Left panel: surface concentration of Fe as a function of T_eff in clusters (M 15, M 68 and M 92) from Behr (2003) with original Fe concentration  ~ −2.3. Models are shown for this metallicity. Each color-coded segment represents the evolution of the surface Fe concentration. The line is solid for the time interval from 10 to 30 Myr after ZAHB, but dotted from 0 to 10 Myr. Bottom part: rotation velocities; three stars have their rotation velocities and [Fe/H] in red to facilitate their identification. Right panel: field stars also from Behr (2003). The distribution of metallicity for the cooler field stars gives an indication of the original metallicity distribution for the hotter field stars as well as for sdBs.