a) The modelled random spectral line profile derived from our toy model (with V_rad = 20 km s^-1) together with the degraded profile (S/N of 10). The vertical lines correspond to the centroid (solid) and Gaussian (dashed) radial velocities. One hundred random spectral lines are calculated. b) The relative uncertainties of the radial velocities as a function of the S/N (same legend). c) The relative uncertainty on the bi-Gaussian line asymmetry as a function of the S/N.