Spin-Orbit Alignment For 110-Day-Period KOI368.01 From Gravity Darkening

Abstract

We fit the \emph{Kepler} photometric light curve of the KOI-368 system using an oblate, gravity-darkened stellar model in order to constrain its spin-orbit alignment. We find that the system is relatively well-aligned with a sky-projected spin-orbit alignment of $\lambda =10^{\circ }\pm 2^{\circ }$, a stellar obliquity of $\psi =3^{\circ }\pm 7^{\circ }$, and a true spin-orbit alignment of $\phi =11^{\circ }\pm 3^{\circ }$. Although our measurement differs significantly from zero, the low value for $\phi$ is consistent with spin-orbit alignment. We also measure various transit parameters of the KOI-368 system: $R_{\star }=2.28\pm 0.02R_{\odot }$, $R_p=1.83\pm 0.02R_{jup}$, and $i=89.221^{\circ }\pm 0.013^{\circ }$. This work shows that our gravity-darkened model can constrain long-period, well-aligned planets and M-class stars orbiting fast-rotators, allowing for measurement of a new subcategory of transiting bodies.

5 Figures, 6 Pages

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