Gaussian in the sense that the third and fourth moments are very close to zero. This density has a mean of 19.2 ms$^{-1}$ an a standard deviation of 4.8 ms$^{-1}$ , which indicates that an offset in the reference velocity of roughly 20 ms$^{-1}$ is significantly present in the CORALIE data sets after the upgrade for the stars included in this work.

HARPS
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For HARPS, the steps are similar to those mentioned above, but the data is automatically processed by the HARPS-DRS version 3.5 which is based in general on the procedure explained in @baranne96. The nightly drift of the ThAr lines are found to be below 0.5  and including the other sources of uncertainty such as centering and guiding ($<$30 ), a stability of less than 1  is found for this spectrograph over the long term (see [@locurto10]).

MIKE
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For the radial velocities measured using the MIKE spectrograph, the reduction steps are similar but the analysis procedure is different. MIKE uses a cell filled with molecular iodine (I2) that is placed directly in the beam of light from the target star before entering the spectrograph, and this is used to record the instrument point spread function (PSF) 