Influence of Stellar Flares on the Chemical Composition of Exoplanets and Spectra

TL;DR

This study investigates how stellar flares from active stars like AD Leo can alter the atmospheric chemistry and spectra of exoplanets, highlighting the importance of considering stellar activity in spectroscopic observations.

Contribution

It introduces a 1D thermo-photochemical model to simulate the impact of stellar flares on exoplanet atmospheres and spectra, providing new insights into transient atmospheric changes.

Findings

Stellar flares can significantly modify atmospheric composition during transit.

Photon flux increases affect species at pressures up to 1 bar.

Spectral variations due to flares can influence observational interpretations.

Abstract

More than 3000 exoplanets have been detected so far, and more and more spectroscopic observations of exoplanets are performed. Future instruments are eagerly awaited as they will be able to provide spectroscopic data with a greater accuracy and sensitivity than what is currently available. An important aspect to consider is temporal stellar atmospheric disturbances that can influence the planetary composition, and hence spectra, and potentially can lead to incorrect assumptions about the steady-state atmospheric composition of the planet. We focus on perturbations that come from the host star in the form of flare events that significantly increase the photon flux impingement on the exoplanet atmosphere. In some cases, and particularly for M stars, this sudden increase may last for several hours. We aim at answering the question to what extent a stellar flare is able to modify the chemical composition of the planetary atmosphere and, therefore influence the resulting spectra. We use a 1D thermo-photochemical model to study the neutral atmospheric composition of two hypothetic planets located around the star AD Leo. This active star has already been observed during a flare. We use the spectroscopic data from this flare event to simulate the evolution of the chemical composition of the atmospheres of the two hypothetic planets. We compute synthetic spectra to evaluate the implications for observations. The increase of the incoming photon flux affects the chemical abundances of some important species down to altitudes associated with an atmospheric pressure of 1 bar, that can lead to variations in planetary spectra if performed during transit.