Structure of the accretion flow (solid lines) and gas opacity (background greyscale). The profiles are for a grid of accretion rates (isochromatic curve groups; from Ṁ = 3 × 10⁻⁴ (top right) to 3 × 10⁻⁸ M_J yr⁻¹ (bottom left)) and masses (M_p = 1, 3, 5, 10, 20 M_J from bottom to top within each group) in the Polar-Cold case. Each profile begins on the left at r_max ≈ 100R_p and ends at the shock at R_p (dot), at (ρ₀, T₀). Only the continuum opacity at H α (no resonance; see text) is shown averaged over Δv = ±50 km s⁻¹. The dust destruction line T_dest(ρ) is indicated (Isella & Natta 2005; long-dashed line), and line segments show pressures P = 10⁻³, 1, 10³ erg cm⁻³. Black dotted lines show where half of the hydrogen is molecular, atomic, or ionised. The opacity depends mostly on temperature, and most models (Ṁ, M_p) include a region of high opacity, often near the shock.