4 Discussion

We compared our results from the stellar counts with those obtained by Bica et al. (2001) for 34 physical systems, catalogued by the authors as possible star clusters in the process of disruption or their fossil remains. Their results show that these possible open cluster remnants, represented by open circles in Fig. 8, are clearly distributed above the line corresponding to regions with uniform stellar densities. On the contrary, our Ruprecht fields are placed very close to this line, Ruprecht 166 having the highest stellar density and the biggest difference between the number of stars counted for the object and for the surrounding field. This result not only is in excellent agreement with the conclusions inferred from the CMD analysis (see Sect. 3.1), in the sense that the studied catalogued objects are not genuine open clusters, but also shows that they do not appear to be candidates of late stages in the star cluster dynamical evolution. According to de la Fuente Marcos (1998), who studied the likely observational properties of open cluster remnants from numerical simulations, a loose cluster should be about ten times denser than the surrounding fields in order to be detected. Hence, it would appear that Ruprecht's classification of the object sample could have been motivated by the apparent concentration of some bright field stars rather than from a visible excess of stars.

With the purpose of investigating the origin of stars in the CMDs of the observed fields, we used the statistical results obtained by Ng et al. (1996) from the decomposition of the disk populations in CMDs of fields towards the Baade's Window. Based on their findings, we identified different stellar disk components in the observed CMDs, namely: the very young disk MS (age $\sim 0.1{-}2.0$ Gyr, $Z \approx 0.018{-}0.022$), the old disk MS (age $\sim 7.0{-}10.0$ Gyr, $Z \approx 0.003{-}0.008$), the intermediate age and old disk Horizontal Branches (HBs) and the intermediate age and old disk Red Giants (RGs). The age and metallicity for the intermediate age disk entered by Ng et al. (1996) are 4.5-7.0 Gyr and 0.008-0.015 dex, respectively. Thus, in the CMDs of Ruprecht 103 the tilted sequence is composed by very young MS stars,while the fainter vertical sequence is formed by intermediate age and old RG stars. HB stars belonging to the intermediate age and old disks form the redder ( $V-I\sim 1.6$) and slightly brighter vertical sequence in the CMDs of Ruprecht 103. The same stellar components can be recognized in the CMDs of Ruprecht 146, where faint MS and HB stars have a smaller colour difference. HB stars are also present in the CMDs of Ruprecht 124 and Ruprecht 166, forming a broad vertical sequence centered at $V-I\sim 2.0$. The CMDs of Ruprecht 124 show a more extended MS composed by very young and young stars and by a remarkable old disk star population at its fainter portion ( $V\sim 18{-}20$). MS stars dominate the CMDs of Ruprecht 129. Finally, the rich star concentration of stars fainter than $V \sim 17$ mag and at $V-I \sim 1.0{-}2.0$ in the CMDs of Ruprecht 166 mainly corresponds to the contribution of old RG stars.