Institut für Astronomie und Astrophysik Abteilung Astronomie Sand 1, D-72076 Tübingen, Germany

Stellar Atmospheres Group - NLTE Spectral Analysis of Hot Stars

Abstract

Our NLTE group analyses post-AGB stars (AGB = Asymptotic Giant Branch). These stars (including the helium-rich PG 1159 stars and DO White Dwarfs) are at their hottest stage of evolution with effective temperatures up to 180 000 K. The analysis of their photospheric parameters (e.g. effective temperature, surface gravity, chemical composition, mass, luminosity) is necessary to compare with evolutionary theory in order to improve our picture of post-AGB evolution.

The analyses are based on spectra which we obtained with various ground-based telescopes (e.g. of the European Southern Observatory at La Silla, Chile, and of the MPG at Calar Alto, Spain) as well as on spectra taken by satellites (e.g. Hubble Space Telescope, ROSAT, EUVE, ORFEUS).

State-of-the-art Non-LTE (LTE = Local Thermodynamical Equilibrium) model atmosphere techniques are employed to calculate reliable models which consider all elements from hydrogen up to the iron group. Due to NLTE conditions, we have to solve simultaneously the statistical equations (for the atomic level populations) and the radiation transfer equations under the constraints of hydrostatic and radiative equilibrium. Our NLTE code is based on the so-called Accelerated Lambda Iteration (ALI) method and is able to account for line blanketing by metals.

[Home Page] [Stellar Atmospheres Group] [Quick Reference] [Feedback]

For further informations, please contact Klaus Werner Jochen Deetjen Last updated 02 Apr 2003