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

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.