Studying the variability of the He triplet to understand the detection limits of evaporating exoplanet atmospheres

TL;DR

This study investigates the variability of the helium triplet in stellar spectra to understand its impact on detecting and characterizing evaporating exoplanet atmospheres, highlighting the importance of accounting for stellar and telluric effects.

Contribution

It provides the first detailed analysis of the helium triplet's temporal variability using multi-epoch solar observations, informing future exoplanet atmospheric studies.

Findings

Significant variability observed across minutes to days.

Telluric contamination affects short-term variability.

Stellar activity influences long-term variability.

Abstract

With more than a dozen significant detections, the helium triplet has emerged as a key tracer of evaporating exoplanet atmospheres. This near-infrared feature can be observed from the ground and holds great promise, especially with upcoming observations provided by new-generation instruments such as the Near Infrared Planet Searcher (NIRPS). However, as the helium triplet is also present in stellar spectra, careful removal of the average stellar contribution is necessary to accurately characterize the atmospheres of transiting exoplanets. In this study, we analyze multi-epoch observations of the Sun obtained with NIRPS to investigate the temporal variability of the helium triplet. Our findings reveal significant variability across different timescales, ranging from minutes to days. We identify telluric contamination and stellar activity as likely sources for the short-term and long-term variability, respectively. Importantly, we demonstrate that this variability has minimal impact on the retrieval of planetary parameters crucial to the study of atmospheric escape.