Theta Aurigae ( Latinized from θ Aurigae, abbreviated Theta Aur, θ Aur) is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Auriga. Based upon

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 objects ...

measurements, the distance to this system is about . The two components are designated Theta Aurigae A (also named Mahasim) and B.

Nomenclature

''θ Aurigae'' ( Latinised to ''Theta Aurigae'') is the system's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. The designations of the two components as ''Theta Aurigae A'' and ''B'' derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU). Some authors state that Theta Aurigae had no traditional name,although Richard Hinckley Allen makes a passing reference about the name ''Mahasim'', as a name also used, with various spellings, for

Eta Aurigae Eta Aurigae (η Aurigae, abbreviated Eta Aur, η Aur), officially named Haedus , is a star in the northern constellation of Auriga. With an apparent visual magnitude of 3.18, it is visible to the naked eye. Based upon parallax measuremen ...

and Lambda Herculis, from the Arabic المِعْصَم ''al-miʽşam'' "the wrist" (of the charioteer). In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Mahasim'' for the component Theta Aurigae A on 30 June 2017 and it is now so included in the List of IAU-approved Star Names. It is known as 五車四 (the Fourth Star of the Five Chariots) in Chinese

Properties

The primary component, Theta Aurigae A, is a large star with more than three times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

and nearly five times the Sun's radius. It is radiating 214 times the Sun's luminosity from its 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 10,220 K, giving it the white hue of an A-type star. The star has a

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 grati ...

of A0pSi, with the 'pSi' suffix indicating it is a chemically peculiar star with an abnormal abundance of silicon. ThetaAurLightCurve

The primary is classified an

Alpha2 Canum Venaticorum Cor Caroli is a binary star designated Alpha Canum Venaticorum or α Canum Venaticorum. The International Astronomical Union uses the name "Cor Caroli" specifically for the brighter star of the binary. Alpha Canum Venaticorum is the brig ...

type variable star and has a surface

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

of about 1 kG. Its projected rotational velocity is , with the star completing a rotation in only 3.6 days. The axis of rotation is inclined by an angle of to the line of sight from the Earth. The secondary, Theta Aurigae B, is a +7.2 magnitude companion, 4.5 magnitudes fainter than the primary, located 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 3.91 arcseconds along a position angle of 304.9° as of 2002. This is an F-type

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 ...

star with a stellar classification in the range F2-5 V. The mean combined apparent magnitude of the system is +2.65 but the variation of the primary causes the system's brightness to range from magnitude +2.62 to +2.70 with a period of 1.37 days. The system is an X-ray source with a luminosity of .

References

External links

HR 2095

CCDM J05597+3713

Image Theta Aurigae
{{DEFAULTSORT:Theta Aurigae 040312 028380 Aurigae, Theta Auriga (constellation) Alpha2 Canum Venaticorum variables Binary stars A-type main-sequence stars K-type main-sequence stars Mahasim Aurigae, 37

2095 In contemporary history, the third millennium of the anno Domini or Common Era in the Gregorian calendar is the current millennium spanning the years 2001 to 3000 ( 21st to 30th centuries). Ongoing futures studies seek to understand what is ...

BD+37 1380 Ap stars