Curve of growth analysis of the December 6, 1997 comet in FeII lines, using a single-component model. Top: curve of growth of Fe II lines. The blue dots indicate the measured absorption depth in 63 Fe II lines, while the red line shows the best-fitting one-component model. Bottom: residuals of the previous fit. A clear remaining trend is visible in the data, hinting that the fit could be improved in order to retrieve more information from the comet’s absorption spectrum.