Epsilon Aquilae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquila |
| Right ascension | 18h 59m 37.356s |
| Declination | +15° 04′ 05.81″ |
| Apparent magnitude (V) | +4.02 |
| Characteristics | |
| Spectral type | K1-IIICN0.5 |
| U−B color index | +1.04 |
| B−V color index | +1.08 |
| R−I color index | +0.52 |
| Astrometry | |
| Radial velocity (Rv) | −45.9±0.3 km/s |
| Proper motion (μ) | RA: −51.062 mas/yr Dec.: −69.439 mas/yr |
| Parallax (π) | 18.1821±0.3319 mas |
| Distance | 179 ± 3 ly (55 ± 1 pc) |
| Absolute bolometric magnitude (Mbol) | +0.30 |
| Orbit | |
| Period (P) | 1,270.6±1.1 d |
| Semi-major axis (a) | ≥ 86.9 ± 2.3 Gm (0.581 ± 0.015 AU) |
| Eccentricity (e) | 0.272±0.026 |
| Periastron epoch (T) | 41718±17 MJD |
| Argument of periastron (ω) (secondary) | 82±5° |
| Semi-amplitude (K1) (primary) | 5.17±0.13 km/s |
| Details | |
| ε Aql Aa | |
| Mass | 2.1+0.4 −0.2 M☉ |
| Radius | 10.13+0.21 −0.22 R☉ |
| Luminosity | 54±5 L☉ |
| Surface gravity (log g) | 2.91 cgs |
| Temperature | 4,760 K |
| Metallicity [Fe/H] | 0.00 dex |
| Rotational velocity (v sin i) | 4.4 km/s |
| ε Aql Ab | |
| Mass | 0.47±0.05 M☉ |
| Other designations | |
| Deneb el Okab, ε Aql, 13 Aql, BD+14 3736, FK5 712, GC 26091, HD 176411, HIP 93244, HR 7176, SAO 104318, PPM 135586, WDS J18596+1504A | |
| Database references | |
| SIMBAD | data |
Epsilon Aquilae is a binary star system in the equatorial constellation of Aquila, near the western constellation boundary with Hercules. Its name is a Bayer designation that is Latinized from ε Aquilae, and abbreviated Epsilon Aql or ε Aql. The system has an apparent visual magnitude of 4.02 and is visible to the naked eye. Based upon an annual parallax of 18.1821 mas, Epsilon Aquilae lies at a distance of approximately 179 light-years (55 parsecs) from Earth, but is drifting closer with a radial velocity of −46 km/s.
It has the traditional name Deneb el Okab /ˈdɛnɛb ɛl ˈoʊkæb/, from an Arabic term ذنب العقاب ðanab al-ʽuqāb "the tail of the eagle", and the Mandarin names Woo /ˈwuː/ and Yuë /ˈjuːeɪ/, derived from and represent the state Wú (吳), an old state was located at the mouth of the Yangtze River, and Yuè (越), an old state in Zhejiang province (together with 19 Capricorni in Twelve States asterism). According to the R.H. Allen's works, it shares names with ζ Aquilae. Epsilon Aquilae could be more precisely called Deneb el Okab Borealis, because is situated to the north of Zeta Aquilae, which can therefore be called Deneb el Okab Australis.