Targets selection. (a) Gaia DR3 CMD for field stars selected within ∼3 arcmin from the cluster centre (grey points) and for the high-probability proper-motion cluster members (black points). (b) Positions of the two samples shown in the (x, y) coordinates. The x-axis has been inverted so that it corresponds to the usual inversion of right ascension. The red, blue, green circles draw the core radius r_c ~ 0.056 arcmin, half-light radius r_h ∼ 0.482 arcmin, and 3r_h, respectively. (c) Vector proper-motion diagram in (x, y) coordinates. (d) RV vs distance from the cluster centre for the four stars listed in Table 2, along with three additional stars with Gaia RVs, listed in Garro et al. (2023). In all panels, the cyan points represent the four giant stars with IGRINS data.