Modeling Spitzer 3.6 and 4.5 $\mu$m Eclipse Depths for the Inflated Hot Jupiter in the Evolved Binary System HD 202772

TL;DR

This study analyzes Spitzer eclipse data of the inflated Hot Jupiter HD 202772 A b, revealing its atmospheric properties and heat redistribution, and suggests follow-up with JWST for detailed characterization.

Contribution

First detailed Spitzer eclipse analysis of HD 202772 A b, providing insights into its atmospheric temperature, albedo, and heat redistribution in a binary system.

Findings

Eclipse depths of 680±68 ppm at 3.6 μm and 1081+54−53 ppm at 4.5 μm.

Day-side temperatures of approximately 2130 K and 2611 K.

Heat redistribution efficiencies indicating weak and strong day-night contrast.

Abstract

As an inflated Hot Jupiter orbiting an early-type primary star in the evolved binary HD 202772 system, HD 202772 A b's presence invites a study of how such a planet forms and evolves. As a prelude to potential atmospheric characterization with the latest generation of observatories, we present a reduction and analysis of eclipse light curve observations of HD 202772 A b acquired with the Spitzer Space Telescope using the 3.6 and 4.5 $\mu$m channels. We find eclipse depths of $680\pm68$ and $1081^{+54}_{-53}$ ppm, respectively, corresponding to day-side effective temperatures of $2130^{+102}_{-91}$ and $2611^{+46}_{-49}$ K. The corresponding Bond albedos are consistent with the distribution of albedos for Hot Jupiters observed with both Spitzer and TESS. The heat redistribution efficiencies consistent with the Bond albedo range predicted by 1-D atmospheric models in radiative-convective equilibrium are $0.71\pm0.10$ and $0.03^{+0.03}_{-0.02}$, respectively, indicating a weak day-night contrast for the former and a strong contrast for the latter. Given this, and the unique environment in which this planet resides, we recommend follow-up observations with JWST to more precisely constrain its atmospheric composition and structure, as well as its host stellar environment, to elucidate if and how the atmospheres of these close-in giants evolve with host stars in binaries past the main sequence.