Knowledge of calculus, special relativity and electromagnetism at the bachelor’s level is required. In terms of the Leiden curriculum, the prerequisites for this course are Analyse 2 or Analyse 2 NA, Introductie Moderne Natuurkunde, Classical Electrodynamics and Inleiding Astrofysica
The main goal of this course is to understand and recognize the different ways matter and light interact in an astrophysical context, including emission, scattering and absorption. This allows us to physically interpret the light that we observe from astrophysical sources. Throughout the course, we will rely on mathematical derivations to gain a deep understanding of the processes involved.
We will define a number of fundamental concepts necessary to unambiguously discuss radiation. This is followed by the introduction of the basic equation of radiative transfer, which describes how radiation changes as it traverses a medium. In the remainder of the course we will keep coming back to this equation. This part will be concluded with a discussion of a few methods to solve the equation of radiative transfer.
Then we take a step back and examine the relation between the concepts introduced earlier. We will find that radiation can only be generated and changed by accelerating electrical charges, and we will deduce several fundamental relations. We will also investigate how the emission of radiation is changed when the emitting particle is moving relativistically (beaming).
This is followed by a discussion of three important mechanisms to produce continuous radiation, i.e., radiation that changes only weakly with wavelength. All these processes involve freely moving electrons: in an ionized plasma (Bremsstrahlung or free-free emission); in the presence of magnetic fields (cyclotron and synchrotron emission, depending on whether the electrons move non-relativistically or relativistically); and the interaction between relativistic electrons and photons (inverse Compton scattering).
We will conclude the lecture series with the production of radiation at discrete wavelengths, i.e. spectral lines. These processes involve electrons bound to atoms or molecules.
The main objective of this course is to be able to physically interpret a spectrum from an astrophysical source, based primarily on its continuum emission and to a lesser extent on its spectral lines.
Upon completion of this course you will be able to:
Describe the physical processes through which radiation is emitted, changed or absorbed
Solve the equation of radiative transfer for a range of physical conditions
Construct a spectrum for a range of astrophysical sources including isothermal ionized clouds, stars and charged particles moving in magnetic fields
Physically interpret continuum spectra including free-free emission, synchrotron emission, inverse Compton radiation and Comptonized blackbody radiation, deducing source properties such as temperature, density and optical depth
Physically interpret spectral lines from single charged particles, simple atoms and diatomic molecules.
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Mode of instruction
Written exam (see Examination schedules bachelor Astronomy)
Homework assignments (bonus points)
Radiative Processes in Astrophysics, Rybicki & Lightman, ISBN 9780471827597 (required). The electronic version of this book is also available in the University library.
Radiative Processes in High Energy Astrophysics, Ghisellini, ISBN 9783319006123, (download here) optional
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Lecturer: Prof. Dr. M (Michiel) Hogerheijde