Diagnostic plots for NGC 2099. (a) Spatial distribution of cluster members and candidates. The stars are coloured according to the membership probability. (b) The spatial distribution of stars along with arrows indicating their PM. (c) Variation of μ_T with radius. (d) Variation of μ_R with radius. (e) Variation of ΔV with PA. The PA_peak is shown as a grey band, and the fitted sin curve is orange. (f) Spatial distribution of stars coloured according to RV_corr. The orbital axis corresponding to PA_peak is shown as the grey arrow. (g) Distribution of RV_corr with XR. (h) Variation of PA_peak for different radial slices of the cluster. The radial distance used here is the average radius of the stars within the selection, and the radial error bars show the minimum–maximum radius within the radial slice. The green wedge points towards the cluster’s orbital motion in (a), (b), and (f). The red curves show the rolling average in (c), (d), and (g). The black lines show the linear fits in (c), (d), and (g). The core radii (grey solid circle or line) and tidal radii (grey dashed circle or line) are shown in (a), (b), and (c).