On the Eccentricity of HD 209458b

We report 85 high-precision Doppler radial velocity measurements taken between 1999.5 and 2005.0 of the parent star of the transiting planet HD 209458b. We obtain an orbital fit to the 68 radial velocities taken out of transit and derive planetary parameters e=0.014+/-0.009, ϖ=80^deg+/-80^deg, and M_pl=(0.69+/-0.06)M_Jup (with M_*=1.14+/-0.10 M_solar). We perform orbital fits to synthetic data sets based on known planetary parameters, and we find that our measured eccentricity e=0.014 is consistent with eccentricities estimated from synthetic radial velocity data sets generated by planets fixed on circular orbits. The orbital model that we derive suggests that structurally significant tidal heating in the interior of the planet is probably not occurring. Furthermore, the current set of radial velocities shows no evidence for additional bodies in the system.

Based on observations obtained at Lick Observatory, which is operated by the University of California, and on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.