5,344 research outputs found
High-gravity central stars
NLTE spectral analyses of high-gravity central stars by means of
state-of-the-art model atmosphere techniques provide information about the
precursor AGB stars. The hydrogen-deficient post-AGB stars allow investigations
on the intershell matter which is apparently exhibited at the stellar surface.
We summarize recent results from imaging, spectroscopy, and spectropolarimetry.Comment: 8 pages, 4 figures, IAU Symposium No. 234, Planetary Nebulae in our
Galaxy and Beyon
AA Dor - An Eclipsing sdOB - Brown Dwarf Binary
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.Comment: 8 pages, 4 figures, Workshop on Extreme Horizontal Branch Stars and
Related Objects, Jun 2003, Keele, U
Spectral Analysis via the Virtual Observatory: The Service Theossa
In the framework of the Virtual Observatory, the newly developed service
TheoSSA provides access to theoretical stellar spectral-energy distributions.
In a pilot phase, this service is based on the well established Tuebingen NLTE
Model-Atmosphere Package for hot, compact stars. We demonstrate its present
capabilities and future extensions.Comment: Proceedings of JENAM-2011, European Week of Astronomy and Space
Science, 8 pages, 6 figure
Non-LTE Spectral Analysis of Extremely Hot Post-AGB Stars: Constraints for Evolutionary Theory
Spectral analysis by means of Non-LTE model-atmosphere techniques has arrived
at a high level of sophistication: fully line-blanketed model atmospheres which
consider opacities of all elements from H to Ni allow the reliable
determination of photospheric parameters of hot, compact stars. Such models
provide a crucial test of stellar evolutionary theory: recent abundance
determinations of trace elements like, e.g., F, Ne, Mg, P, S, Ar, Fe, and Ni
are suited to investigate on AGB nucleosynthesis. E.g., the strong Fe depletion
found in hydrogen-deficient post-AGB stars is a clear indication of an
efficient s-process on the AGB where Fe is transformed into Ni or even heavier
trans iron-group elements. We present results of recent spectral analyses based
on high-resolution UV observations of hot stars.Comment: 6 pages, 2 figure
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