Epsilon Herculis

Epsilon Herculis

ε Herculis in the keystone asterism in the Hercules constellation.
Location of ε Herculis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 00m 17.37378s[1]
Declination 30° 55′ 35.0565″[1]
Apparent magnitude (V) 3.9111[1]
Characteristics
Spectral type A0 V[2] or A0 IV+[3]
U−B color index −0.10[4]
B−V color index −0.01[4]
Astrometry
Proper motion (μ) RA: −47.69[1] mas/yr
Dec.: +26.90[1] mas/yr
Parallax (π)21.04 ± 0.14 mas[1]
Distance155 ± 1 ly
(47.5 ± 0.3 pc)
Absolute magnitude (MV)+0.54[5]
Orbit[6]
Period (P)4.0235 d
Eccentricity (e)0.02
Periastron epoch (T)2417947.2420 ± 10.0 JD
Argument of periastron (ω)
(secondary)		138°
Semi-amplitude (K1)
(primary)		70.7 km/s
Semi-amplitude (K2)
(secondary)		112.0 km/s
Details
Mass2.6±0.1[7] M☉
Radius2.72±0.07[8] R☉
Luminosity64[5] L☉
Surface gravity (log g)3.98±0.02[8] cgs
Temperature10197±57[8] K
Metallicity [Fe/H]−0.25±0.04[5] dex
Rotational velocity (v sin i)60[9] km/s
Age400+50
−40[7] Myr
Other designations
ε Her, 58 Her, BD+31° 2947, FK5 634, GC 22935, HD 153808, HIP 83207, HR 6324, SAO 65716[10]
Database references
SIMBADdata

Epsilon Herculis, Latinized from ε Herculis, is a fourth-magnitude multiple star system in the northern constellation of Hercules. The combined apparent visual magnitude of 3.9111[1] is bright enough to make this system visible to the naked eye. Based upon an annual parallax shift of 21.04 mas as seen from Earth,[1] it is located 155 light years from the Sun. The system is moving closer to the Sun with a radial velocity of −25 km/s.[11]

There is disagreement over the properties of this system. Petrie (1939) classified two components as class A0 and A2 with a visual magnitude difference of 1.5.[3] Batten et al. (1989) catalogued it as a double-lined spectroscopic binary system with an orbital period of four days and an eccentricity of 0.02.[6] However, Hipparcos was not able to detect the duplicity. Tokovinin (1997) and Faraggiana et al. (2001) catalogued it as a triple star system.[3] Cowley et al. (1969) gave it a combined stellar classification of A0 V,[2] whereas Gray & Garrison (1987) classified it as an A0 IV+. Wolff & Preston (1978) listed a magnesium overabundance.[3] Since 1995 it has been classified as a Lambda Boötis star,[12] although this has been brought into question.[13][3]

In Chinese, 天紀 (Tiān Jì), meaning Celestial Discipline, refers to an asterism consisting of ε Herculis, ξ Coronae Borealis, ζ Herculis, 59 Herculis, 61 Herculis, 68 Herculis, HD 160054 and θ Herculis.[14] Consequently, the Chinese name for ε Herculis itself is 天紀三 (Tiān Jì sān, English: the Third Star of Celestial Discipline.)[15]

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