Variation in period and amplitude in RR Lyrae type variable stars
The Blazhko effect, also known as the Tseraskaya–Blazhko effect,[1] and 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.[2][3]
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.[4][5] 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. The magnetic model was ruled out in 2004 by high resolution spectro-polarimetric observations.[6] The third model assumes that cycles in the
convection cause the alternations and the modulations.[7]
Observational evidence based on
Kepler 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 from the daytime maximum.[8][9]
^Stothers, R. B. (2010), "Observational Evidence of Convective Cycles as the Cause of the Blazhko Effect in RR Lyrae Stars", Publications of the Astronomical Society of the Pacific, 122 (891): 536–540,
Bibcode:
2010PASP..122..536S,
doi:10.1086/652909