Beta Cephei variable

Short description: Type of variable star

Beta Cephei variables, also known as Beta Canis Majoris stars, are variable 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 200,000 K in their interiors. These stars are usually hot blue-white stars of spectral class B and should not be confused with Cepheid variables, which are named after Delta Cephei and are luminous supergiant stars.

## Contents

* 1 Properties
* 2 History of observations
* 2.1 List of Beta Cephei variables
* 2.2 List of former, excluded or candidate Beta Cephei variables
* 3 References

## Properties

A light curve for Beta Cephei, plotted from TESS data[1]

Beta Cephei variables are somewhat evolved stars of masses between about 7 and 20 M⊙ (that is, 7–20 times as massive as the Sun). Among their number are some of the brightest stars in the sky, such as Beta Crucis and Beta 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 in apparent 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—in ultraviolet 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 the kappa mechanism and p-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's metallicity).[6] The similar slowly 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

American astronomer Edwin 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 and Sigma 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 and Otto 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 and Sergei Gaposchkin catalogued 17 probable members of the class in their 1938 Variable Stars, though classified them with Delta 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, namely Iota Herculis, 53 Piscium, Nu Eridani, Gamma Pegasi, HD 13745 (V354 Persei) and 53 Arietis had been found to exhibit both Beta Cephei and SPB variability.[15]

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

### List of Beta Cephei variables

Designation (name)  | Constellation  | Discovery  | Maximum Apparent magnitude (mV)[17] | Minimum Apparent magnitude (mV)[17] | Period (hours)[14] | Spectral class[14] | Comment

|
|
|
|
|
|
|

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

### List of former, excluded or candidate Beta Cephei variables

Designation (name)  | Constellation  | Discovery  | Maximum Apparent magnitude (mV)[17] | Minimum Apparent magnitude (mV)[17] | Period (hours)[14] | Spectral class[14] | Comment

