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Semiregular variable star

February 15, 2024

In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curves may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter).

Light curve of semiregular variable star Betelgeuse

Classification edit

The semiregular variable stars have been sub-divided into four categories for many decades, with a fifth related group defined more recently. The original definitions of the four main groups were formalised in 1958 at the tenth general assembly of the International Astronomical Union (IAU). The General Catalogue of Variable Stars (GCVS) has updated the definitions with some additional information and provided newer reference stars where old examples such as S Vul have been re-classified.

Semiregular variable subtypes
Subtype[1] IAU definition[1] GCVS code[2] GCVS definition[2] Standard
stars
SRa semi-regular variable giants of late spectral classes (M, C and S), which retain periodicity with comparative stability and possess, as a rule, small (less than 2m.5) light-variation amplitudes. Amplitudes and forms of light curves are usually liable to strong variations from period to period. Many of these stars differ from Mira Ceti type stars only owing to the smaller amplitude of light variation. SRA Semiregular late-type (M, C, S or Me, Ce, Se) giants displaying persistent periodicity and usually small (<2.5 mag in V) light amplitudes. Amplitudes and light-curve shapes generally vary and periods are in the range of 35–1200 days. Many of these stars differ from Miras only by showing smaller light amplitudes Z Aqr[1][2]
SRb semi-regular variable giants of late spectral classes (M, C and S) with a poorly expressed periodicity, i.e. with a different duration of individual cycles (which leads to the impossibility of predicting the epochs of maximum and minimum brightness), or with the replacement of periodical changes by slow irregular variations, or even by the constancy of brightness. Some of them are characterised by a certain mean value of the period, given in the catalogue. SRB Semiregular late-type (M, C, S or Me, Ce, Se) giants with poorly defined periodicity (mean cycles in the range of 20 to 2300 days) or with alternating intervals of periodic and slow irregular changes, and even with light constancy intervals. Every star of this type may usually be assigned a certain mean period (cycle), which is the value given in the Catalogue. In a number of cases, the simultaneous presence of two or more periods of light variation is observed AF Cyg[1][2]
RR CrB[1][2]
SRc semi-regular variable super-giants of late spectral classes SRC Spectral-type (M, C, S or Me, Ce, Se) supergiants with amplitudes of about 1 mag and periods of light variation from 30 days to several thousand days. μ Cep[1][2]
RW Cyg[1]
SRd semi-regular variable giants and super-giants belonging to spectral classes F, G, K SRD Semiregular variable giants and supergiants of F, G, or K spectral types, sometimes with emission lines in their spectra. Amplitudes of light variation are in the range from 0.1 to 4 mag, and the range of periods is from 30 to 1100 days S Vul[1]
UU Her[1]
AG Aur[1]
SX Her[2]
SV UMa[2]
SRS Semiregular pulsating red giants with short period (several days to a month), probably high-overtone pulsators AU Ari[2]

Pulsation edit

The semiregular variable stars, particularly the SRa and SRb sub-classes, are often grouped with the Mira variables under the long-period variable heading. In other situations, the term is expanded to cover almost all cool pulsating stars. The semi-regular giant stars are closely related to the Mira variables: Mira stars generally pulsate in the fundamental mode; semiregular giants pulsate in one or more overtones.[3]

Photometric studies in the Large Magellanic Cloud looking for gravitational microlensing events have shown that essentially all cool evolved stars are variable, with the coolest stars showing very large amplitudes and warmer stars showing only micro-variations. The semiregular variable stars fall on one of five main period-luminosity relationship sequences identified, differing from the Mira variables only in pulsating in an overtone mode. The closely related OSARG (OGLE small amplitude red giant) variables pulsate in an unknown mode.[4][5]

Many semiregular variables show long secondary periods around ten times the main pulsation period, with amplitudes of a few tenths of a magnitude at visual wavelengths. The cause of the pulsations is not known.[3]

Bright examples edit

η Gem is the brightest SRa variable, and also an eclipsing binary. GZ Peg is an SRa variable and S-type star with a maximum magnitude of 4.95. T Cen is listed as the next-brightest SRa example,[2] but it is suggested that it may actually be an RV Tauri variable, which would make it by far the brightest member of that class.[6]

There are numerous naked-eye SRb stars, with third-magnitude L2 Pup being the brightest listed in the GCVS. σ Lib and ρ Per are also third-magnitude SRb stars at maximum brightness. β Gru is a second magnitude star classified as a slow irregular variable by the GCVS, but reported to be of SRb type by later research.[7] These four are all class M giants, although some SRb variables are carbon stars such as UU Aur or S-type stars such as Pi1 Gru.[2]

Catalogued SRc stars are less numerous, but include some of the brightest stars in the sky such as Betelgeuse and α Her. Although SRc stars are defined as being supergiants, a number of them have giant spectral luminosity classes and some such as α Her are known to be asymptotic giant branch stars.[2]

