Course
2023-2024

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

## Description

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.

## Course objectives

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.

## Timetable

You will find the timetables for all courses and degree programmes of Leiden University in the tool MyTimetable (login). Any teaching activities that you have sucessfully registered for in MyStudyMap will automatically be displayed in MyTimeTable. Any timetables that you add manually, will be saved and automatically displayed the next time you sign in.

MyTimetable allows you to integrate your timetable with your calendar apps such as Outlook, Google Calendar, Apple Calendar and other calendar apps on your smartphone. Any timetable changes will be automatically synced with your calendar. If you wish, you can also receive an email notification of the change. You can turn notifications on in ‘Settings’ (after login).

For more information, watch the video or go the the 'help-page' in MyTimetable. Please note: Joint Degree students Leiden/Delft have to merge their two different timetables into one. This video explains how to do this.

## Mode of instruction

• Lectures

• Exercise classes

## Assessment method

• Radiative Processes in Astrophysics, Rybicki & Lightman, ISBN 9780471827597 (required). The electronic version of this book is also available in the University library.

## Registration

From the academic year 2022-2023 on every student has to register for courses with the new enrollment tool MyStudyMap. There are two registration periods per year: registration for the fall semester opens in July and registration for the spring semester opens in December. Please see this page for more information.

Please note that it is compulsory to both preregister and confirm your participation for every exam and retake. Not being registered for a course means that you are not allowed to participate in the final exam of the course. Confirming your exam participation is possible until ten days before the exam.

Extensive FAQ's on MyStudymap can be found here.

## Contact

Lecturer: Prof. Dr. M (Michiel) Hogerheijde

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