Several attempts have been made in order to isolate the effect of galaxy interactions by comparing galaxy in pairs with isolated galaxies. However, different authors have proposed different ways to build these control samples (CS). By using mock galaxy catalagues built up from the Millennium Simulation, we show that the set of constrains used to

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We derive abundances of Fe, Na, O, α and s-elements from GIRAFFE@VLT spectra for more than 200 red giant stars in the Milky Way satellite ω Centauri. Our preliminary results are that: (i) we confirm that ω Centauri exhibits large star-to-star metallicity variation (~1.4 dex); (ii) the metallicity distribution reveals the presence of at least five

We present CCD observations of the galactic globular cluster M15, in the B and V filters. The cluster was reasonably covered, except in its northern region where our observations present a gap. We obtained a Hertzsprung-Russell (HR) diagram for each region observed, and later we produced a combined HR diagram containing more than 3000 stars. We