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

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest po ...

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 ...

. It has an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

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 lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...

method, yielding an estimated value of . In 1976, this was reported as a spectroscopic binary system by

Helmut A. Abt Helmut Arthur Abt (born 26 May 1925) is a German-born American astrophysicist, having worked at the National Optical Astronomy Observatory and an Elected Fellow of the American Association for the Advancement of Science. He is astronomer emeri ...

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 The Bok Telescope (also known as the 90-inch) is the largest telescope operated solely by Steward Observatory. It finds much use from astronomers from University of Arizona, Arizona State University, and Northern Arizona University, with instrumen ...

in Arizona did show changes of 180 m/s in

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

, although there was not sufficient evidence to support a

Keplerian orbit Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

. There is a 14th-magnitude

common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsi ...

companion to Theta Ursae Majoris at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 4.1

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s, 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 spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting t ...

of F6 IV, indicating it is a

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

that is

evolving Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation te ...

away from the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

. 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 250% 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 6,300 K. At this heat, the star glows with the yellow-white hue of an

F-type star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

. The

McDonald Observatory McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional fac ...

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 Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is by ...

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 Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of v ...

, (), meaning ''

Administrative Center An administrative center 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 administrative language (such as Belgium, L ...

'', refers to an asterism consisting of θ Ursae Majoris,

φ Ursae Majoris Phi Ursae Majoris, Latinized from φ Ursae Majoris, is binary star system in the northern constellation of Ursa Major. It is white-hued and is visible to the naked eye with a combined apparent visual magnitude of +4.60; the p ...

υ Ursae Majoris Upsilon Ursae Majoris, Latinized from υ Ursae Majoris, is a binary star in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye with an apparent visual magnitude of +3.79. Based upon an annual para ...

15 Ursae Majoris 15 Ursae Majoris is a star in the northern circumpolar constellation Ursa Major, located 94 light-years away from the Sun. It has the Bayer designation f Ursae Majoris; ''15 Ursae Majoris'' is the Flamsteed designation. It is vis ...

and

18 Ursae Majoris 18 Ursae Majoris, or e Ursae Majoris, is a single star in the northern circumpolar constellation of Ursa Major. It is faintly visible to the naked eye with an apparent visual magnitude of 4.832. The annual parallax shift measured from E ...

. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...

for φ Ursae Majoris itself is known as (, en, the Fourth Star of Administrative Center.).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 16 日
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References

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