  AA Dor is an eclipsing, close, post common-envelope binary consisting of a
sdOB primary star and an unseen secondary with an extraordinary small mass -
formally a brown dwarf. The brown dwarf may have been a former planet which
survived a common envelope phase and has even gained mass.
  A recent determination of the components' masses from results of NLTE
spectral analysis and subsequent comparison to evolutionary tracks shows a
discrepancy to masses derived from radial-velocity and the eclipse curves.
Phase-resolved high-resolution and high-SN spectroscopy was carried out in
order to investigate on this problem.
  We present results of a NLTE spectral analysis of the primary, an analysis of
its orbital parameters, and discuss possible evolutionary scenarios.
