Binary fraction of BY Draconis and FK Comae Berenices stars

Determine the binary fraction of BY Draconis stars (K–M dwarfs showing rotational photometric variability) and FK Comae Berenices stars (G–K giants showing similar rotational variability) to quantify how frequently each subtype occurs in binary systems and thereby clarify their formation and evolutionary channels.

Background

Within the discussion of active single stars, the paper notes two related subclasses: BY Draconis stars (late-type dwarfs with rotationally modulated variability) and FK Comae Berenices stars (giants with similar variability). Although both groups are rapid rotators and some members show evidence for binarity, the overall fraction that are binaries has not been established.

Knowing the binary fraction is important for interpreting the rotational activity and X-ray properties of these subclasses, distinguishing single-star rotational evolution from binary-induced spin-up, and understanding how these systems fit within the broader framework used in the paper to separate active stars from compact-object accretors in the X-ray Main Sequence diagram.