3.6 and 4.5 $\mu$m ${\it Spitzer}$ Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b

TL;DR

This study presents detailed phase curve observations of hot Jupiters WASP-19b and HAT-P-7b at 3.6 and 4.5 μm, revealing their atmospheric properties, heat circulation, and the presence or absence of thermal inversions, with implications for atmospheric modeling.

Contribution

First comprehensive phase curve analysis of WASP-19b and HAT-P-7b at these wavelengths, comparing observations with atmospheric models to understand their thermal structures and circulation patterns.

Findings

WASP-19b's emission matches a non-inverted atmosphere with efficient heat redistribution.

HAT-P-7b shows signs of a thermal inversion and less efficient heat circulation.

Discrepancies suggest high-altitude clouds or high metallicity for WASP-19b and high C/O ratio for 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 and 4.5 $\mu$m obtained using the Spitzer Space Telescope. For WASP-19b, we measure secondary eclipse depths of $0.485\%\pm 0.024\%$ and $0.584\%\pm 0.029\%$ at 3.6 and 4.5 $\mu$m, which are consistent with a single blackbody with effective temperature $2372 \pm 60$ K. The measured 3.6 and 4.5 $\mu$m secondary eclipse depths for HAT-P-7b are $0.156\%\pm 0.009\%$ and $0.190\%\pm 0.006\%$, which are well-described by a single blackbody with effective temperature $2667\pm 57$ 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, suggesting the presence of a superrotating equatorial jet. In contrast, HAT-P-7b's dayside 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 3.6 $\mu$m nightside planetary brightness for HAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond albedos of 0 ($<0.08$ at $1\sigma$) and $0.38\pm 0.06$ 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-7b fit the general trend of decreasing day-night heat recirculation with increasing irradiation.