0 50 100 150 200 250 300 350 400 0 5 10 15 20 25 30 35 40 0 2.5 5 7.5 10 12.5 15 17.5 20 0 0.5 1 1.5 2 2.5 3  pt  v2 20-60 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 50 100 150 200 250 300 350 400  Npart  v2 chrgd  1 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 0 50 100 150 200 250 300 350 400 K$_{0}$/charged part. /charged part. /charged part. FIG. 7: Centrality dependence of v i 2 $_{ϵ$_{part}$}$( N part ) / v charged hadrons 2 ϵ$_{part}$ ( N part ) for the preliminary p T integrated K 0 , Λ , Ξ data as measured by the STAR collaboration [17] in comparison with the prediction of the core-corona model, eq.4, presented as lines. FIG. 8: EPOS calculation compared with data. The top panel shows v 2 as a function of p T for π + measured in semi-central reactions. The bottom panel shows the p T integrated value of v 2 as a function of the number of participants. Data are from ref. [17]. FIG. 6: N part dependence of v 2 / ( ϵ part f core ) for charged hadrons in AuAu and CuCu at 200 AGeV/62 AGeV measured by the PHOBOS collaboration[14] as compared to theory. 5 be available. Especially data for protons for which f i core and f i corona differ much less than for the multi-strange hadrons would be of help. Such an analysis will not be easy as can be seen from fig. 8 which shows v$_{2}$ of π ’s as a function of p$_{T}$ for semi-central reactions (20%-60% centrality) (top panel) and that of charged particles as a function of N$_{part}$ (bottom panel). We compare results of EPOS calculations with the experimental data. The top panel shows that the v$_{2}$ ( p$_{T}$ ) spectra is qualitatively described up to p$_{T}$ ≈ 1 GeV/c , the range where almost all particles are located. Nevertheless, after integration over p$_{T}$ , bottom panel, we see differences of v$_{2}$ of the order of 10% between theory and experiment, although v$_{2}$ of π ’s and of charged particles should be very similar. This is due to the extrapolation of the experimentally measured curve toward p$_{T}$ → 0, necessary to determine a p$_{T}$ integrated v$_{2}$ value. Summarizing, the centrality dependence of all observ- ables for identified particles, their multiplicity, their av- erage transverse momentum and their elliptical flow, as well as the elliptical flow of charged hadrons can be quan- titatively described from SPS to RHIC energies in the very simple core - corona model. It would be interesting to compare these results in detail with the predictions of (viscous) hydrodynamical calculations, the alternative approach to describe non central heavy ion collisions.