The light-curve modulation of XY And and UZ Vir - Two Blazhko RR Lyrae stars with additional frequencies

TL;DR

This study analyzes multicolour CCD data of two Blazhko RR Lyrae stars, revealing additional frequencies, detailed phase relations, and physical parameter variations, challenging existing theoretical models of the Blazhko effect.

Contribution

It provides the first detailed analysis of additional frequencies and physical parameter variations in two Blazhko RR Lyrae stars using the Inverse Photometric Method.

Findings

Detection of an additional independent frequency in each star.

Opposite phase behavior of pulsation period at maximum amplitude.

Results contradict the predictions of the Stothers (2006) Blazhko model.

Abstract

A thorough analysis of multicolour CCD observations of two modulated RRab-type variables, XY And and UZ Vir is presented. These Blazhko stars show relatively simple light-curve modulation with the usual multiplet structures in their Fourier spectra. One additional, independent frequency with linear-combination terms of the pulsation frequency is also detected in the residual spectrum of each of the two stars. The amplitude and phase relations of the triplet components are studied in detail. Most of the epoch-independent phase differences show a slight, systematic colour dependence, however, these trends have the opposite sign in the two stars. The mean values of the global physical parameters and their changes with Blazhko phase are determined utilizing the Inverse Photometric Method (IPM). The modulation properties and the IPM results are compared for the two variables. The pulsation period of XY And is the shortest when its pulsation amplitude is the highest, while UZ Vir has the longest pulsation period at this phase of the modulation. Despite this opposite behaviour, the phase relations of their mean-physical-parameter variations are similar. These results are not in accord with the predictions of the Blazhko model of Stothers (2006, ApJ, 652, 643).