Blazhko effect

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The Blazhko effect, which is sometimes called long-period modulation, is a variation in period and amplitude in RR Lyrae type variable stars. It was first observed by Sergey Blazhko in 1907 in the star RW Draconis.[1][2]

The physics behind the Blazhko effect is currently still a matter of debate, with there being three primary hypotheses. In the first, referred to as the resonance model, the cause of the modulation is a non-linear resonance among either the fundamental or the first overtone pulsation mode of the star and a higher mode.[3][4]The second, known as the magnetic model, assumes the variation to be caused by the magnetic field being inclined to the rotational axis, deforming the main radial mode. [5] The third model assumes that cycles in the convection cause the alternations and the modulations.[6]

Observational evidence based on Kepler (spacecraft) observations indicates much of the Blazhko effect's two-cycle light curve modulation is due to simple period-doubling. Many RR Lyrae stars have a variability period of approximately 12 hours and ground based astronomers typically make nightly observations about 24 hours apart; thus period-doubling results in brightness maximums during nightly observations that are significantly different than the daytime maximum.[7]


  1. ^ Horace A. Smith (2004). RR Lyrae Stars. Cambridge University Press. p. 103. ISBN 0-521-54817-9. 
  2. ^ Blazhko, S. (1907), "Mitteilung über veränderliche Sterne", Astronomische Nachrichten, 175: 325, Bibcode:1907AN....175..325B 
  3. ^ Kolláth, Z.; Molnár, L.; Szabó, R. (2011), "Period-doubling bifurcation and high-order resonances in RR Lyrae hydrodynamical models", MNRAS, 414: 1111, arXiv:1102.0157Freely accessible, Bibcode:2011MNRAS.414.1111K, doi:10.1111/j.1365-2966.2011.18451.x 
  4. ^ Buchler, J. R.; Kolláth, Z. (2011), "On the Blazhko Effect in RR Lyrae Stars", ApJ, 731: 24, arXiv:1101.1502Freely accessible, Bibcode:2011ApJ...731...24B, doi:10.1088/0004-637x/731/1/24 
  5. ^ Katrien Kolenberg (2008). "Explanations for the Blazhko effect in RR Lyrae stars". The Blazhko Project. Retrieved 2008-12-17. 
  6. ^ Stothers, R. B. (2010), "Observational Evidence of Convective Cycles as the Cause of the Blazhko Effect in RR Lyrae Stars", PASP, 122: 536, Bibcode:2010PASP..122..536S, doi:10.1086/652909 
  7. ^ Szabó, R.; Kolláth, Z.; Molnár, L.; et al. (2010), "Does Kepler unveil the mystery of the Blazhko effect? First detection of period doubling in Kepler Blazhko RR Lyrae stars", MNRAS, 409: 1244, arXiv:1007.3404Freely accessible, Bibcode:2010MNRAS.409.1244S, doi:10.1111/j.1365-2966.2010.17386.x 

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