Theta Aurigae is a

binary star A binary star or binary star system 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 as separate stars us ...

system 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 first constellati ...

of Auriga. Its name is a

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

that is Latinized from θ Aurigae, and abbreviated Theta Aur or θ Aur. This is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

that varies from , which is bright enough to be seen with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

. Based upon

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 ...

measurements, the distance to this system is about . It is drifting further away from the Sun with a mean

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of +29.5 km/s. The two components are designated Theta Aurigae A and B. The former star is the primary and has the proper name Mahasim.

Nomenclature

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

. 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 system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...

s, and adopted by the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

(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 and Lambda Herculis, from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

المِعْصَم ''al-miʽşam'' "the wrist" (of the charioteer). In 2016, the IAU organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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 Five Chariots (五車, pinyin: Wǔ Ju) is a Chinese constellation equivalent to Auriga, minus Delta Aurigae. It is known in Japanese as Gosha (五車). Stars * Iota Aurigae * Alpha Aurigae * Beta Aurigae * Theta Aurigae * Gamma Aurigae Char ...

) in Chinese

Properties

The primary component, Theta Aurigae A, is a large star with more than three times the mass of the Sun and nearly five times the

Sun's radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. It is radiating 214 times the

Sun's luminosity The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

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 gratin ...

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 type

and has a surface

magnetic field A magnetic field (sometimes called B-field) is a physical 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 ...

of about 1 kG. Its

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

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 or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

of 3.91

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

along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...

of 304.9° as of 2002. This is an F-type

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 ...

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 An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

source with a luminosity of .

References

External links

HR 2095

CCDM J05597+3713

Image Theta Aurigae
{{DEFAULTSORT:Theta Aurigae A-type main-sequence stars K-type main-sequence stars Alpha2 Canum Venaticorum variables Ap stars Astronomical X-ray sources Binary stars Auriga Aurigae, Theta

2095 In contemporary history, the third millennium is the current millennium in the ''Anno Domini'' or Common Era, under the Gregorian calendar. It began on 1 January 2001 ( MMI) and will end on 31 December 3000 ( MMM), spanning the 21st to 30th ...

BD+37 1380 Aurigae, 37 040312 028380 Mahasim