Detailed knowledge of the hydrogen population structure is necessary for the interpretation of hydrogen recombination line (HRL) observations. Calculations of
hydrogen departure coefficients using a capture-collision-cascade type model with
the angular momentum quantum levels resolved that includes the effects of external radiation fields are presented. The stimulating processes are important at radio
frequencies and can influence level populations. Updated atomic rates and new numerical techniques with a solid mathematical basis have been incorporated into the
model to ensure convergence of the solution. My results differ from previous results
by up to 20 per cent. The effects on departure coefficients of continuum radiation
from dust, the cosmic microwave background, the stellar ionising radiation, and
free-free radiation are quantified.
Atomic hydrogen masers occur in recombination plasmas in sufficiently dense HII
regions. These HRL masers have been observed in a handful of objects to date and
the analysis of the atomic physics involved has been rudimentary. A new model of
HRL masers is presented which uses an nl-model to describe the atomic populations
interacting with free-free radiation from the plasma, and an escape probability
framework to deal with radiative transfer effects. The importance of including the
collisions between angular momentum quantum states and the free-free emission
in models of HRL masers is demonstrated. The model is used to describe the
general behaviour of radiative transfer of HRLs and to investigate the conditions
under which HRL masers form. The model results show good agreement with
observations collected over a broad range of frequencies. Theoretical predictions
are made regarding the ratio of recombination lines from the same upper quantum
level for these objects. / Physics / Ph. D. (Astronomy)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:uir.unisa.ac.za:10500/26505 |
| Date | January 2019 |
| Creators | Prozesky, Andri |
| Contributors | Smits, D. P. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1 online resource (v, 98 leaves) : illustrations, color graphs, application/pdf |
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