  During the last decade, there was a paradigm-shift in order to consider
terrestrial planets within liquid-water habitable zones (LW-HZ) around M stars,
as suitable places for the emergence and evolution of life. Here we analyze the
influence of UV boundary conditions to three planetary systems around dM (HIP
74995, HIP 109388 and HIP 113020). We apply our model of UV habitable zone
(UV-HZ) (Buccino et al. 2006) to these cases and show that during the quiescent
UV output there would not be enough UV radiation within the LW-HZ in order to
trigger biogenic processes. We also analyze the cases of two other M flare
stars and show that the flares of moderate intensity could provide the
necessary energy to trigger those biogenic processes, while the strong flares
not necessary rule-out the possibility of life-bearing planets.
