that are highly probable co-moving, although they need final confirmation when the radial velocities are measured. We followed the formalism of the convergent-point (CP) method as described in , for instance, and transformed the Cartesian velocity vector of the cluster motion from Eq.\[COPO\] to give predicted velocities $V_{\parallel pred}$ and $V_{\bot pred}$ parallel and perpendicular to the direction to the CP for each star depending on its position on the sky. We note that $V_{\bot pred} \equiv$ 0. Also following , we similarly transformed the measured (observed) tangential velocities for each star, $\kappa\,\mu_{\alpha*}/\varpi$ and $\kappa\,\mu_{\delta}/\varpi$ into $V_{\parallel obs}$ and $V_{\bot obs}$. Here $\varpi$ is the measured trigonometric parallax in Gaia DR2 and $\kappa=4.74047$ is the transformation factor from 1 mas yr$^{-1}$ at 1 kpc to 1 km s$^{-1}$. We set in the following $\Delta V_{\parallel}$ = $V_{\parallel obs}$ - $V_{\parallel pred}$ and $\Delta V_{\bot}$ = $V_{\bot obs}$ - $V_{\bot pred}$. Note that the differences between the predicted and observed velocities ($\Delta V_{\parallel}$, $\Delta V_{\bot}$) will be equal to (0,0), when the space velocity of a star is identical to $\vec{V_c}$ in Eq.\[COPO\]. We also determined the covariance matrix for the velocities $V_{\parallel obs}$ and $V_{\bot obs}$ via error propagation from 