Comparison of an average-combined spectrum and its individual exposures for β UMi (K4III). Thex-axes are wavelengths in Å. The 22 individual exposures are shown as lines, the average combined “deep spectrum” as dots. Panel a: a 0.8-Å section showing the 22 exposures of the K I 7699 Å line profile. The y-axis is relative intensity. No differences can be seen at this plot scale. Panel b: a zoom into a 0.08-Å subsection of the line core. The spacing of the dots represent the CCD pixel dispersion. Panel c: S/N per pixel in the K I line core for the same spectral window as in panel b.
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