(Top) The covariance matrix of high stellar S/N and low-dust spectra used as MADGICS prior for the stellar component. (Middle) Third eigenvector of the stellar covariance matrix. (Bottom) Zoom-in of the third eigenvector near the DIB feature. Guidelines for the central wavelength of the DIB and stellar lines are labeled and color coded. A higher-resolution solar spectrum from Kurucz et al. (1984) is plotted in orange for reference.