Spectral study of the irregular variables

Abstract

Nineteen spectrograms for three variables with periodic fadings of the, namely, SV Cep, UX Ori, and DD Ser, obtained on the two meter telescope of the Shemakha Astrophysical Observatory with a reciprocal dispersion of 94 A/mm in H..gamma.., were used to compile a two dimensional quantitative spectral classification of those variables. On the basis of certain classification criteria based on the lines of the metals, the mean spectral classes were determined for each star: A0 for SV Cep, A3 for UX Ori, and A5 for DD Ser. It was discovered that the spectral class of SV Cep varied from A0 to A3 from night to night; this may possibly be connected with the presence of cold regions on the surface of the star. The mean values of the absolute magnitudes found from the spectra of SV Cep, UX Ori, and DD Ser are, respectively, M /sub V/ = -0 /sup m/ .5, M /sub V/ = 0 /sup m/ .6, and M /sub V/ = 0 /sup m/ .2, which corresponds to giants of luminosity class III. The depths of the hydrogen lines and of K Ca II markedly exceed the depths in the spectra of standard stars of themore » same spectral class and luminosity class, and the explanation for this is the contribution of the additional absorption in the envelope. A consideration of the photographic observations available in the literature for DD Ser, which cover a period of 25 years, suggests a cyclicity of the fadings of about 4 yr.« less