Alpha Cygni variable

{{Short description|Variable stars which exhibit non-radial pulsations}}

Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant stars of spectral types B or A. Variations in brightness on the order of 0.1 magnitudes are associated with the pulsations, which often seem irregular, due to beating of multiple pulsation periods. The pulsations typically have periods of several days to several weeks.

The prototype of these stars, Deneb (α Cygni), exhibits fluctuations in brightness between magnitudes +1.21 and +1.29. Small amplitude rapid variations have been known in many early supergiant stars, but they were not formally grouped into a class until the 4th edition of the General Catalogue of Variable Stars was published in 1985. It used the acronym ACYG for Alpha Cygni variable stars.{{cite journal|bibcode=1996yCat.2139....0K|title=VizieR Online Data Catalog: General Catalog of Variable Stars, 4th Ed. (GCVS4) (Kholopov+ 1988)|journal=VizieR On-Line Data Catalog: II/139B. Originally Published in: Moscow: Nauka Publishing House (1985–1988)|volume=2139|pages=0|last1=Kholopov|first1=P. N.|last2=Samus'|first2=N. N.|last3=Frolov|first3=M. S.|last4=Goranskij|first4=V. P.|last5=Gorynya|first5=N. A.|last6=Kireeva|first6=N. N.|last7=Kukarkina|first7=N. P.|last8=Kurochkin|first8=N. E.|last9=Medvedeva|first9=G. I.|last10=Perova|first10=N. B.|date=1996}} Many luminous blue variables (LBVs) show Alpha Cygni-type variability during their quiescent (hot) phases, but the LBV classification is generally used in these cases.

A large number (32) were discovered by Christoffel Waelkens and colleagues analysing Hipparcos data in a 1998 study.

Pulsations

The pulsations of Alpha Cygni Variable stars are not fully understood. They are not confined to a narrow range of temperatures and luminosities in the way that most pulsating stars are. Instead, most luminous A and B supergiants, and possibly also O and F stars, show some type of unpredictable small-scale pulsations. Nonadiabatic strange mode radial pulsations are predicted but only for the most luminous supergiants. Pulsations have also been modelled for less luminous supergiants by assuming they are low mass post-red supergiant stars, but most Alpha Cygni variables do not appear to have passed through the red supergiant stage.{{cite book|bibcode=2013ASPC..479...47S|arxiv = 1305.4728 |chapter = Strange-Mode Instability for Micro-Variations in Luminous Blue Variables |title = Progress in Physics of the Sun and Stars: A New Era in Helio- and Asteroseismology. Proceedings of a Fujihara Seminar held 25–29 November |series=Astronomical Society of the Pacific Conference Series|volume = 479 |pages = 47 |last1 = Saio |first1 = H. |last2 = Georgy |first2 = C. |last3 = Meynet |first3 = G. |date = 2013 }}

The pulsations are likely induced by kappa mechanism, caused by iron opacity variations, with strange modes producing the observed short periods for both radial and non-radial pulsations. Non-adiabatic g-modes may produce longer period variations, but these have not been observed in Alpha Cygni variables.{{cite journal|last1=Saio|first1=Hideyuki|title=Linear analyses for the stability of radial and non-radial oscillations of massive stars|journal=Monthly Notices of the Royal Astronomical Society|volume=412|issue=3|date=2011|pages=1814–1822|issn=0035-8711|doi=10.1111/j.1365-2966.2010.18019.x|doi-access=free |arxiv = 1011.4729 |bibcode = 2011MNRAS.412.1814S |s2cid=118552910}}

List

= Galactic =

class="wikitable sortable" style="font-size:90%;"

style="background:#efefef;"

! style="width:10%;"|Designation (name)

! style="width:10%;"|Constellation

! style="width:15%;"|Discovery

! style="width:10%;"|Maximum Apparent magnitude (m_V)

! style="width:10%;"|Minimum Apparent magnitude (m_V){{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-Line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=02025|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|date=2009|display-authors=etal}}

! style="width:15%;"|Period (days)

! style="width:10%;"|Spectral class

! style="width:10%;"|Luminosity

! style="width:10%;"|Comment

CE Cam (HD 21389)

| Camelopardalis

| Percy & Welsh (1983)

| 4^m.54

| A0Iab

| 63,000

CS Cam

| Camelopardalis

| Rufener (1982){{cite journal|bibcode=1982A&AS...48..503R|title=List of 333 variable, microvariable or suspected variable stars detected in the Geneva photometry|journal=Astronomy and Astrophysics Supplement Series|volume=48|pages=503|last1=Rufener|first1=F.|last2=Bartholdi|first2=P.|year=1982}}

| 4^m.259

| B9Ia

| 75,900{{cite journal|bibcode=1999A&A...349..553M|title=Galactic B-supergiants: A non-LTE model atmosphere analysis to estimate atmospheric parameters and chemical compositions|journal=Astronomy and Astrophysics|volume=349|pages=553|last1=McErlean|first1=N. D.|last2=Lennon|first2=D. J.|last3=Dufton|first3=P. L.|year=1999}}

