We present a detailed abundance study based on spectroscopic data obtained with HARPS of two solar-analogue main targets for the asteroseismology programme of the CoRoT satellite : HD 42618 and HD 43587 .
The atmospheric parameters and chemical composition are accurately determined through a fully differential analysis with respect to the Sun observed with the same instrumental set-up .
Several sources of systematic errors largely cancel out with this approach , which allows us to narrow down the 1- \sigma error bars to typically 20 K in effective temperature , 0.04 dex in surface gravity , and less than 0.05 dex in the elemental abundances .
Although HD 42618 fulfils many requirements for being classified as a solar twin , its slight deficiency in metals and its possibly younger age indicate that , strictly speaking , it does not belong to this class of objects .
On the other hand , HD 43587 is slightly more massive and evolved .
In addition , marked differences are found in the amount of lithium present in the photospheres of these two stars , which might reveal different mixing properties in their interiors .
These results will put tight constraints on the forthcoming theoretical modelling of their solar-like oscillations and contribute to increase our knowledge of the fundamental parameters and internal structure of stars similar to our Sun .