2015A&A...573A..52B

We present our analysis of Kepler data of a pulsating subdwarf B star, KIC8302197. We used Q5-17 data and applied a Fourier technique to extract 30 significant pulsation modes. We searched for multiplets and period-spacing sequences to perform a mode identification and to derive a rotation period. To our surprise, KIC8302197 does not show any multiplets. We explain the lack of multiplets by either a very slow rotation (longer than ∼1000-days) or a unique (pole-on) orientation of the pulsation axis. Our mode identification relied solely on period spacing. We were successful in identifying modal degrees of most of the detected modes. An analysis of the period stability did not show any evidence of a companion to the host star. In addition to photometric data, several spectroscopic observations were collected. Our twelve radial-velocity measurements constrain a possible orbital radial-velocity amplitude to be smaller than about 10km/s. Furthermore, based on color indices we constrained a possible companion to be an M or later type main sequence, a compact or a substellar object. We found that the atmospheric parameters (T_eff=27450±200K, logg=5.438±0.033dex, and log(nHe/nH)=-2.56±0.07dex) of KIC8302197 are consistent with other slow pulsating subdwarf B stars. From the optical spectra we derived C, N, O, Si and Fe abundances, and set an upper limit for the S abundance.