Period and light curve analysis of the Kepler Cepheid V1154 Cyg: light curve modulation and detection of granulation
Aliz Derekas (ELTE Gothard Astrophysical Observatory), Plachy, E. (Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences), Molnar, L. (Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences), Sodor, A. (Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences), et al.

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. The light curve was extracted by applying aperture photometry of the Kepler pixel data, then a detrending process. The frequency analysis revealed 28 frequencies and we identified modulation of the main pulsation frequency and its harmonics with a period of ∼159 days. In addition, we detected another modulation with a period of about 1200 days. In addition, the Fourier parameters of the light curve and the O–C data show the 159 day modulation. 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, demonstrating that the 159 days modulation is not caused by the presence of a companion star. Finally, we discuss the possible origin of the detected frequency modulations.