TRANSITION IN THE X-RAY LIGHT-CURVE OF THE AM HERCULIS SYSTEM V834 CENTAURI (E1405-451) - 1985-1986 EXOSAT OBSERVATIONS

We analyze the EXOSAT observations of the AM Herculis system V834 Centauri (E1405-451), taken in 1985 March and 1986 August. Archival UV data, simultaneous with the 1986 observations, are also considered. The soft X-ray light curve has a double humped structure, with total eclipse at phi approximately 0.0. It differs significantly from that observed with EXOSAT in 1984. The soft X-ray emission can be described as a black-body of temperature around 10-30 eV, with column density consistent with the interstellar values (5 x 10(19)-1.0 X 10(20) cm-2). The hard X-ray emission is nearly sinusoidally modulated with a dip at phi approximately 0.0. This component is consistent with thermal bremsstrahlung emission, with rather high column densities (approximately 10(22) cm-2). There is indication for absorption variable with orbital phase. At both epochs, evidence for an iron emission feature at approximately 7.0 keV and with high equivalent widths (approximately 0.8-2 keV) is found. The results are discussed in terms of a scenario of the source suggested by the optical and polarization light curves.