Time series showing the formation of an OPU in AR 11158. The individual columns show the observables of the OPU at different times, from 1:00 UT to 7:30 UT on 16 February 2011. From top to bottom:I_c, B, B_LOS, γ, and v_LOS, i.e. the same quantities in the same order as in Fig. 1. All panels have a FOV of 48″ × 48″ and the contours indicate the orphan penumbra. This OPU forms by separating from a sunspot. We show the magnetic field and the velocity at τ = 1. The arrows in the top row point towards disk centre.