Atomic Processes in Gaseous Nebulae
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Transcript of Atomic Processes in Gaseous Nebulae
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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Outdated methods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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