Z Chamaeleontis - Evidence for an eccentric disk during supermaximum

Abstract

Spectroscopic and photometric observations are presented of the eclipsing dwarf nova Z Cha. The principal spectral features in quiescence are broad, double peaked emission lines of H-beta, H-gamma, and H-delta and narrow absorption lines of the higher-order Balmer series. The double structure of the emission profile derives from superposed narrow absorption, which is seen as arising in the line of sight through the outer, cooler parts of the disk. A radial velocity semiamplitude of 87 + or - 14 km/s for the absorption lines is found. From the spectroscopic data and published eclipse light curve characteristics, the principal system parameters of Z Cha are derived. They include orbital inclination (79 + or - 2 deg), stellar masses (0.85 + or - 0.15 solar mass and 0.17 + or - 0.05 solar mass), binary separation, stellar radii, and the size and location of the hot spot.