The Gaia-ESO Survey: CNO Abundances in Open Clusters of our Galaxy

We present the current status of CNO abundance investigations in evolved stars of Galactic open clusters observed in the currently ongoing Gaia-ESO survey. The spectra were observed with the VLT UVES spectrograph and analysed using a differential model atmosphere method. The C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolutionary models. For the corresponding stellar turn-off masses from 1.15 to 3.3 M-circle dot, the observed C/N ratio values are close to the predictions of standard first dredge-up and thermohaline extra mixing models. The recent model in which the thermohaline- and rotation-induced extra-mixing act together seems to provide C/N values that are too low.