Analysis of spiral structure in the accretion disc of the novalike Cataclysmic Variable EC21178--5417

TL;DR

This study uses Doppler tomography to reveal and analyze a rare two-armed spiral structure in the accretion disc of the eclipsing novalike EC21178--5417, showing variability over different nights.

Contribution

First detailed Doppler tomography analysis of EC21178--5417 confirming spiral arms in its accretion disc and observing their temporal fluctuations.

Findings

Detection of a two-armed spiral pattern in the disc

Observation of night-to-night changes in spiral arm properties

EC21178--5417 is among few novalikes with observed disc spirals

Abstract

We present an extensive Doppler tomography study of the eclipsing novalike 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 novalikes 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.