Deep wide-field photometry of the galactic globular cluster M92

The Galactic Globular cluster (GGC) system provides robust constrains concerning the time scale of the Galaxy formation (van den Bergh 1979). The stellar content of a GGC is characterized by the same metallicity and by the same age, therefore the GGC stars are a template of Simple Stellar Population (SSP). This means that the GGCs are perfect laboratories to constrain the plausibility of the physical assumption adopted to construct stellar evolutionary models. Although the GGC have been the crossroad of a large number of empirical and theoretical investigations focused on age distribution, metallicity distribution, abundance patterns, and kinematics we still lack quantitative constrain concerning their formation and evolution. In particular, the absolute ages of the GGC are affected by the uncertainties on the distance modulus (DM) (Gratton et al. 1997, and reference therein). A second significant problem is the occurrence of chemical variations (anticorrelations) in all GGCs (Gratton et al. 2004, and reference therein). Moreover, recent investigations show the presence of photometric multi-populations in massive GGCs (ω Cen, Pancino et al. 2000; Sollima et al. 2005; Calamida et al. 2007; NGC 2808, Piotto et al. 2007; NGC`1851, Milone et al. 2008; Cassisi et al. 2008; Lee et al. 2009). Detailed photometric investigations also show the occurrence of cluster extra-tidal stars beyond the cluster radius. These stars can form halos (Testa et al. 2000; Lee et al 2003; Olszewski et al. 2009) or extended tidal streams (Odenkirchen et al. 2001, 2002, 2003; Grillmair & Dionatos 2006; Leon et al. 2000). In this thesis we investigated the structural parameters and the intrinsic properties of M92. The comparison between data and theory suggest a good agreement with an age of 11±1Gyr. The same result outcomes if we use CNONa extreme mixture models. We also investigated the ∆V bump HB parameter to provide robust constrains on the evolutionary predictions. We found that exist a discrepancy (∼ 0.4 mag) between observed and predicted ∆V bump HB. Finally, we investigated the tidal radius of M92 and the shape of the extra-tidal material discovered by Testa et al. (2000). In this case we found that the M92 tidal radius is ∼ 30% larger than the maximum literature value (see Harris 1996). Investigating the shape of the extra-tidal stars, we found that M92 is surrounding by a spherical halo which extends up to 56 p. Moreover, we found that the triaxial model compared to King model better agrees with data.