Constraints on Post-Superflare Exo-Auroral Emission with SOAR and the Evryscope Fast Transient Engine

Many habitable-zone rocky planets are hosted by M-dwarf stars, which are known for their small sizes, tepid temperatures, and frequent flaring. An Earthlike planet impacted by a superflare—a flare with energy of 10³³ erg or greater—could expect a combination of high-energy photon and particle flux sufficient to destroy atmospheric ozone in extreme cases. A superflare’s effect on an Earthlike atmosphere can also include auroral excitation, making possible the direct detection of the planet’s atmosphere. Prior work has demonstrated that Earthlike atmospheres can produce excess emission in M-dwarf spectra, with the star/planet contrast ratio increasing by orders of magnitude in the green 5577-Å auroral line as well as others in the ultraviolet, to levels potentially detectable by future surveys. The key to placing limits on auroral emission from impacted planets is real-time spectroscopic observation, which requires identifying superflares in their early stages. The Evryscopes are gigapixel-scale telescope arrays at Mount Laguna Observatory and Cerro-Tololo Inter-American Observatory; couple with the Evryscope Fast Transient Engine (EFTE), which scans Evryscope images in real time for transient phenomena, the systems have the unprecedented ability to identify superflares across the entire sky as they begin and flag them for immediate spectroscopic observation. With the Evryscopes’ all-sky coverage, far more—and far brighter—flares are observable than in surveys that focus on individual targets. Using the Goodman spectrograph on the 4.1-m SOAR telescope, we follow the spectroscopic evolution of M-dwarf superflares as they happen, and build a pathfinder survey to constrain upper limits on possible auroral emission from impacted planets. We present our survey and initial findings here.