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5 Age and distance

The knowledge of metallicity and reddening, allows us to infer the distance and age of King 5 by means of fitting with isochrones (Bertelli et al. 1994). The fit is shown in the three panels of Fig. 6, for the planes V vs. (V-I), V vs. (V-K), and K vs. (J-K), respectively.

We have adopted the theoretical metallicity Z = 0.008 above derived, and performed the fitting with a 1.0 Gyr isochrone, which better matches the observational data. The criterion that guided us in performing this comparison was the simultaneous fit of the TO and the clump magnitudes. Since no membership exists for this cluster, it is not possible to define exactly the MS TO, which is populated also by unresolved binary stars, and interlopers (see the field population in Fig. 3 for an interpretation of the TO region in the IR CMD). However the clump luminosity can be reliably determined, since many stars are also spectroscopic members.

By using the reddening estimated derived in the previous section, the apparent distance moduli (m-M)K,(J-K) and (m-M)V,(V-I), in the plots turn out to be 11.90 and 14.00, respectively. The latter values can also be obtained assuming that the mean clump magnitude is MV = 0.80 (Girardi et al. 1998). Once corrected, these values converge to the absolute distance modulus $(m-M)_0~=~11.40\pm 0.15$.

King 5 turns out to be 1.9 kpc distant from the Sun, and about 9.6 kpc far from the Galactic Center.


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