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Beta Cephei variable

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Type of variable star

Beta Cephei variables, also known asBeta Canis Majoris stars, arevariable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200,000K in their interiors. These stars are usually hot blue-white stars of spectral class B and should not be confused withCepheid variables, which are named afterDelta Cephei and are luminous supergiant stars.

Properties

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Alight curve for Beta Cephei, plotted fromTESS data^[1]

Beta Cephei variables are somewhatevolved stars of masses between about 7 and 20 M_{$_{\odot }$} (that is, 7–20 times asmassive as the Sun). Among their number are some of the brightest stars in the sky, such asBeta Crucis andBeta Centauri;Spica is also classified as a Beta Cephei variable but mysteriously stopped pulsating in 1970.^[2] Typically, they change in brightness by 0.01 to 0.3 magnitudes with periods of 0.1 to 0.3 days (2.4–7.2 hours).^[2] The prototype of these variable stars,Beta Cephei, shows variation inapparent magnitude from +3.16 to +3.27 with a period of 4.57 hours. The point of maximum brightness occurs when the star is smallest and hottest. Their variation in brightness is much greater—up to 1 magnitude—inultraviolet wavelengths.^[3] A small number of stars have been identified with periods shorter than one hour, corresponding to 1/4 of the fundamental radial pulsation period and 3/8 of the fundamental period. They also have relatively low amplitudes and a very narrow range of spectral types B2-3 IV-V. They are known as the short period group and the GCVS acronym BCEPS.^[4]^[5]

The pulsations of Beta Cephei variables are driven by thekappa mechanism andp-mode pulsations. At a depth within the star where the temperature reaches 200,000 K, there is an abundance of iron. Iron at these temperatures will increase (rather than decrease) in opacity, resulting in the buildup of energy within the layer. This results in increased pressure that pushes the layer back out again, the cycle repeating itself in a matter of hours. This is known as the Fe bump or Z bump (Z standing for the star'smetallicity).^[6] The similarslowly pulsating B stars show g-mode pulsations driven by the same iron opacity changes, but in less massive stars and with longer periods.^[7]

History of observations

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American astronomerEdwin Brant Frost discovered the variation in radial velocity of Beta Cephei in 1902, initially concluding it was a spectroscopic binary.Paul Guthnick was the first to detect a variation in brightness, in 1913.^[8] Beta Canis Majoris andSigma Scorpii were found to be variable not long afterwards,^[3]Vesto Slipher noted in 1904 that Sigma Scorpii's radial velocity was variable, and R.D. Levee andOtto Struve concluded this was due to the star's pulsations in 1952 and 1955 respectively.^[9] These variables were often called Beta Canis Majoris variables because Beta Canis Majoris was the most closely studied example in the first half of the 20th century, though its location in the southern sky meant that its lowness in the sky hampered observations.^[10] However, Beta Cephei was the first member of the class to be discovered and so they are generally called Beta Cephei variables—despite the similarity of name (and risk of confusion) with Cepheid variables.^[3]

Cecilia Payne-Gaposchkin andSergei Gaposchkin catalogued 17 probable members of the class in their 1938Variable Stars, though classified them withDelta Scuti variables.^[11]16 Lacertae was another star extensively studied before 1952.^[10] The number known jumped from 18 to 41 in 1966.^[12]Otto Struve studied these stars extensively in the 1950s, however research declined after his death.^[3]

Christiaan L. Sterken and Mikolaj Jerzykiewicz classed 59 stars as definite and 79 more as suspected Beta Cephei variables in 1993.^[13] Stankov listed 93 members of the class in a 2005 catalogue, plus 77 candidates and 61 poor or rejected stars.^[14] Six stars, namelyIota Herculis,53 Piscium,Nu Eridani,Gamma Pegasi,HD 13745 (V354 Persei) and53 Arietis had been found to exhibit both Beta Cephei and SPB variability.^[15]

In 2021β Cru became the first star of any kind to have its pulsation modes identified using polarimetricasteroseismology.^[16]

