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Andri ProzeskyMSc StudentUnisaSupervised by Prof. D. P. Smits

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IntroductionInteraction of Light and MatterPrevious ModelsImplementation of the Model

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Spectral lines crucial to the study of low density matter in the UniverseRadio Recombination Lines (RRLs)

Electron captured into very high energy level and cascades downwards

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Optical lines well understoodRRLs discovered much laterCurrent modelling software not accurate in radio regimeResults from optical and radio observations inconsistent

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Objective of the project is to create plasma model relevant to radio regimeAchieved by

Not making unnecessary assumptions

Take all atomic processes into account

Calculation up to very high n (± 1000)

Accuracy takes precedence over fast computing

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Particles of plasma and photons interactCan deduce properties of the plasma by studying the resultant light

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Bound-Bound ProcessesAbsorption

Spontaneous emission

Stimulated emission

Bound-Free ProcessesPhoto-ionization

Radiative recombination

Stimulated recombination

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Free-Free ProcessesBremsstrahlung selfabsorption

Spontaneous emission

Stimulated emission

Collisional ProcessesCollisional transitions

Collisional ionization

Three-body recombination

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State of plasma defined by temperature and level populationsLevel populations expressed ito departure coefficients (bnl)

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Level populations in statistical equilibrium: (rate in) = (rate out)

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Gaseous nebulae have been modelled extensivelyReputable models:

Brocklehurst and Salem (1977), Gordon (1990)

Storey and Hummer (1995)

XSTAR

CLOUDY

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Limitations:Neglecting some processes

Do not consider high n levels

Do not consider l levels explicitly

Outdated methods

Ionizing spectrum not considered

Radiative transfer not properly considered

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Check validity of previous assumptionsExample: Assuming Baker & Menzel (1938) Case B

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Case B

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Case A

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Einstein A-values small for large n

Mean free path large

Lyman radiation will escape if mean free path > size of plasma

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Check validity of previous assumptionsExample: Assuming Baker & Menzel (1938) Case B

Relative importance of processes

Serve as accurate model for RRL studies

Extend atomic data to high n

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