Xi Cephei (ξ Cephei, abbreviated Xi Cep, ξ Cep) is a multiple star system in the constellation of Cepheus. It is approximately 86 light-years from Earth.[6]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 22h 03m 47.455s[1] |
| Declination | +64° 37′ 40.71″[1] |
| Apparent magnitude (V) | 4.2[2] (4.45 + 4.60[3]) |
| Characteristics | |
| ξ Cephei A | |
| Spectral type | kA2.5hF2mF2(IV)[4] |
| ξ Cephei B | |
| Spectral type | F8V[5] |
| Astrometry | |
| Proper motion (μ) | RA: 215.46±1.14[1] mas/yr Dec.: 91.06±0.97[1] mas/yr |
| Parallax (π) | 38.10 ± 2.81 mas[6] |
| Distance | 86 ± 6 ly (26 ± 2 pc) |
| Absolute magnitude (MV) | +1.79[7] |
| Orbit[8] | |
| Period (P) | 810.9 d |
| Eccentricity (e) | 0.46 |
| Periastron epoch (T) | 2438529.8 JD |
| Argument of periastron (ω) (secondary) | 106° |
| Semi-amplitude (K1) (primary) | 7.1 km/s |
| Semi-amplitude (K2) (secondary) | 19.9 km/s |
| Details | |
| ξ Cephei Aa | |
| Mass | 1.045±0.031[6] M☉ |
| ξ Cephei Ab | |
| Mass | 0.408±0.066[6] M☉ |
| Other designations | |
| A: HD 209790 | |
| B: HD 209791 | |
| Database references | |
| SIMBAD | ξ |
| A | |
| B | |
It consists of two binary stars, designated Xi Cephei A and B, together with a more distant companion, Xi Cephei C. A's two components are themselves designated Xi Cephei Aa (officially named Kurhah /ˈkɜːrhə/, the traditional name of the system)[9] and Ab.
Nomenclature
ξ Cephei (Latinised to Xi Cephei) is the system's Bayer designation. The designations of the three constituents as ξ Cephei A, B and C, and those of A's components - ξ Cephei Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[10]
Xi Cephei bore the traditional names Kurhah, Alkirdah or Al Kirduh,[11] the name coming from Qazvini who gave Al Ḳurḥaḥ (القرحة al-qurhah), an Arabic word Ideler translated as a white spot, or blaze, in the face of a horse. Allen indicates that Ideler felt this was not a proper name for a star, and suggested the name Al Ḳirdah (ألقردة al qírada "the Ape").[12] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[14] It approved the name Kurhah for the component Xi Cephei Aa on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[9]
In Chinese, 天鈎 (Tiān Gōu), meaning Celestial Hook, refers to an asterism consisting of Xi Cephei, 4 Cephei, HD 194298, Eta Cephei, Theta Cephei, Alpha Cephei, 26 Cephei, Iota Cephei and Omicron Cephei.[15] Consequently, the Chinese name for Xi Cephei itself is 天鈎六 (Tiān Gōu liù, English: the Sixth Star of Celestial Hook).[16]
Properties
Xi Cephei A is a double-lined spectroscopic binary system with an orbital period of 810.9 days and an eccentricity of 0.46.[8] The primary, component Aa, is a chemically peculiar Am star, a probable subgiant with an apparent magnitude of +4.29. Eight arcseconds away, Xi Cephei B is another spectroscopic binary. Xi Cephei C is a 13th magnitude star nearly two arcminutes away.[3]
References
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