  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Auriga |
| Right ascension | 05h 59m 43.27012s[1] |
| Declination | +37° 12′ 45.3047″[1] |
| Apparent magnitude (V) | 2.62 - 2.70[2] |
| Characteristics | |
| Spectral type | A0pSi + F2-5V[3] |
| U−Bcolor index | −0.18[4] |
| B−Vcolor index | −0.08[4] |
| R−Icolor index | −0.06 |
| Variable type | α2 CVn[2] |
| Astrometry | |
| Radial velocity (Rv) | +29.5[5] km/s |
| Proper motion (μ) | RA: +43.63[1]mas/yr Dec.: −73.79[1]mas/yr |
| Parallax (π) | 19.70±0.16 mas[1] |
| Distance | 166 ± 1 ly (50.8 ± 0.4 pc) |
| Absolute magnitude (MV) | −1.05[6] |
| Details | |
| Mass | 3.24[7] M☉ |
| Radius | 4.68[7] R☉ |
| Luminosity | 214[7] L☉ |
| Surface gravity (log g) | 3.61[7] cgs |
| Temperature | 10,220[7] K |
| Rotation | 3.6187 days[8] |
| Rotational velocity (v sin i) | 55[9] km/s |
| Age | 288[7] Myr |
| Other designations | |
| Mahasim,37 Aurigae,BD+37°1380,HD 40312,HIP 28380,HR 2095,SAO 58636,WDS 05597+3713. | |
| Database references | |
| SIMBAD | data |
Theta Aurigae (Latinized fromθ Aurigae, abbreviatedTheta Aur,θ Aur) is abinary star in theconstellation ofAuriga. Based uponparallax measurements, the distance to this system is about 166light-years (51parsecs).[1]
The two components are designated Theta Aurigae A (also namedMahasim[10]) and B.
θ Aurigae (Latinised toTheta Aurigae) is the system'sBayer designation. The designations of the two components asTheta Aurigae A andB derives from the convention used by the Washington Multiplicity Catalog (WMC) formultiple star systems, and adopted by theInternational Astronomical Union (IAU).[11]
Some authors state that Theta Aurigae had no traditional name,[12]althoughRichard Hinckley Allen makes a passing reference about the nameMahasim, as a name also used, with various spellings, forEta Aurigae andLambda Herculis,[13] from theArabic المِعْصَمal-miʽşam "the wrist" (of the charioteer). In 2016, the IAU organized aWorking Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[15] It approved the nameMahasim for the component Theta Aurigae A on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[10]
It is known as 五車四 (the Fourth Star of theFive Chariots) in Chinese[16]
The primary component, Theta Aurigae A, is a large star with more than three times themass of the Sun and nearly five times theSun's radius. It is radiating 214 times theSun's luminosity from itsouter atmosphere at aneffective temperature of 10,220 K, giving it the white hue of anA-type star. The star has astellar classification of A0pSi,[3] with the 'pSi' suffix indicating it is achemically peculiar star with an abnormal abundance of silicon.
The primary is classified anAlpha2 Canum Venaticorum typevariable star and has a surfacemagnetic field of about 1 kG.[9] Itsprojected rotational velocity is55 km s−1,[9] with the star completing a rotation in only 3.6 days.[8] The axis of rotation is inclined by an angle of51°±6° to the line of sight from the Earth.[9]
The secondary, Theta Aurigae B, is a +7.2 magnitude companion, 4.5[3] magnitudes fainter than the primary, located at anangular separation of 3.91 arcseconds along aposition angle of 304.9° as of 2002.[18] This is anF-typemain sequence star with a stellar classification in the range F2-5 V.[3]
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 anX-ray source with a luminosity of9.49 × 1026 erg s−1.[3]
