Résumé
The 16 Cygni system is composed of two solar analogs with similar masses and ages. They have been observed by Kepler for asteroseismology, and their radii have been precisely determined from interferometry. A red dwarf is in orbit around 16 Cygni A whereas 16 Cygni B hosts a giant planet. The abundances of heavy elements are similar in the two stars but lithium is much more depleted in 16 Cygni B that in 16 Cygni A, by a factor of at least 4.7. We show that fingering convection induced by the accretion of planetary matter onto 16 Cygni B can account for this difference in lithium abundances. This is a general result which may be applied to all planetary-host stars.