The EvryFlare Survey: Temperature Evolution and Habitability Impacts of Superflares Observed Simultaneously by Evryscope and TESS

Ward Howard(UNC Chapel Hill)

Nov 2, 2020

Superflares (stellar flares with energy 10^33 erg or greater) may provide the dominant source of biologically-relevant UV radiation to rocky habitable-zone M-dwarf planets (M-Earths), altering planetary atmospheres and conditions for surface life. Howard will discuss results from his EvryFlare Survey, including observations of hundreds of superflares from a diverse sample of K5-M5 stars with the Evryscope all sky array of small telescopes, including superflares from Proxima Cen and the LTT 1445 system. Next, he will discuss how the combined line and continuum flare emission has usually been approximated by a 9000 K blackbody in the NUV/optical. If superflares are hotter, then the UV emission may be 10X higher than predicted from the optical. However, it is currently unknown how often and for how long M-dwarf superflares reach temperatures above 9000 K. He will present the first systematic optical exploration of the temperature evolution of dozens of M-dwarf superflares using simultaneous Evryscope and TESS observations. The EvryFlare project finds superflare temperatures increase with flare energy and the degree of impulsivity in the light curve. The project finds 43% of the superflares emit at temperatures above 14,000 K. The largest and hottest flare reached 42,000 K. During superflares, the project estimates M-Earths orbiting <200 Myr stars typically receive a top-of-atmosphere UV-C flux 2-3 orders of magnitude above the time-averaged XUV flux from Proxima Cen. Finally, Howard will discuss ongoing observations of superflares at 20 s cadence as part of his TESS Guest Observer program.

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