Spectral fits of the C₂ and CN regions in HD 187861. Upper panel: C₂ band around 5165 Å where the red curve represents the synthesis corresponding to the abundance log ϵ_C = 8.3, with ±0.3 dex on either side represented by the blue and green curves. The black dashed line corresponds to the observed spectrum and the magenta line to a spectral synthesis without carbon. Middle panel: spectral synthesis of the ¹²C¹²C feature at 4737 Å and the ¹²C¹³C feature at 4744 Å with the adopted C abundance and derived isotopic ratio of 16. The spectral synthesis of the CN band around 6315 Å is shown in the bottom panel with the adopted abundances of 8.3 and 7.85 for C and N, respectively.