The Physics of Nebulae and Stars 1
SCQF Level 10
Academic year(s): 2019-2020
SCOTCAT credits : 15
ECTS credits : 7
Level : SCQF Level 10
Availability restrictions: Not automatically available to General Degree students
This module introduces the physics of astrophysical plasmas, as found in stars and interstellar space, where interactions between matter and radiation play a dominant role. A variety of absorption, emission, and scattering processes are introduced to describe exchanges of energy and momentum, which link up in various contexts to control the state and motion of the matter, to regulate the flow of light through the matter, and to impress fingerprints on the emergent spectrum. The theory is developed in sufficient detail to illustrate how astronomers interpret observed spectra to infer physical properties of astrophysical plasmas. Applications are considered to photo-ionise nebulae, interstellar shocks, nova and supernova shells, accretion discs, quasar-absorption-line clouds, radio synchrotron jets, radio pulsars, and x-ray plasmas. Monte-Carlo computational techniques are introduced to model radiative transfer.
Pre-requisite(s): Before taking this module you must ( pass AS2001 or pass AS2101 ) and pass PH2011 and pass PH2012 and ( pass MT2001 or pass MT2501 and pass MT2503 ) and pass PH3081 or pass PH3082 or pass MT2003 or ( pass MT2506 and pass MT2507 )
Anti-requisite(s): You cannot take this module if you take AS4023 or take AS3015
Weekly contact: 3 lectures occasionally replaced by whole-group tutorials.
Scheduled learning hours: 32
Guided independent study hours: 118
As used by St Andrews: 2-hour Written Examination = 75%, Coursework = 25%
As defined by QAA
Written examinations : 75%
Practical examinations : 0%
Re-assessment: Oral Re-assessment, capped at grade 7
Module coordinator: Dr K Wood
Module teaching staff: Dr K Wood
The gas that lies between the stars takes many forms. From the dense, cold molecular clouds in which stars are conceived to the rarefied ionized plasma of HII regions, escaping photons carry information about their nature to distant parts of the Universe, a few of which contain astronomers. Astronomers unravel the nature of these gas clouds by catching photons whose last physical interaction was usually with an atom or ion in the cloud itself. The material with which the radiation last interacted imprints clues to its physical nature on this radiation. To find out the temperature, density, chemical abundance and ionization state of the cloud we must understand how matter behaves in a radiation field: how photons and inter-particle collisions can trigger transitions between different excitation and ionization states in atoms and molecules, and how these transitions create or destroy the photons that we eventually see.
Aims & Objectives
To present an introductory account of radiation transfer and its application to gaseous astrophysical systems, including
By the end of the module, students will have a comprehensive knowledge of the topics covered in the lectures and will be able to:
Definitions of basic radiant quantities. Opacity and emissivity. The equation of radiative transfer. Source function and optical depth. Black-body radiation and the diffusion approximation. Atomic and molecular processes: bound-bound, bound-free and free-free transitions, electron scattering, Boltzmann and Saha laws, the Einstein coefficients and their relation to emission and absorption coefficients and to blackbody radiation. Masers. Line-broadening mechanisms. Stromgren spheres, protoplanetary discs. Derivation of jump conditions across ionization fronts using conservation of mass, momentum and energy. Thermal equilibrium between ionization and cooling via photon escape in nebulae. Collisional cooling and detailed balance; hydrogen recombination spectrum in Case A and Case B; common line-ratio and radio diagnostics for nebular temperature and density. Rotational and vibrational spectra and selection rules in molecules. Monte Carlo radiation transfer, sampling from probability distributions, estimators for intensity moments of the radiation field, scattering codes.
Additional information on continuous assessment etc
Please note that the definitive comments on continuous assessment will be communicated within the module. This section is intended to give an indication of the likely breakdown and timing of the continuous assessment.
The 25% continuous assessment is expected to take the form of writing Monte Carlo radiation transfer computer programs, building on what is taught in class. This homework will be issued around week 5 with a deadline around two weeks later.
This module may not contain material that is part of the IOP “Core of Physics”, but does contribute to the wider and deeper learning expected in an accredited degree programme. The skills developed in this module, and others, contribute towards the requirements of the IOP “Graduate Skill Base”.
Please view University online record:
Please also read the general information in the School's honours handbook that is available via st-andrews.ac.uk/physics/staff_students/timetables.php.