Testing the effect of adopted T_eff on the derived Fe i and Fe ii abundances in the AGB star 97. Horizontal bars show the 2σ uncertainty ranges⁶ for each of the T_eff-colour relations, centred on the T_eff prediction of each relation (see text for details). The temperatures used in the C13 study (4946 K) and the L16 study (4884 K) are indicated by vertical lines, highlighting the magnitude of δFe at each T_eff. Also shown is our IRFM T_eff (5048 K) and associated uncertainty. The (V−K)T_eff is 5051 K. The dashed line shows the average iron abundance of the RGB stellar sample.