1111.0540 (Thomas Rauch)
Thomas Rauch
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 light-curve analysis.
We present details of our recent investigations on AA Dor.
View original:
http://arxiv.org/abs/1111.0540
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