Atmospheric characterization of hot Jupiters using hierarchical models of Spitzer observations

TL;DR

This paper demonstrates the effectiveness of Bayesian hierarchical models in analyzing Spitzer observations of hot Jupiters, improving the precision and consistency of atmospheric measurements across multiple datasets.

Contribution

It introduces hierarchical modeling approaches for exoplanet atmospheric data, showing improved accuracy and uncertainty estimation over traditional methods.

Findings

Hierarchical models outperform single-fit and separate-fit models in eclipse depth analysis.

Hierarchical modeling yields tighter constraints on planetary brightness temperatures.

Uncertainty estimates from hierarchical models suggest possible astrophysical variability or underestimated errors.

Abstract

The field of exoplanet atmospheric characterization is trending towards comparative studies involving many planetary systems, and using Bayesian hierarchical modelling is a natural next step. Here we demonstrate two use cases. We first use hierarchical modelling to quantify variability in repeated observations by reanalyzing a suite of ten Spitzer secondary eclipse observations of the hot Jupiter XO-3b. We compare three models: one where we fit ten separate eclipse depths, one where we use a single eclipse depth for all ten observations, and a hierarchical model. By comparing the Widely Applicable Information Criterion of each model, we show that the hierarchical model is preferred over the others. The hierarchical model yields less scatter across the suite of eclipse depths -- and higher precision on the individual eclipse depths -- than does fitting the observations separately. We find that the hierarchical eclipse depth uncertainty is larger than the uncertainties on the individual eclipse depths, which suggests either slight astrophysical variability or that single eclipse observations underestimate the true eclipse depth uncertainty. Finally, we fit a suite of published dayside brightness measurements for 37 planets using a hierarchical model of brightness temperature vs irradiation temperature. The hierarchical model gives tighter constraints on the individual brightness temperatures than the non-hierarchical model. Although we tested hierarchical modelling on Spitzer eclipse data of hot Jupiters, it is applicable to observations of smaller planets like hot neptunes and super earths, as well as for photometric and spectroscopic transit or phase curve observations.