Chemical evolution of the Galactic bulge as traced by microlensed dwarf
  and subgiant stars. VIII. Carbon and oxygen
  CONTEXT: [ABRIDGED]. For the Milky Way bulge, there are currently essentially
no measurements of carbon in un-evolved stars, hampering our abilities to
properly compare Galactic chemical evolution models to observational data for
this still enigmatic stellar population. AIMS: We aim to determine carbon
abundances for our sample of 91 microlensed bulge dwarf and subgiant stars.
Together with new determinations for oxygen this forms the first statistically
significant sample of bulge stars that have C and O abundances measured, and
for which the C abundances have not been altered by the nuclear burning
processes internal to the stars. METHODS: The analysis is based on
high-resolution spectra for a sample of 91 dwarf and subgiant stars that were
obtained during microlensing events when the brightnesses of the stars were
highly magnified. Carbon abundances were determined through spectral line
synthesis of five CI lines around 9100 A, and oxygen abundances using the three
OI lines at about 7770 A. [ABRIDGED] RESULTS: Carbon abundances was possible to
determine for 70 of the 91 stars in the sample and oxygen abundances for 88 of
the 91 stars in the sample. The [C/Fe] ratio evolves essentially in lockstep
with [Fe/H], centred around solar values at all [Fe/H]. The [O/Fe]-[Fe/H] trend
has an appearance very similar to that observed for other alpha-elements in the
bulge, [ABRIDGED]. When dividing the bulge sample into two sub-groups, one
younger than 8 Gyr and one older than 8 Gyr, the stars in the two groups follow
exactly the elemental abundance trends defined by the solar neighbourhood thin
and thick disks, respectively. Comparisons with recent models of Galactic
chemical evolution in the [C/O]-[O/H] plane shows that the models that best
match the data are the ones that have been calculated with the Galactic thin
and thick disks in mind. [ABRIDGED] ....
