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Atomic Processes in Gaseous Nebulae

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.

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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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