Beta Cephei

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Alfirk, β Cep
Observation data Epoch J2000 Equinox J2000
Location of β Cephei (center right).
Constellation	Cepheus
Right ascension	21^h 28^m 39.5971^s^[1]
Declination	+70° 33′ 38.578″^[1]
Apparent magnitude (V)	3.1438^[2]
Characteristics
Spectral type	B2IIIev^[1]
U−B color index	–0.95^[3]
B−V color index	–0.22^[3]
Variable type	Beta Cephei variable
Astrometry

Radial velocity (R_v)	–8.2^[1] km/s
Proper motion (μ)	RA: +12.54^[2] mas/yr Dec.: +8.39^[2] mas/yr
Parallax (π)	4.76 ± 0.30^[2] mas
Distance	690 ± 40 ly (210 ± 10 pc)
Absolute magnitude (M_V)	–3.468^[2]

Details

Mass	12^[4] M_☉
Radius	9.0^[5] R_☉
Luminosity	36,900^[6] L_☉
Surface gravity (log g)	3.80^[7] cgs
Temperature	26,700^[4] K
Metallicity [Fe/H]	–0.23^[8] dex
Rotational velocity (v sin i)	28^[9] km/s

Other designations
Alfirk, 8 Cep, AAVSO 2127+70, AG+70° 738, BD+69 1173, CCDM J21287+7034A, FK5 809, GSC 04465-02643, HD 205021, HIP 106032, HR 8238, SAO 10057, WDS J21287+7034 Aa,Ab.^[1]
Database references
SIMBAD	data

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

Beta Cephei (β Cep, β Cephei) is a third magnitude star in the constellation Cepheus. It has the traditional name Alfirk (Arabic الفرقة al-firqah), meaning "The Flock" (referring to a flock of sheep) This star, along with α Cep (Alderamin) and η Cep (Alkidr), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg.^[10]^[11] Beta Cephei is the prototype of the Beta Cephei variable stars.

Visibility

Like the star Epsilon Draconis in the constellation of Draco, Alfirk is visible primarily in the northern hemisphere, given its extreme northern declination of 70 degrees and 34 minutes. The star 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. The star 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.

Properties

Beta Cephei is a triple star comprising a spectroscopic binary with a magnitude 8 optical companion.^[12] Its magnitude varies between +3.15 and +3.21 with a period of 0.1904844 days.

Beta Cephei A is a blue giant star with a stellar classification listed in the SIMBAD astronomical database as B2IIIev.^[1] The suffix "ev" comes from the Yerkes classification system and stands for "Spectral emission that exhibits variability". This giant star has a radius that has been estimated at 9R_☉ and a mass of 12M_☉. Like most high mass B class stars, β Cep is a relatively young star with an estimated age of around 50 million years old. Like the majority of giant stars, Beta Cephei A rotates slowly on its axis with a rotational velocity of 28 km/s, a speed which takes the star approximately 51 days to make one complete revolution.

In 2007, Floor van Leeuwen and his team recalibrated the star's apparent magnitude at 3.1438 and updated the star's parallax to 4.76 ± 0.30 mas yielding a distance of 210.1 parsecs (pc) or approximately 685 light years (ly) from Earth.^[2] The previous estimate from the Hipparcos mission had placed the star at about 595 ly. Given a surface temperature of 26,700 Kelvin, theoretical calculations yield a total luminosity for the star of about 36,900L_☉.^{[note 1]}

Notes

↑ The formula for the bolometric luminosity of Beta Cephei is as follows:
${\frac {L_{{{\rm {A}}}}}{L_{{\odot }}}}={\left({\frac {R_{{{\rm {A}}}}}{R_{{\odot }}}}\right)}^{2}{\left({\frac {T_{{{\rm {A}}}}}{T_{{\odot }}}}\right)}^{4}$ where... A = Alfirk, L = Luminosity, R = Radius and T = Temperature.
Therefore:
${\frac {L_{{{\rm {A}}}}}{L_{{\odot }}}}={\left({{\frac {9}{1}}}\right)}^{2}{\left({{\frac {26,700}{5,778}}}\right)}^{4}=36,933L_{{\odot }}$
Note: Luminosity calculations are highly dependent on size and distance variables.

References

↑ 1.0 1.1 1.2 1.3 1.4 1.5 "V* bet Cep -- Variable Star of beta Cep type", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2010-12-26
↑ 2.0 2.1 2.2 2.3 2.4 2.5 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 2010-12-26
↑ 3.0 3.1 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data. (SIMBAD), Bibcode:1986EgUBV........0M
↑ 4.0 4.1 Kaler, James B., "ALFIRK (Beta Cephei)", Stars (University of Illinois), retrieved 2010-12-26
↑ Stebbins, J.; Kron, G. E. (September 1954), "Six-color photometry of stars. VIII. The pulsating star Beta Cephei", The Astrophysical Journal (PDF|format= requires |url= (help)) (GCPD) 120: 189, Bibcode:1954ApJ...120..189S, doi:10.1086/145902
↑ See Notes Section for calculations
↑ Lefever, K. et al. (June 2010), "Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite", Astronomy and Astrophysics 515: A74, arXiv:0910.2851, Bibcode:2010A&A...515A..74L, doi:10.1051/0004-6361/200911956
↑ 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 (PDF|format= requires |url= (help)) 374 (2): 664–690, arXiv:astro-ph/0611618, Bibcode:2007MNRAS.374..664C, doi:10.1111/j.1365-2966.2006.11196.x
↑ Hoffleit (1991), "Bright Star Catalogue", VizieR (5th revised ed.) (Centre de Données astronomiques de Strasbourg), retrieved 2010-12-26
↑ 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.
↑ 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.
↑ Norton, Arthur P. (1973). Norton's Star Atlas. p. 118. ISBN 0-85248-900-5. "Fixed. A is a spectroscopic binary."

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 Stars of Cepheus

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 2 UMi 77 Dra 78 Dra

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 V379 V380 V381 V388 V398 V408 V414 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 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 8473 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 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 4U 2206+54 WISE 0313+7807 WR 152

List

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