Norio Narita, Teruyuki Hirano, Bun'ei Sato, Hiroki Harakawa, Akihiko Fukui, Wako Aoki, Motohide Tamura
We present precise radial velocities of XO-2 taken with the Subaru HDS,
covering two transits of XO-2b with an interval of nearly two years. The data
suggest that the orbital eccentricity of XO-2b is consistent with zero within
2$\sigma$ ($e=0.045\pm0.024$) and the orbit of XO-2b is prograde (the
sky-projected spin-orbit alignment angle $\lambda=10^{\circ}\pm72^{\circ}$).
The poor constraint of $\lambda$ is due to a small impact parameter (the
orbital inclination of XO-2b is almost 90$^{\circ}$). The data also provide an
improved estimate of the mass of XO-2b as $0.62\pm0.02$ $M_{\rm Jup}$. We also
find a long-term radial velocity variation in this system. Further radial
velocity measurements are necessary to specify the cause of this additional
variation.
View original:
http://arxiv.org/abs/1110.6136
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