Benchmark Tests for Markov Chain Monte Carlo Fitting of Exoplanet Eclipse Observations

TL;DR

This paper evaluates the accuracy and biases of Markov Chain Monte Carlo methods in analyzing exoplanet eclipse light curves, highlighting challenges with systematics and proposing benchmark datasets for validation.

Contribution

It introduces a comprehensive suite of benchmark datasets for testing MCMC eclipse analysis methods and provides criteria for verifying eclipse detections.

Findings

Synthetic white-noise models recover eclipse signals within 10% accuracy for sufficiently deep signals.

Red-noise models exhibit greater biases and discrepancies in eclipse measurements.

Systematic biases and false signals can occur even with complex models in real data.

Abstract

Ground-based observations of exoplanet eclipses provide important clues to the planets' atmospheric physics, yet systematics in light curve analyses are not fully understood. It is unknown if measurements suggesting near-infrared flux densities brighter than models predict are real, or artifacts of the analysis processes. We created a large suite of model light curves, using both synthetic and real noise, and tested the common process of light curve modeling and parameter optimization with a Markov Chain Monte Carlo (MCMC) algorithm. With synthetic white-noise models, we find that input eclipse signals are generally recovered within 10% accuracy for eclipse depths greater than the noise amplitude, and to smaller depths for higher sampling rates and longer baselines. Red-noise models see greater discrepancies between input and measured eclipse signals, often biased in one direction. Finally, we find that in real data, systematic biases result even with a complex model to account for trends, and significant false eclipse signals may appear in a non-Gaussian distribution. To quantify the bias and validate an eclipse measurement, we compare both the planet-hosting star and several of its neighbors to a separately-chosen control sample of field stars. Re-examining the Rogers et al. (2009) Ks-band measurement of CoRoT-1b finds an eclipse $3190^{+370}_{-440}$ ppm deep centered at $\phi_{me}$=$0.50418^{+0.00197}_{-0.00203}$. Finally, we provide and recommend the use of selected datasets we generated as a benchmark test for eclipse modeling and analysis routines, and propose criteria to verify eclipse detections.