Ultraviolet intrinsic colours of early type stars

Ultraviolet intrinsic colors of early type stars observed by the S2/68 Sky Survey Telescope in the TD-1A satellite are presented. These ultraviolet intrinsic colors are computed in the spectral region from 1380 to 2540 A in wavelength intervals of 20 A and in the photometric band of about 330 A width centered at 2740 A. The accuracy of the intrinsic colors is related in terms of their rms error. A comparison among luminosity classes shows that giants and dwarfs exhibit the same flux distribution, while supergiants are fainter with regard to those. This set of intrinsic colors is compared to that computed from the grid of stellar model atmospheres. Both sets match very well except for earliest spectral types of main sequence stars and for early-type supergiants for which the discrepancies are greater than twice the rms error in the sense that the observed intrinsic colors are redder than those deduced from the models.