Diagram illustrating the selection method for the angle of intersection. We have the two limiting vectors described by the error in position and proper motion (pm_a ± Δ pm_a and pm_b ± Δ pm_b) for the RS and RB, which yield a minimum (lower) and maximum (upper) possible angle (using the 1σ uncertainties in both directions; see Eqs. (A.10), (A.11), and (A.12)). If a given pair has an angle of intersection consistent with 180^∘ to within these upper and lower bounds, we keep it in our sample and discard it otherwise. We note that the RB is not resolved and the cross point is at the center of light.