atomic processes in gaseous nebulae
DESCRIPTION
Atomic Processes in Gaseous Nebulae. Andri Prozesky MSc Student Unisa Supervised by Prof. D. P. Smits. Outline. Introduction Interaction of Light and Matter Previous Models Implementation of the Model. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
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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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