Left: shape of the 68.3%, 90% and 95.4% confidence contours in the (R₀, τ_λ, ∗ ) parameter plane for the two fits to the nitrogen complex. The dotted contours correspond to the assumption that the line in the RGS spectrum is entirely due to N vii λ24.78, whilst the solid contours correspond to the assumption of an equal contribution from the N vi λ24.90 line. The open hexagon and the asterisk correspond to the formal best-fit models. Right: best-fit model (R₀ = 3.65 R _∗ , τ_λ, ∗  = 0.0) assuming a pure N vii line (top) and a blend with N vi λ24.90 (R₀ = 3.05 R _∗ , τ_λ, ∗  = 1.0, bottom panel). Error bars represent  ± 1σ (one standard deviation). The feature at –500 km s^-1 essentially corresponds to two bins and could be interpreted as the result of noise. Its existence thus needs confirmation.