Révision des caractéristiques de CoRoT-7 et de ses planètes

Accurate parameters of the host stars of exoplanets are important for the
interpretation of the new planet systems that continue to emerge. The CoRoT
satellite recently discovered a transiting rocky planet with a density similar
to the inner planets in our solar system, a so-called Super Earth. This planet
is orbiting a relatively faint G9V star called CoRoT-7, and we wish to refine
its physical properties, which are important for the interpretation of the
properties of the planet system. We used spectra from HARPS@ESO-3.6m and
UVES@VLT-8.2m. From the analysis of Fe-1 and Fe-2 lines we determine Teff, log
g and microturbulence. We use the Balmer lines to constrain Teff and pressure
sensitive Mg-1b and Ca lines to constrain log g. From the analysis we find
Teff=5250+-60K, log g = 4.47+-0.05, [M/H]=+0.12+-0.06, and vsini = 1.1 km/s. We
compared the L/M ratio with isochrones to constrain the evolutionary status.
Using the age estimate of 1.2-2.3 Gyr based on stellar activity, we determine
the mass and radius 0.91+-0.03 Msun and 0.82+-0.04 Rsun. With these updated
constraints we fitted the CoRoT transit light curve for CoRoT-7b. We revise the
planet radius to be slightly smaller, R = 1.58+-0.10 Rearth, and the density
becomes higher, rho = 7.2+-1.8 g/cm3. The host star CoRoT-7 is a slowly
rotating, metal rich, unevolved type G9V star. The star is relatively faint
(V=11.7) and its fundamental parameters can only be determined through indirect
methods. Our methods rely on detailed spectral analyses that depend on the
adopted model atmospheres. From the analysis of spectra of stars with
well-known parameters with similar parameters to CoRoT-7 (the Sun and alpha Cen
B) we demonstrate that our methods are robust within the claimed uncertainties.
Therefore our methods can be reliably used in subsequent analyses of similar
exoplanet host stars.

Stalker a écrit:5,5