The stacked halo spectrum: Co-added spectrum of 53 halo RGB stars with F814W magnitude brighter than 25.72. Red: Co-add spectrum smoothed by a Gaussian kernel of 2 pixels weighted by the inverse variance of the sky spectrum. Blue: The best fit from pPXF. In the upper panel we show the full spectrum wavelength, 4800–8800 Å, used to measure velocity with pPXF, in the bottom panel we show a zoom in the CaT region and mark with a black dashed lines the position of these lines: 8498,8542 and 8662 Å in the restframe and in black solid lines the position of the observed CaT lines.