Analysis of spiral structure in the accretion disc of the nova-like cataclysmic variable EC21178-5417

Abstract

We present an extensive Doppler tomography study of the eclipsing nova-like EC21178-5417, which exhibits the classic accretion disc signature in the form of double-peak emission lines in its spectrum. Doppler tomograms confirm the presence of a strong, two-armed spiral pattern visible in the majority of the spectral lines studied. This makes EC21178-5417 one of the very few nova-likes that show spiral structure in their discs. We also report night-to-night changes in the position and relative strength of the spiral arms, revealing fluctuations on the conditions in the accretion disc.