Improved Constraints for the XUV Luminosity Evolution of Trappist-1

Abstract

Abstract We re-examine the XUV luminosity evolution of TRAPPIST-1 utilizing new observational constraints (XUV and bolometric luminosity) from multi-epoch X-ray/UV photometry. Following the formalism presented in Fleming et al., we infer that TRAPPIST-1 maintained a saturated XUV luminosity, relative to the bolometric luminosity, of log10(L XUV/L bol) = − 3.03 − 0.23 + 0.25 at early times for a period of t sat = 3.14 − 1.46 + 2.22 Gyr. After the saturation phase, we find L XUV decayed over time by an exponential rate of β XUV = − 1.17 − 0.28 + 0.27 . Compared to our inferred age of the system, age = 7.96 − 1.87 + 1.78 Gyr, our result for t sat suggests that there is only a ∼4% chance that TRAPPIST-1 still remains in the saturated phase today, which is significantly lower than the previous estimate of 40%. Despite this reduction in t sat, our results remain consistent in the conclusion that the TRAPPIST-1 planets likely received an extreme amount XUV energy—an estimated integrated XUV energy of ∼1030–1032 erg over the star’s lifetime.