On the dayside thermal emission of hot jupiters

We discuss atmosphere models of HD 209458b in light of the recent dayside flux measurement of HD 209458b's secondary eclipse by Spitzer MIPS at 24 mu m. In addition, we present a revised secondary eclipse IRTF upper limit at 2.2 mu m that places a stringent constraint on the adjacent H2O absorption band depths. These two measurements are complementary because they are both shaped by H2O absorption and because the former is on the Wien tail of the planet's thermal emission spectrum and the latter is near the thermal emission peak. A wide range of models fit the observational data, confirming our basic understanding of hot Jupiter atmospheric physics. Although a range of models are viable, some models at the hot and cold end of the plausible temperature range can be ruled out. One class of previously unconsidered hot Jupiter atmospheric models that fit the data are those with C/O greater than or similar to 1 ( as Jupiter may have), which have a significant paucity of H2O compared to solar abundance models with C/O greater than or similar to 0.5. The models indicate that HD 209458b is in a situation intermediate between pure in situ reradiation and very efficient redistribution of heat, one that will require a careful treatment of atmospheric circulation. We discuss how future wavelength- and phase-dependent observations will further constrain the atmospheric circulation regime. In the shorter term, additional planned measurements for HD 209458b, especially Spitzer IRAC photometry, should lift many of the model degeneracies. Multiwavelength IR observations constrain the atmospheric structure and circulation properties of hot Jupiters and thus open a new chapter in quantitative extrasolar planetology.