Distribution of our stars in the mass – effective temperature plane. The He-MS (Paczyński 1971) is shown as a dashed grey line. The grey-shaded band is centred on a mass of 0.47 M_⊙ and spans ±0.05 M_⊙, corresponding to our mean uncertainties. The pink-shaded region extends down to 0.35 M_⊙, the minimum core mass predicted by the evolutionary tracks of Han et al. (2002). Pentagons indicate the same stars as in Fig. 3.