AA Dor—An Eclipsing sdOB—Brown Dwarf Binary

AA Dor is an eclipsing, close, post common-envelope binary (PCEB) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass (M ₂≈ 0.066 M _⊙)—formally a brown dwarf. The brown dwarf may have been a former planet which survived a common envelope (CE) 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 compared 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 this problem. We present results of a NLTE spectral analysis of the primary, an analysis of its orbital parameters, and discuss possible evolutionary scenarios.