Frequent X-class Far-ultraviolet Flares from the Young Solar Analog DS Tucanae A

Abstract The young solar analog DS Tuc A (∼45 million yr old, spectral type G6V) serves as an excellent proxy to the Sun during early stages of the Earth’s evolution. The young Sun’s enhanced magnetic activity in the form of X-ray and extreme UV emission, stellar wind, and flares likely affected the magnetospheric and atmospheric environments of early Venus, Earth, and Mars. Studies of DS Tuc A help constrain the evolution of the magnetospheric and atmospheric environments of early Venus, Earth, and Mars and create opportunities to study the impact of flares on the transiting exoplanet, DS Tuc A b. We analyze ∼11 hr of far-ultraviolet (FUV; 1130–1450 Å) observations taken by the Hubble Space Telescope Cosmic Origins Spectrograph during late 2023 and early 2024. We find that DS Tuc A exhibited 26 flares over ∼11.1 hr of observations in the transition region lines Si IV (1394 Å + 1402 Å), with durations ranging from 90 to 960 s and FUV absolute energies ranging from ∼10 29 to 10 31 erg over the observed bandpass. Si IV flares are accompanied by increases of other chromospheric and transition region lines; however, the strongest Si IV flares show no enhanced coronal emission traced by Fe XXI 1354 Å. We present an analysis of each detected flare, including X-ray and bolometric luminosities scaled from FUV flare energies, electron density measurements for the strongest flares, and the FUV continuum response to flaring. These results provide constraints on the frequency and energetics of flares comparable to X100-class solar flares and FUV-emitting regions in young solar analogs.