Prof Suzanne Aigrain

Abstract:

Aims: The CoRoT satellite has announced its fourth transiting planet (Aigrain et al. 2008, A&A, 488, L43) with space photometry. We describe and analyse complementary observations of this system performed to establish the planetary nature of the transiting body and to estimate the fundamental parameters of the planet and its parent star. Methods: We have analysed high precision radial-velocity data, ground-based photometry, and high signal-to-noise ratio spectroscopy. Results: The parent star CoRoT-Exo-4 (2MASS 06484671-0040219) is a late F-type star of mass of 1.16 and radius of 1.17 . The planet has a circular orbit with a period of 9.20205 d. The planet radius is 1.19 and the mass is 0.72 . It is a gas-giant planet with a "normal" internal structure of mainly H and He. CoRoT-Exo-4b has the second longest period of the known transiting planets. It is an important discovery since it occupies an empty area in the mass-period diagram of transiting exoplanets.. © 2008 ESO.

Abstract:

Context. The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ∼12 000 stars in the galactic plane. An analysis of the raw data identifies the most promising candidates and triggers the ground-based follow-up.Aims. We report on the discovery of the transiting planet CoRoT-Exo-2b, with a period of 1.743 days, and characterize its main parameters.Methods. We filter the CoRoT raw light curve of cosmic impacts, orbital residuals, and low frequency signals from the star. The folded light curve of 78 transits is fitted to a model to obtain the main parameters. Radial velocity data obtained with the SOPHIE, CORALIE and HARPS spectrographs are combined to characterize the system. The 2.5 min binned phase-folded light curve is affected by the effect of sucessive occultations of stellar active regions by the planet, and the dispersion in the out of transit part reaches a level of 1.0910 in flux units.Results. We derive a radius for the planet of 1.465 0.029 and a mass of 3.31 0.16 , corresponding to a density of 1.31 0.04 g/cm. The large radius of CoRoT-Exo-2b cannot be explained by current models of evolution of irradiated planets.. © 2008 ESO.

Abstract:

Context. The pioneer space mission for photometric planet searches, CoRoT, steadily monitors about 12 000 stars in each of its fields of view. Transit candidates can be detected early in the processing of the data and before the end of a run of observation.Aims. We report the detection of the first planet discovered by CoRoT and characterizing it with the help of follow-up observations.Methods. Raw data were filtered from outliers and residuals at the orbital period of the satellite. The orbital parameters and the radius of the planet were estimated by best fitting the phase folded light curve with 34 successive transits. Doppler measurements with the SOPHIE spectrograph permitted us to secure the detection against binaries and to estimate the mass of the planet.Results. The accuracy of the data is very high with a dispersion in the 2.17 min binned phase-folded light curve that does not exceed ~3.10 in flux unit. The planet orbits a mildly metal-poor G0V star of magnitude in 1.5 days. The estimated mass and radius of the star are 0.950.15 and 1.110.05 . We find the planet has a radius of 1.490.08 , a mass of 1.030.12 , and a particularly low mean density of 0.380.05 gcm. . © 2008 ESO.