The evolution of Lithium: implications of a universal Spite plateau
  The cosmological {7Li problem consists in explaining why the primordial Li
abundance, as predicted by the standard Big Bang nucleosynthesis theory with
constraints from WMAP and Planck, is a factor of 3 larger than the Li abundance
measured in the stars of the Spite plateau defined by old, warm dwarf stars of
the Milky Way halo. Several explanations have been proposed to explain this
difference, including various Li depletion processes as well as non standard
Big Bang nucleosynthesis, but the main question remains unanswered. In this
paper, we present detailed chemical evolution models for dwarf spheroidal and
ultra faint galaxies, compute the galactic evolution of 7Li abundance in these
objects and compare it with observations of similar objects. In our models, Li
is mainly produced by novae and cosmic rays and to a minor extent by low and
intermediate mass stars. We adopt the yield combination which best fits the Li
abundances in the Milky Way stars. It is evident that the observations of dwarf
objects define a Spite plateau, identical to that observed in the Milky Way,
thus suggesting that the Spite plateau could be a universal feature and its
meaning should be discussed. The predictions of our models for dwarf galaxies,
are obtained by assuming as Li primordial abundance either the one detected in
the atmospheres of the oldest halo stars (Spite plateau; A(Li)=2.2 dex), or the
one from cosmological observations (WMAP; A(Li)=2.66 dex). Finally, we discuss
the implications of the universality of the Spite plateau results.
