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A Possible Mechanism for Late Phase in Stellar White-Light Flares

Presentation #206.04 in the session Flare and CME Modeling and Observations.

Published onSep 18, 2023
A Possible Mechanism for Late Phase in Stellar White-Light Flares

M-dwarf flares observed by the Transiting Exoplanet Survey Satellite (TESS) sometimes exhibit a “peak-bump” light-curve morphology, characterized by a secondary, gradual peak well after the main, impulsive peak. A similar “late phase” is frequently detected in solar flares in the extreme-ultraviolet from long, hot coronal loops. White-light emission have also been observed in off-limb flare loops. Here we perform a suite of one-dimensional hydrodynamic loop simulations for M-dwarf flares inspired by these solar examples. Our results suggest that coronal plasma condensation following the impulsive flare heating can yield high electron number density in the loop, allowing it to contribute significantly to the light curves via free-bound and free-free emission mechanisms. Our simulation results qualitatively agree with the observations: the longer evolutionary time scale of coronal loops produces a distinct, secondary emission peak; its intensity increases with the input flare energy density. We argue that coronal plasma condensation is a possible mechanism for the TESS late-phase flares.

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