Exciting stars and the distances of the diffuse nebulae

The early-type stars exciting 220 diffuse nebulae were found from extensive literature survey, as well as from extensive study of the magnetic tape catalogues of the Soviet astronomical data center. The photometric distances of the stars and nebulae were determined from UBV photometry and spectral classification of the stars. The transformation of the spectral classification into absolute visual magnitudes were made by means of the averaged calibration constructed by the authors. The distribution of the diffuse nebulae in the galactic plane shows the internal, local and two external arms of the Galaxy.