The CMD from IR photometry is shown in the lower panel of Fig. 2, and appears significantly different. In fact it is quite similar to the CMD of old open clusters like M 67 (Montgomery et al. 1993) and Berkeley 39 (Kassis et al. 1997). The MS extends down to K = 16.5, and the TO is located at K = 12.5, (J-K) = 0.70. The region above the TO might contain some interlopers (see Fig. 3).
Apparently there is no Hertzsprung gap,
and the RGB is sparsely populated, like in all clusters with age
greater that 4 Gyr. The stars at
,
might represent the clump of core He burners, quite small in this
age range. We recall that IR photometry covers all the cluster,
and the foreground contamination is negligible, as it can be seen in Fig. 3,
where two comparison fields
eastwards
and
northwards, respectively, are shown.
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Figure 4: Two colors diagram for MS stars in King 5. The solid line is a Zero Age MS for [Fe/H] = -0.38. In the lower left corner the reddening vector is shown. See text for any detail |
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Figure 5: Two colors diagram for MS stars in King 5. The solid line is a Zero Age MS for [Fe/H] = -0.38. In the lower left corner the reddening vector is shown. See text for any detail |
In order to clarify the nature and age range of this cluster, and whether the differences are simply due to the use of different colors, we have combined optical and IR data to construct the CMD in V - (V-K), which is shown in the lower right panel Fig. 2. This CMD looks quite similar to the optical CMD shown in the same figure, demonstrating that King 5 is an intermediate age open cluster. To better assess this point, in the next sections we are going to determine in details the cluster basic parameters.
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