Repeatability of Spitzer/IRAC exoplanetary eclipses with Independent Component Analysis

TL;DR

This paper introduces a wavelet-based Independent Component Analysis method to improve the repeatability of exoplanetary eclipse measurements from Spitzer/IRAC data, demonstrating stable results over multiple observations.

Contribution

The paper presents a novel wavelet pixel-ICA technique that enhances the analysis of low-S/N Spitzer data for exoplanet eclipses, improving reproducibility and accuracy.

Findings

Consistent eclipse depth measurements within 1 sigma over three years.

Wavelet pixel-ICA extends applicability to low-S/N data.

Photometry stability at 1 part in 10^4 in stellar flux.

Abstract

The research of effective and reliable detrending methods for Spitzer data is of paramount importance for the characterization of exoplanetary atmospheres. To date, the totality of exoplanetary observations in the mid- and far-infrared, at wavelengths $>$3 $\mu$m, have been taken with Spitzer. In some cases, in the past years, repeated observations and multiple reanalyses of the same datasets led to discrepant results, raising questions about the accuracy and reproducibility of such measurements. Morello et al. 2014, 2015 proposed a blind-source separation method based on the Independent Component Analysis of pixel time series (pixel-ICA) to analyze IRAC data, obtaining coherent results when applied to repeated transit observations previously debated in the literature. Here we introduce a variant to pixel-ICA through the use of wavelet transform, wavelet pixel-ICA, which extends its applicability to low-S/N cases. We describe the method and discuss the results obtained over twelve eclipses of the exoplanet XO3b observed during the "Warm Spitzer" era in the 4.5 $\mu$m band. The final results will be reported also in Ingalls et al. (in prep.), together with results obtained with other detrending methods, and over ten synthetic eclipses that were analyzed for the "IRAC Data Challenge 2015". Our results are consistent within 1 $\sigma$ with the ones reported in Wong et al. 2014. The self-consistency of individual measurements of eclipse depth and phase curve slope over a span of more than three years proves the stability of Warm Spitzer/IRAC photometry within the error bars, at the level of 1 part in 10$^4$ in stellar flux.