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4 Reddening

In order to derive the interstellar extinction for King 5, we have combined optical and IR photometry (600 stars in total), and construct two color diagrams, namely (J-K) vs. (V-K) and (V-I) vs. (V-K), which are shown in Fig. 4 and Fig. 5, respectively. Only MS stars are considered. We superimposed a Zero Age MS (ZAMS) for the theoretical metal content Z = 0.008, obtained translating the observed [Fe/H] by means of the relation:


\begin{displaymath}[{\rm Fe/H}]= \log \frac{Z}{0.019}
\end{displaymath}

taken from Bertelli et al. (1994). Since the cluster does not exhibit a RGB, it is not possible to derive an independent photometric estimate for the metal content.

In Fig. 4 the fit has been obtained shifting the ZAMS with E(J-K) = 0.50 and E(V-K) = 2.45, which corresponds to a ratio $\frac{E(V-K)}{E(J-K)}~=~4.9$, relatively close to the value 5.3suggested by Cardelli et al. (1989).

The fit in Fig. 5, on the other hand, has been achieved shifting the ZAMS by E(V-I) = 1.10 and E(V-K) = 2.45, whose ratio turns out to be $\frac{E(V-I)}{E(V-K)}~=~0.44$, in agreement with the value 0.42from Cardelli et al. (1989). Although reasonable, these estimates are affected by the limitation that the reddening vector is almost parallel to the ZAMS. However, at least for E(V-I), our results do not differ to much from Durgapal et al. (1998), although these authors did not use the spectroscopic metallicity from Friel et al. (1995). Indeed, by using a lower metallicity, one should expect a larger reddening.


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