Alpha Cephei

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α Cephei
Template:Location mark
Location of α Cephei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 2.46[2]
Characteristics
Evolutionary stage Subgiant[3]Template:Rp
Spectral type A8Vn[4] or A7IV-V[3]
U−B Template:Engvar +0.12[5]
B−V Template:Engvar +0.21[5]
Variable type suspected δ Sct[6]
Astrometry
Radial velocity (Rv)Script error: No such module "val".[7] km/s
Proper motion (μ) RA: +150.55[1] mas/yr
Dec.: 49.09[1] mas/yr
Parallax (π)66.50±0.11 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)1.57[8]
Details
MassScript error: No such module "val".[9] Template:Solar mass
RadiusScript error: No such module "val". (polar)[9]
Script error: No such module "val". (equator)[9] Template:Solar radius
LuminosityScript error: No such module "val".[9] Template:Solar luminosity
TemperatureScript error: No such module "val". (polar)[9]
Script error: No such module "val". (equator)[9] K
Metallicity [Fe/H]+0.09[4] dex
RotationScript error: No such module "val".[3] hours
Rotational velocity (v sin i)Script error: No such module "val".[3] km/s
AgeScript error: No such module "val".[9] Myr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[10]
Database references
SIMBADdata

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Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin Template:IPAc-en,[11][12] is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (ly) and drifting closer with a heliocentric radial velocity of about −16 km/s.

Nomenclature

α Cephei (Latinised to Alpha Cephei) is the star's Bayer designation. It has a Flamsteed designation of 5 Cephei.

It bore the traditional name Alderamin, a contraction of the Arabic phrase الذراع اليمين al-dhirā‘ al-yamīn, meaning "the right arm". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Alderamin for this star.

Visibility

With a declination in excess of 62 degrees north, Alpha Cephei never rises south of −27° latitude, which means for much of South America, Australia, South Africa, and all of New Zealand, the star stays below the horizon. The star is circumpolar throughout all of Europe, northern Asia, Canada, and American cities as far south as San Diego. Since Alpha Cephei has an apparent magnitude of about 2.5, the star is the brightest in the constellation and is easily observable to the naked eye, even in light-polluted cities.

Pole star

Alpha Cephei is located near the precessional path traced across the celestial sphere by the Earth's North pole. That means that it periodically comes within 3° of being a pole star,[15] a title currently held by Polaris. Alpha Cephei will next be the North Star in about the year 7500 AD.[16] The north pole of Mars points to the midpoint of the line connecting the star and Deneb.[17]

Preceded by Pole Star Succeeded by
Iota Cephei circa 19,000BC and 7500AD to 8700AD Deneb

Properties

File:AlphaCepLightCurve.png
A light curve for Alpha Cephei, plotted from TESS data[18]

Alderamin is a white class A star, evolving off the main sequence into a subgiant, probably on its way to becoming a red giant as its hydrogen supply runs low.[3] On average, Alderamin has an apparent magnitude of 2.46.[2] In 2007, the star's parallax was measured at Script error: No such module "val". yielding a distance of 15 parsecs or approximately 49 light years from Earth.[1]

Interferometry by the CHARA array show that Alderamin has an oblate shape, its equatorial size measures Template:Solar radius and the polar radius measures Template:Solar radius. The star's temperature varies as well, from 8,558 K in the poles to 6,574 K in the equator.[9] A more recent but less detailed measurement by the Navy Precision Optical Interferometer gives Template:Solar radius, which likely corresponds to the equatorial radius.[19] Like other stars in its class, it is slightly variable with a range in brightness of 0.06 magnitude, and is listed as a Delta Scuti variable.

Alderamin has a very high rotation speed of at least 246 km/s, completing one complete revolution in less than 12 hours, with such a rapid turnover appearing to inhibit the differentiation of chemical elements usually seen in such stars.[20] By comparison, the Sun takes almost a month to turn on its axis. Alpha Cephei is also known to emit an amount of X radiation similar to the Sun, which along with other indicators suggests the existence of considerable magnetic activity—something unexpected (though not at all unusual) for a fast rotator.

Etymology and cultural significance

This star, along with Beta Cephei (Alfirk) and Eta Cephei (Alkidr) were al-Kawākib al-Firq (الكواكب الفرق), meaning "the Stars of the Flock" by Ulug Beg.[21][22]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Celestial Hook, refers to an asterism consisting of α Cephei, 4 Cephei, HD 194298, Eta Cephei, Theta Cephei, Xi Cephei, 26 Cephei, Iota Cephei and Omicron Cephei.[23] Consequently, the Chinese name for Alpha Cephei itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.).[24]

Alderamin on the Sky is a Japanese light novel series named after the star.

Namesakes

USS Alderamin (AK-116) was a United States Navy Crater class cargo ship named after the star.

See also

References

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  1. ↑ a b c d e f Script error: No such module "Citation/CS1".
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  3. ↑ a b c d e Script error: No such module "Citation/CS1".
  4. ↑ a b Script error: No such module "Citation/CS1".
  5. ↑ a b Script error: No such module "Citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ Script error: No such module "Citation/CS1".
  8. ↑ Script error: No such module "Citation/CS1".
  9. ↑ a b c d e f g h Script error: No such module "Citation/CS1".
  10. ↑ Template:Cite simbad
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "citation/CS1".
  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. ↑ Script error: No such module "citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "Citation/CS1".
  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. ↑ Template:In lang 香港太空館 – 研究資源 – 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.

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External links

Template:Sky Template:Stars of Cepheus

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