and characterize, for the first time, the three distinct stellar populations of NGC6752 at the bottom of the MS. The paper is organized as follows. In Section \[sec:data\] we describe the dataset, the data reduction and analysis. The NIR CMD of NGC6752 is presented in Section \[sec:cmd\], where we also derive the fraction of stars in the three sequences of M-dwarfs and constrain their chemical composition. Finally, Section \[sec:discussion\] provides the summary and the discussion of the results.

Data and data analysis {#sec:data}
======================

We used WFC3/NIR on board of [*HST*]{} to investigate stellar populations in a field located $\sim$4.8 arcmin north-east from the center of NGC6752. The images are collected between September 7$^{\rm th}$ and September 18$^{\rm th}$, 2018 as part of GO-15096 (PI.L.R.Bedin). All the observations are obtained during 35 orbits of [*HST*]{}, including 25 and 10 orbits for images in F110W and F160W, respectively. During each orbit we collected one short exposure of 143s in multiaccum mode (with instrument parameters NSAMP = 15, SAMP-SEQ = SPARS10)[^2] and two long exposures of 1303s each (with instrument parameters NSAMP = 14, SAMP-SEQ = SPARS100). All the images are properly dithered.

To derive photometry and astrometry we adapted to WFC3/NIR 