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
October 29th, 2003

3. Problem 9.2 NJIT Center for Solar-Terrestrial Research
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4. Problem 9.7 NJIT Center for Solar-Terrestrial Research
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5. Stellar Atmospheres The Description of the Radiation Field
Stellar Opacity
Radiative Transfer
The Structure of Spectral Lines
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6. Opacity
Any process that removes photons from a beam of light will be called absorption.
NJIT Center for Solar-Terrestrial Research
October 29th, 2003

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.
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October 29th, 2003

8. Photon Interactions Bound–bound transitions Bound–free absorption
Free–free absorption (bremsstrahlung)
Electron scattering
free–free absorption of a photon
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October 29th, 2003

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
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10. Emission
Any process that adds photons to a beam of light will be called emission.
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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.
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12. Radiative Transfer Equation
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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.
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14. Solving RTE NJIT Center for Solar-Terrestrial Research
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15. Solving RTE (cont.) NJIT Center for Solar-Terrestrial Research
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16. Eddington Approximation
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17. Structure of Spectral Lines
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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!
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October 29th, 2003

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
October 29th, 2003