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arXiv · 1110.6136

XO-2b: a Prograde Planet with a Negligible Eccentricity, and an Additional Radial Velocity Variation

Norio Narita·Teruyuki Hirano·Bun'ei Sato·Hiroki Harakawa·Akihiko Fukui·Wako Aoki·Motohide Tamura
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Abstract

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$σ$ ($e=0.045\pm0.024$) and the orbit of XO-2b is prograde (the sky-projected spin-orbit alignment angle $λ=10^{\circ}\pm72^{\circ}$). The poor constraint of $λ$ 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.

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Norio Narita, Teruyuki Hirano, Bun'ei Sato, Hiroki Harakawa, Akihiko Fukui, Wako Aoki, Motohide Tamura. 2011-10-27. XO-2b: a Prograde Planet with a Negligible Eccentricity, and an Additional Radial Velocity Variation. https://doi.org/10.1093/pasj%2F63.6.l67

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