Epsilon Herculis
Multiple star system in the constellation Hercules
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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]
 | |
| 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] |
| Distance | 155 ± 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 | |
| Mass | 2.6±0.1[7] M☉ |
| Radius | 2.72±0.07[8] R☉ |
| Luminosity | 64[5] L☉ |
| Surface gravity (log g) | 3.98±0.02[8] cgs |
| Temperature | 10197±57[8] K |
| Metallicity [Fe/H] | −0.25±0.04[5] dex |
| Rotational velocity (v sin i) | 60[9] km/s |
| Age | 400+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 | |
| SIMBAD | data |
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]