On the use of Gaia magnitudes and new tables of bolometric corrections

The availability of reliable bolometric corrections and reddening estimates, rather than the quality of parallaxes, will be one of the main limiting factors in determining the luminosities of a large fraction of Gaia stars. With this goal in mind, we provide GaiaG_BP, G, and G_RP synthetic photometry for the entire MARCS grid and test the performance of our synthetic colours and bolometric corrections against space-borne absolute spectrophotometry. We find indication of a magnitude-dependent offset in Gaia DR2 G magnitudes, which must be taken into account in high-accuracy investigations. Our interpolation routines are easily used to derive bolometric corrections at desired stellar parameters and to explore the dependence of Gaia photometry on T_eff, log g, {[Fe/H]}, [α /{Fe}], and E(B - V). Gaia colours for the Sun and Vega, and T_eff-dependent extinction coefficients are also provided.