Monochromatic opacity (values shown in the colour–bars) for the F3V (first row), G2V (second row), KOV (third row), and M2V stars (fourth row) versus wavelength (horizontal axis) and geometrical height (vertical axis). Horizontal grey lines: Rosseland optical depths. The zero geometrical height is taken where log-τ_Ros = 0. Other lines are shifted by Alogτ_Ros = 1. Black dashed thin line: height at which the continuum optical depth at each wavelength is unity (). Black solid thick line: heights at which the total optical depth τ_λ is unity. Values are averaged over 25 nm intervals. Tick marks on the top indicate wavelengths of the hydrogen series. Hydrogen lines gradually vanish with decreasing effective temperature. The colour-bar values of each star range from min log ϰ to max log ϰ.