Panel a: three selected observations (each shifted on y by 0.2 for better visibility) with the weakest telluric feature (black) and the separated spectra (purple and blue) from these observations. The separated spectra are shifted in wavelength to match the topmost observation. The separated spectra are scaled such that the line strength matches the strengths in the observations. Panel b: synthetic spectra (used as templates to create an artifical binary data set) in comparison with the separated spectra (see text). Panel c: separated spectrum (red) of the G0III secondary of Capella with a synthetic spectrum (green). This was derived with the stellar parameters as listed in Table 2 and the line list given in Table B.1. It shows predominantly only the strong Fe I 7999 Å line. The blue line is a synthetic spectrum based on the ¹³CN lines as with an abundance as derived for the primary.