Chemical evolution of the Galactic bulge as traced by microlensed dwarf
  and subgiant stars. VII. Lithium
  Lithium abundances are presented for 91 dwarf and subgiant stars in the
Galactic bulge. The analysis is based on line synthesis of the 7Li line at 6707
{\AA} in high-resolution spectra obtained during gravitational microlensing
events, when the brightnesses of the targets were highly magnified. Our main
finding is that the bulge stars at sub-solar metallicities, and that are older
than about eight billion years, does not show any sign of Li production, that
is, the Li trend with metallicity is flat (or even slightly declining). This
indicates that no lithium was produced during the first few billion years in
the history of the bulge. This finding is essentially identical to what is seen
for the (old) thick disk stars in the Solar neighbourhood, and adds another
piece of evidence for a tight connection between the metal-poor bulge and the
Galactic thick disk. For the bulge stars younger than about eight billion
years, the sample contains a group of stars at very high metallicities at
[Fe/H]~+0.4 that have lithium abundances in the range A(Li)=2.6-2.8. In the
Solar neighbourhood the lithium abundances have been found to peak at a
A(Li)~3.3 at [Fe/H]~ +0.1 and then decrease by 0.4-0.5 dex when reaching
[Fe/H]~+0.4. The few bulge stars that we have at these metallicities, seem to
support this declining A(Li) trend. This could indeed support the recent claim
that the low A(Li) abundances at the highest metallicities seen in the Solar
neighbourhood could be due to stars from the inner disk, or the bulge region,
that have migrated to the Solar neighbourhood.
