Hot UV-bright stars of galactic globular clusters
  We have performed a census of the UV-bright population in 78 globular
clusters using wide-field UV telescopes. This population includes a variety of
phases of post-horizontal branch (HB) evolution, including hot post-asymptotic
giant branch (AGB) stars, and post-early AGB stars. There are indications that
old stellar systems like globular clusters produce fewer post-(early) AGB stars
than currently predicted by evolutionary models, but observations are still
scarce. We obtained FORS2 spectroscopy of eleven of these UV-selected objects
(covering a range of -2.3<[Fe/H]<-1.0), which we (re-)analysed together with
previously observed data. We used model atmospheres of different metallicities,
including super-solar ones. Where possible, we verified our atmospheric
parameters using UV spectrophotometry and searched for metal lines in the
optical spectra. We calculated evolutionary sequences for four metallicity
regimes and used them together with information about the HB morphology of the
globular clusters to estimate the expected numbers of post-AGB stars. Seven of
the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars,
two are evolving away from the HB, one is a foreground white dwarf, and one is
a white dwarf merger. So spectroscopy is clearly required to identify the
evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model
spectra are required to reproduce their optical and UV spectra, which may
affect the flux contribution of hot post-AGB stars to the UV spectra of evolved
populations. Adding published information on other hot UV-bright stars in
globular clusters, we find that the number of observed hot post-AGB stars
generally agrees with the predicted values, although the numbers are still low.
