Offset between spectroscopic and IRFM T_eff. The distribution includes 408 turnoff stars from the GALAH catalog, restricted according to the selection explained in Sect. 2. Only stars with halo-like orbits, i.e., those confined within the retrograde and null net rotation areas in Fig. 4, are shown. The thick continuous line connects the medians computed in equally spaced bins of IRFM T_eff. Vertical bars indicate the 1σ dispersion.