Atmospheric profiles predicted for the hot (1500 K) 5 M_⊕ sub-Neptune under moderate XUV irradiation (model planet 4.2B in Table A.1). The different line styles correspond to different model configurations, as indicated in the legend located in panel b. From top to bottom, the panels show profiles for volume heating rate (a), mass density (b), temperature (c), and bulk outflow velocity (d) as a function of radial distance. In the case of the basic hydrodynamic code (model #0), the volume heating rate corresponds to the sum of the input from the X-ray and EUV heating functions given in Sect. 2.2 (H_X + H_EUV). The maximum distance r = 4 R_pl shown in panel a is smaller than that considered in the other panels to facilitate the inspection of the details of the heating functions. The vertical grey line in panels b–d denotes the position of the Roche lobe. The 10¹⁵ cm⁻³ high-density limit of Cloudy lies at the lower boundary.