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tokens: giant branches and computed the difference between the obtained interpolated [Fe/H] values and those given by the respective isochrones ([Fe/H] = −2.0, −1.5, −1.0, −0.5, and 0.0 dex). We repeated this procedure for log(age/yr) = 9.4 and 9.8. By using these theoretical points and the general trend observed in Fig. 11 , we adopted weighted mean [Fe/H] values for each cluster (see Table 1 ). Figure 13 depicts the resulting distribution using the adopted mean metallicities. Fig. 11. Metallicity difference as a function of the star cluster’s age. Filled circles, squares, and triangles correspond to high-resolution spectroscopy, low-resolution spectroscopy, and photometry reference values, respectively. Open magenta diamonds represent metallicity differences derived from theoretical isochrones (see text for details). Fig. 12. Theoretical red giant branches for log(age/yr) = 9.0 (dotted lines) and 10.10 (solid lines); [Fe/H] = −2.0, −1.5, −1.0, −0.5, and 0.0 dex shown with blue, magenta, green, orange, and red, respectively. With the aim of providing an expression for the metallicity correction that covers a wide age range, we added ten LMC old globular clusters studied by Piatti Koch (2018) from Strömgren photometry. We took from that study the star clusters’ ages as well as both reference and Strömgren metallicities, with their respective uncertainties. They are represented in Figs. 11 and 13 with open circles. When performing a least square fit to all the data points, we obtained the following expression: Fig. 13. Same as Fig. 11 for adopted weighted mean [Fe/H] values. The solid line represents the least squared fit obtained (see text for details). with a standard deviation, a correlation factor, and an F-test coefficient of 0.05, 0.98, and 0.97, respectively. Strömgren metallicities calculated from Eq. ( 4 ) should be corrected by an amount equal to −Δ[Fe/H]. 5. Summary Based on our previous knowledge that metallicities derived from standard giant branches in several photometric systems are affected by the age-metallicity degeneracy for star clusters younger than the old globular clusters, and bearing in mind the fundamental role that metallicities play in our understanding of the formation and chemical evolution processes at different universe scales, we decided to investigate metallicities for the Strömgren v b y bandpasses. Until now, it has been straightforward to compute [Fe/H] values from the Strömgren reddening free ( v − y ) 0 and m 1 0 indices, the latter being a metallicity-sensitive index. In general, they have been used for the study of globular cluster metallicity distributions (e.g., Calamida et al. 2014 ; Frank et al. 2015 ) to unveil multiple stellar populations (e.g., Carretta et al. 2011 ; Massari et al. 2016 ) rather than estimate the metal content of intermediate-age star clusters. In order to probe whether such an age dependency also affects the Strömgren metallicities, we made use of unexploited publicly available