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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 starsgif

Detailed abundance analysis of 47 G and K dwarf stars with [Me/H] > 0.10 dex

S. Feltzingtex2html_wrap3871 and B. Gustafssontex2html_wrap3873

Send offprint request: S. Feltzing

tex2html_wrap3875  Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ, UK
tex2html_wrap3877  Astronomiska observatoriet, Box 515, S-75120 Uppsala, Sweden


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 tex2html_wrap_inline3845 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 tex2html_wrap_inline3849 dex. The spectroscopic [Fe/H] correlate well with the [Me/H] derived from tex2html_wrap_inline3845 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 tex2html_wrap_inline3853 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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