2019AJ....157..172S

We measure the rotation periods of 19 stars in the Kepler transiting planetary systems, P_rot,astero from asteroseismology and P_rot,phot from the photometric variation of their light curves. Two stars exhibit two clear peaks in the Lomb-Scargle periodogram, neither of which agrees with the seismic rotation period. Other four systems do not show any clear peak, whose stellar rotation period is impossible to estimate reliably from the photometric variation; their stellar equators may be significantly inclined with respect to the planetary orbital plane. For the remaining 13 systems, P_rot,astero and P_rot,phot agree within 30%. Interestingly, 3 out of the 13 systems are in the spin-orbit resonant state in which P_orb,b/P_rot,astero~1 with P_orb,b being the orbital period of the innermost planet of each system. The corresponding chance probability is (0.2-4.7)% based on the photometric rotation period data for 464 Kepler transiting planetary systems. While further analysis of stars with reliable rotation periods is required to examine the statistical significance, the spin-orbit resonance between the star and planets, if confirmed, has important implications for the star-planet tidal interaction, in addition to the origin of the spin-orbit (mis-)alignment of transiting planetary systems.