arXiv subjects

Ellen Ringat

Publications and source records attributed to Ellen Ringat.

7 recordsLinked to original sources

arXiv2011

IrOnIc: How to Consider Hundreds of Millions of Iron-Group Lines in NLTE Model-Atmosphere Calculations

Iron-group elements have a very high number of atomic levels and an overwhelming number of spectral lines. No NLTE model-atmosphere code can cope with these in a classical way. A statistical approach was developed over the last decade to decrease the number of levels and lines to a manageable amount. The Iron Opacity and Interface (IrOnIc) calculates sampled cross-sections and model-atom files as input for model-atmosphere computations. IrOnIc is presently transferred into a parallelized code to reduce the calculation time to a reasonable value. It will be accessible by the public as a service of the German Astrophysical Virtual Observatory.

astro-ph.SR↗

arXiv2011

Quality Control for Theoretical Data in the Virtual Observatory: Establishing Benchmark Tests for Synthetic Spectra

The Virtual Observatory (VO) provides access to both, data and theory. Quality control is a general problem and the VO user needs partly some experience to judge the reliability of the VO products. As far as spectral analysis is concerned, many different areas are involved, from atomic data to stellar model-atmosphere codes. Within the framework of the German Astrophysical Virtual Observatory (GAVO) project, the service TheoSSA is developed. It allows the VO user an easy access to synthetic spectral energy distributions (SEDs). We discuss quality control problems and the reliability of SEDs provided by TheoSSA.

astro-ph.SR↗

arXiv2011

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.

astro-ph.SR↗

arXiv2011

Spectral Analysis within the Virtual Observatory: The GAVO Service TheoSSA

In the last decade, numerous Virtual Observatory organizations were established. One of these is the German Astrophysical Virtual Observatory (GAVO) that e.g. provides access to spectral energy distributions via the service TheoSSA. In a pilot phase, these are based on the Tuebingen NLTE Model-Atmosphere Package (TMAP) and suitable for hot, compact stars. We demonstrate the power of TheoSSA in an application to the sdOB primary of AA Doradus by comparison with a "classical" spectral analysis.

astro-ph.SR↗

arXiv2011

Metal-Abundance Peculiarities in the sdOB Star EC11481-2303: A Progress Report

Spectral analyses of extreme horizontal branch (EHB) stars indicate a trend to supersolar heavy-metal abundances that is increasing with effective temperature. The sdOB EC11481-2303 is such a star, located at the very hot end of the EHB. In contrast to other sdOB stars, it is exhibiting an extraordinary flat UV continuum. This may be the result of extreme metal-line blanketing. We present preliminary results of a spectral analysis by means of static as well as stratified NLTE model atmospheres.

astro-ph.SR↗

arXiv2011

UV Spectroscopy of the Central Star of the Planetary Nebula A43

About 25% of all post-AGB stars are hydrogen-deficient, e.g. the PG1159 stars with a typical abundance pattern He:C:O = 33:50:17 (by mass). Only four of about 40 known PG1159 stars exhibit H in their spectra. The exciting star of the planetary nebula A43 is one of these so-called hybrid PG1159 stars. We present preliminary results of an on-going spectral analysis by means of NLTE model-atmosphere techniques based on UV spectra obtained with FUSE, HST/GHRS, and IUE as well as on optical observations.

astro-ph.SR↗

arXiv2010

Spectral Analyses Of The Hottest White Dwarfs: Grids Of Spectral Energy Distributions For Extremely Hot, Compact Stars In The Framework Of The Virtual Observatory

Present X-ray missions like Chandra and XMM-Newton provide high-resolution and high-S/N observations of extremely hot white dwarfs, e.g. burst spectra of novae. Their analysis requires adequate Non-LTE model atmospheres. The Tübingen Non-LTE Model-Atmosphere Package TMAP can calculate such model atmospheres and spectral energy distributions at a high level of sophistication. In the framework of the Virtual Observatory, the German Astrophysical Virtual Observatory (GAVO) offers TheoSSA, a Virtual Observatory (VO) service that provides easy access to theoretical SEDs. We present a new grid of SEDs, that is calculated in the parameter range of novae and supersoft X-ray sources.

astro-ph.SR↗