We present new calibrations of stellar parameters of O stars at solar metallicity taking non-LTE , wind , and line-blanketing effects into account .
Gravities and absolute visual magnitudes are derived from results of recent spectroscopic analyses .
Two types of effective temperature scales are derived : one from a compilation based on recent spectroscopic studies of a sample of massive stars – the “ observational scale ” – and the other from direct interpolations on a grid of non-LTE spherically extended line-blanketed models computed with the code CMFGEN ( Hillier & Miller [ 1998 ] ) – the “ theoretical scale ” .
These T _ { \mathrm { eff } } scales are then further used together with the grid of models to calibrate other parameters ( bolometric correction , luminosity , radius , spectroscopic mass and ionising fluxes ) as a function of spectral type and luminosity class .
Compared to the earlier calibrations of Vacca et al .
( [ 1996 ] ) the main results are :

• The effective temperature scales of dwarfs , giants and supergiants are cooler by 2000 to 8000 K , the theoretical scale being slightly cooler than the observational one .
The reduction is the largest for the earliest spectral types and for supergiants .

• Bolometric corrections as a function of T _ { \mathrm { eff } } are reduced by 0.1 mag due to line blanketing which redistributes part of the UV flux in the optical range .
For a given spectral type the reduction of BC is larger for early types and for supergiants .
Typically BC s derived using the theoretical T _ { \mathrm { eff } } scale are 0.40 to 0.60 mag lower than that of Vacca et al .
( [ 1996 ] ) , whereas the differences using the observational T _ { \mathrm { eff } } scale are somewhat smaller .

• Luminosities are reduced by 0.20 to 0.35 dex for dwarfs , by \sim 0.25 for all giants and by 0.25 to 0.35 dex for supergiants .
The reduction is essentially the same for both T _ { \mathrm { eff } } scales .
It is independent of spectral type for giants and supergiants and is slightly larger for late type than for early type dwarfs .

• Lyman continuum fluxes are reduced .
Our theoretical values for the hydrogen ionising photon fluxes for dwarfs are 0.20 to 0.80 dex lower than those of Vacca et al .
( [ 1996 ] ) , the difference being larger at late spectral types .
For giants the reduction is of 0.25 to 0.55 dex , while for supergiants it is of 0.30 to 0.55 dex .
Using the observational T _ { \mathrm { eff } } scale leads to smaller reductions at late spectral types .

The present results should represent a significant improvement over previous calibrations , given the detailed treatment of non-LTE line-blanketing in the expanding atmospheres of massive stars .