Improved Constraints for the XUV Luminosity Evolution of Trappist-1

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. (2020), we infer that TRAPPIST-1 maintained a saturated XUV luminosity, relative to the bolometric luminosity, of ${\log }_{10}$(L${}_{\mathrm{XUV}}$/L${}_{\mathrm{bol}}$) $=-3.03_{-0.23}^{+0.25}$ at early times for a period of $t_{sat}=3.14_{-1.46}^{+2.22}$ Gyr. After the saturation phase, we find L${}_{\mathrm{XUV}}$ decayed over time by an exponential rate of ${\hat{I}}_{\mathrm{XUV}}^2=-1.17_{-0.28}^{+0.27}$. Compared to our inferred age of the system, $\mathrm{age}=7.96_{-1.87}^{+1.78}$ Gyr, our result for $t_{sat}$ suggests that there is only a $\sim 4\%$~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 $\sim 10^{30}-10^{32}$ erg over the star's lifetime.

4 pages, 1 figure