Claim: First found to be variable in 1865, W Ursae Majoris is the variable star designation for an overcontact binary star system in the constellation Cygnus wherein the primary star, appears to have a spectral type of F6V, while the secondary is slightly cooler with a spectral type of G5V (though having multiple stars, the mass transfer will likely eventually cause the system to evolve into a single star with a very high rotation rate).
Evidence: Ursa Major