We present new , full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 µm bands using the Spitzer Space Telescope .
When combined with previous phase curve observations at 8.0 and 24 µm , these data allow us to characterize the exoplanet ’ s emission spectrum as a function of planetary longitude and to search for local variations in its vertical thermal profile and atmospheric composition .
We utilize an improved method for removing the effects of intrapixel sensitivity variations and robustly extracting phase curve signals from these data , and we calculate our best-fit parameters and uncertainties using a wavelet-based Markov Chain Monte Carlo analysis that accounts for the presence of time-correlated noise in our data .
We measure a phase curve amplitude of 0.1242 \% \pm 0.0061 \% in the 3.6 µm band and 0.0982 \% \pm 0.0089 \% in the 4.5 µm band , corresponding to brightness temperature contrasts of 503 \pm 21  K and 264 \pm 24  K , respectively .
We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium , consistent with the eastward advection of gas by an equatorial super-rotating jet .
The locations of the flux minima in our new data differ from our previous observations at 8 µm , and we present new evidence indicating that the flux minimum observed in the 8 µm is likely caused by an over-shooting effect in the 8 µm array .
We obtain improved estimates for HD 189733b ’ s dayside planet-star flux ratio of 0.1466 \% \pm 0.0040 \% in the 3.6 µm band and 0.1787 \% \pm 0.0038 \% in the 4.5 µm band , corresponding to brightness temperatures of 1328 \pm 11  K and 1192 \pm 9  K , respectively ; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet .
We compare our new dayside and nightside spectra for HDÂ 189733b to the predictions of 1D radiative transfer models from Burrows et al .
( 15 ) , and conclude that fits to this planet ’ s dayside spectrum provide a reasonably accurate estimate of the amount of energy transported to the night side .
Our 3.6 and 4.5 µm phase curves are generally in good agreement with the predictions of general circulation models for this planet from Showman et al .
( 81 ) , although we require either excess drag or slower rotation rates in order to match the locations of the measured maxima and minima in the 4.5 , 8.0 , and 24 µm bands .
We find that HD 189733b ’ s 4.5 µm nightside flux is 3.3 \sigma smaller than predicted by these models , which assume that the chemistry is in local thermal equilibrium .
We conclude that this discrepancy is best-explained by vertical mixing , which should lead to an excess of CO and correspondingly enhanced 4.5 µm absorption in this region .
This result is consistent with our constraints on the planet ’ s transmission spectrum , which also suggest excess absorption in the 4.5 µm band at the day-night terminator .