Many SRd stars are extremely luminous hypergiants, including the naked-eye ρ Cas, V509 Cas, and ο1 Cen. Others are classified as giant stars, but the brightest example is the seventh-magnitude LU Aqr.[2]

Most SRS variables have been discovered in deep large-scale surveys, but the naked-eye stars V428 And, AV Ari, and EL Psc are also members.[2]

See also edit

References edit

  1. ^ a b c d e f g h i j Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988.
  2. ^ a b c d e f g h i j k l m n "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24.
  3. ^ a b Nicholls, C. P.; Wood, P. R.; Cioni, M.-R. L.; Soszyński, I. (2009). "Long Secondary Periods in variable red giants". Monthly Notices of the Royal Astronomical Society. 399 (4): 2063. arXiv:0907.2975. Bibcode:2009MNRAS.399.2063N. doi:10.1111/j.1365-2966.2009.15401.x. S2CID 19019968.
  4. ^ Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. (2009). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud". Acta Astronomica. 59 (3): 239. arXiv:0910.1354. Bibcode:2009AcA....59..239S.
  5. ^ Soszynski, I.; Dziembowski, W. A.; Udalski, A.; Kubiak, M.; Szymanski, M. K.; Pietrzynski, G.; Wyrzykowski, L.; Szewczyk, O.; Ulaczyk, K. (2007). "The Optical Gravitational Lensing Experiment. Period--Luminosity Relations of Variable Red Giant Stars". Acta Astronomica. 57: 201. arXiv:0710.2780. Bibcode:2007AcA....57..201S.
  6. ^ Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
  7. ^ Otero, S. A.; Moon, T. (December 2006). "The Characteristic Period of Pulsation of β Gruis". The Journal of the American Association of Variable Star Observers. 34 (2): 156–164. Bibcode:2006JAVSO..34..156O.

External links edit

  • EU Delphini and the Small-Amplitude Pulsating Red Giants
  • Y Lyncis
  • Pulsating variable stars and the H-R diagram
  • OGLE Atlas of Variable Star Light Curves - Semiregular Variables

