Pulsation-driven helium transport as a potential source of the Blazhko effect

TL;DR

This paper introduces a simplified nonlinear hydrodynamical model suggesting that pulsation-driven helium transport causes amplitude modulation in RR Lyrae stars, potentially explaining the Blazhko effect.

Contribution

The model links helium transport and Rayleigh-Taylor instability to the Blazhko effect, offering a new physical mechanism for amplitude modulation in RR Lyrae stars.

Findings

Periodic helium flow causes amplitude modulation in the model.

Helium surplus leads to Rayleigh-Taylor instability and back-flow.

Variation in helium affects radiation flux blocking and pulsation amplitude.

Abstract

We present a highly simplified nonlinear hydrodynamical model to emulate the main observed features of amplitude modulation (commonly known as Blazhko effect) in RR Lyrae stars. The model is based on the assumption that the periodic flow generated by the pulsation carries surplus helium in the ionization zones He I and II. Once this extra helium reaches a critical amount, a Rayleigh-Taylor-type instability leads to a back-flow of the surplus helium and the process starts over again, due to the continuing effect of pumping helium upward by the pulsation. This periodic variation of helium leads to various efficiency of radiation flux blocking in the helium ionization zone that shows up as a long-term periodic variation of the pulsation amplitude.