Epicyclic frequencies and shape of tori. Left: epicyclic frequency ratio and shape of tori in the limit of β → 0. The dashed coloured vertical lines denote the locations of the ISCO calculated for different space-time parameters. The frequency-ratio values calculated for different space-time parameters at given radii are indicated by the coloured curves and labelled on the standard (left and bottom) axes. Several additional dashed ellipses, drawn for a non-rotating star (j = 0) and described by the upper and right axes, show the limiting cross-sections of slender tori located at a radius marked by the (common) lower axis. Middle: radial extension and shape of a torus with its centre located at radius r₀ in the case of a non-rotating NS (j = 0). The dependence of the inner (r_in) and outer (r_out) torus radii on r₀ is marked by orange (β = β_cusp) and red (β = 0.2 β_cusp) curves. Equipotential curves (black contours) are shown for two torus centre locations, r₀ = 6.75 r_G and r₀ = 8 r_G. The torus radial profile coordinates are identical to those on the bottom axes. Right: profiles of Keplerian specific angular momentum, l, corresponding to the same space-time parameters as in the left panel. The red horizontal line denotes a particular (chosen) value of l₀. The shape of the cusp torus corresponding to this value of l₀ and j = 0 is shown. As in the middle panel, the torus radial profile coordinates are identical to those on the bottom axis. The shape of equipotentials for the same value of l₀ and the same space-time parameters is shown in Fig. 4.