# Asteroseismic determination of the stellar rotation period of the Kepler transiting planetary systems and its implications for the spin-orbit architecture

## TL;DR

This study measures stellar rotation periods in Kepler transiting planetary systems using asteroseismology and photometry, revealing potential spin-orbit resonances and implications for star-planet interactions and system alignment.

## Contribution

It provides the first comparison of asteroseismic and photometric rotation periods for multiple systems, identifying possible spin-orbit resonances and stellar inclination effects.

## Key findings

- 13 systems show consistent rotation periods within 30%
- 3 systems exhibit potential spin-orbit resonance
- Some stars have ambiguous or no clear photometric rotation signals

## Abstract

We measure the rotation periods of 19 stars in the {\it Kepler} transiting planetary systems, $P_{\rm rot, astero}$ from asteroseismology and $P_{\rm rot, phot}$ from photometric variation of their lightcurve. 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, $P_{\rm rot, astero}$ and $P_{\rm rot, phot}$ agree within 30\%. Interestingly, three out of the 13 systems are in the spin-orbit resonant state in which $P_{\rm orb, b}/P_{\rm rot, astero} \approx 1$ with $P_{\rm orb, b}$ being the orbital period of the inner-most planet of each system. The corresponding chance probability is ($0.2$-$4.7$) \% based on the photometric rotation period data for 464 {\it 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, have important implications for the star-planet tidal interaction, in addition to the origin of the spin-orbit (mis-)alignment of transiting planetary systems.