η CMa (Aludra)

| Canis Major

| Kazarovets et al. (1999){{cite journal|bibcode=1999IBVS.4659....1K|title=The 74th Special Name-list of Variable Stars|journal=Information Bulletin on Variable Stars|volume=4659|pages=1|last1=Kazarovets|first1=E. V.|last2=Samus|first2=N. N.|last3=Durlevich|first3=O. V.|last4=Frolov|first4=M. S.|last5=Antipin|first5=S. V.|last6=Kireeva|first6=N. N.|last7=Pastukhova|first7=E. N.|date=1999}}

| 2^m.38

| 2^m.48

| 4.70433

| B5Ia

| 105,000{{citation | last1=Hohle | first1=M. M. | last2=Neuhäuser | first2=R. | last3=Schutz | first3=B. F. | title=Masses and luminosities of O- and B-type stars and red supergiants | journal=Astronomische Nachrichten | volume=331 | issue=4 | page=349 |date=April 2010 | doi=10.1002/asna.200911355 | bibcode=2010AN....331..349H |arxiv = 1003.2335 | s2cid=111387483 }}

ο² CMa

| Canis Major

| Waelkens et al. (1998)

| 2^m.98

| 3^m.04

| 24.44

| B3Ia

| 219,000

κ Cas

| Cassiopeia

| Percy & Welsh (1983)

| 4^m.12

| 4^m.21

| 2.64690

| B1Ia

| 331,000

6 Cas

| Cassiopeia

| Abt (1957){{cite journal|last1=Abt|first1=Helmut A.|title=The Variability of Supergiants.|journal=The Astrophysical Journal|volume=126|date=1957|pages=138|issn=0004-637X|doi=10.1086/146379|bibcode = 1957ApJ...126..138A }}

| 5^m.34

| 5^m.45

| 30

| B2 Ia⁺

| 200,000{{cite journal|bibcode=1997A&A...320..196A|title=Radiation driven wind models for A, F and G supergiants|journal=Astronomy and Astrophysics|volume=320|pages=196|last1=Achmad|first1=L.|last2=Lamers|first2=H. J. G. L. M.|last3=Pasquini|first3=L.|year=1997}}

| Hypergiant

ο² Cen

| Centaurus

| 5^m.12

| 5^m.22

| 46.3

| A2Ia

| 136,000{{cite journal|author=Kaufer, A.|author2=Stahl, O.|author3=Wolf, B.|author4=Gaeng, T.|author5=Gummersbach, C. A.|author6=Kovacs, J.|author7=Mandel, H.|author8=Szeifert, T.|date=1996|title=Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.|journal=Astronomy and Astrophysics|volume=305|pages=887–901 | bibcode=1996A&A...305..887K}}

ν Cep

| Cepheus

| Percy & Welsh (1983){{cite journal|last1=Percy|first1=J. R.|last2=Welch|first2=D. L.|title=Photometric variability of B- and A-type supergiants|journal=Publications of the Astronomical Society of the Pacific|volume=95|date=1983|pages=491|issn=0004-6280|doi=10.1086/131198|bibcode = 1983PASP...95..491P |doi-access=free}}

| 4^m.25

| 4^m.35

| A2 Iab

| 254,000

DL Cru

| Crux

| Waelkens et al. (1998)

| 6^m.24

| 6^m.28

| 2.8778

| B1.5Ia

| 242,000{{cite journal|last1=Lamers|first1=Henny J. G. L. M.|last2=Snow|first2=Theodore P.|last3=Lindholm|first3=Douglas M.|title=Terminal Velocities and the Bistability of Stellar Winds|journal=The Astrophysical Journal|volume=455|date=1995|pages=269|issn=0004-637X|doi=10.1086/176575|bibcode = 1995ApJ...455..269L }}

Deneb{{cite journal|last1=Saio|first1=H.|last2=Georgy|first2=C.|last3=Meynet|first3=G.|title=Evolution of blue supergiants and Cygni variables: puzzling CNO surface abundances|journal=Monthly Notices of the Royal Astronomical Society|volume=433|issue=2|date=2013|pages=1246–1257|bibcode=2013MNRAS.433.1246S|doi=10.1093/mnras/stt796|doi-access=free |arxiv = 1305.2474 }}

| Cygnus

| Lee (1910){{cite journal|last1=Lee|first1=O. J.|title=Four stars having variable radial velocities.|journal=The Astrophysical Journal|volume=31|date=1910|pages=176|issn=0004-637X|doi=10.1086/141741|bibcode = 1910ApJ....31..176L }}

| 1^m.21

| 1^m.29

| A2 Ia

| 196,000

{{cite journal

|last1=Schiller |first1=F.

