Physics 320: Astronomy and Astrophysics

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Physics 320 Astronomy and Astrophysics Lecture
IX

• Carsten Denker
• Physics Department
• Center for SolarTerrestrial Research

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Problem 9.1
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Problem 9.2
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Problem 9.7
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Stellar Atmospheres

• The Description of the Radiation Field
• Stellar Opacity
• Radiative Transfer
• The Structure of Spectral Lines

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Opacity
Any process that removes photons from a beam of
light will be called absorption.
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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 rays path.
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Photon Interactions

• Boundbound transitions
• Boundfree absorption
• Freefree absorption (bremsstrahlung)
• Electron scattering

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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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Emission
Any process that adds photons to a beam of light
will be called emission.
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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
lineofsight.
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Radiative Transfer Equation
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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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Solving RTE
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Solving RTE (cont.)
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Eddington Approximation
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Structure of Spectral Lines
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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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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!