An extensive photometric study of the Blazhko RR Lyrae star DM Cyg

TL;DR

This study presents detailed photometric observations of the RR Lyrae star DM Cyg, revealing very small amplitude Blazhko modulation and subtle changes in its physical parameters, contributing to understanding the Blazhko effect in RR Lyrae stars.

Contribution

It provides the first detailed analysis of DM Cyg's small-amplitude Blazhko modulation, including detection of frequency components and physical parameter variations.

Findings

Detected 10.57-day modulation period with very small amplitude.

Identified frequency triplets and quintuplet components in the Fourier spectrum.

Observed small but systematic changes in physical parameters during the Blazhko cycle.

Abstract

DM Cyg, a fundamental mode RRab star was observed in the 2007 and 2008 seasons in the frame of the Konkoly Blazhko Survey. Very small amplitude light curve modulation was detected with 10.57 d modulation period. The maximum brightness and phase variations do not exceed 0.07 mag and 7 min, respectively. In spite of the very small amplitude of the modulation, beside the frequency triplets characterizing the Fourier spectrum of the light curve two quintuplet components were also identified. The accuracy and the good phase coverage of our observations made it possible to analyse the light curves at different phases of the modulation separately. Utilizing the IP method (S\'odor, Jurcsik and Szeidl, 2009) we could detect very small systematic changes in the global mean physical parameters of DM Cyg during its Blazhko cycle. The detected changes are similar to what we have already found for a large modulation amplitude Blazhko variable MW Lyrae. The amplitudes of the detected changes in the physical parameters of DM Cyg are only about 10% of that what have been found in MW Lyr. This is in accordance with its small modulation amplitude being about one tenth of the modulation amplitude of MW Lyr.