Luyten 726-8
Both the stars are variables. The most spectacular is Luyten 726-8B, which was given the variable star designation UV Ceti (the other star is also known as BL Ceti). Although UV Ceti was not the first flare star discovered, it is the most prominent example of such a star, and similar flare stars are now known as UV Ceti type variable stars.  This star goes through fairly extreme changes of brightness: for instance, in 1952, its brightness increased by 75 times in only 20 seconds. UV Ceti is a red dwarf of spectral type M6.0e.