Origin of the Galactic Halo: accretion vs. in situ formation
  We test the hypothesis that the classical and ultra-faint dwarf spheroidal
satellites of the our Galaxy have been the building blocks of the Galactic halo
by comparing their [O/Fe] and [Ba/Fe] vs. [Fe/H] patterns with the ones
observed in Galactic halo stars. The [O/Fe] ratio deviates substantially from
the observed abundance ratios in the Galactic halo stars for [Fe/H] > -2 dex,
while they overlap for lower metallicities. On the other hand, for the neutron
capture elements, the discrepancy is extended at all the metallicities,
suggesting that the majority of stars in the halo are likely to have been
formed in situ. We present the results for a model considering the effects of
an enriched gas stripped from dwarf satellites on the chemical evolution of the
Galactic halo. We find that the resulting chemical abundances of the halo stars
depend on the adopted infall time-scale, and the presence of a threshold in the
gas for star formation.
