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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 464; no. 2; p. 1553
• Main Authors: Derekas, A, Plachy, E, Molnar, L, Sodor, A, Benko, J M, Szabados, L, Bognar, Zs, Csak, B, Szabo, Gy M, Szabo, R, Pal, A
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11-01-2017
• Subjects: Fourier transforms; Giant stars; Granulation; Harmonics; Light curve; Modulation; Oscillations; Pulsation; Red giant stars; Scaling; Space telescopes; Stars & galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw2399

We present a detailed analysis of the bright Cepheid-type variable star V1154 Cygni using 4 yr of continuous observations by the Kepler space telescope. We detected 28 frequencies using the 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 time-scale 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 that 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.