KIC 9533489: a genuine γ Doradus – δ Scuti Kepler hybrid pulsator with transit events

Abstract

Context. Several hundred candidate hybrid pulsators of type A–F have been identified from space-based observations. Their large number allows both statistical analyses and detailed investigations of individual stars. This offers the opportunity to study the full interior of the genuine hybrids, in which both low radial order p- and high-order g-modes are self-excited at the same time. However, a few other physical processes can also be responsible for the observed hybrid nature, related to binarity or to surface inhomogeneities. The finding that most δ Scuti stars also show long-period light variations represents a real challenge for theory. Aims. We aim at determining the pulsation frequencies of KIC 9533489, to search for regular patterns and spacings among them, and to investigate the stability of the frequencies and the amplitudes. An additional goal is to study the serendipitously detected transit events: is KIC 9533489 the host star? What are the limitations on the physical parameters of the involved bodies? Methods. We performed a Fourier analysis of all the available Kepler light curves. We investigated the frequency and period spacings and determined the stellar physical parameters from spectroscopic observations. We also modelled the transit events. Results. The Fourier analysis of the Kepler light curves revealed 55 significant frequencies clustered into two groups, which are separated by a gap between 15 and 27 d^(1). The light variations are dominated by the beating of two dominant frequencies located at around 4 d^(-1). The amplitudes of these two frequencies show a monotonic long-term trend. The frequency spacing analysis revealed two possibilities: the pulsator is either a highly inclined moderate rotator (v ≈ 70 km s^(-1), i> 70°) or a fast rotator (v ≈ 200 km s^(-1)) with i ≈ 20°. The transit analysis disclosed that the transit events that occur with a ≈197 d period may be caused by a 1.6 R_(Jup) body orbiting a fainter star, which would be spatially coincident with KIC 9533489.

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