I will discuss the chemical evolution of the globular cluster Omega Centauri
assuming it is the leftover of an ancient dwarf spheroidal galaxy (dSph)
swallowed by our Galaxy some 10 Gyr ago. We based our model on existing
3D hydrodynamical simulations of isolated dSphs (Marcolini et al. 2006).
It is shown that Type II SNe and Type Ia SNe play different roles in the
chemical enrichment of the gas. While the SNe II pollute the ISM rather
uniformly, the SNe Ia ejecta may remain confined inside pockets of gas as
long as succesive SNe II explosions spread them out. Stars forming in such
pockets have lower [alpha/Fe] ratios than the stars forming elsewhere and having
a significant alpha-enhancement ([alpha/Fe]>0.35). Owing to the inhomogeneous
pollution by Type SNe Ia, the metal distribution of the stars in the central
region differs from that of the main population of the dwarf galaxy, and
resembles that of Omega Cen. Our model succeeds in reproducing both the
[Fe/H] and the [Ca/H] distributions observed in Omega Cen and the main
features observed in the [alpha/Fe]-[Fe/H] diagram of this system.
Finally, our model reproduces the overall morphology of the color-magnitude
diagram, but fails in reproducing the puzzling metal abundance of the stars on
the blue branch of the cluster main sequence. However, the inhomogeneous
pollution halves the amount of the enigmatic helium enhancement required to
explain the anomalous position of the metal-rich main sequence.