List of Beta Cephei variables

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Designation (name)	Constellation	Discovery	MaximumApparent magnitude (m_V)^[17]	MinimumApparent magnitude (m_V)^[17]	Period (hours)^[14]	Spectral class^[14]	Comment
β CMa	Canis Major	1909 (William Wallace Campbell^[18])	1^m.93	2^m.00	6.031	B1II-III	Pulsations of 6.03, 6.00, and 4.74 hours.^[19]
ξ¹ CMa	Canis Major	^[20]	4^m.33	4^m.36	5.030	B0.5IV
15 CMa	Canis Major	^[20]	4^m.79	4^m.84	4.429	B1III-IV
V376 Car^[21]	Carina		4^m.91	4^m.96	0.4992	B2IV-V	BCEPS star
V372 Car	Carina	^[22]	5^m.70		2.78	B2III
β Cen	Centaurus		0^m.61		3.768^[13]	B1II
ε Cen	Centaurus		2^m.29	2^m.31	4.070	B1V
κ Cen	Centaurus		3^m.13	3^m.14	2.288	B2IV
χ Cen^[21]	Centaurus		4^m.40^[14]		0.84	B2V	BCEPS star
β Cep	Cepheus	1902 (Edwin Brant Frost)^[23]	3^m.16	3^m.27	4.572	B2IIIe	Prototype
δ Cet	Cetus	^[20]	4^m.05	4^m.1	3.867	B2IV
β Cru	Crux		1^m.23	1^m.31	4.589	B0.5IV
δ Cru^[17]^[24]	Crux		2^m.78	2^m.84	3.625	B2IV
ω¹ Cyg	Cygnus		4^m.94			B2.5IV	confirmed on hi res spectroscopy.^[24]
ν Eri	Eridanus		3^m.87	4^m.01	4.164	B2III	Multiperiodic; also a slowly pulsating B star
12 Lac	Lacerta		5^m.16	5^m.28	4.634	B1.5III	Also aslowly pulsating B star
16 Lac	Lacerta		5^m.30 (B)	5^m.52 (B)	4.109	B2IV
α Lup	Lupus	1956 (Bernard Pagel)^[25]	2^m.29	2^m.34	6.235	B1.5III
δ Lup^[14]	Lupus		3^m.20	3^m.24	3.972	B2IV
ε Lup^[26]	Lupus		3^m.36	3^m.38	2.316	B2IV + B3V	Triple star system; primary is aspectroscopic binary
ι Lup^[27]	Lupus		3^m.54	3^m.3.55		B2.5IV	not recorded as BCEP since 1997
τ¹ Lup^[14]	Lupus		4^m.54	4^m.58	4.257	B2IV
19 Mon	Monoceros		4^m.96	5^m.01	4.589	B1IV-Vea
α Mus^[17]	Musca		2^m.68	2^m.73	2.167	B2IV-V	initially questionable, confirmed on hi res spectroscopy.^[24]
θ Oph	Ophiuchus		3^m.25	3^m.31	3.373	B2IV
η Ori	Orion		3^m.31	3^m.35	7.247	B0.5Vea + B3V	Quadruple star; also anAlgol variable; component Ab is the pulsating star
γ Peg	Pegasus	1953 (D. Harold McNamara)	2^m.78	2^m.89	3.643	B2IV	Also aslowly pulsating B star
ε Per	Perseus		2^m.88	3^m.00	3.847	B0.5V
PT Pup	Puppis	^[14]	5^m.72	5^m.74	3.908	B2III
λ Sco	Scorpius		1^m.59	1^m.65	5.129	B1.5IV + PMS + B2IV	Triple system; also anAlgol variable
κ Sco	Scorpius		2^m.41	2^m.42	4.795	B1.5III
σ Sco	Scorpius	1904 (Vesto Slipher)	2^m.86	2^m.94	5.923	B1III	Quadruple system
Spica	Virgo		0^m.85	1^m.05	6.520	B1IV	Brightness variations stopped in 1970^[28]
BW Vul	Vulpecula		6^m.44	6^m.68	4.8	B2IIIv	Beta Cephei variable with largest change in radial velocity

