Layout of the simultaneous observations of NGC 1846 (bottom) and NGC 1844 (top) (from the HST Astronomer’s Proposal Tool). The individual ACS/WFC images are shown in magenta, and those of WFC3 (in both UVIS and NIR channels) in blue. Note the intrinsic different size of the two clusters, as they are at almost the same distance.

Stacked trichromatic image of the studied NGC 1844 ACS/WFC-field. The green circle indicates the considered cluster region (cluster field), while the red circle is a random region of equal size shown for comparison (comparison field). The magenta circle indicates the inner limit of the portion of the ACS/WFC field used as reference to statistically remove the LMC field contamination from the CMD of NGC 1844.

Completeness contours in the radial-distance versus m_F814W magnitude plane. The completeness is proportional to the gray level as indicated by the scale ot the top. Continuous lines correspond to a completeness level of 0.50. Dotted lines indicate differences of completeness of 0.10.

Upper-left panel: CMD of stars in the cluster field zoomed-in around the region where the MS broadening is more evident. Stars on the blue and the red MS side are color coded in blue and red, respectively. The continuous and the dashed-dotted lines are the fiducial of the two MS regions drawn by hand. Upper-right panel: spatial distribution of blue and red MS stars. Lower panels: CMDs for stars in the four quadrants defined in the upper-right panel.

Cumulative radial distribution of blue MS (blue line) and red MS (red line).