Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation
and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and
accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a
few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars.
We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and
giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical evolution
of the Bulge.
Methods. We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based
on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events.
The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully
differential comparison between the Bulge and the local stellar populations in the Galactic disc.
Results. We present
detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous
events, here re-analysed with the same methods, we study a homogeneous sample of 15 stars, which constitute the largest sample
to date of microlensed dwarf stars in the Galactic bulge. We find that the stars span the full range of metallicities from
[Fe/H] = -0.72 to +0.54, and an average metallicity of [Fe/H] = -0.08 ± 0.47, close to the average metallicity based on giant
stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]<0 are very similar to
those of the local Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, comparable
chemical histories. At sub-solar metallicities we find the Bulge dwarf stars to have consistently old ages, while at super-solar
metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate
possible formation scenarios for the Bulge.