Relative proper motions (0.1 mas yr⁻¹ ≈ 25 km s⁻¹) for the 79 O-type VFTS stars in 30 Doradus that have proper motion errors less than 0.07 mas yr⁻¹. VFTS 16 and 72 are labelled (marked with +), as are three additional outliers (marked with ×) that are discussed briefly in the text. Panel a: standard proper motion diagram with the error ellipses indicated for these 5 stars, though for clarity the ellipses for the full sample are omitted. The inner dashed ellipse denotes the velocity dispersion of the local reference frame around R136/NGC 2070 sample discussed in Sect. 2.2. Panel: polar plot of the radial and tangential components relative to the direction from R136, concentric circles denoting relative proper motions of 0.1, 0.2 and 0.4 mas yr⁻¹. In this diagram the positive x-axis, 0°, denotes a direction radially outward from R136, with positive angles indicating that the tangential component is counterclockwise with respect to the position angle of the star relative to R136.