A type of rotating variable star; abbr. BY. The variations are caused by non-uniform surface brightness and show a quasi-periodicity related to the rotation period. The latter ranges from a few hours to about 120 days, and the amplitude from a few thousandths to 0.5 mag. BY Draconis stars are K–M dwarfs. The non-uniform brightness is caused by starspots and chromospheric activity, similar to that on the Sun. A BY Draconis star may simultaneously be a flare star.
Subjects: Astronomy and Astrophysics.