Can turbulent convective variations drive the Blazhko cycle? Dynamical investigation of the Stothers idea

TL;DR

This study investigates whether convective variations can explain the Blazhko effect in RR Lyrae stars, finding that the proposed mechanism only works for long modulation periods and cannot account for short-period, high-amplitude modulations.

Contribution

The paper provides a dynamical analysis of Stothers' convective cycle hypothesis, demonstrating its limitations in explaining the full range of Blazhko modulations.

Findings

Effective only for modulation periods over 100 days

Short-period, high-amplitude modulations are not reproduced

Convective cycle model alone is insufficient to explain the Blazhko effect

Abstract

The Blazhko-phenomenon, the modulation of the pulsation of RR Lyrae stars remains one of the most stubborn unsolved problems of stellar pulsation. The recent idea of Stothers proposes that periodic variations in the properties of the convective envelope may be behind the amplitude and phase modulation. In this work we approximated the mechanism by introducing variations in the convective parameters of the Florida-Budapest hydrodynamic code and also by means of amplitude equations. We found that the process is only effective for long modulation periods, typically for more than hundred days, in agreement with the thermal time scales of the pulsation in RR Lyrae stars. Due to the slow response of the pulsation to the structure changes, short period, high amplitude Blazhko-modulation cannot be reproduced with this mechanism or would require implausible variations in the convective parameters on short time scales. We also found that the modulation of the mixing length results in strong differences between both the luminosity and radius variations and the respective phase modulations of the two quantities, suggesting notable differences between the energy output of the photosphere and the mechanical variations of the layers. The findings suggest that the convective cycle model is not well suited as a standalone mechanism behind the Blazhko-effect.