CHT candidates selection. Left panel: Histogram of ∆K. The vertical dashed red line shows our threshold for selecting CHT candidate systems (marked in blue). Right panel: RV-based semi-amplitude as a function of the astrometric semi-amplitude $\left(K_1^{*}-K_0\right)$ of the Gaia astrometric binaries sample. Blue points mark sources with ∆K > 5, which can be considered possible CHT systems (inner close binary and an outer astrometric binary), while black points and respective contours indicating regions of higher data concentration mark probable astrometric binaries with ∆K ≤ 5. The dashed red line marks a 1:1 relation.