Spectral classification and extinction using ANS satellite ultraviolet photometry

Performance of satellite-borne experiments for studying UV extinction and defining a finer spectral grid than the ground based spectroscopic one is summarized. In small regions (a few tenths of a square degree) local extinction can deviate significantly from galactic average. Dereddening a much reddened field star, using a general extinction law, gives very uncertain intrinsic colors. Physical associations of stars seen behind single dust clouds can be dereddened accurately if the local extinction law has an intrinsic spread much smaller than the average. Reddening-free parameters are strongly affected by extinction. A finer classification of early type stars cannot be achieved, although stars having E(B - V) 0.3 can be classified as well as with the MK system provided it is known that they have luminosity class 4 or 5. For certain homogeneous groups of early stars located behind single dust clouds, local extinction can be obtained by iteration. Temperatures of AO to KO stars can be determined accurately.