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. 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 A pulse, in physiology, is the throbbing of arteries resulting from heartbeat. Pulse, The Pulse or Pulses may also refer to: Botany * Pulse (legume), any agriculturally significant annual leguminous food crop, such as peas, beans, lentils, and ...

mode of the star and a higher mode. The second, known as the magnetic model, assumes the variation to be caused by the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

being inclined to the

rotational axis Rotation around a fixed axis is a special case of rotational motion. The fixed-axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's rota ...

, deforming the main radial mode. The magnetic model was ruled out in 2004 by high resolution spectro-polarimetric observations. The third model assumes that cycles in the

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

cause the alternations and the modulations. Observational evidence based on

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of ...

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.

References

External links

The Blazhko Project

Period doubling as an explanation of Blazhko modulation

AAVSO The American Association of Variable Star Observers (AAVSO) is an international nonprofit organization, founded in 1911, focused on coordinating, analyzing, publishing, and archiving variable star observations made largely by amateur astronomers ...

Stellar phenomena RR Lyrae variables {{astronomy-stub