Planetary candidates around the pulsating sdB star KIC 5807616 considered doubtful

Abstract

Context. It has been suggested that two weak signals observed in the low frequency region of the Fourier transform amplitude spectra from the KIC 5807616 Q5-Q8 data can be interpreted as a result of the light reflection from planets orbiting the host star. Ever since the last results on KIC 5807616 were presented, the Kepler spacecraft has collected over two years of additional data, which we analysed using asteroseismological methods. Aims. To verify and improve on previous results, we used the Q 5-Q 17 Kepler data to identify pulsational modes, determine multiplet splitting, and to re-analyse the low frequency region between 33−49 μ Hz where two frequencies, claimed as the planetary signature, were found. Methods. Since Fourier transform amplitude spectra of the KIC 5807616 data do not show any clear multiplets, we used two stable acoustic modes to determine the theoretical width of gravity mode multiplets and their splittings. The period spacing and histograms of common multiplet component separations were used to identify pulsation modes and the observed gravity mode splittings. In the low frequency region, we analysed the amplitude variations of two planetary signature frequencies over the whole observing run. Results. We determined the rotational period of the star from the splittings. Analysis of the low frequency region shows that the amplitude and frequency change of the signals found there have similar characteristics to other gravity modes. Conclusions. New data allow for identifying gravity modes in a limited period range, as well as better rotational period estimations. We suggest that the so-called planetary signature frequencies found in previous work might instead be pulsation modes visible beyond the cut-off frequency of the star.