V473 Lyrae, a unique second-overtone Cepheid with two modulation cycles

TL;DR

V473 Lyrae is a unique Galactic Cepheid exhibiting Blazhko-like modulation with two cycles, and this study investigates its pulsation mode and potential resonance mechanisms through extensive data analysis and modeling.

Contribution

This work provides the first detailed analysis of V473 Lyrae's dual modulation cycles and explores possible mode resonances driving its unique pulsation behavior.

Findings

Confirmed second overtone pulsation in V473 Lyrae

Detected a secondary modulation cycle of approximately 14.5 years

Identified potential mode resonances that could explain the modulation

Abstract

V473 Lyrae is the only Galactic Cepheid with confirmed periodic amplitude and phase variations similar to the Blazhko effect observed in RR Lyrae stars. We collected all available photometric data and some radial velocity measurements to investigate the nature of the modulation. The comparison of the photometric and radial velocity amplitudes confirmed that the star pulsates in the second overtone. The extensive data set, spanning more than 40 years, allowed us to detect a secondary modulation cycle with a period of approximately 5300 days or 14.5 years. The secondary variations can be detected in the period of the primary modulation, as well. Phenomenologically, the light variations are analogous to the Blazhko effect. To find a physical link, we calculated linear hydrodynamic models to search for potential mode resonances that could drive the modulation and found two viable half-integer (n:2) and three n:4 resonances between the second overtone and other modes. If any of these resonances will be confirmed by non-linear models, it may confirm the mode resonance model, a common mechanism that can drive modulations both in RR Lyrae and Cepheid stars.