Coordinated UV and optical observations of the AM Herculis object E 1405-451 in thehigh and low sta

Abstract

Simultaneous UV and optical observations of the magnetic white dwarf binary E1405-451 taken in February 1983, March, and April are reported. In March the source was found in a low state analogous to those observed in AM Her. In this state the ultraviolet spectrum of E1405-451 can be interpreted as the emission from a hot white dwarf/T = 26,500 K, R = 3 x 10 to the 8th x (d/100 pc) cm, and the R and I magnitudes can be accounted for by a Roche lobe filling secondary, of spectral type between M3 V and M8 V at a distance between 50 and 200 pc. Emission from a residual accretion column may still be present. In the high state, the UV continuum is described by a power law, F-gamma varies as gamma to the power-alpha with alpha = 1.9, while the optical and infrared magnitudes lie above the extrapolation of this power law. Subtracting the emission of the white dwarf and of the secondary from the overall energy distribution in the high state, the residual spectrum seems to contain two components. A steep one, emerging shortward of 2000 A, could be associated with a hot polar cap; a flatter one, between 2000 and 6000 A, rapidly decreasing in the infrared, could be due to cyclotron radiation.