Reference spectrum obtained following the methodology described in Section 2.3 (red), compared to the simple time-averaged spectrum (green) and the HARPS data (black). Smoothing using Tikhonov regularization reduces the noise in the reference spectrum at the 0.5% level (inset). As expected for an unbiased estimator, the reference spectrum tends to the time-averaged spectrum at wavelengths where no exocomet activity is present.