Epsilon Arietis

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]

ε Arietis

Location of ε Arietis (circled)
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]