|
|
|
|
|
|
|

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

## References

1. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
2. ↑ 2.0 2.1 BSJ (16 July 2010). "The Beta Cephei Stars and Their Relatives". Variable Star of the Season. American Association of Variable Star Observers. http://www.aavso.org/vsots_betacep.
3. ↑ 3.0 3.1 3.2 3.3 Lesh, Janet Roundtree; Aizenman, Morris L. (1978). "The Observational Status of the β Cephei Stars". Annual Review of Astronomy and Astrophysics 16: 215–240. doi:10.1146/annurev.aa.16.090178.001243. Bibcode: 1978ARA&A..16..215L.
4. ↑ Bezdenezhnyi, V. P. (2001). "On the Periods of the β Cephei Stars". Odessa Astronomical Publications 14: 118. Bibcode: 2001OAP....14..118B.
5. ↑ Good, Gerry A. (2003). "Pulsating Variable Stars". Observing Variable Stars. pp. 57–95. doi:10.1007/978-1-4471-0055-3_4. ISBN 978-1-85233-498-7. https://archive.org/details/observingvariabl0000good.
6. ↑ LeBlanc, Francis (2010). An Introduction to Stellar Astrophysics. John Wiley and Sons. p. 196. ISBN 978-0-470-69957-7. https://books.google.com/books?id=jAe4P3GIZRoC&pg=PT217.
7. ↑ Miglio, A. (2007). "Revised instability domains of SPB and β Cephei stars". Communications in Asteroseismology 151: 48–56. doi:10.1553/cia151s48. ISSN 1021-2043. Bibcode: 2007CoAst.151...48M.
8. ↑ Guthnick, P. (1913). "Nachweis der Veränderlichkeit des kurzperiodischen spektroskopischen Doppelsternsβ Cephei mittels photoelektrischer Messungen.". Astronomische Nachrichten 196 (26): 357–364. doi:10.1002/asna.19131962602. ISSN 0004-6337. Bibcode: 1913AN....196..357G. https://zenodo.org/record/1424896.
9. ↑ Tkachenko, A.; Aerts, C.; Pavlovski, K.; Degroote, P.; Papics, P. I.; Moravveji, E.; Lehmann, H.; Kolbas, V. et al. (2014). "Modelling of Scorpii, a high-mass binary with a Cep variable primary component". Monthly Notices of the Royal Astronomical Society 442 (1): 616–628. doi:10.1093/mnras/stu885. Bibcode: 2014MNRAS.442..616T.
10. ↑ 10.0 10.1 Struve, Otto (1952). "The present state of our knowledge of the β Canis Majoris or β Cephei Stars". Annales d'Astrophysique 15: 157. Bibcode: 1952AnAp...15..157S.
11. ↑ Payne-Gaposchkin, Cecilia; Gaposchkin, Sergei (1938). "Variable stars". Cambridge 5. Bibcode: 1938HarMo...5.....P. Reprinted in Payne-Gaposchkin, Cecilia; Gaposchkin, Sergei (1942). "On the Dimensions and Constitution of Variable Stars". Proc. Natl. Acad. Sci. U.S.A. 28 (11): 490–5. doi:10.1073/pnas.28.11.490. PMID 16578062. Bibcode: 1942PNAS...28..490P.
12. ↑ Percy, John R. (1967). "The Beta Cephei Stars". Journal of the Royal Astronomical Society of Canada 61: 117. Bibcode: 1967JRASC..61..117P.
13. ↑ 13.0 13.1 Sterken, Christiaan; Jerzykiewicz, Mikolaj (1993). "Beta Cephei stars from a photometric point of view". Space Science Reviews 62 (1–2): 95–171. doi:10.1007/bf00208707. ISSN 0038-6308. Bibcode: 1993SSRv...62...95S.
14. ↑ 14.00 14.01 14.02 14.03 14.04 14.05 14.06 14.07 14.08 14.09 14.10 14.11 14.12 14.13 14.14 14.15 14.16 14.17 14.18 14.19 14.20 14.21 14.22 14.23 Stankov, Anamarija; Handler, Gerald (2005). "Catalog of Galactic β Cephei Stars". The Astrophysical Journal Supplement Series 158 (2): 193–216. doi:10.1086/429408. ISSN 0067-0049. Bibcode: 2005ApJS..158..193S.
15. ↑ de Cat, P. (2007). "Observational Asteroseismology of slowly pulsating B stars". Communications in Asteroseismology 150: 167–74. doi:10.1553/cia150s167. Bibcode: 2007CoAst.150..167D.
16. ↑ Cotton, D. V.; Buzasi, D. B; Aerts, C.; Bailey, J. et al. (2021). "Polarimetric detection of non-radial oscillation modes in the β Cephei star β Crucis". Nature Astronomy 6: 154–164. doi:10.1038/s41550-021-01531-9.
17. ↑ 17.00 17.01 17.02 17.03 17.04 17.05 17.06 17.07 17.08 17.09 17.10 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: 02025. Bibcode: 2009yCat....102025S.
18. ↑ Campbell, W. W. (1909). "Eleven stars having variable radial velocities.". The Astrophysical Journal 29: 224. doi:10.1086/141644. ISSN 0004-637X. Bibcode: 1909ApJ....29..224C. http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1909LicOB...5...61C&link_type=ARTICLE&db_key=AST&high=.
19. ↑ Mazumdar, A. et al. (November 2006), "An asteroseismic study of the β Cephei star β Canis Majoris", Astronomy and Astrophysics 459 (2): 589–596, doi:10.1051/0004-6361:20064980, Bibcode: 2006A&A...459..589M
