Astronomy and Astrophysics – Astrophysics
Scientific paper
1995-09-01
Astron.J.110:2771,1995
Astronomy and Astrophysics
Astrophysics
Plain tex file, to appear in Astron J (Dec 1995 scheduled). Figures hard copy only available from Rosie Wyse at JHU address
Scientific paper
10.1086/117729
The immediate Solar neighborhood should be a fair sample of the local Galaxy. However, the chemical abundance distribution of long-lived disk stars very near the Sun contains a factor of five to ten more metal-poor stars, $-1 \simlt {\rm [Fe/H]} \simlt -0.4$ dex, than is consistent with modern star-count models of larger scale Galactic structure. The metallicity distribution of complete samples of long-lived stars has long been recognised as providing unique constraints on the early stages of chemical evolution of the Galaxy, so that one would like to resolve this anomaly. We present a new derivation of the local G-dwarf metallicity distribution, based on the Third Gliese catalog combined with Olsen's (1983) Str\"omgren photometry. Kinematic data for these same stars, as well as for a high-precision sample studied by Edvardsson {\sl et al.} (1993), provide clear evidence that the abundance distribution below [Fe/H]$\sim -0.4$ contains two over-lapping distributions, the thick disk and the thin disk. We achieve a reliable deconvolution of the relative numbers in each population by comparing the local metallicity distribution with a recent determination (Gilmore, Wyse \& Jones 1995) of the metallicity distribution of F/G stars {\sl in situ} some 1500pc from the Sun. The gravitational sieve of the Galactic potential acts on this second sample to segregate the low velocity dispersion, thin-disk, component of the local sample, leaving predominantly the second, higher velocity dispersion component. The combination of these two datasets allows us to determine the source of the local paradox: there is a substantial tail of the thin disk (defined kinematically) metallicity distribution, which extends below ${\rm [Fe/H] \approx -0.4}$dex. This is a robust conclusion, being consistent with the sum of star count, stellar spatial
Gilmore Gerard
~Wyse Rosemary F. G.
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