This course concentrates on how the motions of particles, and the details of their radiation processes, affect observed astrophysical spectra. The emphasis is on the astrophysics of spectral line broadening, and the physical processes that can be probed using observations of these lines. The course covers a range of thermal effects in astrophysics, including thermal equilibrium and non-equilibrium, particle speed distributions and planetary atmospheres.
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The definition of a spectral line in term of a power spectrum. Time and frequency domains and the basic idea of a Fourier transform. Loss of information in a power pesctrum. The Doppler effect. Broadening of spectral lines as a consequence of an ensemble of emitters. Doppler broadening. Rotational broadening and its spectrum. Examples of the Sun, and Galaxy rotation curves. The velocity mapping of the Galaxy in H I.The H I line (1420 MHz) as an example of radio spectral line.
Pictures: [ Dopplergram of the Sun | HI
map of the Milky Way | Galactic rotation
Websites: [Fourier applet 1, Fourier applet 2, MDI homepage ]
Natural line widths
The spectrum of a classical damped harmonic oscillator as a function of its decay time. Spectral width and Lorentzian profiles. Quantum mechanical interpretation of natural width as the lifetime of an excited state, and its conection with the Heisenberg energy-time uncertainty relation. Oscillator strangths, allowed and forbidded transitions. Einstein A coefficient as a spontaneous emission rate. Line cooling from clouds.
|lecture notes:||Slides used for introduction (8)||1||2||3||4||5||6||7||8||9||10||11||12|
The Planck function
Blackbody radiation as a consequence of thermal population of modes. Oscillator statistics. The Planck function. Wien and Rayleigh-Jeans approximations. Planetary temperatures: Extension of A1 treatment. Factors influencing planetary temperature
Handouts:[blackbody curves and equations]
The recommended textbook for A2 is An Introduction to Modern Astrophysics, B W Carroll and D A Ostlie, Addison Wesley . If you are a physicist you will find that your thermal physics textbooks will help too!