Transiting exoplanets from the CoRoT space mission

Abstract

Aims. We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. Methods. We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial 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 0.063 0.001 AU. It has a radius of 0.57 0.02 R J , a mass of 0.22 0.03 M J , and therefore a mean density of 1.6 0.1 g cm -3 . Conclusions. With 67% of the size of Saturn and 72% of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g cm -3 ). We estimate its content in heavy elements to be 47-63 M , and the mass of its hydrogen-helium envelope to be 7-23 M . At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than 0.1% over an assumed integrated lifetime of 3 Ga.