An extensive photometric study of the Blazhko RR Lyrae star MW Lyr: II. Changes in the physical parameters

TL;DR

This study reveals how the physical parameters of the Blazhko RR Lyrae star MW Lyr vary during its modulation cycle, showing small but significant changes in radius, luminosity, and temperature consistent with pulsation models.

Contribution

It provides the first detailed observational evidence of physical parameter variations during the Blazhko cycle in MW Lyr, linking phase modulation to period changes and luminosity perturbations.

Findings

Mean radius varies by about 1-2% during the cycle.

Surface temperature shows similar magnitude variations.

Pulsation remains purely radial throughout the modulation.

Abstract

The analysis of the multicolour photometric observations of MW Lyr, a large modulation amplitude Blazhko variable, shows for the first time how the mean global physical parameters vary during the Blazhko cycle. About 1-2 percent changes in the mean radius, luminosity and surface effective temperature are detected. The mean radius and temperature changes are in good accordance with pulsation model results, which show that these parameters do indeed vary within this order of magnitude if the amplitude of the pulsation changes significantly. We interpret the phase modulation of the pulsation to be a consequence of period changes. Its magnitude corresponds exactly what one expects from the detected changes of the mean radius assuming that the pulsation constant remains the same during the modulation. Our results indicate that during the modulation the pulsation remains purely radial, and the underlying mechanism is most probably a periodic perturbation of the stellar luminosity with the modulation period.