Transiting exoplanets from the CoRoT space mission


Aims. We report the discovery of very shallow ($\Delta F/F \approx 3.4\times 10^{-4}$), periodic dips in the light curve of an active $V = 11.7$ G9V star observed by the CoRoT  satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion.Methods. We used CoRoT  colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT  light curve to derive parameters of the companion.Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation $>$0.40´´or triple systems are almost excluded with a $8 \times 10^{-4}$ risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 $59 \pm 3 \times 10^{-5}$ day and a radius of $R_{\rm p} = 1.68 \pm 0.09$ $R_{\rm Earth}$. Analysis of preliminary radial velocity data yields an upper limit of 21 $M_{\rm Earth}$  for the companion mass, supporting the finding.Conclusions. CoRoT-7b  is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b  remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, $\approx$1800–2600 K at the substellar point, and a very low one, $\approx$50 K, on its dark face assuming no atmosphere, have been derived.

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    • "Gold and Soter 1969). The role of tides has been recently investigated for systems composed of a star and a close-in companion to tentatively explain, for instance, the spin-up of stars with hot Jupiters (Pont 2009; Damiani and Lanza 2010), the radius anomaly of short orbital period planets (Leconte et al. 2010a,b), and the synchronisation or quasi-synchronisation of the stellar spin (Aigrain et al. 2008). Recent observations have attracted our interest to reconsider the possible consequences of an often neglected phenomenon: the socalled elliptical instability. "
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    ABSTRACT: Several studies have already considered the influence of tides on the evolution of systems composed of a star and a close-in companion to tentatively explain different observations such as the spin-up of some stars with hot Jupiters, the radius anomaly of short orbital period planets and the synchronization or quasi-synchronization of the stellar spin in some extreme cases. However, the nature of the mechanism responsible for the tidal dissipation in such systems remains uncertain. In this paper, we claim that the so-called elliptical instability may play a major role in these systems, explaining some systematic features present in the observations. This hydrodynamic instability, arising in rotating flows with elliptical streamlines, is suspected to be present in both planet and star of such systems, which are elliptically deformed by tides. The presence and the influence of the elliptical instability in gaseous bodies, such as stars or hot Jupiters, are most of the time neglected. In this paper, using numerical simulations and theoretical arguments, we consider several features associated to the elliptical instability in hot-Jupiter systems. In particular, the use of ad hoc boundary conditions makes it possible to estimate the amplitude of the elliptical instability in gaseous bodies. We also consider the influence of compressibility on the elliptical instability, and compare the results to the incompressible case. We demonstrate the ability for the elliptical instability to grow in the presence of differential rotation, with a possible synchronized latitude, provided that the tidal deformation and/or the rotation rate of the fluid are large enough. Moreover, the amplitude of the instability for a centrally-condensed mass of fluid is of the same order of magnitude as for an incompressible fluid for a given distance to the threshold of the instability. Finally, we show that the assumption of the elliptical instability being the main tidal dissipation process in eccentric inflated hot Jupiters and misaligned stars is consistent with current data.
    Full-text · Article · Sep 2013 · Icarus