UBVJHK synthetic photometry of Galactic O stars
  The development of powerful infrared observational technics enables the study of very extincted objects and young embedded star forming regions. This is especially interesting in the context of massive stars which form and spend a non negligible fraction of their life still enshrouded in their parental molecular cloud. Spectrophotometric calibrations are thus necessary to constrain the physical properties of heavily extincted objects. Here, we derive UBVJHK magnitudes and bolometric corrections from a grid of atmosphere models for O stars. Bessel passbands are used. Bolometric corrections (BC) are derived as a function of Teff and are subsequently used to derive BC - spectral type (ST) and Absolute Magnitudes - ST relations. Infrared magnitudes and, for the first time, bolometric corrections are given for the full range of spectral types and luminosity classes. Infrared colors are essentially constant. Intrinsic H-K colors are 0.05 mag bluer than previously proposed. Optical calibrations are also provided and are similar to previous work, except for (B-V)0 which is found to be at minimum -0.28 for standard O stars, slightly larger (0.04 mag) than commonly accepted. 
F. Martins (1) and B. Plez (2) ((1) MPE Garching, (2) GRAAL   Montpellier)