A Survey of IUE Spectra of the Active Binary System UX Arietis

Abstract

To investigate the ultraviolet (UV) activity of the bright, non-eclipsing, double-lined spectroscopic binary system UX Ari, IUE spectra (194 images) were taken from the IUE archive. The spectra, obtained during the period 1978-1996, show emission lines originating in the chromosphere and transition region. The long-wavelength low dispersion spectra were examined for ultraviolet excess by comparing the UV continuum level of UX Ari with the levels of $\kappa$ Cet and $\eta$ Cep in the spectral range 2100 $\AA$ - 3200 $\AA$ . The individual MgII h and k emission-line fluxes of component stars show that the contributions to the activity of the system for G5 V and K0 IV are about 20% and 80%, respectively. Apart from the flare event observed on 1979 Jan 1, there are some flux enhancements in the years 1987, 1991 and 1994 which may suggest existence of a periodicity of about 7-9 years. Examination of the ultraviolet excess in the system showed that there is some UV excess in UX Ari, which varies from 1% up to 24% with the exception of two images which showed no UV excess. The results revealed that there was an agreement on the source of emission regions which could be attributed to the magnetic activity. The contribution of G5 V and K0 IV components to the MgII activity of the system suggests a need to take into consideration the spot distribution not only on the surface of K0 IV but also on the surface of G5 V component of UX Ari.Comment: 15 pages, 10 figure