Tau_Ursae_Majoris
Tau Ursae Majoris
Binary star in the constellation Ursa Major
Tau Ursae Majoris (τ UMa) is the Bayer designation for a binary star in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye, having an apparent visual magnitude of 4.66.[2] With an annual parallax shift of 25.82 mas,[1] it is located about 126 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.19 due to interstellar dust.[9]
This is a single-lined spectroscopic binary star system with an orbital period of 2.9 years and an eccentricity of 0.48.[6] The primary member, component A, is an evolved bright giant with a stellar classification of kA5hF0mF5 II.[3] This notation indicates the star's spectrum shows the calcium K lines of an A5 star, the hydrogen lines of an F0 star, and the metallic lines of an F5 star.[12] It is an evolved Am star of the ρ Puppis type, a class of evolved stars showing the Am chemical peculiarities.[13] It is located in the instability strip of the Hertzsprung–Russell diagram but is not thought to be variable.[7]