Xi Cephei
Star in the constellation Cepheus
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Xi Cephei is a multiple star system in the northern constellation of Cepheus. Its name is a Bayer designation. This system is visible to the naked eye as a point of light with a combined apparent visual magnitude of 4.29.[13] Based on parallax measurements, it is located at a distance of approximately 102 light-years from Earth.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| A | |
| Right ascension | 22h 03m 47.440s[1] |
| Declination | +64° 37′ 40.70″[1] |
| Apparent magnitude (V) | 4.45[2] (4.61 + 6.50)[3] |
| B | |
| Right ascension | 22h 03m 46.217s[4] |
| Declination | +64° 37′ 41.47″[4] |
| Apparent magnitude (V) | 6.34[5] |
| Characteristics | |
| A | |
| Spectral type | kA2.5hF2mF2(IV)[6] (A3Vm + F2III)[3] |
| B | |
| Evolutionary stage | main sequence[4] |
| Spectral type | F8V[7] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | −7.2±2[8] km/s |
| Proper motion (μ) | RA: +212.563 mas/yr[1] Dec.: +89.058 mas/yr[1] |
| Parallax (π) | 32.12±0.8066 mas[1] |
| Distance | 102 ± 3 ly (31.1 ± 0.8 pc) |
| B | |
| Radial velocity (Rv) | −6.2±2[8] km/s |
| Proper motion (μ) | RA: +202.094 mas/yr[4] Dec.: +81/933 mas/yr[4] |
| Parallax (π) | 32.1835±0.0184 mas[4] |
| Distance | 101.34 ± 0.06 ly (31.07 ± 0.02 pc) |
| Orbit[9] | |
| Period (P) | 2.245+0.001 −0.000 years |
| Semi-major axis (a) | 0.072+0.000 −0.001″ |
| Eccentricity (e) | 0.460+0.009 −0.008 |
| Inclination (i) | 67.447+0.508 −0.443° |
| Longitude of the node (Ω) | 272.995+0.702 −0.301° |
| Periastron epoch (T) | 1968.751+7 −5 |
| Argument of periastron (ω) (secondary) | 90.354+0.315 −0.418° |
| Semi-amplitude (K1) (primary) | 7.81[10] km/s |
| Semi-amplitude (K2) (secondary) | 19.98[10] km/s |
| Details | |
| Aa | |
| Mass | 1.721+0.134 −0.120[9] M☉ |
| Luminosity | 6.6[11] L☉ |
| Temperature | 7,943[11] K |
| Age | 200[11] Myr |
| Ab | |
| Mass | 0.512[9][a] M☉ |
| Luminosity | 1.8[11] L☉ |
| Temperature | 6,310[11] K |
| Age | 525[11] Myr |
| B | |
| Mass | 1.14[4] M☉ |
| Radius | 1.28[4] R☉ |
| Luminosity | 2.08[4] L☉ |
| Surface gravity (log g) | 4.26[4] cgs |
| Temperature | 6,123[4] K |
| Age | 3.98[4] Gyr |
| Other designations | |
| Kurhah, 17 Cephei, BD+63°1802, HIP 108917, HR 8417, SAO 19827, CCDM J22038+2407, WDS J22038+6438[12] | |
| A: HD 209790 | |
| B: HD 209791 | |
| Database references | |
| SIMBAD | ξ |
| A | |
| B | |
This system consists of a binary pair, designated Xi Cephei A, together with a more distant companion, Xi Cephei B. A's two components are themselves designated Xi Cephei Aa (officially named Kurhah /ˈkɜːrhə/, the traditional name of the system)[14] and Ab.
Nomenclature
ξ Cephei, Latinized to Xi Cephei, is the system's Bayer designation. It is abbreviated Xi Cep or ξ Cep. 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).[15]
Xi Cephei bore the traditional names Kurhah, Alkirdah or Al Kirduh,[16] 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").[17] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[19] 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.[14]
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.[20] Consequently, the Chinese name for Xi Cephei itself is 天鈎六 (Tiān Gōu liù, English: the Sixth Star of Celestial Hook).[21]
Properties
Xi Cephei A is a double-lined spectroscopic binary system with an orbital period of 820 days and an eccentricity of 0.5.[10] The primary, component Aa, is a chemically peculiar Am star with an apparent magnitude of +4.61. The spectroscopic secondary, component Ab, is an F-type star.[3]
Eight arcseconds away from Xi Cephei A, Xi Cephei B is a 6th-magnitude main sequence star.[3]
Xi Cephei C is a 13th magnitude star nearly two arcminutes away.[22] It has a small parallax and is an unrelated background star only accidentally in line with Xi Cephei.[23]
Notes
- from primary mass and mass ratio