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A&A Supplement series, Vol. 129, April II 1998, 237-266
Received June 25; accepted September 26, 1997
Abundances in metal-rich stars
Detailed abundance analysis of 47 G and K dwarf stars with [Me/H] > 0.10 dex
S. Feltzing
and B. Gustafsson
Send offprint request: S. Feltzing sofia@ast.cam.ac.uk
Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ,
UK
Astronomiska observatoriet, Box 515, S-75120 Uppsala, Sweden
Abstract:
We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr,
Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K
dwarf, with [Me/H]>0.1 dex. The selection of stars was based on their
kinematics as well as on their 
photometry. One sample of
stars on rather eccentric orbits traces the chemical evolution
interior to the solar orbit and another, on circular orbits, the
evolution around the solar orbit. A few Extreme Population I stars
were included in the latter sample.
The stars have -0.1 dex 
dex. The
spectroscopic [Fe/H] correlate well with the [Me/H] derived from
photometry. We find that the elemental abundances of
Mg, Al, Si, Ca, Ti, Cr and Ni all follow [Fe/H]. Our data put further
constraints on models of galactic chemical evolution, in particular of
Cr, Mn and Co which have not previously been studied for dwarf stars
with 
dex. The increase in [Na/Fe] and [Al/Fe] as
a function of [Fe/H] found previously by Edvardsson et al. (1993a)
has
been confirmed for [Na/Fe]. This upturning relation, and the scatter
around it, are shown not to be due to a mixture of populations with
different mean distances to the galactic centre. We do not confirm the
same trend for aluminium, which is somewhat surprising since both
these elements are thought to be produced in the same environments in
the pre-supernova stars. Nor have we been able to trace any tendency
for relative abundances of O, Si, and Ti relative to Fe to vary with
the stellar velocities, i.e. the stars present mean distance to the
galactic centre. These results imply that there is no significant
difference in the chemical evolution of the different stellar
populations for stars with [Me/H]>0.1 dex. We find that [O/Fe]
continue to decline with increasing [Fe/H] and that oxygen and
europium correlate well. However [Si/Fe] and [Ca/Fe] seem to stay
constant. A real ("cosmic'') scatter in [Ti/Fe] at given [Fe/H] is
suggested as well as a decreasing abundance of the s-elements relative
to iron for the most metal-rich dwarf stars. We discuss our results
in the context of recent models of galactic chemical evolution.
In our sample we have included a few very metal rich stars, sometimes called SMR (super metal rich) stars. We find these stars to be among the most iron-rich in our sample but far from as metal-rich as indicated by their photometric metallicities. SMR stars on highly eccentric orbits, alleged to trace the evolution of the chemical evolution in the galactic Bulge, have previously been found overabundant in O, Mg and Si. We have included three such stars from the study by Barbuy & Grenon (1990). We find them to be less metal rich and the other elemental abundances remain puzzling.
Detailed spectroscopic abundance analyses of K dwarf stars are rare. Our study includes 5 K dwarf stars and has revealed what appears to be a striking example of overionization. The overionization is especially prominent for Ca, Cr and Fe. The origin of this apparent overionization is not clear and we discuss different explanations in some detail.
keywords: Galaxy: abundances -- evolution -- stars: abundances -- late-type -- fundamental parameters
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