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Atomic Processes in Gaseous Nebulae

Study on interaction of light and matter in low-density gaseous nebulae to create a comprehensive plasma model. Analyzing spectral lines, radio recombination lines, and various atomic processes.

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Atomic Processes in Gaseous Nebulae

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  1. Atomic Processes in Gaseous Nebulae Andri Prozesky MSc Student Unisa Supervised by Prof. D. P. Smits

  2. Outline • Introduction • Interaction of Light and Matter • Previous Models • Implementation of the Model

  3. Introduction • Spectral lines crucial to the study of low density matter in the Universe • Radio Recombination Lines (RRLs) • Electron captured into very high energy level and cascades downwards

  4. Introduction • Optical lines well understood • RRLs discovered much later • Current modelling software not accurate in radio regime • Results from optical and radio observations inconsistent

  5. Introduction • Objective of the project is to create plasma model relevant to radio regime • Achieved by • Not making unnecessary assumptions • Take all atomic processes into account • Calculation up to very high n (± 1000) • Accuracy takes precedence over fast computing

  6. Interaction of Matter and Light • Particles of plasma and photons interact • Can deduce properties of the plasma by studying the resultant light

  7. Interaction of Matter and Light • Bound-Bound Processes • Absorption • Spontaneous emission • Stimulated emission • Bound-Free Processes • Photo-ionization • Radiative recombination • Stimulated recombination

  8. Interaction of Matter and Light • Free-Free Processes • Bremsstrahlung selfabsorption • Spontaneous emission • Stimulated emission • Collisional Processes • Collisional transitions • Collisional ionization • Three-body recombination

  9. Interaction of Light and Matter • State of plasma defined by temperature and level populations • Level populations expressed ito departure coefficients (bnl)

  10. Interaction of Light and Matter • Level populations in statistical equilibrium: (rate in) = (rate out)

  11. Previous Models • Gaseous nebulae have been modelled extensively • Reputable models: • Brocklehurst and Salem (1977), Gordon (1990) • Storey and Hummer (1995) • XSTAR • CLOUDY

  12. Previous Models • 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

  13. Implementation of the Model • Check validity of previous assumptions • Example: Assuming Baker & Menzel (1938) Case B

  14. Implementation of the Model

  15. Implementation of the Model Case B

  16. Implementation of the Model Case A

  17. Implementation of the Model • Einstein A-values small for large n • Mean free path large • Lyman radiation will escape if mean free path > size of plasma

  18. Implementation of the Model

  19. Implementation of the Model

  20. Implementation of the Model • Check validity of previous assumptions • Example: Assuming Baker & Menzel (1938) Case B • Relative importance of processes • Serve as accurate model for RRL studies • Extend atomic data to high n

  21. Thank you

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