T_eff−log(g) diagram of the program stars as in Fig. 3. ³He stars from our sample showing no evidence for helium stratification are marked in blue, and the stratified ³He ones are marked in red. The zero-age (ZAHB) and terminal-age horizontal branch (TAHB) as well as evolutionary tracks for different stellar masses but solar metallicity according to Dorman et al. (1993) are also shown with dashed and dotted lines, respectively.