Transiting exoplanets from the CoRoT space mission. XI. CoRoT-8b: a hot and dense sub-Saturn around a K1 dwarf
Mazeh, T.; Guterman, P.; Aigrain, S.; Alonso, R.; Auvergne, M.; Barge, P.; Bordé, P.; Bouchy, F.; Deeg, H.; Deleuil, M.; Dvorak, R.; Erikson, A.; Fridlund, M.; Jorda, L.; Lammer, H.; Léger, A.; Moutou, C.; Ollivier, M.; Pätzold, M.; Queloz, D.; Rauer, H.; Rouan, D.; Schneider, J.; Wuchterl, G.; Gandolfi, D.; Cabrera, J.; Baglin, A.; Benz, W.; Gillon, M.; Lovis, C.; Udry, S.; Pepe, F.; Hébrard, G.; Mayor, M.; Bonomo, A. S.; Almenara, J. M.; Carone, L.; Bruntt, H.; Carpano, S.; Santerne, A.; Ferraz-Mello, S.; Guillot, T.; Hatzes, A.; Tingley, B.; Weingrill, J.; Csizmadia, S.; Gazzano, J. -C.; Guenther, E.; Havel, M.; Samuel, B.
France, Germany, Switzerland, United Kingdom, Spain, Netherlands, Austria, Brazil, Belgium, Israel
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 RJ, a mass of 0.22 ± 0.03 MJ, 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.