The regions of formation of C IV resonance lines in β Persei

Abstract

New IUE images of the close binary β Persei in the phase interval 0.6P-0.8P were analysed in order to confirm or rectify conclusions previously suggested concerning the region where C IV lines are formed. Based on IUE observations taken with high dispersion and small aperture, Sahade and Hernández (1985) concluded that the resonance lines of Si IV would originate in regions near the B8 V component. Instead, the C IV behaviour of velocity-wise in phases 0.65P-0.78P would seem to suggest that this ion would form in a region of the extended envelope that surrounds the whole system. Our recent IUE images, taken with high dispersion and large aperture that cover precisely the phase interval that was not well covered with the first set of observations, show that, in fact, the C IV resonance doublet behaves in the same way as the Si IV. Therefore, Si IV and C IV are formed in the same region of the envelope that surrounds the B8 V component and there is not, indeed, evidence for the existence of more than one high temperature region in the system of Per, such as it had been thought on the basis of former material. On each spectrum the C IV lines are weaker than Si IV. As the available material is not homogeneous, we can not determine variations, with phase in the line profiles and intensities. A new set of observations covering all the orbital cycle ought to be secured to be able to explain the different behaviour of the intensities.