A Spectroscopic Study of WX Cen

Abstract

WX Cen is currently classified as a nova-like (Vogt, 1989 in Classical Novae, edts. Bode & Evans, p225) but its peculiar spectral characteristics have resisted interpretations since its discovery. Time-resolved spectrophotometry was obtained with the 1.5m and 1.0m telescopes of CTIO in 1991. The emission line spectrum of WX Cen is similar to that of V Sge, V617 Sgr and GQ Mus. An E(B-V) = 0.3 was derived from the HeII4686/10124 ratio. The strong HeII4686 line and Hβ show an orbital radial velocity modulation with a period of 0.416994(±42) days, while the continuum at 5135 A displays a quasi-sinusoidal orbital hump with a semi-amplitude of 0.14^m. The possibility that the system contains an evolved lowmass secondary is unlikely due to the lack of molecular bands up to 1µ. No signatures of a main sequence companion were found. The diagnostic diagram of the Hβ wings presents an unusual situation where the radial velocity semiamplitude (K) increases continuously with the sampling velocity. The radial velocity curves derived from the wings above 1100 km/s have a non-sinusoidal shape. The Doppler tomogram in HeII4686 shows a symmetric component centered about the center of mass of the binary which may be understood as a circunstellar/wind emission. In addition, a central dip in the map is probably associated with self-absorption in this transition. Using the HeII4686 and the Hβ maps it is possible to trace the abundance of helium (He++/H+) in the velocity space.