Geometry adopted in the model calculations. GC stands for Galactic centre. The bar is along the y-axis. The outline of the ellipsoid (the bar) is indicated by a black ellipse. In red inside the bar is the largest possible elliptical orbit (see text). The angle P-Sun-Star, α, is found by the relation asinα = ( | x_s−x_z | ) /d, where d is the distance between the Sun and the star. The angle P-Sun-GC is β. The longitude l = α−β. The Sun is located at (−8.0sinβ, 8.0cosβ kpc). The maximum and minimum velocity will be reached where the orbit cuts the x-axis. The units in x and in y are kpc.