* Astronomy

Title: Measurements of Stellar Inclinations for Kepler Planet Candidates
Authors: Teruyuki Hirano, Roberto Sanchis-Ojeda, Yoichi Takeda, Norio Narita, Joshua N. Winn, Atsushi Taruya, Yasushi Suto

We present an investigation of spin-orbit angles for planetary system candidates reported by Kepler. By combining the rotational period P_s inferred from the flux variation due to starspots and the projected rotational velocity V\sin I_s and stellar radius obtained by a high resolution spectroscopy, we attempt to estimate the inclination I_s of the stellar spin axis with respect to the line-of-sight. For transiting planetary systems, in which planetary orbits are edge-on seen from us, the stellar inclination I_s can be a useful indicator of a spin-orbit alignment/misalignment. We newly conducted spectroscopic observations with Subaru/HDS for 15 KOI systems, whose lightcurves show periodic flux variations. After detailed analyses of their lightcurves and spectra, it turned out that some of them are binaries, or the flux variations are too coherent to be caused by starspots, probably representing ellipsoidal variations, and consequently we could constrain stellar inclinations I_s for eight systems. Among them, KOI-262 and 280 are in good agreement with I_s=90° suggesting a spin-orbit alignment, while at least one system, KOI-261, shows a possible spin-orbit misalignment. We also obtain a small I_s for KOI-1463, but the transiting companion seems to be a star rather than a planet. The results for KOI-257, 269, 367, and 974 are ambiguous, and can be explained with either misalignments or moderate differential rotation. Since our method can be applied to any system having starspots regardless of the planet size, future observations will allow for the expansion of the parameter space in which the spin-orbit relations are investigated.

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