Sim, Stuart Alan

Contact Email: sim@thphys.ox.ac.uk
Institute: Dept. of Physics (Theoretical Physics), Oxford
University
Presenting Thesis: Yes
Subject Area: Stellar Atmospheres, Circumstellar Material
Waveband: Ultraviolet
Technique: Spectroscopy
Presentation: Poster Display
Title: Partial redistribution in the hydrogen Lyman lines of late-type stars.
Abstract: The importance of partial redistribution (PRD) in the formation of the hydrogen Lyman $\alpha$ and $\beta$ lines will be discussed with reference to simple atmospheric models of several late-type stars at different evolutionary stages. Radiative transfer calculations have been performed using Carlsson's MULTI code which has been modified to include PRD by Hubeny & Lites, 1995, ApJ, 455, 376. The atmospheric models will be used to demonstrate the effects of PRD in hydrogen and to show explicitly that there is a rapid escalation in the importance of PRD effects in stars with surface gravity lower than the Sun. It will be shown that PRD predicts line profiles that are in significantly better agreement with observations than are those calculated using the assumption of complete redistribution and comparisons will be made with various approximate PRD techniques. The repercussions of PRD effects in hydrogen on the atmospheric properties (via the ionization balance in hydrogen) and the relevance of PRD to Fe II fluorescence will also be discussed.