Beta Cephei

Coordinates: Sky map 21h 28m 39.60s, +70° 33′ 39.0″
Source: Wikipedia, the free encyclopedia.
β Cephei
Location of β Cephei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension 21h 28m 39.59685s[1]
Declination +70° 33′ 38.5747″[1]
Apparent magnitude (V) 3.16 – 3.27[2]
Characteristics
Spectral type B1 IV[3]
U−B color index –0.95[4]
B−V color index –0.22[4]
Variable type β Cep[2]
Distance
690 ± 40 ly
(210 ± 10 pc)
Absolute magnitude (MV)–3.03[3]
Semi-amplitude
(K1)
(primary)		9.63 ± 0.26 km/s
Details
β Cep Aa
Myr
β Cep Ab
Mass5.0[6] M☉
HR 8238, SAO 10057, WDS
 J21287+7034
Database references
SIMBADdata

Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a

triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-years distant from the Sun. It is the prototype of the Beta Cephei variable
stars.

It consists of a binary pair (designated Beta Cephei A) together with a third companion (B). The binary's two components are themselves designated Beta Cephei Aa (officially named Alfirk /ˈælfərk/, the traditional name for the system)[9][10] and Ab.

Nomenclature

β Cephei (Latinised to Beta Cephei) is the system's Bayer designation. The designations of the two constituents as Beta Cephei A and B, and those of A's components - Beta 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).[11]

Beta Cephei bore the traditional name Alfirk, derived from the

multiple systems.[15] It approved the name Alfirk for the component Beta Cephei Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[10]

Visibility

Like the star

northern hemisphere, given its extreme northern declination of 70 degrees and 34 minutes. It is nevertheless visible to most observers throughout the world reaching as far south as cities like Harare in Zimbabwe, Santa Cruz de la Sierra in Bolivia or other settlements north ± 19° South latitude. It is circumpolar throughout all of Europe, northern Asia, and North American cities as far south as Guadalajara in west central Mexico. All other locations around the globe having a latitude greater than ± 20° North will notice that the star is always visible in the night sky. Because Beta Cephei is a faint third magnitude star, it may be difficult to identify in most light polluted
cities, though in rural locations the star should be easily observable.

Pole Star

Beta Cephei is a visible star located within 5° of the

pole stars, a title currently held by unambiguously by Polaris
.

Preceded by
Pole Star
 Succeeded by
Errai 5200AD to 7500AD
with
Iota Cephei
Alderamin

Properties

A light curve for Beta Cephei, plotted from TESS data[16]

Beta Cephei is a

triple star comprising a spectroscopic binary with a magnitude 8 optical companion.[17] Its magnitude varies between +3.16 and +3.27 with a period of 0.19048 days.[2]

Beta Cephei Aa is a

blue subgiant star with a stellar classification of B1 IV. It has previously been classified with either a main sequence or giant luminosity class.[18] This star has a radius that has been estimated at 6 R☉[3] and a mass of 7 M☉. Other sources have given higher masses on the order of 12 M☉.[3] Like most high-mass B-class
stars, Beta Cephei Aa is a relatively young star with an estimated age of just a few million years. Like the majority of giant stars, it rotates slowly on its axis with a rotational velocity of 7 deg/day, a speed which takes the star approximately 51 days to make one complete revolution.

Beta Cephei Ab is a Be star in an 81-year orbit with the giant primary.[6] It has been resolved using speckle interferometry at a distance of 0.25" in 1972.[19] With a mass of about 5 M☉, it is likely a B-class star with a classification of B6.[6]

B Cephei B is a magnitude 7.8 A2 main sequence star 13.6" distant.[3]

Variability

Beta Cephei pulsates regularly every 4 hours 34 minutes, producing a variation in its visual brightness of 0.11 magnitudes. It is the prototype of the

Cepheid variables but with the pulsations driven by iron opacity rather than by helium.[2]

References

  1. ^
    S2CID 18759600
    .
  2. ^
    Bibcode:2009yCat....102025S
    .
  3. ^
    S2CID 119227033
    .
  4. ^
    Bibcode:1986EgUBV........0M
    .
  5. Bibcode:1953GCRV..C......0W
    .
  6. ^
    S2CID 237503492
    .
  7. S2CID 119428437
    .
  8. Centre de Données astronomiques de Strasbourg
    . Retrieved 2010-12-26.
  9. ISBN 978-1-931559-44-7
    .
  10. ^ a b "Naming Stars". IAU.org. Retrieved 18 June 2018.
  11. arXiv:1012.0707 [astro-ph.SR
    ].
  12. ISBN 0-486-21079-0
    . Retrieved 2010-12-12.
  13. Bibcode:1944PA.....52....8D
    .
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  16. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  17. ISBN 0-85248-900-5
    . Fixed. A is a spectroscopic binary.
  18. Bibcode:2014yCat....1.2023S
    .
  19. doi:10.1086/180906
    .

External links


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