Puzzling Low-Frequency Variations in the δ Scuti-type Kepler Star KIC 5988140 (HD 188774)

Lampens, Patricia and Tkachenko, A. and Lehmann, H. and Debosscher, J. and Aerts, C. and Beck, P. G. and Bloemen, S. and Kochiashvili, N. and Derekas, A. and Smith, J. and Tenenbaum, P. and Twicken, J. (2013) Puzzling Low-Frequency Variations in the δ Scuti-type Kepler Star KIC 5988140 (HD 188774). In: Progress in Physics of the Sun and Stars: A New Era in Helio- and Asteroseismology, 25-29 November, 2012, Hakone, Japan.

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Abstract

At first sight, the Kepler data of the A-type star KIC 5988140 mimics the light curve of an eclipsing binary system with a superposed short-period variability of type δ Scuti. It was attributed by the Kepler Asteroseismology Consortium (KASC) to the working group “Binary and Multiple Stars”, where we picked it up. We used the high-quality space photometry supplemented by recent high-resolution spectra to investigate the cause of the variability of this late A-type object. We considered three different possible scenarios: (1) binarity, (2) co-existence of γ Doradus and delta Scuti pulsations (the hybrid case) and (3) rotation of the stellar surface with an asymmetric intensity distribution (i.e. rotational modulation). We confirm the presence of various pressure modes of type delta Scuti. However, none of the previous scenarios is capable of reproducing all of the observed characteristics of the variations. Thus, the cause of the remaining light and radial velocity variations remains presently unexplained by any of the considered physical processes.

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