Results of RGS spectral fitting (see text and Table 8 for details). We show the stacked old and new RGS spectra (grey and magenta data points, respectively; the RGS1 and RGS2 spectra in each subgroup were co-added for plotting purposes). The model (solid black and red lines) fitted to the data in XSPEC is tbabs(bbody-gauss). The best-fit parameters differ in the two subgroups (see text). The two absorption lines at around λ = 20−23 Å are instrumental.