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]

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. [2] [3] 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. [4] The third model assumes that cycles in the convection cause the alternations and the modulations. [5]

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. [6]


  1. ^ Horace A. Smith (2004). RR Lyrae Stars. Cambridge University Press. p. 103. ISBN 0-521-54817-9. 
  2. ^ Z. Kollath, L. Molnar & R. Szabo, 2011, Monthly Notices of the Royal Astronomical Society, Vol 414 p. 1111; (also
  3. ^ J. R. Buchler & Z. Kollath, 2011, Astrophysical Journal, Vol 731, p. 24 (also
  4. ^ Katrien Kolenberg (2008). "Explanations for the Blazhko effect in RR Lyrae stars". The Blazhko Project. Retrieved 2008-12-17. 
  5. ^ Stothers, R.B. 2010, Publications of the Astronomical Society of the Pacific Vol. 122, p. 536
  6. ^ R. Szabo et al. , 2010, Monthly Notices of the Royal Astronomical Society, Vol. 409, p. 1244

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