Beta Cephei

Short description: Star in the constellation Cepheus

β Cephei

Location of β Cephei (circled)

Observation data
Equinox J2000.0]] (ICRS)
Constellation | Cepheus
Right ascension |  21h 28m 39.59685s[1]
Declination | +70° 33′ 38.5747″[1]
Apparent magnitude (V) | 3.16 to 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]
Astrometry
Radial velocity (Rv)| −8.2[5] km/s
Proper motion (μ)|  RA: +12.54 mas/yr
Dec.: +8.39 mas/yr
Parallax (π)| 4.76 ± 0.30[1] mas
Distance| 690 ± 40 ly
(210 ± 10 pc)
Absolute magnitude (MV)| −3.03[3]
Orbit[6]
Primary| β Cep Aa
Companion| β Cep Ab
Period (P)| 29616.54±1.36 d
Semi-major axis (a)| 206.96±0.53 mas
Eccentricity (e)| 0.7478±0.0005
Inclination (i)| 88.80±0.07°
Longitude of the node (Ω)| 227.83±0.14°
Periastron epoch (T)| 2450944.5±24.2
Argument of periastron (ω)
(secondary)| 202.43±0.31°
Semi-amplitude (K1)
(primary)| 9.63±0.26 km/s
Details
β Cep Aa
Mass| 7.4[6] M☉
Radius| 7.22±0.42[7] R☉
Luminosity| 20,000+5,200
−4,100[8] L☉
Surface gravity (log g)| 4.12±0.07[7] cgs
Temperature| 23,600±1,000[7] K
Metallicity [Fe/H]| −0.23[9] dex
Rotational velocity (v sin i)| 28[10] km/s
Age| 8.7[3] Myr
β Cep Ab
Mass| 5.0[6] M☉
Other designations

Alfirk, β Cep, 8 Cephei, BD+69°1173, FK5 809, HD 205021, HIP 106032, HR 8238, SAO 10057, CCDM J21287+7034A, WDS J21287+7034, GSC 04465-02643[11]

Database references
SIMBAD| data

Beta Cephei is a triple star system in the northern constellation of Cepheus. Its name is a Bayer designation that is Latinized from β Cephei, and abbreviated Beta Cep or β Cep. This system is a visible to the naked eye as a point of light with a combined apparent visual magnitude that ranges from 3.16 to 3.27, making it a third magnitude star.[2] 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)[12][13] and Ab.

## Contents

* 1 Nomenclature
* 2 Visibility
* 3 Pole Star
* 4 Properties
* 5 Variability
* 6 References
* 7 External links

## 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).[14]

Beta Cephei bore the traditional name Alfirk, derived from the Arabic الفرقة al-firqah "the flock" (of sheep). With Alpha Cephei (Alderamin) and Eta Cephei (Alkidr), they were Al Kawākib al Firḳ الكوكب الفرق "the stars of the flock" by Ulug Beg.[15][16] In 2016, the IAU organized a Working Group on Star Names (WGSN)[17] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[18] 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.[13]

## Visibility

Like the star Epsilon Draconis in the constellation of Draco, Beta Cephei is visible primarily in the 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 precessional path traced across the celestial sphere by the Earth's North pole. During the same period Iota Cephei will also be within 5° of the precessional path, on the other side so that both are in contention as 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[19]

Beta Cephei is a triple star comprising a spectroscopic binary with a magnitude 8 optical companion.[20] 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.[21] This star has a radius that has been estimated at 7.2 R☉[7] 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.[22] 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 Beta Cephei class of variables, hot main sequence and giant stars that pulsate analogously to Cepheid variables but with the pulsations driven by iron opacity rather than by helium.[2]

