Top left: meridional cuts of line-profile-averaged total optical depths into the envelope (τ_los = 0.7 contours where emissions from the inside are attenuated by more than 50%), for model B, with [O I] λ 63.2 µm (dark red), [OI] λ 145.5 µm (bright red), [C II] λ 157.7 µm (black), [FeII] λ 26.0 µm (magenta), and [S I] λ 25.2 µm (gold). Spectral-line opacities dominate the [O I]_λ145, [O I]_λ63 and [C II]_{λ 158} transitions, while in [FeII]_{λ 26} and [S I]_{λ 25}, the λ25 µm continuum opacity prevails. The gray disk represents the extent of the stellar photosphere, the salmon-filled area that of the chromosphere. The sightline to the observer is indicated by the black arrow. Top center to bottom right: contribution functions (i.e., the integrands of Eq. (E.1), normalized to unity at peak) for the respective emissions.