Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b
Year: 2026
Type: preprint
Abstract: Transmission spectroscopy is 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 10-30 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 potentially 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.
Source: arXiv (Cornell University)
Authors: Porqueras-León, Ò., Perger, M., Morales, J. C., Ribas, I., Blanco-Pozo, J., Tabernero, H., Herrero, E., Pallé, E., Parviainen, H., Murgas, F., Rodríguez-López, C., Hauschildt, P. H., Schweitzer, A., Nèmec, N. -E., Baroch, D., Gomes, N. R. C., Anglada-Escudé, G., Aceituno, J., Narita, N., Fukui, A., Mori, M., Smolyarova, Y.
Institutions: Institute of Space Sciences, Institut d'Estudis Espacials de Catalunya, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Instituto de Astrofísica de Andalucía, Universität Hamburg, Calar Alto Observatory, Komaba Institute for Science, The University of Tokyo, The University of Tokyo, Astrobiology Center, National Astronomical Observatory of Japan, Barcelona School of Economics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Ministerio de Ciencia, Innovación y Universidades, Centres de Recerca de Catalunya, European Commission, Generalitat de Catalunya, Ministerio de Ciencia e Innovación, Universitat Autònoma de Barcelona, Instituto de Astrofísica de Andalucía, Institut de Física d'Altes Energies, HORIZON EUROPE Framework Programme, Japan Society for the Promotion of Science, European Regional Development Fund, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Agencia Estatal de Investigación, Integrated Electronics Engineering Center, Binghamton University, H2020 Marie Skłodowska-Curie Actions
Awards: G1105844351, G1129048233, G1171257612, G121809054, G1272900390, G1353885700, G1381791653, G1610079134, G1622782223, G1855990336, G1858345700, G193230900, G2064873908, G223336455, G2309174360, G2462415295, G2499501003, G2579336268, G2660406951, G279363373, G3005324705, G302750986, G322776270, G3320050967, G3439265645, G3518538256, G3546882995, G3715634343, G373897614, G3772858555, G3817602061, G390761925, G410571670, G4212894969, G430777504, G451917667, G463062595, 原子炉による悪性皮膚腫瘍の選択的治療, G491712853, G5195188938, G5404395142, G5421974903, G5434874113, G5539308778, G5635532810, G5783525505, G5805502524, G5811331711, G5881647929, G5894067328, G5967599077, G617610489, G6180974586, G6217019444, G624877701, G6513613686, 農学に関する基礎的研究, G6656126374, G6731524417, G6877667232, G69051668, G717256432, G745419941, 古代説話における諸寺縁起の研究, G7805626310, G7863371703, G8118709007, G8284171658, G8497050386, G8637226926, G8920660035, G8971985624, G897484643, G929308097, G944666937, G99296377
OpenAlex ID: W7214751850