W Ursae Minoris

W Ursae Minoris is an eclipsing binary star system in the constellation Ursa Minor. Its apparent magnitude ranges from 8.51 to 9.59 over 1.7 days as one star passes in front of the other relative to observers on Earth. The combined spectrum of the system is A1/2V.

Slight changes in the orbital period suggest that there is a third component of the multiple star system, most likely a red dwarf, with an orbital period of $−15.3$. Another study suggests that the third star has a minimum mass of and an orbit of about $−12.128$.

The two main stars are currently thought to have masses of and  respectively. Models of their evolution and mass transfer suggest that the secondary star was initially the more massive of the two and that it has lost mass to what is now the primary as well as losing mass completely from the system. The two stars have also spiralled in towards each other over the few hundred million years since they formed.