The Kepler Cepheid V1154 Cyg revisited: light curve modulation and detection of granulation

Derekas, A. and Plachy, E. and Molnár, L. and Sódor, Á. and Benkő, J.M. and Szabados, L. and Bognár, Zs. and Csák, B. and Szabó, Gy.M. and Szabó, R. and Pál, A. (2016) The Kepler Cepheid V1154 Cyg revisited: light curve modulation and detection of granulation. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. ISSN 0035-8711

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Abstract

We present a detailed analysis of the bright Cepheid-type variable star V1154 Cygni using 4 years of continuous observations by the Kepler space telescope. We detected 28 frequencies using standard Fourier transform method.We identified modulation of the main pulsation frequency and its harmonics with a period of ~159 d. This modulation is also present in the Fourier parameters of the light curve and the O-C diagram. We detected another modulation with a period of about 1160 d. The star also shows significant power in the low-frequency region that we identified as granulation noise. The effective timescale of the granulation agrees with the extrapolated scalings of red giant stars. Non-detection of solar-like oscillations indicates that the pulsation inhibits other oscillations. We obtained new radial velocity observations which are in a perfect agreement with previous years data, suggesting that there is no high mass star companion of V1154 Cygni. Finally, we discuss the possible origin of the detected frequency modulations.

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