Regular orbital variations in the ultraviolet resonance lines of YZ Cnc.

Abstract

Observations with the International Ultraviolet Explorer of the dwarf nova YZ Cnc show regular orbital variations in the line profiles of the ultraviolet resonance lines. The P Cygni profile of the C IV λ1549 line changes drastically from absorption-dominated to emission-dominated, during the three observed orbits in each of two observation shifts, separated by one day, shortly after an outburst maximum. Similar changes are visible in the N V λ1240 and Si IV λ1400 lines. The authors argue that these observations indicate a strong deviation in the wind geometry from a spherical outflow pattern, and imply an asymmetry with respect to the disc rotation axis.