Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-12-12
New Astron.13:314-339,2008
Astronomy and Astrophysics
Astrophysics
63 pages, 13 figures
Scientific paper
10.1016/j.newast.2007.11.007
The empirical differential metallicity distribution (EDMD) is deduced for (i) local thick disk stars; (ii) likely metal-weak thick disk stars; (iii) chemically selected local G dwarfs, with the corrections performed in order to take into account the stellar scale height; in addition to previous results related to (iv) solar neighbourhood halo subdwarfs; and (v) K-giant bulge stars. The thick disk is conceived as made of two distinct regions: the halo-like and the bulge-like thick disk, and the related EDMD is deduced. Under the assumption that each distribution is typical for the corresponding subsystem, the EDMD of the thick disk, the thick + thin disk, and the Galaxy, is determined by weighting the mass. Models of chemical evolution are computed for each subsystem assuming the instantaneous recycling approximation. The EDMD data are reasonably fitted by simple models implying both homogeneous and inhomogeneous star formation, provided that star formation is inhibited during thick disk evolution. The initial mass function (IMF) is assumed to be a universal power law, which implies an unchanged true yield in different subsystems. The theoretical differential metallicity distribution (TDMD) is first determined for the halo-like thich disk, the bulge-like thick disk, and the thin disk separately, and then for the Galaxy by weighting the mass. An indicative comparison is performed between the EDMD deduced for the disk both in presence and in absence of [O/Fe] plateau, and its counterpart computed for (vi) nearby stars for which the oxygen abundance has been determined both in presence and in absence of the local thermodynamical equilibrium (LTE) approximation. Both distributions are found to exhibit a similar trend, though systematic differences exist.
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