Average [C II] spectrum towards [C II]-bright shell of NGC 1977 (without OMC3). The inlaid panel shows the (smoothed) residual of the spectrum, in the systemic velocity of the [¹³C II] F = 2 − 1 line, after subtracting the [¹²C II] fit. The [¹²C II] component can be approximated by a Gaussian with T_P ≃ 16.5 ± 0.1 K, v_P ≃ 12.0 ± 0.1 km s⁻¹, Δv_FWHM ≃ 3.2 ± 0.1 km s⁻¹; the [¹³C II] F = 2 − 1 component is fitted by a Gaussian with T_P ≃ 0.21 ± 0.03 K, v_P ≃ 11.8 ± 0.2 km s⁻¹, Δv_FWHM ≃ 2.1 ± 0.5 km s⁻¹.