3.6 AND 4.5 μm PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b

Abstract

We present new, full-orbit observations of the infrared phase variations of\nthe canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 micron bands\nusing the Spitzer Space Telescope. When combined with previous phase curve\nobservations at 8.0 and 24 micron, these data allow us to characterize the\nexoplanet's emission spectrum as a function of planetary longitude. We utilize\nimproved methods for removing the effects of intrapixel sensitivity variations\nand accounting for the presence of time-correlated noise in our data. We\nmeasure a phase curve amplitude of 0.1242% +/- 0.0061% in the 3.6 micron band\nand 0.0982% +/- 0.0089% in the 4.5 micron band. We find that the times of\nminimum and maximum flux occur several hours earlier than predicted for an\natmosphere in radiative equilibrium, consistent with the eastward advection of\ngas by an equatorial super-rotating jet. The locations of the flux minima in\nour new data differ from our previous observations at 8 micron, and we present\nnew evidence indicating that the flux minimum observed in the 8 micron is\nlikely caused by an over-shooting effect in the 8 micron array. We obtain\nimproved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466%\n+/- 0.0040% at 3.6 micron and 0.1787% +/- 0.0038% at 4.5 micron; these are the\nmost accurate secondary eclipse depths obtained to date for an extrasolar\nplanet. We compare our new dayside and nightside spectra for HD 189733b to the\npredictions of models from Burrows et al. (2008) and Showman et al. (2009). We\nfind that HD 189733b's 4.5 micron nightside flux is 3.3 sigma smaller than\npredicted by the Showman et al. models, which assume that the chemistry is in\nlocal thermal equilibrium. We conclude that this discrepancy is best-explained\nby vertical mixing, which should lead to an excess of CO and correspondingly\nenhanced 4.5 micron absorption in this region. [abridged]\n