Top: evolution of the bolometric luminosity of a 0.120-M_⊙ star as predicted by the models of Baraffe et al. (2015) and normalized to today’s Proxima luminosity L_bol = 0.00151 L_⊙. Marked with vertical dashed lines are today’s Proxima age (4.8 Gyr) and the approximate age at which the Proxima protoplanetary disk may have dissipated (10 Myr, Pecaut & Mamajek 2016). The horizontal dotted lines mark the current inner limit of the habitable zone according to different assumptions on the spin rate of the planet (Kopparapu 2013): synchronous, that is, 1.5 times Earth’s irradiance (S_⊕); asynchronous, that is, 0.9 S_⊕. Bottom: XUV flux evolution calculated using the two prescriptions explained in Sects. 5.2.1 (solid) and 5.2.2 (thick dashed). Vertical dashed lines mark the same features as in the top panel.