Hat-P-9b: A low-density planet transiting a moderately faint F star

Abstract

We report the discovery of a planet transiting a moderately faint (V = 12.3 mag) late F star, with an orbital period of 3.92289 ± 0.00004 days. From the transit light curve and radial velocity measurements, we determine that the radius of the planet is Rp = 1.40 ± 0.06 R Jup and that the mass is Mp = 0.78 ± 0.09 M Jup. The density of the new planet, ρp = 0.35 ± 0.06 g cm -3, fits to the low-density tail of the currently known transiting planets. We find that the center of transit is at T c = 2454417.9077 ± 0.0003 (HJD), and the total transit duration is 0.143 ± 0.004 days. The host star has M ⊙ = 1.28 ± 0.13 M ⊙ and R ⊙ = 1.32 ± 0.07 R ⊙. © 2009. The American Astronomical Society. All rights reserved.