¹²C/¹³C data in our red giant stars that are segregated according to their metallicity (left and right panels include respectively sample stars with metallicity close to solar and [Fe/H] = −0.56). Same symbols as in Fig. 11. Theoretical ¹²C/¹³C surface abundance is shown from the ZAMS up to the TP-AGB. Various lines correspond to predictions of stellar models of different masses including effects of rotation-induced mixing (with an initial V_ZAMS/V_crit = 0.30) and thermohaline instability.