Separating Flare and Secondary Atmospheric Signals with RADYN Modeling of Near-infrared JWST Transmission Spectroscopy Observations of TRAPPIST-1

Journal article

Although TRAPPIST-1’s temperate planets have the highest transmission signals of any known system, flares contaminate 50%–70% of transits at the 1000 ppm level, far above 100 ppm secondary atmospheric signals. Efforts to mitigate flare contamination and assess impacts on radiation environments are each hampered by a lack of empirical spectral analysis and physics-based modeling. We present spectrotemporal analysis and radiative-hydrodynamic modeling of 5.5 hr of NIRISS and NIRSpec observations of six TRAPPIST-1 flares of 2.2–8.7 × 1030 erg. The flare lines and continua are characterized using grid searches of RADYN beam-heating models spanning 104 times in electron beam parameters. Best-fit models indicate these flares result from moderate-intensity beams with emergent electron fluxes of Fe = 1012 erg s−1 cm−2 and energies ≤37 keV, although all models overpredict the Paschen jump. These models predict X-ray and extreme UV (XUV), far-UV, and near-UV counterparts to the IR peak fluxes of 8.9–28.9 × 1027, 4.3–13.9 × 1026, and 3.4–11.4 × 1027 erg s−1, respectively. Scaling the flare rate into the XUV suggests flaring contributes 1.35 −0.15+2.0× quiescence yr−1. We bin integrations of similar flare effective temperature to construct fiducial flare spectra from 2000 to 4500 K, in order to develop separate empirical and RADYN-based mitigation pipelines. Both pipelines are applied to all 5.5 hr of R = 10 data, resulting in maximum residuals from 1 to 2.8 μm of 100–140 ppm and typical residuals of 54 ± 14 and 65 ± 17 ppm for the empirical and RADYN-based pipelines, respectively. Injection testing supports a 3σ detection capability for CO2 atmospheres with features of 150–250 ppm, with weak evidence (Bayes factor ≈ 3) still obtained at 130 ppm. Our results motivate multiwavelength observations to improve model fidelity and test high-energy predictions.

Authors: Howard, WS; Kowalski, AF; Radica, M; Flagg, L; Vasilyev, V

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal Letters
• Volume: 994
• Issue: 1
• Article number: L31
• Publication date: 2025-11-20
• Acceptance date: 2025-10-26
• DOI: 10.3847/2041-8213/ae1960
• EISSN: 2041-8213
• ISSN: 2041-8205
• Language: English
• Keywords: M dwarf stars; Transmission spectroscopy; Stellar flares; Planet hosting stars; Exoplanet atmospheres