Proper-motion diagram in the field of Stock 2. The ellipse (dashed brown line) is centred on the average proper motions of the cluster and has semi-axes of four times the sigmas of the μ_α* and μ_δ distributions of the cluster members according to Cantat-Gaudin et al. (2018). It represents the cluster extent in astrometric space. Grey dots represent field stars, and the remaining symbols are the same as in Fig. 1.