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Astron. Astrophys. 360, 499-508 (2000)


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Chemical composition of evolved stars in the open cluster M 67 * **

G. Tautvaiien 1, B. Edvardsson 2, I. Tuominen 3 and I. Ilyin 3

1 Institute of Theoretical Physics and Astronomy, Gotauto 12, Vilnius 2600, Lithuania
2 Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
3 Astronomy Division, Department of Physical Sciences, P.O. Box 3000, 90014 University of Oulu, Finland

Received 25 March 1999 / Accepted 25 May 2000

Abstract

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 [FORMULA] Swan (0,1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and [FORMULA] isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å.

The overall metallicity of the cluster stars was found to be close to solar ([Fe/H]=[FORMULA]). 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 [FORMULA] ratios are lowered to the values of [FORMULA] and [FORMULA] in the giants and to the values of [FORMULA] and [FORMULA] 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.

Key words: stars: abundances – stars: atmospheres – stars: horizontal-branch – Galaxy: open clusters and associations: individual: M 67

* Based on observations obtained at the Nordic Optical Telescope, La Palma
** Tables 2 and 3 are only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.frpub/cats/J/A+A/360/499 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/360/499

Send offprint requests to: G. Tautvaiien (taut@itpa.it)

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000

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