PHY242: Astronomical Spectroscopy

PHY242: Astronomical Spectroscopy#

These notes have been produced by Prof Paul Crowther (Hicks E43) and are intended to support and complement (not replace) lectures for PHY242, Astronomical spectroscopy. The notebook version converted from the original LaTeX notes. PHY242 is intended to build on material provided in PHY104 (Introduction to Astrophysics), complement aspects of PHY241 (Observational Astronomy) and PHY216 (Galaxies) and provide a link to more advanced material in PHY305 (Stellar Atmospheres). This course provides an overview of astronomical spectroscopy, covering how spectrographs work, the nature of emission line spectra, atomic physics for astrophysics and how spectroscopy can be applied to nebulae, involving the use of specialist software for spectral analysis, There are 5 topics covered in PHY242 across 13 lectures. These are as follows

Chapter 1: Introduction (1 lecture)

Chapter 2: Spectrographs (4 lectures, 1 problem class)

Chapter 3: Atomic physics (3 lectures, 1 problem class)

Chapter 4: Interstellar medium (1 lecture)

Chapter 5: Ionized nebulae (4 lectures, 1 problem class)

plus worked examples at the end of each chapter, together with symbols and common nebular lines at the end of the notes.

Learning outcomes#

Key learning outcomes from PHY242 are as follows:

  • Understand and apply the impact of distance in an expanding universe on measure spectral quantities (e.g. Doppler shifts)

  • Describe the optical layout of spectrographs, and explain the purpose of different components

  • Derive, calculate and use appropriate optical quantities related to spectrographs

  • Recognise and define key characteristics of spectral data

  • Describe the key steps involved with data reduction of spectroscopic observations (new in 2023/24)

  • Predict, describe and explain the energy levels of H and H-like ions, and understand their correspondence with quantum numbers

  • Know and apply selection rules for transitions between quantum states for simple and complex atoms

  • Know the difference between permitted, semi-forbidden and forbidden lines.

  • Understand radiatively and collisionally excited levels in the two level approximation, including the origin of emission lines in the coronal approximation (new in 2023/24)

  • Recognise and define key properties of the interstellar medium (new in 2023/24)

  • Understand how gas is heated in HII regions and derive an expression for the Strömgren radius

  • Understand why forbidden lines are key coolants in HII regions

  • Understand and apply nebular diagnostics for density, temperature, extinction and abundances in HII regions

  • Understand differences between HII regions, planetary nebulae, shock ionized regions and nebulae ionized by Active Galactic Nuclei.

The following topics are not examinable

  • Details of multi object and integral field spectrographs

  • Details of absorption lines, including optical depth and radiative transfer effects (new in 2023/24)

  • Molecular astrophysics

Key equations from PHY242 that you are expected to know are provided in the Assessment and Feedback folder of the Blackboard site.

Contents