T_eff − log g diagram of sample of fast stars. The colour scales with the helium abundance from light orange to dark purple. The light grey symbols mark the results of the preliminary spectroscopic analysis on which the target selection was based. They are connected with the corresponding values from the new homogeneous analysis. The zero-age and terminal-age EHBs for a subsolar metallicity of −1.48 (solid grey lines) were interpolated from evolutionary tracks by Dorman et al. (1993). The helium main sequence (dashed line) is taken from Paczynski (1971).