Macroscopic structure of the spectra of hot stars in the ultraviolet

Abstract

Observational material from Orion-2 is used to obtain new results on the macroscopic structure of the continuous spectra of 26 hot B2-A3 stars in the ultraviolet region 2000-3700 A. In particular, a new proof is found that the depression of the continuum in the region near 2400 A is indeed different for different stars of strictly the same spectral subclass and luminosity class and may fluctuate in an appreciable range. It is noted that the depression itself comes about as a result of additional absorption in a circumstellar cloud. The observed spread in the magnitudes of the depression can therefore be interpreted as a spread in the thickness (optical thickness) of the circumstellar cloud on the transition from one star to another. A list of hot stars for which the existence of circumstellar clouds can be regarded as probable is included.