Chemical composition of evolved stars in the open cluster NGC 7789 *,**
1
Vilnius University Institute of Theoretical Physics and Astronomy, Goštauto 12, Vilnius 01108, Lithuania e-mail: taut@itpa.lt
2
Department of Astronomy and Space Physics, Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
3
Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
Received:
1
September
2004
Accepted:
15
October
2004
High-resolution spectra of six giants and three core-helium-burning
“clump” stars in the open cluster NGC 7789 have been obtained with the SOFIN
spectrograph on the Nordic Optical Telescope to investigate abundances of up to
20 chemical elements. Abundances of carbon were studied using the 
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 
isotope ratios.
The oxygen abundances were determined from the [O I] line at 6300 Å.
The overall metallicity of evolved stars in the cluster was found to be close
to solar (
). Compared with the Sun and other dwarf
stars of the Galactic disk, mean abundances in the investigated giant stars
suggest that carbon is depleted by about 0.2 dex, and nitrogen and oxygen are
close to solar. In the clump stars investigated, carbon is depleted
by about 0.2 dex, the mean abundance of nitrogen is enhanced by 0.26 dex and
oxygen is lower by 0.14 dex.
This has the effect of lowering the mean C/N ratios to the value of 
in the giant stars
and to the value of 
in the clump stars.
The mean ratios are lowered
to about the same value of 
in the giants and clump stars investigated.
Concerning other chemical elements an overabundance
of sodium is noticeable and of silicon and calcium one is suspected.
Abundances of iron-group and heavier chemical elements in all nine stars were
found to be close to solar.
Key words: stars: abundances / stars: atmospheres / stars: horizontal-branch / Galaxy: open clusters and associations: individual: NGC 7789
© ESO, 2005