Spectroscopic determination of stellar parameters to constrain atomic diffusion in the old open cluster M67

Sammanfattning: In an attempt to check published results on diffusion effects in M67 a non-LTE analysis is made on 28 high resolution FLAMES-UVES spectra of dwarfs and sub-giants around the turnoff point, where core hydrogen fusion halts. This analysis utilizes the software-suites LOTUS and iSpec to determine stellar parameters from equivalent-width measurements. With larger parameter scatter than expected diffusion effects were difficult to pin down. Eight spectra from either known variable stars (Kepler K2 data) or having low signal-to-noise data were therefore removed. This new reduced dataset confirms \citet{diffusionm672} that non-LTE analyses reduces scatter and makes diffusion trends easier to identify. This may however also be the result of systematic errors in LOTUS and requires more (and independent) confirmation.