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Neutral hydrogen in the Galaxy

Neutral hydrogen in the Galaxy. Neutral hydrogen in the Galaxy. HII regions. Orion nebula Triangulum nebula . Interstellar extinction law. Dust in the Eagle nebula. Dust: reddening in colour-colour plot. Calculating E(B-V) from colour-colour plot.

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Neutral hydrogen in the Galaxy

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  1. Neutral hydrogen in the Galaxy

  2. Neutral hydrogen in the Galaxy

  3. HII regions Orion nebula Triangulum nebula

  4. Interstellar extinction law

  5. Dust in the Eagle nebula

  6. Dust: reddening in colour-colour plot

  7. Calculating E(B-V) from colour-colour plot Consider observations of a set of stars in the (U-B) vs (B-V) plane. The reddening vector will have a specific direction: which for Aλ 1/λ gives Using this, any star can be de-reddened back to the stellar locus, allowing both E(B-V) and spectral type to be determined

  8. Atmospheric Extinction

  9. HII regions Orion nebula Triangulum nebula

  10. HII region spectra Different HII regions can have very different ratios of emission line strengths.

  11. Temperature diagnostics

  12. OIII diagnostic temperatures

  13. Nebula temperatures (T/104)0.25 exp(-39000/Te) = 2.5x10-7 T*

  14. The Cooling Curve Volume emissivity ε = Λ(T) nH2

  15. Density diagnostics

  16. Shocks in the interstellar medium

  17. Discussion Question What would happen if the piston were moved faster than the sound speed of the gas? What properties would you expect to be conserved for material passing through the shock discontinuity? (With what complications?)

  18. Supernovae 1A as standard candles for cosmology • Light-curve stretch correlates with luminosity • Correcting for this gives distances accurate to ~5%

  19. Isothermal Shocks

  20. Shocks in the interstellar medium

  21. The Cooling Curve Volume emissivity ε = Λ(T) nH2

  22. Course Summary 1. Observational Astronomy - Quantifying light (flux density, intensity) - Magnitude system (m = m0 - 2.5 log10f) - Measuring distances (parallax) - Luminosities, absolute magnitudes - Stars as black bodies (L=4πR2Teff4) - Stellar classification (OBAFGKM) - Hertzsprung-Russell (colour-magnitude) diagram - Astronomical co-ordinates (Right ascension, Declination)

  23. Course Summary 2. Main sequence stars - Energy generation (nuclear fusion; tunnelling; pp/CNO) - Escape of light from a star (random walk diffusion process) - Equations of stellar structure (mass continuity, hydrostatic equilibrium, energy generation and radiative diffusion) - Simple solutions (dimensionless variables) - Explained observed main sequence properties (e.g. LM≈3). - Complication: convection - Upper and lower limits of the main sequence: radiation pressure (Eddington luminosity), and degeneracy pressure

  24. Course Summary 3. Degenerate stars - Later stages of stellar evolution (red giants etc; briefly) - Electron degeneracy pressure - Accurately with 6D density of states - Roughly, using the uncertainty principal - Fermi momentum - Maximum mass for White Dwarfs (Chandrasekhar limit) - Sizes, densities and ages of White Dwarfs - Neutron stars and black holes

  25. Course Summary 4. The interstellar medium - Its effect on starlight (extinction and reddening) - Photo-ionisation by stars, giving HII regions - Radiative recombination, and the Strömgren radius - Temperatures and densities from emission line ratios - Propagation of perturbations: sound waves - Shocks: derived conditions of the step-change - Supernova shocks: feed metals back in to new star formation

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