Gamma Cephei

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Gamma Cephei
File:Cepheus constellation map.png
Location of γ Cephei (top center)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 3.21[2]
Characteristics
Gamma Cephei A
Evolutionary stage Red-giant branch[3]
Spectral type K1III-IV CN1[4]
U−B Template:Engvar +0.94[2]
B−V Template:Engvar +1.03[2]
Variable type Suspected[5]
Gamma Cephei B
Spectral type M4V[6]
Astrometry
Radial velocity (Rv)Template:Val[7] km/s
Proper motion (μ) RA: –64.860 mas/yr[1]
Dec.: 171.159 mas/yr[1]
Parallax (π)72.5167±0.1470 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)2.62[8]
Orbit[3]
PrimaryA
CompanionB
Period (P)66.84±1.32 yr
Semi-major axis (a)1.419±0.012"
(19.56±0.18 AU)
Eccentricity (e)0.4144±0.0066
Inclination (i)120.18±0.27°
Longitude of the node (Ω)18.32±0.78°
Periastron epoch (T)1991.581±0.048
Argument of periastron (ω)
(secondary)		340.49±0.50°
Semi-amplitude (K1)
(primary)		1.898±0.014 km/s
Details[9]
Gamma Cephei A
MassTemplate:Val Template:Solar mass
RadiusTemplate:Val Template:Solar radius
LuminosityTemplate:Val[10] Template:Solar luminosity
Surface gravity (log g)3.18 cgs
TemperatureTemplate:Val K
Metallicity [Fe/H]Template:Val dex
Rotational velocity (v sin i)1.63[7] km/s
AgeTemplate:Val Gyr
Gamma Cephei B
MassTemplate:Val Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist
Database references
SIMBADdata
Exoplanet Archivedata

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Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the northern constellation of Cepheus. The primary (designated Gamma Cephei A, officially named Errai Template:IPAc-en, the traditional name of the system)[11][12] is a stellar class K1 orange giant or subgiant star; it has a red dwarf companion (Gamma Cephei B). An exoplanet (designated Gamma Cephei Ab, later named Tadmor) has been confirmed to be orbiting the primary.

Gamma Cephei is the naked-eye star that will succeed Polaris as the Earth's northern pole star, due to axial precession. It will be closer to the northern celestial pole than Polaris around 3160 CE and will make its closest approach around 4250 CE. The 'title' will pass to Iota Cephei some time around 5200 CE.

Description

Gamma Cephei has an apparent magnitude of 3.21, nearly all of which is accounted for by the primary component, Gamma Cephei A. It is a binary star system with an orbital period of 66.8 years and an eccentricity (ovalness) of 0.14.[3] The pair are orbiting at a separation of Template:Val.[3]

The primary is about 5.7 billion years old and has evolved off the main sequence, having fused all of the hydrogen in its core. It has 1.3 times the mass of the Sun and has expanded to 4.7 times the Sun's radius.[9] The star is radiating nearly 12[10] times the luminosity of the Sun from its photosphere at an effective temperature of 4,806 K.[9] The secondary component, Gamma Cephei B, has a mass approximately 0.40 times that of the Sun.[6] It is probably a red dwarf of class M4, 6.2 magnitudes fainter than the primary.[6] It is assumed to be of similar age to its primary.

The spectrum of this star has served as one of the stable anchor points by which other stars are classified. It was listed as a standard star for the spectral class K1 IV in 1943, 1953 and 1973.[13] However, in 1989, it was given as a spectral standard for K1 III-IV. Its spectrum is notable for the strength of the cyano radical (CN) bands.[4] Analysis of the spectrum in 2018 gave a best match for a spectral type of K1 III.[10]

γ Cephei is catalogued as a suspected variable star with a brightness range between magnitudes 3.18 and 3.24,[5] based on its inclusion in an 1884 list of suspected variable stars.[14]

Nomenclature

γ Cephei (Latinised to Gamma Cephei) is the system's Bayer designation. Under the rules for naming objects in multiple star systems the two components are designated A and B.[15] Following its discovery the planet was designated Gamma Cephei Ab.

The system bore a traditional name variously spelled as Errai, Er Rai or Alrai, deriving from the Arabic الراعي (ar-rā‘ī), meaning 'the shepherd'. (The star Beta Ophiuchi is sometimes also called Alrai, but it is more commonly known as Cebalrai or Kelb Alrai, meaning 'shepherd's dog'.) In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] included a table of the first two batches of names approved by the WGSN; which included Errai for Gamma Cephei A.

In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets.[18] The process involved public nomination and voting for the new names.[19] In December 2015, the IAU announced the winning name was Tadmor for this planet.[20] It was submitted by the Syrian Astronomical Association and is the ancient Semitic name and modern Arabic name for the city of Palmyra, a World Heritage Site.[21]

In Chinese, the star is named Script error: No such module "Lang". (Shàowèi Zēng Bā, literally, the 8th added star of the Xingguan Shaowei, Shaowei: the Minor Guard[22]) belonging to the Left Wall of the Purple Forbidden enclosure (Script error: No such module "Lang"., Script error: No such module "Lang".), which refers to an asterism consisting of Gamma Cephei, Iota Draconis, Theta Draconis, Eta Draconis, Zeta Draconis, Upsilon Draconis, 73 Draconis and 23 Cassiopeiae.[23]

Planetary system

A planet orbiting Gamma Cephei A with a 2.7-year period was discovered in 1988.[24] Its existence was also announced in 1989.[25] This was the first-discovered extrasolar planet and its ostensible discovery was based on the same radial velocity technique later used successfully by others. However, the claim was challenged in 1992 by a paper[26] which favoured K-giant variability with a period equal to the stellar rotation, but in 2002, the existence of a planet with an orbital period of about 2.5 years was confirmed.[27]

The secondary star B orbits A at only 9.8 times the semimajor axis of A's planet.[28] The orbit of the planet is roughly perpendicular to the orbit of the binary. Dynamical modelling suggests that the Kozai–Lidov mechanism is at play here.[29]

Template:OrbitboxPlanet begin Template:OrbitboxPlanet Template:Orbitbox end

References

Template:Reflist

External links

Template:S-endTemplate:Stars of CepheusTemplate:Authority controlTemplate:Sky
Preceded byTemplate:S-bef/check Pole Star
3000–5200 Template:S-ttl/check 		Template:S-aft/check Succeeded by
  1. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named GaiaDR3
  2. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named bsc
  3. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named Mugrauer2022
  4. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named perkins
  5. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  6. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Neuhäuser2007
  7. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named jofre
  8. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named park2013
  9. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Knudstrup
  10. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Baines2018
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named baas25_1319
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gore
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "citation/CS1".
  18. ↑ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Cepheus
  23. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN
  24. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Campbell1988
  25. ↑ Script error: No such module "Citation/CS1".
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Hatzes2003
  28. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Torres2007
  29. ↑ Script error: No such module "Citation/CS1".
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