Transiting exoplanets from the CoRoT space mission - XI. CoRoT-8b: a hot and dense sub-Saturn around a K1 dwarf

摘要

Aims. We report the discovery of CoRoT-8b, a dense smallSaturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and wederive its orbital parameters, mass, and radius. Methods. We analyzed two complementary data sets: thephotometric transit curve of CoRoT-8b as measured by CoRoT and theradial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. Results. We find that CoRoT-8b is on a circular orbit with a semi-major axis of AU. It has a radius of ,a mass of ,and therefore a mean density of gcm-3. Conclusions. With 67% of the size of Saturn and 72% of its mass,CoRoT-8b has a density comparable to that of Neptune(1.76gcm-3). We estimate its content in heavy elements to be 47-63,and the mass of its hydrogen-helium envelope to be 7-23.At 0.063AU, the thermal loss of hydrogen of CoRoT-8b should be no more than 0.1% over an assumed integrated lifetime of 3Ga. Key words: planets and satellites: detection - stars:fundamental parameters - techniques: photometric - techniques:spectroscopic - techniques: radial velocities - planets and satellites:fundamental parameters