Theta Aurigae ( Latinized from θ Aurigae, abbreviated Theta Aur, θ Aur) is a binary star in the constellation of

Auriga AURIGA (''Antenna Ultracriogenica Risonante per l'Indagine Gravitazionale Astronomica'') is an ultracryogenic resonant bar gravitational wave detector in Italy. It is at the Laboratori Nazionali di Legnaro of the Istituto Nazionale di Fisica Nuclea ...

. Based upon parallax 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. 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. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

s, and adopted by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(IAU). Some authors state that Theta Aurigae had no traditional name,although

Richard Hinckley Allen In astronomy, stars have a variety of different stellar designations and names, including catalogue designations, current and historical proper names, and foreign language names. Only a tiny minority of known stars have proper names; all others ha ...

makes a passing reference about the name ''Mahasim'', as a name also used, with various spellings, for Eta Aurigae and

Lambda Herculis Lambda Herculis (λ Herculis. abbreviated Lambda Her, λ Her), formally named Maasym , is a star in the constellation of Hercules. From parallax measurements taken during the Gaia mission, it is approximately 393 light-years from the S ...

, from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

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 constellation in Chinese astronomy. Introduction A five-star Chinese constellation equivalent to Auriga minus δ Aur ( Delta Aurigae). Also known in Japanese as Gosha (Five Chariots; 五車). Stars * ...

) 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. 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 ...

from its outer atmosphere at an effective temperature of 10,220 K, giving it the white hue of an A-type star. The star has a stellar classification of A0pSi, with the 'pSi' suffix indicating it is a

chemically peculiar star In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual metal abundances, at least in their surface layers. Classification Chemically peculiar stars are common among hot main-sequence (hydrogen-burning) stars. Thes ...

with an abnormal abundance of silicon. ThetaAurLightCurve

The primary is classified an Alpha2 Canum Venaticorum type

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

and has a surface magnetic field 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 bulg ...

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 of 3.91

arcseconds 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 ...

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 north celestial pole (NCP), turning positive into the ...

of 304.9° as of 2002. This is an F-type main sequence 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, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

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 li ...

BD+37 1380 Ap stars