Various reduction steps applied for an individual ESPRESSO order of DS1. (a) Before telluric removal with MOLECFIT. (b) After telluric removal with MOLECFIT and shifted to the stellar rest frame. (c) Each spectrum is placed on a common blaze function (see Sect. 2.4). (d) Residuals after division through by the mean out-of-transit spectrum, weighted on their uncertainties. This panel shows the final data product used in the MOLECFIT preprocessing analysis. (e) Residuals after division through by the mean out-of-transit spectrum, weighted on their uncertainties, and subtraction of the SYSREM model. This panel shows the final data product used in the SYSREM preprocessing analysis. It is worth noting that for this procedure, we do not perform any preceding telluric removal (i.e., Sect. 2.4, Step (2)). (f) A magnification of panel (e) showing the wavelength shifts caused by each injected model. The planetary velocity curve for P2 is shown as a white dashed curve, whereas the slower moving planet’s (P12) velocity curve is shown as a white dotted curve.