List of former, excluded or candidate Beta Cephei variables

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Designation (name)	Constellation	MaximumApparent magnitude (m_V)^[17]	MinimumApparent magnitude (m_V)^[17]	Period (hours)^[14]	Spectral class^[14]	Comment
ι CMa	Canis Major	4^m.36	4^m.40	33.6^[17]	B3Ib/II	Not considered a β Cep variable^[14]^[29]
FN CMa^[30]	Canis Major	5^m.38	5^m.42	36.7^[31]	B0.5IV	No longer considered a β Cep variable^[14]
χ Car^[32]	Carina	3^m.46		2.42	B2IV	Not considered a β Cep variable^[14]
V343 Car	Carina	4^m.30^[14]		57.11	B1.5III	Not considered a β Cep variable^[14]
ζ Cha^[27]	Chamaeleon	5^m.06	5^m.17	25.91^[27]	B5V	considered as a SBP as of 2011^[22]
λ Cru	Crux	4^m.60	4^m.64	9.482^[17]	B4Vne	Not considered a β Cep variable^[14]
θ² Cru	Crux	4^m.70	4^m.74	2.134^[17]	B2IV	Not considered a β Cep variable^[14]
25 Cyg	Cygnus	5^m.09^[33]	5^m.21^[33]	5.04^[34]	B3IVe	γ Cas variable, not considered a β Cep variable^[14]
ι Her	Hercules	2^m.93			B3IV	No longer classed as Beta Cephei type^[14]
η Hya	Hydra	4^m.27	4^m.33	~4^[32]	B3V	No longer classed as Beta Cephei type^[14]
NW Pup	Puppis	5^m.04	5^m.18	3.00	B3Vea	Also arotating ellipsoidal variable, not considered a β Cep variable^[14]
α Pyx^[20]	Pyxis	3^m.67	3^m.70		B1.5III	Candidate β Cephei variable
Merope	Taurus	4^m.17	4^m.19		B6IVe	B(e) star, not Beta Cephei type^[14]
IS Vel^[17]	Vela	5^m.23		2.592	B1IVn	Candidate β Cephei variable^[14]
HR 3440 (HW Vel)^[17]	Vela	5^m.46	5^m.52	6.275	B6V	Candidate β Cephei variable^[14]
2 Vul	Vulpecula	5^m.36	5^m.48	14.63	O8IV-B0.5IVeV	B(e) star, not Beta Cephei type^[14]

References

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^"MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved8 December 2021.
^^a ^bBSJ (16 July 2010)."The Beta Cephei Stars and Their Relatives".Variable Star of the Season. American Association of Variable Star Observers. Retrieved2 August 2015.
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^LeBlanc, Francis (2010).An Introduction to Stellar Astrophysics. John Wiley and Sons. p. 196.ISBN 978-0-470-69957-7.
^Miglio, A. (2007). "Revised instability domains of SPB and β Cephei stars".Communications in Asteroseismology.151:48–56.arXiv:0706.3632.Bibcode:2007CoAst.151...48M.doi:10.1553/cia151s48.ISSN 1021-2043.S2CID 16623201.
^Guthnick, P. (1913)."Nachweis der Veränderlichkeit des kurzperiodischen spektroskopischen Doppelsternsβ Cephei mittels photoelektrischer Messungen".Astronomische Nachrichten.196 (26):357–364.Bibcode:1913AN....196..357G.doi:10.1002/asna.19131962602.ISSN 0004-6337.
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^^a ^b ^cTelting, J. H.; Schrijvers, C.; Ilyin, I. V.; Uytterhoeven, K.; De Ridder, J.; Aerts, C.; Henrichs, H. F. (2006)."A high-resolution spectroscopy survey of β Cephei pulsations in bright stars".Astronomy and Astrophysics.452 (3):945–953.Bibcode:2006A&A...452..945T.doi:10.1051/0004-6361:20054730.hdl:2066/36162.ISSN 0004-6361.
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Variable stars

Pulsating

Cepheids and cepheid-like	Type I(Classical cepheids,Delta Scuti) Type II(BL Herculis,W Virginis,RV Tauri) RR Lyrae Rapidly oscillating Ap SX Phoenicis
Blue-white with early spectra	Alpha Cygni Beta Cephei Slowly pulsating B-type PV Telescopii Blue large-amplitude pulsator
Long-period	Mira Semiregular Slow irregular
Other	Gamma Doradus Heartbeat Solar-like oscillations White dwarf

Eruptive

Protostar andPMS	Herbig Ae/Be Orion FU Orionis T Tauri
Giants and supergiants	Luminous blue variable R Coronae Borealis(DY Persei) Yellow hypergiant
Eruptive binary	Double periodic FS Canis Majoris RS Canum Venaticorum
Other	Flare Gamma Cassiopeiae Lambda Eridani Wolf–Rayet

Cataclysmic

Rotating

Non-spherical	Rotating ellipsoidal
Stellar spots	BY Draconis FK Comae Berenices
Magnetic fields	α² Canum Venaticorum Pulsar SX Arietis

Eclipsing

Star portal *List

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