SSP seminar

Period doubling in Kepler RR Lyrae stars - one step closer to the understanding of the enigmatic Blazhko effect

Robert Szabo (Konkoly Observatory of the Hungarian Academy of Sciences Budapest, Hungary)

Monday 25th July 2011, 12:30 pm
Pratt conference room, 60 Garden Street

RR Lyrae stars are pulsating Helium-burning objects on the horizontal branch. These Pop II stars are good standard candles, important laboratories for stellar pulsation and evolution, as well as good tracers of the galactic history. I will review the current status of RR Lyrae research focusing on problems where Kepler may reach a breakthrough due to its unprecedented long and precise photometry.

The physical origin of the conspicuous amplitude and phase modulation of the RR Lyrae pulsation - known as the Blazhko effect – is still a mystery after more than 100 years of its discovery. Kepler helped us to reveal a new phenomenon, the period doubling, that is directly connected to the Blazhko modulation. Period doubling was found in RR Lyr - the eponym and prototype of its class - as well as in a few other Kepler Blazkho RR Lyrae stars.

With hydrodynamical model calculations we succeeded in reproducing the period doubling and proved that the root cause of this effect is a high order resonance (9:2) between the fundamental mode and the 9th radial overtone, which is a strange mode. This new type of dynamical effect may have significant impact on our understanding of the century-old Blazkho problem. I conclude my talk with discussing the consequences of this finding.


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