NLTE Analysis of the Ultra-short Period White-dwarf Binary RX\n J0806.3+1527

RX J0806.3+1527 is suspected to be a double-degenerate white dwarf binary. We\npresent first results of our NLTE analysis of its optical spectrum. The\nVLT/FORS1 data show a composite spectrum consisting of a blue continuum and\nsuperimposed emission lines of the HeII Pickering series and, possibly, the H\nBalmer series. Our models are based on hot white dwarf atmospheres and include\nillumination effects onto the secondary star. The physical parameters and\nchemical abundances derived from the comparison of the observed spectrum with a\ngrid of model atmospheres provide constraints on the true nature of this\nenigmatic binary and on the models proposed so far.\n