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Seismic evidence for non-synchronization in two close sdb+dM binaries from Kepler photometry




We report on extended photometry of two pulsating subdwarf B (sdB) stars in close binaries. For both cases, we use rotational splitting of the pulsation frequencies to show that the sdB component rotates much too slowly to be in synchronous rotation. We use a theory of tidal interaction in binary stars to place limits on the mass ratios that are independent of estimates based on the radial velocity curves. The companions have masses below 0.26 M. The pulsation spectra show the signature of high-overtone g-mode pulsation. One star, KIC 11179657, has a clear sequence of g modes with equal period spacings as well as several periodicities that depart from that trend. KIC 02991403 shows a similar sequence, but has many more modes that do not fit the simple pattern.

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