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Physics 320: Astronomy and Astrophysics – Lecture IX

Physics 320: Astronomy and Astrophysics – Lecture IX. Carsten Denker Physics Department Center for Solar–Terrestrial Research. Problem 9.1. Problem 9.2. Problem 9.7. Stellar Atmospheres. The Description of the Radiation Field Stellar Opacity Radiative Transfer

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Physics 320: Astronomy and Astrophysics – Lecture IX

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  1. Physics 320: Astronomy and Astrophysics – Lecture IX Carsten Denker Physics Department Center for Solar–Terrestrial Research

  2. Problem 9.1 NJIT Center for Solar-Terrestrial Research

  3. Problem 9.2 NJIT Center for Solar-Terrestrial Research

  4. Problem 9.7 NJIT Center for Solar-Terrestrial Research

  5. Stellar Atmospheres • The Description of the Radiation Field • Stellar Opacity • Radiative Transfer • The Structure of Spectral Lines NJIT Center for Solar-Terrestrial Research

  6. Opacity Any process that removes photons from a beam of light will be called absorption. NJIT Center for Solar-Terrestrial Research

  7. Opacity (cont.) The optical depth may be thought of as the number of mean free paths from the original position to the surface, as measured along the ray’s path. NJIT Center for Solar-Terrestrial Research

  8. free–free absorption of a photon Photon Interactions • Bound–bound transitions • Bound–free absorption • Free–free absorption (bremsstrahlung) • Electron scattering NJIT Center for Solar-Terrestrial Research

  9. Continuum Opacity Photoionization of H– ions. The total opacity depends not only on the wavelength of the light being absorbed but also on the composition, density, and temperature of the stellar material.  Rosseland mean opacity NJIT Center for Solar-Terrestrial Research

  10. Emission Any process that adds photons to a beam of light will be called emission. NJIT Center for Solar-Terrestrial Research

  11. Limb Darkening Looking into a star at any angle, we always look back to an optical depth of about  = 2/3, as measured by a straight line back along the line–of–sight. NJIT Center for Solar-Terrestrial Research

  12. Radiative Transfer Equation NJIT Center for Solar-Terrestrial Research

  13. Radiative Transfer Equation (cont.) The intensity of the light tends to become equal to the local value of the source function. For the case of thermodynamic equilibrium, the source function is equal to the Planck function S = B. NJIT Center for Solar-Terrestrial Research

  14. Solving RTE NJIT Center for Solar-Terrestrial Research

  15. Solving RTE (cont.) NJIT Center for Solar-Terrestrial Research

  16. Eddington Approximation NJIT Center for Solar-Terrestrial Research

  17. Structure of Spectral Lines NJIT Center for Solar-Terrestrial Research

  18. Homework Class Project • Continue improving the PPT presentation. • Use the abstract from the previous assignment as a starting point for a PowerPoint presentation. • The PPT presentation should have between 5 and 10 slides. • Bring a print-out of the draft version to the next class as a discussion template for group work • Homework is due Wednesday November 5th, 2003 at the beginning of the lecture! • Exhibition name competition! NJIT Center for Solar-Terrestrial Research

  19. Homework • Homework is due Wednesday November 5th, 2003 at the beginning of the lecture! • Homework assignment: Problems 9.9, 9.12, and 9.13! • Late homework receives only half the credit! • The homework is group homework! • Homework should be handed in as a text document! NJIT Center for Solar-Terrestrial Research

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