Toomre diagram for stars on the two age sequences in Fig. 3. Stars on the old age sequence are shown with filled red circles and those on the younger age sequence with filled blue circles. The dotted lines correspond to respectively V_total = 50 km s⁻¹ and V_total = 100 km s⁻¹. The uncertainty of the velocity components is about 1.5 km s⁻¹, corresponding to the size of the circles.