Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b
Abstract
Transmission spectroscopy has emerged as an essential tool for characterising the atmospheres of transiting exoplanets. However, stellar surface inhomogeneities contaminate transmission spectra, posing a major challenge to high-precision observations such as those from the James Webb Space Telescope (JWST). We develop and apply methods to correct for stellar contamination, improving the accuracy of exoplanet atmospheric characterisation. We obtained coordinated multi-band photometry and high-resolution spectroscopy around JWST observations of GJ 1214 b and applied two frameworks: (i) a StarSim inversion, which infers stellar activity parameters from the monitoring data and propagates them to corrections; and (ii) UnSPOTTER, in which neural networks trained on StarSim simulations learn the mapping from monitoring data to corrections. Both frameworks agree within uncertainties and indicate that the JWST observations of GJ 1214 occurred at a favourable rotation phase with low stellar contamination. For UnSPOTTER, the inferred corrections can be constrained at approximately 15 ppm across the JWST wavelength range, implying post-correction residuals of the same order. If the same system were observed near activity maximum, the predicted contamination would be strongly chromatic and affect atmospheric retrievals, highlighting the importance of coordinated monitoring and robust activity correction techniques. The two approaches are complementary but serve different roles. The inversion yields physically interpretable parameters and surface maps, whereas UnSPOTTER marginalises over surface-configuration degeneracies and provides tighter predictive corrections within its validated simulation domain. Our pipeline can be generalised to other active stars: with multi-band and multi-technique monitoring around JWST visits, it can provide activity forecasts for scheduling and activity corrections.
Related
- High-resolution transmission spectroscopy of KELT-18b. Metastable helium detection at 1083 nm
- TSD: An Inverse Problem Approach for Recovering the Exoplanetary Atmosphere Transmission Spectrum from High-resolution Spectroscopy
- High-resolution transmission spectroscopy of KELT-18b Metastable helium detection at 1083 nm
- Model-driven Stellar Spectroscopy with the Total Differential Spectral Model ( TDSM ): Framework and Its Application to 11 Million LAMOST Low-resolution Spectra
- GA-NIFS: sRMS, a new method for disentangling resolved and unresolved emission in integral field spectroscopy. Application to distant quasars
BibTeX
@misc{porquerasleon2026correcting,
title = {{Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b}},
author = {Ò. Porqueras-León and M. Perger and J. C. Morales and I. Ribas and J. Blanco-Pozo and H. Tabernero and E. Herrero and E. Pallé and H. Parviainen and F. Murgas and C. Rodríguez-López and P. H. Hauschildt and A. Schweitzer and N. -E. Nèmec and D. Baroch and N. R. C. Gomes and G. Anglada-Escudé and J. Aceituno and N. Narita and A. Fukui and M. Mori and Y. Smolyarova},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.35721},
eprint = {2609.35721},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.35721},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b
AU - Ò. Porqueras-León
AU - M. Perger
AU - J. C. Morales
AU - I. Ribas
AU - J. Blanco-Pozo
AU - H. Tabernero
AU - E. Herrero
AU - E. Pallé
AU - H. Parviainen
AU - F. Murgas
AU - C. Rodríguez-López
AU - P. H. Hauschildt
AU - A. Schweitzer
AU - N. -E. Nèmec
AU - D. Baroch
AU - N. R. C. Gomes
AU - G. Anglada-Escudé
AU - J. Aceituno
AU - N. Narita
AU - A. Fukui
AU - M. Mori
AU - Y. Smolyarova
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.35721
UR - https://arxiv.org/abs/2609.35721
AB - Transmission spectroscopy has emerged as an essential tool for characterising the atmospheres of transiting exoplanets. However, stellar surface inhomogeneities contaminate transmission spectra, posing a major challenge to high-precision observations such as those from the James Webb Space Telescope (JWST). We develop and apply methods to correct for stellar contamination, improving the accuracy of exoplanet atmospheric characterisation. We obtained coordinated multi-band photometry and high-resolution spectroscopy around JWST observations of GJ 1214 b and applied two frameworks: (i) a StarSim inversion, which infers stellar activity parameters from the monitoring data and propagates them to corrections; and (ii) UnSPOTTER, in which neural networks trained on StarSim simulations learn the mapping from monitoring data to corrections. Both frameworks agree within uncertainties and indicate that the JWST observations of GJ 1214 occurred at a favourable rotation phase with low stellar contamination. For UnSPOTTER, the inferred corrections can be constrained at approximately 15 ppm across the JWST wavelength range, implying post-correction residuals of the same order. If the same system were observed near activity maximum, the predicted contamination would be strongly chromatic and affect atmospheric retrievals, highlighting the importance of coordinated monitoring and robust activity correction techniques. The two approaches are complementary but serve different roles. The inversion yields physically interpretable parameters and surface maps, whereas UnSPOTTER marginalises over surface-configuration degeneracies and provides tighter predictive corrections within its validated simulation domain. Our pipeline can be generalised to other active stars: with multi-band and multi-technique monitoring around JWST visits, it can provide activity forecasts for scheduling and activity corrections.
ER -