||Recent Investigations on AA Doradus
||452, Fifth Meeting on Hot Subdwarf Stars and Related Objects
||AA Dor is an eclipsing, post common-envelope binary with an
sdOB-type primary and an unseen low-mass secondary, believed to
be a brown dwarf. Eleven years ago, a NLTE spectral analysis
of the primary showed a discrepancy with the surface gravity
that was derived by radial-velocity and light-curve analysis
that could not be explained.
Since then, emission lines of the secondary were identified in
optical spectra and its orbital-velocity amplitude was measured.
Thus, the masses of both components are known, however, within
relatively large error ranges. The secondary's mass was found
to be around the stellar hydrogen-burning mass limit and, thus,
it may be a brown dwarf or a late M-type dwarf. In addition, a
precise determination of the primary's rotational velocity
showed recently, that it rotates at about 65% of bound
rotation—much slower than previously assumed.
A new spectral analysis by means of metal-line blanketed,
state-of-the-art, non-LTE model atmospheres solves the so-called
gravity problem in AA Dor—our result for the surface gravity
is, within the error limits, in agreement with the value from
We present details of our recent investigations on AA Dor.