## References

1. ↑ 1.0 1.1 1.2 van Leeuwen, F. (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.
2. ↑ 2.0 2.1 2.2 2.3 2.4 Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1. Bibcode: 2009yCat....102025S.
3. ↑ 3.0 3.1 3.2 3.3 3.4 Nieva, María-Fernanda; Przybilla, Norbert (2014). "Fundamental properties of nearby single early B-type stars". Astronomy & Astrophysics 566: A7. doi:10.1051/0004-6361/201423373. Bibcode: 2014A&A...566A...7N.
4. ↑ 4.0 4.1 Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data (SIMBAD). Bibcode: 1986EgUBV........0M.
5. ↑ Wilson, Ralph Elmer (1953). General catalogue of stellar radial velocities. Washington: Carnegie Institution of Washington. Bibcode: 1953GCRV..C......0W.
6. ↑ 6.0 6.1 6.2 6.3 6.4 Hutter, D. J. et al. (2021). "Surveying the Bright Stars by Optical Interferometry. III. A Magnitude-limited Multiplicity Survey of Classical Be Stars". The Astrophysical Journal Supplement Series 257 (2): 69. doi:10.3847/1538-4365/ac23cb. Bibcode: 2021ApJS..257...69H.
7. ↑ 7.0 7.1 7.2 7.3 Gordon, Kathryn D. et al. (2019). "Angular Sizes, Radii, and Effective Temperatures of B-type Stars from Optical Interferometry with the CHARA Array". The Astrophysical Journal 873 (1): 91. doi:10.3847/1538-4357/ab04b2. Bibcode: 2019ApJ...873...91G.
8. ↑ Shultz, M. E. et al. (2019). "The magnetic early B-type Stars II: Stellar atmospheric parameters in the era of Gaia". Monthly Notices of the Royal Astronomical Society 485 (2): 1508. doi:10.1093/mnras/stz416. Bibcode: 2019MNRAS.485.1508S.
9. ↑ Cenarro, A. J. et al. (2007). "Medium-resolution Isaac Newton Telescope library of empirical spectra – II. The stellar atmospheric parameters". Monthly Notices of the Royal Astronomical Society 374 (2): 664–690. doi:10.1111/j.1365-2966.2006.11196.x. Bibcode: 2007MNRAS.374..664C.
10. ↑ Hoffleit, D.; Warren Jr, W. H. (1991). "Bright Star Catalogue". VizieR. Centre de Données astronomiques de Strasbourg. http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR 8238. Retrieved 2010-12-26.
11. ↑ "bet Cep". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=bet+Cep.
12. ↑ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
13. ↑ 13.0 13.1 "Naming Stars". IAU.org. https://www.iau.org/public/themes/naming_stars/. Retrieved 18 June 2018.
14. ↑ Hessman, F. V.; et al. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
15. ↑ Allen, R. H.. Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc.. p. 157. ISBN 0-486-21079-0. https://archive.org/details/starnamestheirlo00alle/page/157. Retrieved 2010-12-12.
16. ↑ Davis, George R. (1944). "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names". Popular Astronomy 52: 8. Bibcode: 1944PA.....52....8D.
17. ↑ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. https://www.iau.org/science/scientific_bodies/working_groups/280/. Retrieved 22 May 2016.
18. ↑ "WG Triennial Report (2015-2018) - Star Names". p. 5. https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf. Retrieved 2018-07-14.
19. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
20. ↑ Norton, Arthur P. (1973). Norton's Star Atlas. Gall & Inglis. p. 118. ISBN 0-85248-900-5. https://archive.org/details/nortonsstaratlas0000nort. "Fixed. A is a spectroscopic binary."
21. ↑ Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009–2016)". VizieR On-line Data Catalog: B/Mk. Originally Published in: Lowell Observatory (October 2014) 1. Bibcode: 2014yCat....1.2023S.
22. ↑ Gezari, D. Y. et al. (1972). "Speckle Interferometry: Diffraction-Limited Measurements of Nine Stars with the 200-INCH Telescope". Astrophysical Journal 173: L1. doi:10.1086/180906. Bibcode: 1972ApJ...173L...1G.

## External links

* Jim Kaler's Stars, University of Illinois:ALFIRK (Beta Cephei)
* AAVSO Variable Star of the Month, Winter 2005: The Beta Cephei Stars and Their Relatives
* An Atlas of the Universe: Multiple Star Orbits

* v
* t
* e

Cepheus constellation

Stars (list)|

| Bayer|

* α (Alderamin)
* β (Alfirk)
* γ (Errai)
* δ
* ε
* ζ
* η
* θ
* ι
* κ
* λ
* μ (Garnet Star)
* ν
* ξ (Kurhah)
* ο
* π
* ρ1
* ρ2

|

Flamsteed|

* 4
* 6
* 7
* 9
* 11
* 12
* 13
* 14
* 15
* 16
* 18
* 19
* 20
* 24
* 25
* 26
* 30
* 31
* 77 Dra
* 78 Dra
* 79 Dra
* 80 Dra
* 2 UMi