20. ↑ 20.0 20.1 20.2 20.3 Hubrig, S.; Briquet, M.; De Cat, P.; Schöller, M.; Morel, T.; Ilyin, I. (April 2009). "New magnetic field measurements of β Cephei stars and slowly pulsating B stars". Astronomische Nachrichten 330 (4): 317. doi:10.1002/asna.200811187. Bibcode: 2009AN....330..317H.
21. ↑ 21.0 21.1 Jakate, S. M. (1979). "A new class of early-type ultra-short-period variables". The Astronomical Journal 84: 1042. doi:10.1086/112510. ISSN 0004-6256. Bibcode: 1979AJ.....84.1042J.
22. ↑ 22.0 22.1 Dubath, P.; Rimoldini, L.; Süveges, M.; Blomme, J.; López, M.; Sarro, L. M.; De Ridder, J.; Cuypers, J. et al. (2011). "Random forest automated supervised classification of Hipparcos periodic variable stars". Monthly Notices of the Royal Astronomical Society 414 (3): 2602–17. doi:10.1111/j.1365-2966.2011.18575.x. Bibcode: 2011MNRAS.414.2602D.
23. ↑ Lesh, Janet Roundtree; Aizenman, Morris L. (1978). "The Observational Status of the β Cephei Stars". Annual Review of Astronomy and Astrophysics 16 (1): 215–240. doi:10.1146/annurev.aa.16.090178.001243. ISSN 0066-4146. Bibcode: 1978ARA&A..16..215L.
24. ↑ 24.0 24.1 24.2 Telting, 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. doi:10.1051/0004-6361:20054730. ISSN 0004-6361. Bibcode: 2006A&A...452..945T.
25. ↑ Pagel, B. E. J. (1956), "Results of a search for bright β Cephei variables in the southern sky", Monthly Notices of the Royal Astronomical Society 116: 10–24, doi:10.1093/mnras/116.1.10, Bibcode: 1956MNRAS.116...10P
26. ↑ Uytterhoeven, K. et al. (September 2005), "The orbit of the close spectroscopic binary epsilon Lup and the intrinsic variability of its early B-type components", Astronomy and Astrophysics 440 (1): 249–260, doi:10.1051/0004-6361:20053009, Bibcode: 2005A&A...440..249U
27. ↑ 27.0 27.1 27.2 ESA (1997). The HIPPARCOS and TYCHO catalogues. Astrometric and photometric star catalogues derived from the ESA HIPPARCOS Space Astrometry Mission. 1200. ISBN 978-9290923992. Bibcode: 1997ESASP1200.....E.
28. ↑ Palate, M.; Koenigsberger, G.; Rauw, G.; Harrington, D.; Moreno, E. (2013). "Spectral modelling of theαVirginis (Spica) binary system". Astronomy & Astrophysics 556: A49. doi:10.1051/0004-6361/201321909. ISSN 0004-6361. Bibcode: 2013A&A...556A..49P.
29. ↑ Balona, L. A.; Engelbrecht, C. A. (1985). "Photometry and frequency analysis of line profile variables". Monthly Notices of the Royal Astronomical Society 214 (4): 559–574. doi:10.1093/mnras/214.4.559. Bibcode: 1985MNRAS.214..559B.
30. ↑ Hill, Graham (1967). "On Beta Cephei Stars: a Search for Beta Cephei Stars". The Astrophysical Journal Supplement Series 14: 263. doi:10.1086/190156. ISSN 0067-0049. Bibcode: 1967ApJS...14..263H.
31. ↑ Lefèvre, L.; Marchenko, S. V.; Moffat, A. F. J.; Acker, A. (2009). "A systematic study of variability among OB-stars based on HIPPARCOS photometry". Astronomy and Astrophysics 507 (2): 1141–1201. doi:10.1051/0004-6361/200912304. ISSN 0004-6361. Bibcode: 2009A&A...507.1141L.
32. ↑ 32.0 32.1 Elst, E. W. (1979). "Short Periodic Variation of One Northern and Five Southern Bright Early B-Type Stars". Information Bulletin on Variable Stars 1562: 1. Bibcode: 1979IBVS.1562....1E.
33. ↑ 33.0 33.1 Percy, J. R.; Harlow, J.; Hayhoe, K. A. W.; Ivans, I. I.; Lister, M.; Plume, R.; Rosebery, T.; Thompson, S. et al. (1997). "Photometric Monitoring of Bright Be Stars. III. 1988–89 and 1992–95". Publications of the Astronomical Society of the Pacific 109: 1215. doi:10.1086/133998. ISSN 0004-6280. Bibcode: 1997PASP..109.1215P.
34. ↑ Percy, J. R.; Jakate, S. M.; Matthews, J. M. (1981). "Short-period light variations in Be stars". The Astronomical Journal 86: 53. doi:10.1086/112855. ISSN 0004-6256. Bibcode: 1981AJ.....86...53P.

* v
* t
* e

Variable stars

Pulsating|

| Cepheids and
cepheid-like|

* Classical
* Type II (BL Herculis, W Virginis, RV Tauri)
* RR Lyrae
* Delta Scuti
* 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
* Solar-like oscillations
* White dwarf

Eruptive|

| Protostar and PMS|

* 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|

* AM Canum Venaticorum
* Dwarf nova
* Luminous red nova
* Nova
* Polar
* Intermediate polar
* Supernova
* Hypernova
* SW Sextantis
* Symbiotic
* Symbiotic nova
* Z Andromedae

Rotating|

| Non-spherical|

* Rotating ellipsoidal

|

Stellar spots|

* BY Draconis
* FK Comae Berenices

Magnetic fields|

* Alpha² Canum Venaticorum
* Pulsar
* SX Arietis

Eclipsing|

* Algol
* Beta Lyrae
* Planetary transit
* W Ursae Majoris

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