Left: observed CMD of likely Hercules stars (large open black circles) compared to a synthetic CMD composed by three stellar populations (red circles) with t = 14, 13, and 10 Gyr and [Fe/H] = −3.27, −2.27, and −1.79, respectively. Four boxes (solid lines) are used to count stars on the blue, intermediate and red part of the galaxy HB and RGB+AGB. Observed star counts in boxes are N = 12, 9, 20, and 98 (from left to right, respectively). In the dotted line box, the star count is 21. Observed variables are marked with green diamonds. Small grey circles are background galaxies and Galactic stars discarded via the colour–colour diagram. Middle: a stellar population with [Fe/H] = −1.79 and t = 1 Gyr (blue circles) is over plotted to obtain the same stellar count in the dotted box. Right: a stellar population with [Fe/H] = −2.27 and t = 1.9 Gyr (blue circles) is over plotted to obtain one star almost located in the same position of the AC.
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