# Towards robust corrections for stellar contamination in JWST exoplanet transmission spectra

**Authors:** Benjamin V. Rackham, Julien de Wit  
**arXiv:** [2303.15418](https://arxiv.org/abs/2303.15418)  
**Date:** 2023-03-27  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.15418v1/

## Key points

- Transmission spectroscopy faces challenges in characterizing exoplanet atmospheres due to stellar contamination
- Current stellar models may not reliably correct for contamination and yield an uncontaminated transmission spectrum
- Discrepancies between state-of-the-art stellar models and measured spectra can dominate the noise budget of JWST transmission spectra of planets around stars with heterogeneous photospheres
- Increased efforts towards developing model spectra of stars and their active regions in a data-driven manner are suggested, as well as empirical approaches for deriving spectra of photospheric components using observatories during atmospheric explorations
- Synthetic datasets were generated and analyzed using a retrieval approach to test the suggested approach, exploring two systems with five levels of heterogeneity in their sensitivity analysis
- Under optimistic circumstances where stellar models have sufficient fidelity, the contribution of stellar contamination to the noise budget is considerably below that of photon noise for standard transit observation setups
- Accurately characterizing exoplanet atmospheres using transmission spectroscopy requires addressing challenges related to stellar contamination
- Potential solutions include improving model spectra through data-driven methods and developing empirical approaches for deriving photospheric component spectra during observations.

## Summary

This paper discusses the challenges of using transmission spectroscopy as a characterization technique for exoplanet atmospheres, particularly in the presence of stellar contamination. The authors explore the extent to which current stellar models can be used to reliably correct for this contamination and yield an uncontaminated transmission spectrum. They find that discrepancies between state-of-the-art stellar models and measured spectra, as well as between different models themselves, can dominate the noise budget of JWST transmission spectra of planets around stars with heterogeneous photospheres. In order to address this issue, they suggest increased efforts towards developing model spectra of stars and their active regions in a data-driven manner, as well as empirical approaches for deriving spectra of photospheric components using the observatories with which atmospheric explorations are carried out. To test their approach, the authors generate synthetic datasets and analyze them using a retrieval approach for inferring constraints from simulated out-of-transit stellar spectra. They explore two systems - an Earth-sized planet around a M-dwarf star and a Jupiter-sized planet around a K-dwarf star - with five levels of heterogeneity in their sensitivity analysis. The results show that under optimistic circumstances where stellar models have sufficient fidelity, the contribution of stellar contamination to the noise budget of a transmission spectrum is considerably below that of photon noise for standard transit observation setups. Overall, this paper highlights the importance of addressing challenges related to stellar contamination in order to accurately characterize exoplanet atmospheres using transmission spectroscopy. It suggests potential solutions such as improving model spectra through data-driven methods and developing empirical approaches for deriving photospheric component spectra during observations.