Li depletion in solar analogues with exoplanets Extending the sample

Aims. We want to study the effects of the formation of planets and planetary systems on the atmospheric Li abundance of planet host stars. Methods. In this work we present new determinations of lithium abundances for 326 main sequence stars with and without planets in the T-eff range 5600-5900 K. The 277 stars come from the HARPS sample, the remaining targets were observed with a variety of high-resolution spectrographs. Results. We confirm significant differences in the Li distribution of solar twins (T-eff = T-circle dot +/- 80 K, log g = log g(circle dot) +/- 0.2 and [Fe/H] = [Fe/H](circle dot) +/- 0.2): the full sample of planet host stars (22) shows Li average values lower than single stars with no detected planets (60). If we focus on subsamples with narrower ranges in metallicity and age, we observe indications of a similar result though it is not so clear for some of the subsamples. Furthermore, we compare the observed spectra of several couples of stars with very similar parameters that show differences in Li abundances up to 1.6 dex. Therefore we show that neither age, mass, nor metallicity of a parent star is the only cause for enhanced Li depletion in solar analogues. Conclusions. We conclude that another variable must account for that difference and suggest that this could be the presence of planets that causes additional rotationally induced mixing in the external layers of planet host stars. Moreover, we find indications that the amount of depletion of Li in planet-host solar-type stars is higher when the planets are more massive than Jupiter.