n °

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0,2 0.3 0.4 0.5 0.6

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0,2 0.3 0.4 0.5 0.6

.8 Metallicity of stars with exoplanets

7 When a planet is observed in transit, the planetary system is seen from the side, so that the value of the radial velocity measured gives the mass directly, because (sin(i) = 1).

Mass [UJup]

Fig. 3.9 Mass/radius diagram for giant planets observed in transit

Mass [UJup]

Fig. 3.9 Mass/radius diagram for giant planets observed in transit of the internal structure of these objects have enabled us to estimate the mass of the rocky cores. A complete discussion of this point is given in Chap. 7.

3.8 Characteristics of Extrasolar Planetary Atmospheres

Even if, 2MSS 1207 excepted, no direct detections sensu stricto have been achieved, the observation of transiting extrasolar systems during transits both in front of, and behind their stars (see Chap. 3) has enabled the identification of atmospheres and several compounds within them. The first identification of an atomic element was that of sodium in the atmosphere of HD 209458b by Charbonneau et al. in 2002. Using the FUSE satellite data, Vidal Madjar et al. (2004) then announced the observation of atomic hydrogen, carbon, and oxygen, and concluded that the atmosphere was evaporating. Several observations using the HST provided constraints on the radius of several planetary candidates as a function of the wavelength, thus probing the structure of their atmospheres. Recently, the observation of several objects in the thermal infrared using the Spitzer telescope had enabled several molecules to be identified in certain atmospheres and, in particular, H20 in the atmosphere of HD 209458b (Berman, 2007). Richardson et al. (2007) published the identification (by the same techniques) of silicate features in the same object, interpreted as the presence of clouds in the atmosphere. The detection of CH4 in the atmosphere of HD 189733b has also been announced recently by Swain et al. (2008)

To conclude, the study of the objects detected in the last 10 years allows us to gain an initial statistical view of giant exoplanets orbiting stars close to the Sun. This picture will be rendered complete by:

• the exploration of more distant regions of the Galaxy to confirm the (implicit) theories that the distribution is spatially homogeneous

• study and analysis of terrestrial-type objects.

These two points are the focus of the next five years of research, in particular with the advent of dedicated observations from space, such as those provided by COROT and KEPLER.


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