  High-resolution spectra of six core helium-burning `clump' stars and three
giants in the open cluster M 67 have been obtained with the SOFIN spectrograph
on the Nordic Optical Telescope to investigate abundances of up to 25 chemical
elements. Abundances of carbon were studied using the C2 Swan (0,1) band head
at 5635.5 A. The wavelength interval 7980-8130 A with strong CN features was
analysed in order to determine nitrogen abundances and 12C/13C isotope ratios.
The oxygen abundances were determined from the [O I] line at 6300 A.
  The overall metallicity of the cluster stars was found to be close to solar
([Fe/H]=-0.03+-0.03). Compared with the Sun and other dwarf stars of the
Galactic disk, as well as with dwarf stars of M 67 itself, abundances in the
investigated stars suggest that carbon is depleted by about 0.2 dex, nitrogen
is enhanced by about 0.2 dex and oxygen is unaltered. Among other mixing-
sensitive chemical elements an overabundance of sodium may be suspected. The
mean C/N and 12C/13C ratios are lowered to the values of 1.7+-0.2 and 24+-4 in
the giants and to the values of 1.4+-0.2 and 16+-4 in the clump stars. These
results suggest that extra mixing of CN-cycled material to the stellar surface
takes place after the He-core flash. Abundances of heavy chemical elements in
all nine stars were found to be almost identical and close to solar.
