5-7073, NAG5-7211, NAG2-6007, NAG5-4988, and NAG5-4987, and by NSF Grant AST-96-24878.