Theta Ursae Majoris (Theta UMa, θ Ursae Majoris, θ UMa) is a suspected spectroscopic binary star system in the northern circumpolar constellation of

Ursa Major Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa M ...

. It has an apparent visual magnitude of 3.17, placing it among the brighter members of this constellation. The distance to this star has been measured directly using the

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

method, yielding an estimated value of . In 1976, this was reported as a spectroscopic binary system by Helmut A. Abt and Saul G. Levy, giving it an orbital period of 371 days. However, this was brought into question by Christopher L. Morbey and Roger F. Griffin in 1987, who suggested that the data could be explained by random chance. Further observations in 2009 with observations with the Bok Telescope in Arizona did show changes of 180 m/s in radial velocity, although there was not sufficient evidence to support a Keplerian orbit. There is a 14th-magnitude common proper motion companion to Theta Ursae Majoris at an angular separation of 4.1 arcseconds, so this may potentially be a triple star system. The primary component of this putative system has a published

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of F6 IV, indicating it is a subgiant star that is evolving away from the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

. In 2009, Helmut A. Abt listed it with a stellar classification of F7 V, suggesting that it is still on the main sequence. It is larger than the Sun with 141% of the Sun's mass and 241% of the Sun's radius. Consequently, it is shining brighter and evolving more rapidly than the Sun, with a luminosity nearly eight times the Sun's at an age of 2.2 billion years. This energy is being radiated from the star's outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 6,256 K. At this heat, the star glows with the yellow-white hue of an F-type star. The McDonald Observatory team has set limits to the hypothetical presence of one or more planets around the primary with masses between 0.24 and 4.6 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.

Naming and etymology

* With τ, h, υ, φ, e, and f, it composed the Arabic asterism Sarīr Banāt al-Na'sh, the Throne of the daughters of ''Na'sh'', and Al-Haud, the Pond. According to the catalogue of stars in the ''Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars'', ''Al-Haud'' were the title for seven stars : f as ''Alhaud I'', τ as ''Alhaud II'', e as ''Alhaud III'', h as ''Alhaud IV'', this star (θ) as ''Alhaud V'', υ as ''Alhaud VI'' and φ as ''Alhaud VII'' . * In Chinese, (), meaning ''

Administrative Center An administrative centre is a seat of regional administration or local government, or a county town, or the place where the central administration of a commune, is located. In countries with French as the administrative language, such as Belgiu ...

'', refers to an asterism consisting of θ Ursae Majoris, φ Ursae Majoris, υ Ursae Majoris, 15 Ursae Majoris and 18 Ursae Majoris. Consequently, the Chinese name for φ Ursae Majoris itself is known as (, .).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 16 日

References

{{Stars of Ursa Major Ursae Majoris, Theta Ursa Major Binary stars F-type subgiants Alhaud V Ursae Majoris, 25 046853 3775 082328 Durchmusterung objects