Stellar pulsation

Stellar pulsations are caused by expansions and contractions in the outer layers as a star seeks to maintain equilibrium. These fluctuations in stellar radius cause corresponding changes in the luminosity of the star. Astronomers are able to deduce this mechanism by measuring the spectrum and observing the Doppler effect.^[1] Many intrinsic variable stars that pulsate with large amplitudes, such as the classical Cepheids, RR Lyrae stars and large-amplitude Delta Scuti stars show regular light curves.

This regular behavior is in contrast with the variability of stars that lie parallel to and to the high-luminosity/low-temperature side of the classical variable stars in the Hertzsprung–Russell diagram. These giant stars are observed to undergo pulsations ranging from weak irregularity, when one can still define an average cycling time or period, (as in most RV Tauri and semiregular variables) to the near absence of repetitiveness in the irregular variables. The W Virginis variables are at the interface; the short period ones are regular and the longer period ones show first relatively regular alternations in the pulsations cycles, followed by the onset of mild irregularity as in the RV Tauri stars into which they gradually morph as their periods get longer.^[2]^[3] Stellar evolution and pulsation theories suggest that these irregular stars have a much higher luminosity to mass (L/M) ratios.

Many stars are non-radial pulsators, which have smaller fluctuations in brightness than those of regular variables used as standard candles.^[4]^[5]

^ Koupelis, Theo (2010). In Quest of the Universe. Jones and Bartlett Titles in Physical Science (6th ed.). Jones & Bartlett Learning. ISBN 978-0-7637-6858-4.
^ Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Griest, K.; Lawson, W. A.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Pollard, Karen R.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Sutherland, W.; Tomaney, A.; Welch, D. L. (1998). "The MACHO Project LMC Variable Star Inventory. VII. The Discovery of RV Tauri Stars and New Type II Cepheids in the Large Magellanic Cloud". The Astronomical Journal. 115 (5): 1921. arXiv:astro-ph/9708039. Bibcode:1998AJ....115.1921A. doi:10.1086/300317.
^ Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. (2008). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II.Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud". Acta Astronomica. 58: 293. arXiv:0811.3636. Bibcode:2008AcA....58..293S.
^ Grigahcène, A.; Antoci, V.; Balona, L.; Catanzaro, G.; Daszyńska-Daszkiewicz, J.; Guzik, J. A.; Handler, G.; Houdek, G.; Kurtz, D. W.; Marconi, M.; Monteiro, M. J. P. F. G.; Moya, A.; Ripepi, V.; Suárez, J. -C.; Uytterhoeven, K.; Borucki, W. J.; Brown, T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.; Kjeldsen, H.; Koch, D.; Bernabei, S.; Bradley, P.; Breger, M.; Di Criscienzo, M.; Dupret, M. -A.; García, R. A.; García Hernández, A.; et al. (2010). "Hybrid γ Doradus-δ Scuti Pulsators: New Insights into the Physics of the Oscillations from Kepler Observations". The Astrophysical Journal. 713 (2): L192. arXiv:1001.0747. Bibcode:2010ApJ...713L.192G. doi:10.1088/2041-8205/713/2/L192.
^ Mosser, B.; Belkacem, K.; Goupil, M. -J.; Miglio, A.; Morel, T.; Barban, C.; Baudin, F.; Hekker, S.; Samadi, R.; De Ridder, J.; Weiss, W.; Auvergne, M.; Baglin, A. (2010). "Red-giant seismic properties analyzed with CoRoT". Astronomy and Astrophysics. 517: A22. arXiv:1004.0449. Bibcode:2010A&A...517A..22M. doi:10.1051/0004-6361/201014036. S2CID 27138238.

[1] Koupelis, Theo (2010). In Quest of the Universe. Jones and Bartlett Titles in Physical Science (6th ed.). Jones & Bartlett Learning. ISBN 978-0-7637-6858-4.

[2] Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Griest, K.; Lawson, W. A.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Pollard, Karen R.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Sutherland, W.; Tomaney, A.; Welch, D. L. (1998). "The MACHO Project LMC Variable Star Inventory. VII. The Discovery of RV Tauri Stars and New Type II Cepheids in the Large Magellanic Cloud". The Astronomical Journal. 115 (5): 1921. arXiv:astro-ph/9708039. Bibcode:1998AJ....115.1921A. doi:10.1086/300317.

[3] Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. (2008). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II.Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud". Acta Astronomica. 58: 293. arXiv:0811.3636. Bibcode:2008AcA....58..293S.

[4] Grigahcène, A.; Antoci, V.; Balona, L.; Catanzaro, G.; Daszyńska-Daszkiewicz, J.; Guzik, J. A.; Handler, G.; Houdek, G.; Kurtz, D. W.; Marconi, M.; Monteiro, M. J. P. F. G.; Moya, A.; Ripepi, V.; Suárez, J. -C.; Uytterhoeven, K.; Borucki, W. J.; Brown, T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.; Kjeldsen, H.; Koch, D.; Bernabei, S.; Bradley, P.; Breger, M.; Di Criscienzo, M.; Dupret, M. -A.; García, R. A.; García Hernández, A.; et al. (2010). "Hybrid γ Doradus-δ Scuti Pulsators: New Insights into the Physics of the Oscillations from Kepler Observations". The Astrophysical Journal. 713 (2): L192. arXiv:1001.0747. Bibcode:2010ApJ...713L.192G. doi:10.1088/2041-8205/713/2/L192.

[5] Mosser, B.; Belkacem, K.; Goupil, M. -J.; Miglio, A.; Morel, T.; Barban, C.; Baudin, F.; Hekker, S.; Samadi, R.; De Ridder, J.; Weiss, W.; Auvergne, M.; Baglin, A. (2010). "Red-giant seismic properties analyzed with CoRoT". Astronomy and Astrophysics. 517: A22. arXiv:1004.0449. Bibcode:2010A&A...517A..22M. doi:10.1051/0004-6361/201014036. S2CID 27138238.

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