The Gaia-ESO Survey: The analysis of the hot-star spectra
  The Gaia-ESO Survey (GES) is a large public spectroscopic survey that has
collected, over a period of 6 years, spectra of ~ 10^5 stars. This survey
provides not only the reduced spectra, but also the stellar parameters and
abundances resulting from the analysis of the spectra. The GES dataflow is
organised in 19 working groups. Working group 13 (WG13) is responsible for the
spectral analysis of the hottest stars (O, B and A type, with a formal cut-off
of Teff > 7000 K) that were observed as part of GES. We present the procedures
and techniques that have been applied to the reduced spectra, in order to
determine the stellar parameters and abundances of these stars. The procedure
used is similar to that of other working groups in GES. A number of groups
(called `Nodes') each independently analyse the spectra, using their
state-of-the-art techniques and codes. Specific for the analysis in WG13 is the
large temperature range that is covered (Teff = 7000 - 50,000 K), requiring the
use of different analysis codes. Most Nodes can therefore only handle part of
the data. Quality checks are applied to the results of these Nodes by comparing
them to benchmark stars, and by comparing them one to another. For each star
the Node values are then homogenised into a single result: the recommended
parameters and abundances. Eight Nodes each analysed (part of) the data. In
total 17,693 spectra of 6462 stars were analysed, most of them in 37 open star
clusters. The homogenisation led to stellar parameters for 5584 stars.
Abundances were determined for a more limited number of stars. Elements studied
are He, C, N, O, Ne, Mg, Al, Si and Sc. Abundances for at least one of those
elements were determined for 292 stars. The hot-star data analysed here, as
well as the Gaia-ESO Survey data in general, will be of considerable use in
future studies of stellar evolution and open clusters.
