We present simulations of the accretion of a massive planet or brown dwarf by
an AGB star. In our scenario, close planets will be engulfed by the star,
spiral-in and be dissipated in the ``accretion region'' located at the bottom
of the convective envelope of the star. The deposition of mass and chemical
elements in this region will release a large amount of energy that will produce
a significant expansion of the star. For high accretion rates, hot bottom
burning is also activated. Finally, we present some observational signatures of
the accretion of a planet/brown dwarf and we propose that this process may be
responsible for the IR excess and high lithium abundance observed in 4-8% of
single G and K giants.Comment: 4 pages, 1 figure, to appear in "Unsolved Problems in Stellar
Evolution", ed. M. Livio, Cambridge University Press, in pres
