the procedure. Finally, we corrected the photometry of cluster members for differential reddening using the method in [@milone2012 see their Section 3.1]. The final CMDs are shown in the left panels of Figure \[fig:cmds\].

In the case of the [*HST*]{} dataset, the photometric catalogues by @milone2017 [@milone2018] already distinguished cluster members and field stars, based on stellar proper motions. Hence, we included in the analysis only those stars that, according to Milone and collaborators, belong to M22 and $\omega\,$Centauri.

Multiple populations along the color-magnitude diagrams {#sec:cmds}
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As shown in [@marino2019], Type II GCs exhibit multimodal SGBs and RGBs in the photometric diagrams made with $U-V$ and $U-I$ colors that correspond to stellar populations with different metallicities. Hence, we exploit the $I$ vs.$U-I$ CMD of $\omega\,$Centauri and the $V$ vs.$U-V$ CMD of M22 to separate the stellar populations with low content of iron and s-process elements (Fe-poor) from the chemically enriched ones (Fe-rich).

The main procedure (I) to identify Fe-poor and Fe-rich stars is similar to that used in @cordoni2019 [see their Figure 2]. Briefly, we determined the RGB boundaries as the 4$^{\rm th}$ and 96$^{\rm th}$ percentile of the color distributions, and we verticalized the CMD following the procedure 