3.6 and 4.5 μm Spitzer Phase Curves of the Highly Irradiated Hot Jupiters WASP-19b and HAT-P-7b

Abstract

We analyze full-orbit phase curve observations of the transiting hot Jupiters WASP-19b and HAT-P-7b at 3.6 and4.5μm, obtained using the Spitzer Space Telescope. For WASP-19b, we measure secondary eclipse depths of0.485% 0.024%and0.584% 0.029%at 3.6 and 4.5μm, which are consistent with a single blackbody with effective temperature 2372±60 K. The measured 3.6 and 4.5μm secondary eclipse depths for HAT-P-7b are0.156% 0.009%and0.190% 0.006%, which are well described by a single blackbody with effective temperature 2667±57 K. Comparing the phase curves to the predictions of one-dimensional and three-dimensional atmospheric models, we find that WASP-19b’s dayside emission is consistent with a model atmosphere with no dayside thermal inversion and moderately efficient day–night circulation. We also detect an eastward-shifted hotspot, which suggests the presence of a superrotating equatorial jet. In contrast, HAT-P-7b’sdayside emission suggests a dayside thermal inversion and relatively inefficient day–night circulation; no hotspot shift is detected. For both planets, these same models do not agree with the measured nightside emission. The discrepancies in the model-data comparisons for WASP-19b might be explained by high-altitude silicate clouds on the nightside and/or high atmospheric metallicity, while the very low 3.6μm nightside planetary brightness forHAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond albedos of 0.38±0.06 and 0(<0.08ats1)for WASP-19b and HAT-P-7b, respectively. In the context of other planets with thermal phase curve measurements, we show that WASP-19b and HAT-P-7bfit the general trend of decreasing day–night heat recirculation with increasing irradiation.