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Harvard ADS: Characterizing the Near-infrared Spectra of Flares from TRAPPIST-1 During JWST Transit Spectroscopy Observations

Paper abstract: We present the first analysis of JWST near-infrared spectroscopy of stellar flares from TRAPPIST-1 during transits of rocky exoplanets. Four flares were observed from 0.6--2.8 \mum with NIRISS and 0.6--3.5 \mum with NIRSpec during transits of TRAPPIST-1b, f, and g. We discover P\alpha and Br\beta line emission and characterize flare continuum at wavelengths from 1--3.5 \mum for the first time. Observed lines include H\alpha, P\alpha-P\epsilon, Br\beta, He I \lambda0.7062\mum, two Ca II infrared triplet (IRT) lines, and the He I IRT. We observe a reversed Paschen decrement from P\alpha-P\gamma alongside changes in the light curve shapes of these lines. The continuum of all four flares is well-described by blackbody emission with an effective temperature below 5300 K, lower than temperatures typically observed at optical wavelengths. The 0.6--1 \mum spectra were convolved with the TESS response, enabling us to measure the flare rate of TRAPPIST-1 in the TESS bandpass. We find flares of 10^{30} erg large enough to impact transit spectra occur at a rate of 3.6\substack{+2.1 \\ -1.3} flare d^{-1}, ~10\times higher than previous predictions from K2. We measure the amount of flare contamination at 2 \mum for the TRAPPIST-1b and f transits to be 500\pm450 and 2100\pm400 ppm, respectively. We find up to 80% of flare contamination can be removed, with mitigation most effective from 1.0--2.4 \mum. These results suggest transits affected by flares may still be useful for atmospheric characterization efforts.