Variable|

* S
* T
* U
* V
* W
* RW
* RZ
* SV
* VV
* VW
* WX
* WZ
* XX
* XZ
* ZZ
* AH
* AK
* BH
* BO
* CP
* CQ
* CR
* CW
* CX
* DH
* DI
* DO
* DQ
* EE
* EG
* EI
* EK
* EM
* GP
* GW
* IL
* IR
* IV
* NY
* OV
* PQ
* PV
* V350
* V354
* V368
* V374
* V379
* V380
* V381
* V388
* V398
* V408
* V414
* V419
* V421
* V422
* V426
* V431
* V438
* V444
* V458

HR|

* 20
* 55
* 158
* 240
* 306
* 312
* 333
* 357
* 386
* 572
* 597
* 774
* 881
* 906
* 961
* 965
* 1107
* 1304
* 1317
* 1523
* 1616
* 1885
* 7742
* 7925
* 7938
* 7955
* 7967
* 7993
* 8029
* 8043
* 8049
* 8065
* 8099
* 8119
* 8133
* 8150
* 8168
* 8174
* 8179
* 8226
* 8239
* 8243
* 8281
* 8312
* 8327
* 8342
* 8347
* 8357
* 8374
* 8375
* 8384
* 8388
* 8395
* 8442
* 8472
* 8474
* 8476
* 8479
* 8483
* 8490
* 8493
* 8506
* 8535
* 8537
* 8546
* 8557
* 8568
* 8595
* 8598
* 8599
* 8625
* 8677
* 8683
* 8687
* 8696
* 8702
* 8707
* 8736
* 8745
* 8748
* 8779
* 8808
* 8811
* 8844
* 8867
* 8918
* 8938
* 8952
* 8971
* 8972
* 9005
* 9013
* 9038
* 9104

HD|

* 12918
* 12927
* 25904
* 200775
* 204521
* 204827
* 207538
* 207826
* 208132
* 208392
* 212136
* 215588
* 217903
* 224890

Gliese|

* Gliese 48
* Gliese 809
* GJ 1277

Other|

* Cepheus A HW 2
* Cepheus X-4
* IRAS 21391+5802
* Kruger 60
* NGC 7538 IRS 1
* NGC 7538 IRS 9
* OH 104.9+2.4
* PSR B2224+65
* PSR J2229+6114
* S140 IRS 1
* TYC 3980-1081-1
* 4U 2206+54
* WISE 0313+7807
* WR 152
* WR 156

Star clusters|

| Association|

* Cepheus OB2
* Cepheus OB3
* Cepheus OB4

|

Open|

* NGC 188
* NGC 6939
* NGC 7023
* NGC 7129
* NGC 7142
* NGC 7160
* NGC 7226
* NGC 7234
* NGC 7261
* NGC 7281
* NGC 7380
* NGC 7419
* NGC 7423
* NGC 7429
* NGC 7510
* NGC 7762
* S 140
* Trumpler 37

Globular|

* Palomar 1

Molecular clouds|

* Cepheus A
* Cepheus B
* Cepheus C

Nebulae|

| Dark|

* Barnard 150
* CB 244
* Elephant's Trunk Nebula
* IC 1396N
* L1157
* L1228

|

H II|

* IC 1396
* NGC 7538
* NGC 7822
* S 128
* S 140
* S 155
* S 156

Reflection|

* Ghost Nebula
* Iris Nebula
* NGC 7129
* VdB 157

Planetary|

* NGC 40
* NGC 7076
* NGC 7139
* NGC 7354

SNR|

* CTA 1
* SSTGFLS J222557+601148

Galaxies|

| NGC|

* 1184
* 1544
* 2276
* 2300
* 6949
* 6952

|

Other|

* 3C 61.1
* 3C 427.1
* 4C +74.26
* QSO B2021+614
* S5 0014+81

Other|

* GRB 980519
* SN 2008S

Coordinates:  21h 28m 39.60s, +70° 33′ 39.0″

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