# Forecasting the Impact of Stellar Activity on Transiting Exoplanet Spectra

## TL;DR

This paper presents a method to correct for stellar activity effects in multi-epoch exoplanet transit spectra, demonstrating that such activity minimally impacts infrared observations of most TESS targets with current and upcoming telescopes.

## Contribution

The authors develop an analytical approach to quantify and correct stellar activity effects in multi-epoch exoplanet spectra, improving the accuracy of atmospheric characterization.

## Key findings

- Stellar activity has limited impact on infrared transit observations of most TESS targets.
- The method effectively characterizes stellar variability using out-of-transit spectral data.
- Predicted JWST transit precisions are sufficient to mitigate stellar activity effects.

## Abstract

Exoplanet host star activity, in the form of unocculted star spots or faculae, alters the observed transmission and emission spectra of the exoplanet. This effect can be exacerbated when combining data from different epochs if the stellar photosphere varies between observations due to activity. redHere we present a method to characterize and correct for relative changes due to stellar activity by exploiting multi-epoch ($\ge$2 visits/transits) observations to place them in a consistent reference frame. Using measurements from portions of the planet's orbit where negligible planet transmission or emission can be assumed, we determine changes to the stellar spectral amplitude. With the analytical methods described here, we predict the impact of stellar variability on transit observations. Supplementing these forecasts with Kepler-measured stellar variabilities for F-, G-, K-, and M-dwarfs, and predicted transit precisions by JWST's NIRISS, NIRCam, and MIRI, we conclude that stellar activity does not impact infrared transiting exoplanet observations of most presently-known or predicted TESS targets by current or near-future platforms, such as JWST.