Kavli Affiliate: Sara Seager
| First 5 Authors: Valeriy Vasilyev, Valeriy Vasilyev, , ,
| Summary:
TRAPPIST-1 is an M8 dwarf hosting seven known exoplanets and is currently one
of the most frequently observed targets of the James Webb Space Telescope
(JWST). However, it is notoriously active, and its surface is believed to be
covered by magnetic features that contaminate the planetary transmission
spectra. The radiative spectra of these magnetic features are needed to clean
transmission spectra, but they currently remain unknown. Here, we develop a new
approach for measuring these spectra using time-resolved JWST/NIRISS
observations. We detect a persistent post-flare enhancement in the spectral
flux of TRAPPIST-1. Our analysis rules out lingering flare decay as the cause
of the flux enhancement and, thus, points to structural changes on the stellar
surface induced by flares. We suggest that the flaring event triggers the
disappearance of (part of) a dark magnetic feature, producing a net
brightening. This suggestion is motivated by solar data: flare-induced
disappearance of magnetic features on the solar surface has been directly
detected in high spatial resolution images, and our analysis shows that this
process produces changes in solar brightness very similar to those we observe
on TRAPPIST-1. The proposed explanation for the flux enhancement enables, to
our knowledge, the first measurement of the spectrum of a magnetic feature on
an M8 dwarf. Our analysis indicates that the disappearing magnetic feature is
cooler than the TRAPPIST-1 photosphere, but by at most a few hundred kelvins.
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