Menu
Home Explore People Places Arts History Plants & Animals Science Life & Culture Technology
On this page
Semiregular variable star
Type of variable star

In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type. It shows 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).

Related Image Collections Add Image
Profiles
1 Image
We don't have any YouTube videos related to Semiregular variable star yet.
We don't have any PDF documents related to Semiregular variable star yet.
We don't have any Books related to Semiregular variable star yet.
We don't have any archived web articles related to Semiregular variable star yet.

Classification

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
Subtype1IAU definition2GCVS code3GCVS definition4Standardstars
SRasemi-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.SRASemiregular 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 amplitudesZ Aqr56
SRbsemi-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.SRBSemiregular 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 observedAF Cyg78RR CrB910
SRcsemi-regular variable super-giants of late spectral classesSRCSpectral-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 Cep1112RW Cyg13
SRdsemi-regular variable giants and super-giants belonging to spectral classes F, G, KSRDSemiregular 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 daysS Vul14UU Her15AG Aur16SX Her17SV UMa18
SRSSemiregular pulsating red giants with short period (several days to a month), probably high-overtone pulsatorsAU Ari19

Pulsation

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.20

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.2122

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.23

Bright examples

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,24 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.25

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.26 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.27

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.28

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.29

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.30

See also

References

  1. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  2. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  3. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  4. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  5. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  6. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  7. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  8. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  9. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  10. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  11. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  12. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  13. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  14. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  15. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  16. Kukarkin, B. V. (2016). "27. Commission des Etoiles Variables". Transactions of the International Astronomical Union. 10: 398–431. doi:10.1017/S0251107X00020988. https://doi.org/10.1017%2FS0251107X00020988 ↩

  17. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  18. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  19. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  20. 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. https://doi.org/10.1111%2Fj.1365-2966.2009.15401.x ↩

  21. 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. /wiki/ArXiv_(identifier) ↩

  22. 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. /wiki/ArXiv_(identifier) ↩

  23. 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. https://doi.org/10.1111%2Fj.1365-2966.2009.15401.x ↩

  24. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  25. 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. /wiki/Bibcode_(identifier) ↩

  26. 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. /wiki/Bibcode_(identifier) ↩

  27. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  28. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  29. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩

  30. "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12 Feb 2009. Retrieved 2010-11-24. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt ↩