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Transiting exoplanets from the CoRoT space mission . VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert
Context: The CoRoT space mission routinely provides high-precisionphotometric measurements of thousands of stars that have beencontinuously observed for months. Aims: The discovery andcharacterization of the first very massive transiting planetarycompanion with a short orbital period is reported. Methods: A series of34 transits was detected in the CoRoT light curve of an F3V star,observed from May to October 2007 for 152 days. The radius wasaccurately determined and the mass derived for this new transiting,thanks to the combined analysis of the light curve and complementaryground-based observations: high-precision radial-velocity measurements,on-off photometry, and high signal-to-noise spectroscopic observations. Results: CoRoT-Exo-3b has a radius of 1.01 ± 0.07 R_Jup andtransits around its F3-type primary every 4.26 days in a synchronousorbit. Its mass of 21.66 ± 1.0 M_Jup, density of 26.4 ±5.6 g cm-3, and surface gravity of logg = 4.72 clearlydistinguish it from the regular close-in planet population, making itthe most intriguing transiting substellar object discovered so far. Conclusions: With the current data, the nature of CoRoT-Exo-3b isambiguous, as it could either be a low-mass brown-dwarf or a member of anew class of “superplanets”. Its discovery may helpconstrain the evolution of close-in planets and brown-dwarfs better.Finally, CoRoT-Exo-3b confirms the trend that massive transiting giantplanets (M ≥ 4 M_Jup) are found preferentially around more massivestars than the Sun.The CoRoT space mission, launched on December 27th 2006, has beendeveloped and is operating by CNES, with the contribution of Austria,Belgium, Brasil, ESA, Germany and Spain. The first CoRoT data will beavailable to the public in February 2009 from the CoRoT archive:http://idoc-corot.ias.u-psud.fr/ Table of the COROT photometry is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/491/889
| On the Origins of Eccentric Close-In Planets
Strong tidal interaction with the central star can circularize theorbits of close-in planets. With the standard tidal quality factor Q ofour solar system, estimated circularization times for close-inextrasolar planets are typically shorter than the ages of the hoststars. While most extrasolar planets with orbital radii a<~0.1 AUindeed have circular orbits, some close-in planets with substantialorbital eccentricities have recently been discovered. This new class ofeccentric close-in planets implies that either their tidal Q factor isconsiderably higher, or circularization is prevented by an externalperturbation. Here we constrain the tidal Q factor for transitingextrasolar planets by comparing their circularization times withaccurately determined stellar ages. Using estimated secular perturbationtimescales, we also provide constraints on the properties ofhypothetical second planets exterior to the known ones.
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