Comparison of abundance patterns with models of metallicity [Fe/H]  = −1.3 and with turbulence anchored at . Left panel: surface abundances expected at six HB ages, from 0.0 to 31 Myr, for a 0.55    M_⊙ model compared with observations for WF4–3085, a star of M 13 with T_eff ~ 14   000 K, from Behr (2003). Right panel: surface abundances at five HB ages, from 0.0 to 16 Myr, for a 0.58    M_⊙ model compared with observations of the T_eff =  12 000 K star 469 of NGC 1904 from Fabbian et al. (2005).