I investigate the multi-wavelength nature of stellar flares to better understand the atmospheres of potentially habitable planets
Simultaneous IR, optical, and UV flares with Early eVolution Explorer
TESS has now measured the flare rate of essentially every bright, nearby star. However, the lack of simultaneous UV observations prevents us from inferring their photochemical impacts. I am leading the development of the stellar activity science objective for the Early eVolution Explorer (EVE; PI: MacGregor), a multi-wavelength successor to TESS that will be submitted as part of JPL’s mission portfolio in response to the 2025 NASA astrophysics SMEX call. EVE will observe the first statistical flare sample from 10,000 stars of 5—100 Myr with simultaneous NUV and optical photometry to assess how the UV radiation environment impacts sub-Neptune transmission spectra and photochemically produces key biosignature species for rocky planets. Although photochemical models generally assume flares emit their energy according to a 9000 K spectrum, a trend toward higher UV—optical ratios with size has been reported. EVE will confirm if this trend extends to the highest energies where abiotic oxygen production in rocky atmospheres is underestimated by 60X relative to the 9000 K assumption
How rapidly do flares change?
Most stellar flares are observed at cadences of minutes or slower, although flares change on timescales of seconds to tens of seconds. I am PI of two NASA TESS guest observer programs to observe the first statistical sample of large flares at rapid cadence in order to resolve flares and discover clues to their emission mechanisms.
Which planets orbit flare stars?
Although more than 5000 planet candidates have been discovered by TESS, no one had carried out a systematic survey of the stellar flare rates of their host stars. I performed the first flare survey encompassing all TESS planets with short-cadence light curves to measure or place upper limits on their flare rates. I found 93 planets orbit flare stars and measures their flare frequency distributions. Surprisingly, I discovered that a fourth of terrestrial planets that will be observed with JWST transmission spectroscopy orbit flare stars.
How hot can flares get?
Superflares are a key source of biologically relevant UV radiation for rocky planets in the habitable zones of M-dwarfs, altering planetary atmospheres and conditions for surface life. The combined line and continuum flare emission has usually been approximated by a 9000 K blackbody. If superflares are hotter, then the UV emission may be 10X higher than typically predicted from the optical. Using TESS and Evryscope, I carried out the first multi-facility, multi-wavelength population study estimating superflare temperatures from the broadband optical emission of these stars. We find superflare temperatures increase with flare energy. Across the sample, 43% of the flares emit above 14,000 K, 23% emit above 20,000 K and 5% emit above 30,000 K. The largest and hottest flare briefly reached 42,000 K, suggesting the UV stellar flux reaching their planets is underestimated by an order of magnitude.
Proxima Centauri superflares and the habitability of Proxima b
A likely Earth-sized planet orbits in the habitable zone of the nearest star to our Sun. Using the Evryscope array of small telescopes in Chile, I led a team in detecting the first “superflare” seen from this star and exploring whether an Earthlike atmosphere could survive its extreme radiation.