DM variations (upper panel) and the optical depth at ν = 1.4 GHz (bottom panel) for PSR B1259−63. The dotted lines and dashed lines correspond to the contributions from the polar wind and equatorial disc, respectively. The solid lines are the sum of both components. The wind parameters adopted in the calculations are Ṁ = 2 × 10⁻⁸ M_⊙ yr⁻¹, v_w = 3 × 10⁸ cm s⁻¹, therefore, the corresponding wind base density is n_w, 0 ≃ 4.12 × 10⁸ cm⁻³, and the momentum rate ratio is η ≃ 0.07. The disc parameters adopted here are n_d, 0 = 4.5 × 10¹¹ cm⁻³, i_d = 60°, and ϕ_d = 188°, which are obtained by fitting the DM data. The data points in the upper panel are the observed DM variations of PSR B1259−63 during the 1994, 1997, 2000, and 2004 periastron passages which are taken from Johnston et al. (1996, 2005), Wang et al. (2004), and Connors et al. (2002), respectively.