The dwarf nova Z Cha. II. Spectroscopy.

Abstract

Spectroscopic observations are presented of Z Cha in quiescence. The data include moderate spectral resolution scans over the greater part of an orbit and with high time resolution through eclipse. Also discussed are various lower resolution spectra and UV and optical spectrophotometry. The spectrum is found to be dominated by broad double peaked Balmer emission lines; He I emission and absorption lines are visible and there is no Balmer discontinuity. The Balmer line wings extend to + or - 2100 km/sec, implying a minimum mass greater than 0.4 solar mass if the compact object is a helium white dwarf. The depth of the central dip in the double peaked profiles and the peak-to-peak velocity separation increase from H-alpha through to H-delta, indicating absorption effects. The values of the peak-to-peak velocity separation vary from 1100 km/sec (H-alpha) to 1650 km/sec (H-delta). The line emissivity as a function of disc radius is discussed and power-law fits are given. It is found that the Balmer line fluxes do not vary very much with orbital phase. The Balmer decrement is fairly flat and is consistent with densities between approximately 10 to the 8th and 10 to the 16th/cu cm.