Epsilon Arietis
Binary star system in the constellation Aries
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Epsilon Arietis is a visual binary[8] star system in the northern constellation of Aries. Its name is a Bayer designation that is Latinized from ε Arietis, and abbreviated Epsilon Ari or ε Ari. This system has a combined apparent visual magnitude of 4.63[2] and can be seen with the naked eye, although the two components are too close together to be resolved without a telescope. With an annual parallax shift of 9.03 mas,[9] the distance to this system can be estimated as 361 light-years (111 parsecs), give or take a 7 light-year margin of error. It is located behind the dark cloud MBM12.[6]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aries |
| Right ascension | 02h 59m 12.726s[1] |
| Declination | +21° 20′ 25.54″[1] |
| Apparent magnitude (V) | 4.63[2] (5.2/5.5)[3] |
| Characteristics | |
| Spectral type | A2 Vs + A2 Vs[4] |
| U−B color index | +0.08[2] |
| B−V color index | +0.04[2] |
| R−I color index | 0.02[citation needed] |
| Astrometry | |
| Radial velocity (Rv) | +0.9±0.9[5] km/s |
| Proper motion (μ) | RA: −15.884 mas/yr[1] Dec.: −7.151 mas/yr[1] |
| Parallax (π) | 9.0296±0.1851 mas[1] |
| Distance | 361 ± 7 ly (111 ± 2 pc) |
| Orbit[6] | |
| Period (P) | 704.111±1.778 yr |
| Semi-major axis (a) | 2.174±0.035″ |
| Eccentricity (e) | 0.317±0.006 |
| Inclination (i) | 84.2±0.8° |
| Longitude of the node (Ω) | 25.6±0.7° |
| Periastron epoch (T) | 704.111±1.778 |
| Argument of periastron (ω) (secondary) | 162.1±1.0° |
| Details | |
| ε Ari A | |
| Mass | 2.4[6] M☉ |
| Rotational velocity (v sin i) | 60[4] km/s |
| ε Ari B | |
| Mass | 2.4[6] M☉ |
| Rotational velocity (v sin i) | 60[4] km/s |
| Other designations | |
| 48 Arietis, BD+20 484, HIP 13914, ADS 2257, WDS J02592+2120AB[7] | |
| ε Ari A: GC 3582, HD 18520, HR 888, SAO 75673, PPM 92122 | |
| ε Ari B: HD 18519, HR 887 | |
| Database references | |
| SIMBAD | ε Ari |
| ε Ari A | |
| ε Ari B | |
The brighter member of this pair has an apparent magnitude of 5.2.[3] At an angular separation of 1.426″±0.010″ from the brighter component, along a position angle of 209.2°±0.3°,[8] is the magnitude 5.5 companion.[3] Both are A-type main sequence stars with a stellar classification of A2 Vs.[4] (The 's' suffix indicates that the absorption lines in the spectrum are distinctly narrow.) In the 2009 Catalogue of Ap, HgMn and Am stars, the two stars have a classification of A3 Ti,[3] indicating they are Ap stars with an anomalous abundance of titanium. Within the measurement margin of error, their projected rotational velocities are deemed identical at 60 km/s.[4]
Name
This star system, along with δ Ari, ζ Ari, π Ari, and ρ3 Ari, were Al Bīrūnī's Al Buṭain (ألبطين), the dual of Al Baṭn, the Belly.[10] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Buṭain were the title for five stars :δ Ari as Botein, π Ari as Al Buṭain I, ρ3 Ari as Al Buṭain II, ε Ari as Al Buṭain III and ζ Ari as Al Buṭain IV[11]
In Chinese astronomy, Epsilon Arietis may be or may be part of Tso Kang (from Cantonese 左更 zogang, Mandarin pronunciation zuǒgēng).[12][13]