  Due to their short timescale, stellar flares are a challenging target for the
most modern synoptic sky surveys. The upcoming Vera C. Rubin Legacy Survey of
Space and Time (LSST), a project designed to collect more data than any
precursor survey, is unlikely to detect flares with more than one data point in
its main survey. We developed a methodology to enable LSST studies of stellar
flares, with a focus on flare temperature and temperature evolution, which
remain poorly constrained compared to flare morphology. By leveraging the
sensitivity expected from the Rubin system, Differential Chromatic Refraction
can be used to constrain flare temperature from a single-epoch detection, which
will enable statistical studies of flare temperatures and constrain models of
the physical processes behind flare emission using the unprecedentedly high
volume of data produced by Rubin over the 10-year LSST. We model the refraction
effect as a function of the atmospheric column density, photometric filter, and
temperature of the flare, and show that flare temperatures at or above ~4,000K
can be constrained by a single g-band observation at airmass X > 1.2, given the
minimum specified requirement on single-visit relative astrometric accuracy of
LSST, and that a surprisingly large number of LSST observations is in fact
likely be conducted at X > 1.2, in spite of image quality requirements pushing
the survey to preferentially low X. Having failed to measure flare DCR in LSST
precursor surveys, we make recommendations on survey design and data products
that enable these studies in LSST and other future surveys.