February 15, 2024
semiregular, variable, star, astronomy, semiregular, variable, star, type, variable, star, giant, supergiant, intermediate, late, cooler, spectral, type, showing, considerable, periodicity, light, changes, accompanied, sometimes, interrupted, various, irregula. In astronomy a semiregular variable star a type of variable star is a giant or supergiant of intermediate and late cooler spectral type showing considerable periodicity in its light changes accompanied or sometimes interrupted by various irregularities Periods lie in the range from 20 to more than 2000 days while the shapes of the light curves may be rather different and variable with each cycle The amplitudes may be from several hundredths to several magnitudes usually 1 2 magnitudes in the V filter Light curve of semiregular variable star Betelgeuse Contents 1 Classification 2 Pulsation 3 Bright examples 4 See also 5 References 6 External linksClassification editThe semiregular variable stars have been sub divided into four categories for many decades with a fifth related group defined more recently The original definitions of the four main groups were formalised in 1958 at the tenth general assembly of the International Astronomical Union IAU The General Catalogue of Variable Stars GCVS has updated the definitions with some additional information and provided newer reference stars where old examples such as S Vul have been re classified Semiregular variable subtypes Subtype 1 IAU definition 1 GCVS code 2 GCVS definition 2 StandardstarsSRa semi regular variable giants of late spectral classes M C and S which retain periodicity with comparative stability and possess as a rule small less than 2m 5 light variation amplitudes Amplitudes and forms of light curves are usually liable to strong variations from period to period Many of these stars differ from Mira Ceti type stars only owing to the smaller amplitude of light variation SRA Semiregular late type M C S or Me Ce Se giants displaying persistent periodicity and usually small lt 2 5 mag in V light amplitudes Amplitudes and light curve shapes generally vary and periods are in the range of 35 1200 days Many of these stars differ from Miras only by showing smaller light amplitudes Z Aqr 1 2 SRb semi regular variable giants of late spectral classes M C and S with a poorly expressed periodicity i e with a different duration of individual cycles which leads to the impossibility of predicting the epochs of maximum and minimum brightness or with the replacement of periodical changes by slow irregular variations or even by the constancy of brightness Some of them are characterised by a certain mean value of the period given in the catalogue SRB Semiregular late type M C S or Me Ce Se giants with poorly defined periodicity mean cycles in the range of 20 to 2300 days or with alternating intervals of periodic and slow irregular changes and even with light constancy intervals Every star of this type may usually be assigned a certain mean period cycle which is the value given in the Catalogue In a number of cases the simultaneous presence of two or more periods of light variation is observed AF Cyg 1 2 RR CrB 1 2 SRc semi regular variable super giants of late spectral classes SRC Spectral type M C S or Me Ce Se supergiants with amplitudes of about 1 mag and periods of light variation from 30 days to several thousand days m Cep 1 2 RW Cyg 1 SRd semi regular variable giants and super giants belonging to spectral classes F G K SRD Semiregular variable giants and supergiants of F G or K spectral types sometimes with emission lines in their spectra Amplitudes of light variation are in the range from 0 1 to 4 mag and the range of periods is from 30 to 1100 days S Vul 1 UU Her 1 AG Aur 1 SX Her 2 SV UMa 2 SRS Semiregular pulsating red giants with short period several days to a month probably high overtone pulsators AU Ari 2 Pulsation editThe semiregular variable stars particularly the SRa and SRb sub classes are often grouped with the Mira variables under the long period variable heading In other situations the term is expanded to cover almost all cool pulsating stars The semi regular giant stars are closely related to the Mira variables Mira stars generally pulsate in the fundamental mode semiregular giants pulsate in one or more overtones 3 Photometric studies in the Large Magellanic Cloud looking for gravitational microlensing events have shown that essentially all cool evolved stars are variable with the coolest stars showing very large amplitudes and warmer stars showing only micro variations The semiregular variable stars fall on one of five main period luminosity relationship sequences identified differing from the Mira variables only in pulsating in an overtone mode The closely related OSARG OGLE small amplitude red giant variables pulsate in an unknown mode 4 5 Many semiregular variables show long secondary periods around ten times the main pulsation period with amplitudes of a few tenths of a magnitude at visual wavelengths The cause of the pulsations is not known 3 Bright examples edith Gem is the brightest SRa variable and also an eclipsing binary GZ Peg is an SRa variable and S type star with a maximum magnitude of 4 95 T Cen is listed as the next brightest SRa example 2 but it is suggested that it may actually be an RV Tauri variable which would make it by far the brightest member of that class 6 There are numerous naked eye SRb stars with third magnitude L2 Pup being the brightest listed in the GCVS s Lib and r Per are also third magnitude SRb stars at maximum brightness b Gru is a second magnitude star classified as a slow irregular variable by the GCVS but reported to be of SRb type by later research 7 These four are all class M giants although some SRb variables are carbon stars such as UU Aur or S type stars such as Pi1 Gru 2 Catalogued SRc stars are less numerous but include some of the brightest stars in the sky such as Betelgeuse and a Her Although SRc stars are defined as being supergiants a number of them have giant spectral luminosity classes and some such as a Her are known to be asymptotic giant branch stars 2 Many SRd stars are extremely luminous hypergiants including the naked eye r Cas V509 Cas and o1 Cen Others are classified as giant stars but the brightest example is the seventh magnitude LU Aqr 2 Most SRS variables have been discovered in deep large scale surveys but the naked eye stars V428 And AV Ari and EL Psc are also members 2 See also editList of semiregular variable stars Low dimensional chaos in stellar pulsations Variable star designationReferences edit a b c d e f g h i j Kukarkin B V 2016 27 Commission des Etoiles Variables Transactions of the International Astronomical Union 10 398 431 doi 10 1017 S0251107X00020988 a b c d e f g h i j k l m n GCVS Variability Types General Catalogue of Variable Stars Sternberg Astronomical Institute Moscow Russia 12 Feb 2009 Retrieved 2010 11 24 a b Nicholls C P Wood P R Cioni M R L Soszynski I 2009 Long Secondary Periods in variable red giants Monthly Notices of the Royal Astronomical Society 399 4 2063 arXiv 0907 2975 Bibcode 2009MNRAS 399 2063N doi 10 1111 j 1365 2966 2009 15401 x S2CID 19019968 Soszynski I Udalski A Szymanski M K Kubiak M Pietrzynski G Wyrzykowski L Szewczyk O Ulaczyk K Poleski R 2009 The Optical Gravitational Lensing Experiment The OGLE III Catalog of Variable Stars IV Long Period Variables in the Large Magellanic Cloud Acta Astronomica 59 3 239 arXiv 0910 1354 Bibcode 2009AcA 59 239S Soszynski I Dziembowski W A Udalski A Kubiak M Szymanski M K Pietrzynski G Wyrzykowski L Szewczyk O Ulaczyk K 2007 The Optical Gravitational Lensing Experiment Period Luminosity Relations of Variable Red Giant Stars Acta Astronomica 57 201 arXiv 0710 2780 Bibcode 2007AcA 57 201S Watson C L 2006 The International Variable Star Index VSX The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science Held May 23 25 25 47 Bibcode 2006SASS 25 47W Otero S A Moon T December 2006 The Characteristic Period of Pulsation of b Gruis The Journal of the American Association of Variable Star Observers 34 2 156 164 Bibcode 2006JAVSO 34 156O External links editEU Delphini and the Small Amplitude Pulsating Red Giants Y Lyncis Pulsating variable stars and the H R diagram OGLE Atlas of Variable Star Light Curves Semiregular Variables Retrieved from https en wikipedia org w index php title Semiregular variable star amp oldid 1181919637, wikipedia, wiki, book, books, library,

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