Revisiting the surface brightness-colour relation in the context of the Araucaria Project and the PLATO space mission

The ease of use of Surface Brightness-Colour Relations (SBCRs) is a major advantage in the determination of stellar angular diameters. It currently plays a significant role for the distance determination of eclipsing binaries and also for the characterization of exoplanets host stars. Despite the large number of existing SBCRs, strong discrepancies occur on the outer edges of the surface brightness F_V versus V-K colour diagram. \citet{Challouf} reached a precision of 7% on the estimate of the angular diameter for V-K < 0 mag, while 10% of accuracy only is expected on the other part of the diagram. To overcome these discrepancies, we apply the same methodology to all the angular diameter and photometric estimates available in the literature. We also observe new stars using the CHARA/VEGA and PAVO instruments. We show that the SBCR strongly depends on the spectral type and the luminosity class of stars. An unique SBCR can therefore not be used for any type of star.