Steps of data processing. In black the data for one of the brightest stars in the field with a S/N ~ 120. In red the best fit to the data including the telluric absorption line fit as well. In blue below the fitting residuals to scale with the plotted spectrum. The enlargement windows to the left, highlight the region around the DIBs 5780, 5797 and the Na I D doublet. On the right hand side, the zoom illustrates the success of the telluric absorption line fit. We note that the zoom into the fitting residuals for this region is scaled by a factor of 10. For this example based on a single star of particularly high S/N, the K I  doublet stands out even for an individual stellar fit (red triangles).