A spectrophotometric study of the emission lines in the quiescent dwarf nova Z Chamaeleontis.

Abstract

The main goal of the present time-resolved spectrophotometric study of Z Cha is to examine the behaviour of the emission lines during the eclipse of the disc by the secondary star. The observations and data reduction techniques are presented first. Then, the white dwarf spectrum is examined, which produces broad absorption wings around the Balmer emission lines and causes their narrow absorption cores to dip below the level of the continuum. The authors find a low temperature which constrains the age of Z Cha. Eclipse phenomena in the emission lines and consequences for the stellar masses are discussed. The eclipse times, durations and depths all vary systematically with velocity across the emission-line profile, since the emission at different velocities arises from different regions of the accretion disc. A distortion of the velocity field in the disc produces spurious K velocities and an asymmetric eclipse of the lines. The authors develop a kinematic description of the required distortion, and suggest an underlying physical mechanism.