Overview of the structure of the accretion flow and of the shock region (see labels). Top panel: temperature (double logarithmic scale), showing the shock temperature T₀, the Zel’dovich spike up to T ≈ T₁, and the dust destruction front at radius R_dest. The shock defines the planet’s radius. The temperature flattening at T ≈ T_dest (e.g. Marleau et al. 2019) is not shown. The next two panels focus on the dashed box. Middle panel: temperature near the shock on a linear scale. Below the hydrodynamic jump, in the NLTE cooling and settling zone, the “population temperature” of the electrons T_pop and the kinetic temperature T_gas differ at first. The temperature structure is simplified; Fig. 8 of Vaytet et al. (2013b) gives a more accurate schematic. Bottom panel: upward-moving flux at one restframe wavelength within the H α line (red line), from the microphysical models of Aoyama et al. (2018). We illustrate the line-formation region (red) and the self-absorption (dark grey) in the settling zone, and the absorption by the accretion flow, calculated in this work. The features in the opacity (dotted grey curve; arbitrary linear scale) come from the Doppler-shift gradient (Eq. (15); Fig. 4).