  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 46m 12.68236s[1] |
| Declination | +33° 58′ 12.9250″[1] |
| Apparent magnitude (V) | 2.480[2] |
| Characteristics | |
| Evolutionary stage | Horizontal branch[3] |
| Spectral type | K0 III[4] |
| U−Bcolor index | +0.860[2] |
| B−Vcolor index | +1.030[2] |
| Astrometry | |
| Radial velocity (Rv) | −12.41[5] km/s |
| Proper motion (μ) | RA: 355.66[1]mas/yr Dec.: 330.60[1]mas/yr |
| Parallax (π) | 44.86±0.12 mas[1] |
| Distance | 72.7 ± 0.2 ly (22.29 ± 0.06 pc) |
| Absolute magnitude (MV) | +0.74 ± 0.02[4] |
| Orbit[3] | |
| Primary | ε Cyg Aa |
| Companion | ε Cyg Ab |
| Period (P) | 53.693+0.321 −0.328 yr |
| Semi-major axis (a) | 15.8±0.2 AU |
| Eccentricity (e) | 0.9295±0.0003 |
| Argument of periastron (ω) (primary) | 275.30±0.06° |
| Semi-amplitude (K1) (primary) | 4.6 km/s |
| Details | |
| A | |
| Mass | 1.103±0.042[3] M☉ |
| Radius | 11.13[6] R☉ |
| Luminosity | 56.4±0.6[7] L☉ |
| Surface gravity (log g) | 2.79±0.23[7] cgs |
| Temperature | 4,699[6] K |
| Metallicity[Fe/H] | −0.126[6] dex |
| Rotation | 0.67[4] years |
| Rotational velocity (v sin i) | 2.3 ± 0.2[4] km/s |
| Age | 9.62±0.12[3] Gyr |
| B | |
| Mass | ≥0.265±0.007[3] M☉ |
| Other designations | |
| Aljanah, Gienah,[8] ε Cyg, 53 Cygni,BD+33°4018,FK5 780,GCTP 4959.00,Gl 806.1,HD 197989,HIP 102488,HR 7949,LHS 5358,SAO 70474,WDS 20462+3358[9] | |
| Database references | |
| SIMBAD | data |
Epsilon Cygni (ε Cygni, abbreviatedEpsilon Cyg,ε Cyg) is abinary star in theconstellation ofCygnus. With anapparent visual magnitude of 2.48, it isreadily visible to the naked eye at night, and is thethird-brightest star in the constellation. Based uponparallax measurement, Epsilon Cygni is about 73light-years distant.
The system has two confirmed constituents, Epsilon Cygni Aa (officially namedAljanah/ˈældʒənə/) and Ab. Additionally, a visual companion (Epsilon Cygni C) is likely bound to the system.[3]
ε Cygni (Latinised toEpsilon Cygni) is the system'sBayer designation. The designations of the three constituents asEpsilon Cygni A,B andC, and those ofA's components -Epsilon Cygni Aa andAb - derive from the convention used by the Washington Multiplicity Catalog (WMC) formultiple star systems, and adopted by theInternational Astronomical Union (IAU).[10]
Epsilon Cygni bore the traditional nameGienah from theArabical janāħ (Arabic:جناح) meaning "thewing".[11] However that name was more usually applied toGamma Corvi.[8] For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized aWorking Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[13] It approved the nameAljanah for the component Epsilon Cygni Aa on 30 June 2017. It had previously approved the nameGienah for Gamma Corvi A on 6 November 2016. Both are now so included in the List of IAU-approved Star Names.[14]
InChinese astronomy, the "Celestial Ford" (Chinese:天津;pinyin:Tiān Jīn) refers to anasterism consisting of Epsilon Cygni,Gamma Cygni,Delta Cygni,30 Cygni,Alpha Cygni,Nu Cygni,Tau Cygni,Upsilon Cygni andZeta Cygni.[15] Consequently, theChinese name for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" (Chinese:天津九;pinyin:Tiān Jīn jiǔ).[16]
Epsilon Cygni A has an optical companion, Epsilon Cygni B, with which it is not physically associated, and a 13th magnitude candidate commonproper motion companion, Epsilon Cygni C, at an angular separation of 78arcseconds.[17] If the latter star isgravitationally bound to Epsilon Cygni A, then they are currently separated by 1,700 AU or more, and have anorbital period of at least 50,000 years.[18]
Epsilon Cygni A is asingle-lined spectroscopic binary.[19] The components take 53 years to complete an orbit and are in a highlyeccentric orbit, which put their distances from 1.1 astronomical units inapoapsis to 30.5 astronomical units inperiapsis.[3][a] Its main component is agiant star with astellar classification of K0 III.[20] This indicates that the star has left themain sequence and has begun the final stages in itsstellar evolution. After passing through the red-giant branch stage, it underwent a helium flash event and is now a horizontal branch star generating energy through the thermonuclear fusion of helium at itscore.[3] Theeffective temperature of itsphotosphere is 4,700 K,[6] giving an orange hue that is a characteristic ofK-type stars.[21] Being 10% more massive than the Sun and nine billion years old,[3] it has 11 times theradius of the Sun[6] and is about 56 times more luminous.[7]
The secondary has never been observed directly, its existence was inferred solely onastronomical spectroscopy. Based on this data, it should have a mass of at least 0.265 M☉.[3]
Since 1943, thespectrum of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.[22]
ε Cygni lies about three degrees north of theVeil Nebula, a probable ancientsupernova remnant. The nebula is far more distant than the star.