Alpha Cephei

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Alpha Cephei
Diagram showing star positions and boundaries of the Cepheus constellation and its surroundings
Cercle rouge 100%.svg

Location of α Cephei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension 21h 18m 34.7715s[1]
Declination 62° 35′ 08.061″[1]
Apparent magnitude (V) 2.5141[2]
Characteristics
Spectral type A7IV-V[2]
U−B color index +0.12[3]
B−V color index +0.21[3]
Variable type Delta Scuti
Astrometry
Radial velocity (Rv) −10[1] km/s
Proper motion (μ) RA: +150.55[2] mas/yr
Dec.: 49.09[2] mas/yr
Parallax (π) 66.50 ± 0.11[2] mas
Distance 49.05 ± 0.08 ly
(15.04 ± 0.02 pc)
Absolute magnitude (MV) 1.57[4]
Details
Mass 1.74[4] M
Radius 2.3[5] R
Luminosity 17[5] L
Surface gravity (log g) 3.99[5] cgs
Temperature 7,740 ± 170[5] K
Rotational velocity (v sin i) 246[6] km/s
Other designations
Alderamin, 5 Cep, 2MASS J21183475+6235081, AG+62° 1226, BD +61°2111, CCDM J21186+6236A, FK5 803, GCTP 5139.00, Gl 826, HD 203280, HIP 105199, HR 8162, SAO 19302.
Database references
SIMBAD data

Alpha Cephei (α Cep, α Cephei) is a second magnitude star in the constellation of Cepheus that is relatively close to Earth at only 49 light years. It has the traditional name Alderamin, an Arabic name meaning "the right arm".

Visibility[edit]

With a declination in excess of 62 degrees north, Alderamin is mostly visible to observers in the northern hemisphere, though the star is still visible to latitudes as far south as -27°, albeit just above the horizon. The star is circumpolar throughout all of Europe, northern Asia, Canada and American cities as far south as San Diego. Since Alderamin has an apparent magnitude of about 2.5, the star is easily observable to the naked eye, even in light-polluted cities.

Properties[edit]

Alderamin is a white Class A star, evolving off of the main sequence into a subgiant, probably on its way to becoming a red giant as its hydrogen supply runs low. In 2007, the star's apparent magnitude was recalibrated at 2.5141 along with an updated parallax of 66.50 ± 0.11 mas yielding a distance of 15 parsecs or approximately 49 light years from Earth.[2]

Given a surface temperature of 7,740 Kelvin, stellar models yield a total luminosity for the star of about 17 times the luminosity of the Sun. Alderamin has a radius of 2.3 times the Sun's radius and boasting a mass that is 1.74 that of the Sun.[5] 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.[6] By comparison, the Sun takes almost a month to turn on its axis. α Cep 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.

Pole star[edit]

Alderamin 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, much as Polaris is at present. This will next occur about the year 7500 AD. The north pole of Mars lies halfway between Alderamin and the star Deneb.

Preceded by Pole Star Succeeded by
Iota Cephei circa 6,800 BC Deneb

Ethnological influences[edit]

Etymology[edit]

The name Alderamin is a contraction of the Arabic phrase الذراع اليمين að-ðirā‘ al-yamīn "the right arm," with the first definite article transliterated literally as al, as is often the case with Arabic star names.

This star, along with β Cep (Alfirk) and η Cep (Alkidr) were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg.[7][8]

In Chinese, 天鈎 (Tiān Gōu), meaning Celestial Hook, refers to an asterism consisting of α Cephei, 4 Cephei, HD 194298, η Cephei, θ Cephei, ξ Cephei, 26 Cephei, ι Cephei and ο Cephei.[9] Consequently, α Cephei itself is known as 天鈎五 (Tiān Gōu wu, English: the Fifth Star of the Celestial Hook.).[10]

Namesakes[edit]

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

See also[edit]

References[edit]

  1. ^ a b c "SIMBAD query result: NAME ALDERAMIN -- Variable Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-12-20. 
  2. ^ a b c d e f van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics (Centre de Données astronomiques de Strasbourg) 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Retrieved 2010-12-19. 
  3. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. Bibcode:1986EgUBV........0M. 
  4. ^ a b Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics 361: 614–628, Bibcode:2000A&A...361..614P 
  5. ^ a b c d e Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M 
  6. ^ a b "Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-12-20. 
  7. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 157. ISBN 0-486-21079-0. Retrieved 2010-12-12. 
  8. ^ Davis Jr., G. A., "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names,"Popular Astronomy, Vol. LII, No. 3, Oct. 1944, p. 16.
  9. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  10. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.

External links[edit]

Coordinates: Sky map 21h 18m 34.8s, +62° 35′ 08″