The Influence of Atmospheric Dynamics on the Infrared Spectra and Light Curves of Hot Jupiters

We explore the infrared spectrum of a three-dimensional dynamical model ofplanet HD209458b as a function of orbital phase. The dynamical model predictsday-side atmospheric pressure-temperature profiles that are much moreisothermal at pressures less than 1 bar than one-dimensionalradiative-convective models have found. The resulting day-side thermal spectraare very similar to a blackbody, and only weak water absorption features areseen at short wavelengths. The dayside emission is consequently insignificantly better agreement with ground-based and space-based secondaryeclipse data than any previous models, which predict strong flux peaks and deepabsorption features. At other orbital phases, absorption due to carbon monoxideand methane is also predicted. We compute the spectra under two treatments ofatmospheric chemistry: one uses the predictions of equilibrium chemistry, andthe other uses non-equilibrium chemistry, which ties the timescales of methaneand carbon monoxide chemistry to dynamical timescales. As a function of orbitalphase, we predict planet-to-star flux ratios for standard infrared bands andall Spitzer Space Telescope bands. In Spitzer bands, we predict 2-fold to15-fold variation in planetary flux as a function of orbital phase withequilibrium chemistry, and 2-fold to 4-fold variation with non-equilibriumchemistry. Variation is generally more pronounced in bands from 3-10 $\mu$mthan at longer wavelengths. The orbital phase of maximum thermal emission ininfrared bands is 15--45 orbital degrees before the time of secondary eclipse.Changes in flux as a function of orbital phase for HD209458b should beobservable with Spitzer, given the previously acheived observational errorbars.Comment: Accepted to the Astrophysical Journal, 8/10/06. Includes 5 color figure