the On Eccentricity of HD 209458b1
Gregory Laughlin2 , Georey W. Marcy3 , Steven S. Vogt2 , Debra A. Fischer4 , R. Paul Butler5 [e-mail] ABSTRACT 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 t to the 69 radial velocities taken out of transit, and derive planetary parameters e = 0.0130.009, = 80 82 , and MP = 0.6760.007 MJUP . Using bootstrap Monte Carlo analyses of synthetic data sets based on known planetary parameters, we nd that our measured eccentricity e = 0.013 0.009 is consistent with eccentricities estimated from synthetic radial velocity data sets generated by planets xed on circular orbits. The orbital model that we derive suggests that structurally signicant tidal heating in the interior of the planet is currently not occurring. Furthermore, the current set of radial velocities shows no evidence for additional bodies in the system. Subject headings: stars: HD 209458 planetary systems planets and satellites: general
1.
Introduction
The identication of a planet transiting the G0V, V=7.65 star HD 209458 (Henry et al. 2000, Charbonneau et al. 2000) has spurred a profusion of detailed follow-up measurements, including the rst direct and accurate measurements of an extrasolar planets radius (1.350.06 RJUP [Brown et al. 2001] and mass (0.69 0.05 MJUP [Mazeh et al. 2000]). HD 209458 bs large planetary radius is in conict with baseline theoretical planetary models obtained by Guillot & Showman (2002), Bodenheimer et al (2003), and Barae et al (2003), which all predict planetary radii that are 0.20.3 RJU P smaller than observed, that is, in the range 1.1 RJUP at an age of 5 Gyr. Additional
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.
2 3 4 5 1
UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz,...
gm