  Context. Large spectroscopic surveys devoted to the study of the Milky Way,
including Gaia, use automated pipelines to massively determine the atmospheric
parameters of millions of stars. The Gaia FGK Benchmark Stars are reference
stars with Teff and log g derived through fundamental relations, independently
of spectroscopy, to be used as anchors for the parameter scale. The first and
second versions of the sample have been extensively used for that purpose, and
more generally to help constrain stellar models. Aims. We provide the third
version of the Gaia FGK Benchmark Stars, an extended set intended to improve
the calibration of spectroscopic surveys, and their interconnection. Methods.
We have compiled about 200 candidates which have precise measurements of
angular diameters and parallaxes. We determined their bolometric fluxes by
fitting their spectral energy distribution. Masses were determined using two
sets of stellar evolution models. In a companion paper we describe the
determination of metallicities and detailed abundances. Results. We provide a
new set of 192 Gaia FGK Benchmark Stars with their fundamental Teff and logg,
and with uncertainties lower than 2% for most stars. Compared to the previous
versions, the homogeneity and accuracy of the fundamental parameters are
significantly improved thanks to the high quality of the Gaia data reflecting
on distances and bolometric fluxes.
