combine. Finally, the cumulative signal-to-noise ratio, $S/N(a_{k}) $, as a function of $a_{k}$, is calculated from:

$$S/N(a_{k}) = \frac{N_{c}(a_{k}) - gN_{f}
(a_{k})}{\sqrt{N_{c} (a_{k})  + g^{2} N_{f} (a_{k})}}
\label{eq3}$$

where,

$$N_{c}(a_{k}) = \sum_{l=1}^{k} n_{c}(l), ~~~N_{f}(a_{k}) = \sum_{l=1}^{k} n_{f}(l) \label{eq4}$$

The parameter $n_{c}(l)$ denotes the number of stars within the cluster region having ordered color-magnitude index $l$; $n_{f}(l)$ represents the same quantity for the field region. Based on the maximum value of $S/N(a_{k})$, a threshold value of $s/n$ is picked in order to select high- contrast surface-density areas (i.e, high $s/n$) between the cluster and field regions. These are considered to be the sub-grids that contain likely cluster members. After removing single-star events in areas of the CMDs where the field-star density is low, all stars in sub-grids with $s/n(i,j)$ greater than the threshold value of $s/n$ are selected. These stars are considered as the photometrically likely member stars for a given cluster.

The red squares shown in the left panel of Figure 2 are the sub-grids with $s/n$ greater than the threshold value; the corresponding sub-grids in the field region are shown as green squares in the right panel of this Figure. Figure 3 depicts the CMD of the selected likely 