Context : 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 .
The mass was determined using ground-based follow-up spectroscopy , which also revealed a second , non-transiting super Earth .

Aims : These planets are orbiting a relatively faint ( m _ { V } = 11.7 ) G9V star called CoRoT-7 .
We wish to refine the determination of the physical properties of the host star , which are important for the interpretation of the properties of the planet system .

Methods : We have used high-quality spectra from HARPS @ ESO 3.6m and UVES @ VLT 8.2m .
We use various methods to analyse the spectra using 1D LTE atmospheric models .
From the analysis of Fe i and Fe ii lines we determine the effective temperature , surface gravity and microturbulence .
We use the Balmer lines to constrain the effective temperature and pressure sensitive Mg 1b and Ca lines to constrain the surface gravity .
We analyse both single spectra and co-added spectra to identify systematic errors .
We determine the projected rotational velocity and macroturbulence by fitting the line shapes of isolated lines .
We finally employ the Wilson-Bappu effect to determine the approximate absolute magnitude .

Results : From the analysis of the three best spectra using several methods we find T _ { eff } = 5250 \pm 60 K , \log g = 4.47 \pm 0.05 , [ { M / H } ] = +0.12 \pm 0.06 , and v \sin i = 1.1 ^ { +1.0 } _ { -0.5 } km s ^ { -1 } .
The chemical composition of 20 analysed elements are consistent with a uniform scaling by the metallicity +0.12 dex .
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 \pm 0.03 M _ { \odot } and 0.82 \pm 0.04 R _ { \odot } .
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 \pm 0.10 R _ { \oplus } , and using the planet mass the density becomes slightly higher , \rho = 7.2 \pm 1.8 { g cm } ^ { -3 } .

Conclusions : The host star CoRoT-7 is a slowly rotating , metal rich , unevolved type G9V star .
The star is relatively faint and its fundamental parameters can only be determined through indirect methods .
Our methods rely on detailed spectral analyses that in turn 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 .