Chemical evolution of the Galactic bulge [...] (Bensby et al.)

Vol. 549
In section 5. Galactic structure, stellar clusters and populations

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. V. Evidence for a wide age distribution and a complex MDF

by T. Bensby, J.C. Yee, S. Feltzing, et al., A&A 549, A147

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This work is based on the follow-up of gravitational microlensing events that result in dwarf and subgiant stars in the Galactic bulge becoming bright enough to obtain VLT/UVES high-resolution spectra. This paper presents observations of 32 new targets. When combined with the 26 previous observations by the same group, this gives a homogeneously analyzed sample of 58. The main properties of this sample are that the metallicity distribution is wide, spanning the range -1.9 > [Fe/H] < +0.6. The distribution over this range has a complex structure with indications of multiple components, each with a different scale height (e.g., the thin disk, the thick disk, and the bar). Stars that are more metal poor than [Fe/H] ~ -0.1 are shown to be old, with ages ~10-12Gyr, whereas stars more metal rich than this show a wide variety of ages ranging from 2 to 12 Gyr old, with a dominant peak around 4-5Gyr ago. In combination with other findings in the literature these results are consistent with the picture that the Milky Way is an almost pure disk galaxy, where the central region is a conglomeration of the various Galactic stellar populations that are all strongly affected by the presence of a bar.