Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation

Abstract

Noting the weakest modulation and relatively high metal abundance of the ab-type RR Lyrae star V838 Cyg, we collected the photometric data of this star from several sky surveys to carry out an in-depth analysis. The O-C diagram shows that the pulsation period of V838 Cyg increases linearly over a long timescale. In a reanalysis of the high-precision Kepler data, we confirmed the modulation with a period of 59.45\pm0.07 days found by Benko et al., (2014), and also found an additional weak modulation with a longer period (840\pm21 days). After a series of analyses, we incline to the view that the mechanisms causing the two modulations are different: the former is more similar to the typical Blazhko effect, while the mechanism leading to the latter may be an extrinsic factor. We also collected and compared the modulation and physical parameters of other Blazhko RR Lyrae stars from several works in the literature, and find that there is a potential negative correlation between the modulation amplitude (or upper limit of amplitude) and the metal abundance. We infer that the relatively high metal abundance will promote convection in the outer stellar atmosphere, and then inhibit those factors (turbulence, shock wave, etc.) that may cause Blazhko modulation. Future observations and research work can be carried out with reference to this viewpoint. We also introduce the moire effects that appear in the Kepler long-cadence light curves and their possible interference in the previous analyses.

22 pages, 12 figures

References in corpus (17)

• The Transiting Exoplanet Survey Satellite
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• The first WASP public data release
• Spectroscopic Comparison of Metal-Rich RRab Stars of the Galactic Field with Their Metal-Poor Counterparts
• Stellar evolution through the ages: period variations in galactic RRab stars as derived from the GEOS database and TAROT telescopes
• Long time-scale behavior of the Blazhko effect from rectified Kepler data
• RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation
• The Kepler Cepheid V1154 Cyg revisited: light curve modulation and detection of granulation
• Long-term variability of T Tauri stars using WASP
• Blazhko effect in the Galactic bulge fundamental mode RR~Lyrae stars I: Incidence rate and differences between modulated and non-modulated stars
• On the use of field RR Lyrae as Galactic probes: IV. New insights into and around the Oosterhoff dichotomy
• Multiple Populations in Globular Clusters and the Origin of the Oosterhoff Period Groups
• On the modulation of RR Lyrae stars in the globular cluster M3
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae
• Revisiting the Kepler non-Blazhko RR Lyrae sample: Cycle-to-cyle variations and additional modes
• Reanalysis of c-type RR Lyrae Variable BE Dor, Period Modulations and Possible Mechanism
• Is the Blazhko effect the beating of a near-resonant double-mode pulsation?

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