The Photometric Periods from TESS Light Curves of the Superflare Stars Kappa Ceti, MT Tauri, and Pi1 Ursae Majoris

We use TESS light curves to measure the photometric periods of Kappa Ceti and MT Tauri. Both are G5 V stars and were suspected by Schaefer, King, and Deliyannis and published in 2000 to show superflares, with flare energies 1000-3000 times greater than the most energetic flares observed on the Sun. The periods we measure, probably from starspots, are 9.07 days for Kappa Ceti, and 6.02 days for MT Tauri. Pi1 Ursae Majoris (HD 72905) is a G1.5 Vb star observed to have a superflare with energy 100 times greater than a big solar flare. Its TESS light curve shows a period of 4.97 days, and a curious increase in amplitude over 5 cycles. We conclude that all three stars are rapidly rotating and likely young stars, which may or may not be related to the “ordinary solar-type stars” suggested by Schaefer et al.