The First Measurement of an M Dwarf Flare Temperature Profile using Single-band Photometry

Differential chromatic refraction (DCR) manifests as a wavelength dependent shift in source position
towards the zenith of an observer, and must be corrected for in terrestrial surveys to ensure accurate
astrometric solutions. Despite this, DCR can also be employed as a tool to extract additional color
information from astrometry. M dwarf flares are particularly well suited to this technique due to their
ubiquity across various regions of the sky, and the dramatic contrast between the red photosphere and
blue flare emission. While flares are challenging targets for sky surveys due to their short durations,
DCR can be used to infer color temperatures across the unprecedentedly large sample of flares that
will be detected in next-generation astronomical surveys, such as the Legacy Survey of Space and Time
(LSST) that will be carried out by the Vera C. Rubin Observatory, starting in 2025. By combining
Rubin’s high image quality and astrometric precision with the truly massive amount of data it will pro-
duce over 10 years, DCR can be used to carry out a population-level statistical analysis of stellar flare
temperatures, constraining models of energy release in stellar atmospheres and informing habitability
surveys. We additionally validated this technique on flare data obtained from an LSST precursor, the
Deeper, Wider, Faster Programme, and showed how certain choices made when modeling the spectral
and geometric properties of the flare could lead to overestimating the true flare temperature.