|last2=Przybilla |first2=N.

|date=2008

|title=Quantitative spectroscopy of Deneb

|journal=Astronomy & Astrophysics

|volume=479 |issue=3 |pages=849–858

|arxiv=0712.0040

|bibcode=2008A&A...479..849S

|doi=10.1051/0004-6361:20078590

|s2cid=119225384

}}

| Prototype

σ Cyg

| Cygnus

| Abt (1957)

| 4^m.19

| 4^m.26

| 120.2

| B9 Iab

| 39,000{{cite journal|last1=Markova|first1=N.|last2=Puls|first2=J.|title=Bright OB stars in the Galaxy|journal=Astronomy and Astrophysics|volume=478|issue=3|date=2008|pages=823–842|issn=0004-6361|doi=10.1051/0004-6361:20077919|arxiv = 0711.1110 |bibcode = 2008A&A...478..823M |s2cid=14510634}}

55 Cyg

| Cygnus

| Hill et al. (1976){{cite journal|bibcode=1979IBVS.1581....1K|title=64th Name-List of Variable Stars|journal=Information Bulletin on Variable Stars|volume=1581|pages=1|last1=Kholopov|first1=P. N.|last2=Kukarkina|first2=N. P.|last3=Perova|first3=N. B.|year=1979}}

| 4^m.81

| 4^m.87

| B2.5 Ia

| ~400,000{{cite journal|bibcode=2015A&A...581A..75K|arxiv=1507.01846|title=Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198 478|journal=Astronomy & Astrophysics|volume=581|pages=A75|last1=Kraus|first1=M.|last2=Haucke|first2=M.|last3=Cidale|first3=L. S.|last4=Venero|first4=R. O. J.|last5=Nickeler|first5=D. H.|last6=Németh|first6=P.|last7=Niemczura|first7=E.|last8=Tomić|first8=S.|last9=Aret|first9=A.|last10=Kubát|first10=J.|last11=Kubátová|first11=B.|last12=Oksala|first12=M. E.|last13=Curé|first13=M.|last14=Kamiński|first14=K.|last15=Dimitrov|first15=W.|last16=Fagas|first16=M.|last17=Polińska|first17=M.|year=2015|doi=10.1051/0004-6361/201425383|s2cid=55392478}}

3 Gem

| Gemini

| Waelkens et al. (1998)

| 5^m.75

| 13.70

| B3 Ia

| 200,000{{cite journal|bibcode=1999A&A...350..970K|arxiv = astro-ph/9910449 |title = The wind momentum-luminosity relationship of galactic A- and B-supergiants |journal = Astronomy and Astrophysics |volume = 350 |pages = 970 |last1 = Kudritzki |first1 = R. P. |last2 = Puls |first2 = J. |last3 = Lennon |first3 = D. J. |last4 = Venn |first4 = K. A. |last5 = Reetz |first5 = J. |last6 = Najarro |first6 = F. |last7 = McCarthy |first7 = J. K. |last8 = Herrero |first8 = A. |date = 1999 }}

ρ Leo

| Leo

| Olsen (1974){{cite journal|bibcode=1974IBVS..925....1O|title=Variable Stars among the Four-Colour (uvby) Standard Stars|journal=Information Bulletin on Variable Stars|volume=925|pages=1|last1=Olsen|first1=E. H.|date=1974}}

| 3^m.83

| 3^m.9

| 3.4271

| B1Iab

| 295,000

β Ori (Rigel)

| Orion

| Waelkens et al. (1998){{cite journal|author=Waelkens, C.|author2=Aerts, C.|author3=Kestens, E.|author4=Grenon, M.|author5=Eyer, L.|date=1998|title=Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B star|journal=Astronomy and Astrophysics|volume=330|pages=215–21|bibcode=1998A&A...330..215W}}

| 0^m.17

| 0^m.22

| B8Ia

| 279,000

218,000

| Brightest member

ε Ori (Alnilam)

| Orion

| Cousins (1960){{cite journal|bibcode=1960MNSSA..19...56C|title=New Bright Variable Stars|journal=Monthly Notes of the Astronomical Society of Southern Africa|volume=19|pages=56|last1=Cousins|first1=A. W. J.|date=1960}}

| 1^m.64

| 1^m.74

| B0.5Iabea

| 275,000

537,000{{cite journal|author=Searle, S. C.|author2=Prinja, R. K.|author3=Massa, D.|author4=Ryans, R.|date=2008|title=Quantitative studies of the optical and UV spectra of Galactic early B supergiants. I. Fundamental parameters|journal=Astronomy and Astrophysics|volume=481|issue=3|pages=777–97|doi=10.1051/0004-6361:20077125 |bibcode=2008A&A...481..777S |arxiv = 0801.4289 |s2cid=1552752}}

