Upper panel: evolutionary tracks for selected HB models with a 0.8 M_⊙ RGB progenitor with scaled solar Z = 10^-5, Y = 0.245. From left to right the tracks are for masses M/M_⊙  0.517,0.518, and 0.520, then in steps of 0.005 M_⊙ up to 0.55 M_⊙, in steps of 0.01 M_⊙ up to 0.6 M_⊙, in steps of 0.02 M_⊙ up to 0.7 M_⊙, and then ΔM = 0.1 M_⊙ up to 0.8 M_⊙. The approximate positions of the blue and red boundaries of the RR Lyrae instability strip are also displayed as thin dashed lines. Lower panel: as in the upper panel, but for Z = 0.05, Y = 0.316, and a RGB progenitor with mass equal to 1 M_⊙. The less massive HB model has a mass equal to 0.465 M_⊙. The mass steps are as in the upper panel, but for masses larger than 0.6 M_⊙, where ΔM = 0.1 M_⊙.