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 100 d, 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 stand‐alone mechanism behind the Blazhko effect.

New results in RR Lyrae modeling: Convective cycles, additional modes and more

“…Our calculations focused on the dynamics of the process (Molnár, Kolláth & Szabó 2012a). The results confirmed our initial concerns: planting the same internal modulation into a stellar model created very different modulation in the observable quantitites (luminosity, radius), depending on the modulation periods.…”

Fitting Blazhko light curves

“…This fact hints at the possibility that during the Blazhko cycle the radial pulsation of an RR Lyrae star is modulated in phase/frequency and amplitude, and the fundamental period is subject to real oscillation. Up to now, the only model that is in conformation with this scenario has been suggested by Stothers (2006), although the inside physics of this model has been strongly criticized by Smolec et al (2011) and Molnár, Kolláth & Szabó (2012) recently.…”

Period doubling and Blazhko modulation in BL Herculis hydrodynamic models

“…Guggenberger et al , ; Kolenberg et al ). The recent idea of Stothers (), which assumes that modulation of turbulent convection by transient magnetic fields causes modulation of pulsation, was also questioned (Smolec et al ; Molnár, Kolláth & Szabó ). The discovery of the period‐doubling effect in some Blazhko variables led to the new model behind the Blazhko modulation – the radial mode resonance model proposed by Buchler & Kolláth ().…”