χ² Ori

| Orion

| Waelkens et al. (1998)

| 4^m.68

| 4^m.72

| 2.8682

| B2Ia

| 446,000{{Cite journal | last1 = Crowther | first1 = P. A. | last2 = Lennon | first2 = D. J. | last3 = Walborn | first3 = N. R. | title = Physical parameters and wind properties of galactic early B supergiants | doi = 10.1051/0004-6361:20053685 | journal = Astronomy and Astrophysics | volume = 446 | issue = 1 | pages = 279–293 | date = 2006 |arxiv = astro-ph/0509436 |bibcode = 2006A&A...446..279C | s2cid = 18815761 }}

9 Per

| Perseus

| Abt (1957)

| 5^m.15

| 5^m.25

| A2 Ia

| 141,000{{cite journal|bibcode=1999A&A...346..819V|title=Understanding A-type supergiants. II. Atmospheric parameters and rotational velocities of Galactic A-type supergiants|journal=Astronomy and Astrophysics|volume=346|pages=819|last1=Verdugo|first1=E.|last2=Talavera|first2=A.|last3=Gómez De Castro|first3=A. I.|year=1999}}

= Extragalactic =

class="wikitable sortable" style="font-size:90%;"

style="background:#efefef;"

! style="width:10%;"|Designation (name)

! style="width:10%;"|Galaxy

! style="width:15%;"|Discovery

! style="width:10%;"|Maximum Apparent magnitude (m_V)

! style="width:10%;"|Minimum Apparent magnitude (m_V)

! style="width:15%;"|Period (days)

! style="width:10%;"|Spectral class

! style="width:10%;"|Luminosity

! style="width:10%;"|Comment

LHA 115-S 18

| SMC

| 13^m.3

| Complex

| B[e]sg

| Possible LBV

HDE 268835

| LMC

| 10^m.60

| 10^m.68

| >100

| B8p

HD 37974

| LMC

| 10^m.92

| 11^m.00

| 400

| B0.5Ia⁺

HD 37836{{Cite journal |last1=Balona |first1=L A |last2=Handler |first2=G |last3=Chowdhury |first3=S |last4=Ozuyar |first4=D |last5=Engelbrecht |first5=C A |last6=Mirouh |first6=G M |last7=Wade |first7=G A |last8=David-Uraz |first8=A |last9=Cantiello |first9=M |date=2019-02-27 |title=Rotational modulation in TESS B stars |journal=Monthly Notices of the Royal Astronomical Society |volume=485 |issue=3 |pages=3457–3469 |doi=10.1093/mnras/stz586 |issn=0035-8711|doi-access=free |arxiv=1902.09470 }}

|LMC

|10^m.55

|B0Iae

|LBV candidate

References

{{reflist|refs=

{{cite journal|author=Chesneau, O.|author2=Kaufer, A.|author3=Stahl, O.|author4=Colvinter, C.|author5=Spang, A.|author6=Dessart, L.|author7=Prinja, R.|author8=Chini, R.|date=2014|title=The variable stellar wind of Rigel probed at high spatial and spectral resolution|journal=Astronomy & Astrophysics|volume=566|id=A125 |pages=18|doi=10.1051/0004-6361/201322894 |bibcode=2014A&A...566A.125C|arxiv = 1405.0907 |s2cid=118404460}}

{{cite journal | display-authors=1 | last1=Przybilla | first1=N. | last2=Butler | first2=K. | last3=Becker | first3=S. R. | last4=Kudritzki | first4=R. P. | title=Quantitative spectroscopy of BA-type supergiants | journal=Astronomy and Astrophysics | volume=445 | issue=3 | pages=1099–1126 |date=January 2006 | doi=10.1051/0004-6361:20053832 | bibcode=2006A&A...445.1099P |arxiv = astro-ph/0509669 | s2cid=118953817 }}

{{cite journal|last1=van Genderen|first1=A. M.|last2=Sterken|first2=C.|title=Light variations of massive stars (α Cyg variables)|journal=Astronomy and Astrophysics|volume=386|issue=3|date=2002|pages=926–935|bibcode=2002A&A...386..926V|doi=10.1051/0004-6361:20020360|doi-access=free}}

}}

Sources

Samus N.N., Durlevich O.V., et al. Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.)