Relation between X-ray and bolometric luminosity. The stars belonging to NGC 6357 and NGC 6334 are indicated by squares and circles, respectively. The O and B stars are coded as red and black symbols. Symbols marked by a triangle are stars with poor spectra, while crosses indicate stars with distances greater than 3 kpc or less than 1.1 kpc. The X-ray fluxes are evaluated in the [0.5–8 keV] energy band and corrected for interstellar extinction. The line corresponds to the scaling relation log(L_X/L_bol) = −7.07.