HD 147506b: A Supermassive Planet in an Eccentric Orbit Transiting a Bright Star

Abstract

We report the discovery of a massive (M_p = 9.04 ± 0.50 M_J) planet transiting the bright (V = 8.7) F8 star HD 147506, with an orbital period of 5.63341 ± 0.00013 days and an eccentricity of e = 0.520 ± 0.010. From the transit light curve we determine that the radius of the planet is R_p = 0.982 R_J. HD 147506b (also coined HAT-P-2b) has a mass about 9 times the average mass of previously known transiting exoplanets and a density of ρ_p ≈ 12 g cm^-3, greater than that of rocky planets like the Earth. Its mass and radius are marginally consistent with theories of structure of massive giant planets composed of pure H and He, and accounting for them may require a large (100 M_⊕) core. The high eccentricity causes a ninefold variation of insolation of the planet between peri- and apastron. Using follow-up photometry, we find that the center of transit is T_mid = 2,454,212.8559 ± 0.0007 (HJD) and the transit duration is 0.177 ± 0.002 days.