(Course description last updated for academic year 2016-17).
Learning Outcomes and Assessment

The course is an entry to the observational and analysis techniques of astrophysics and cosmology.  It outlines the underlying physics and studies example issues at the forefront of current research.  It is about exactly what limits what we know about the Universe and why.

 

The material is not covered in the Relativistic Astrophysics and Cosmology major option and so complements that option, and by the same token it doesn’t matter if you didn’t attend that option.  Indeed, it doesn’t matter whether or not you took the Astrophysical Fluids option last year nor how well you fared with the Relativity course.

 

Synopsis

Introduction:  Some basics.  The mass-radius relationship of everything. 

Observational design and statistical inference:  The replacing of lab measurements by the study of samples of objects.  Hidden correlations and Malmquist bias.  Eddington bias.  Completeness and false detection.  Selection effects: the critical problems in trying to measure apparently simple things such as the space density of quasars as a function of their power outputs and the space density of  planets as a function of their masses.  Bayesian methods including Bayesian evidence and the need for these as you push the forefronts.  Lutz-Kelker bias and the influence of priors.

Example:  We “know” from supernovae observations that the cosmic expansion is accelerating; the course looks at what this is based on, the assumptions and the uncertainties – which may surprise you.

Probes of the Universe:  Black-body radiation (stars and cosmic microwave background (CMB)), brightness temperature.  Radio and X-ray Bremsstrahlung.  Self absorption.  Photoionisation, permitted and forbidden UV-optical-IR emission lines.  Production of emission and absorption lines across the wavebands.  Absorption features in the spectra of high-redshift quasars.  Measuring temperatures and densities.  Measuring the sizes of objects that are observationally unresolved…

Fundamental requirements and limitations:  range of angular scale; spectral resolution and matched filtering; shot noise, Johnson noise, coherent and incoherent addition, sensitivity; systematics.

Astronomical measurement techniques:  Traditional collectors.  Interferometry: coupling to angular scales, resolving out, sensitivity, clever removal of many systematics, coherence length and path compensation.  Following the electric field of the incident radiation versus photon counting.  Sky noise, instrument noise, and the hidden problem of surface brightness.  Charge coupled devices.

Example:  Imaging the CMB – pros and cons of interferometric methods, confusing foregrounds, handling of systematics, the Sunyaev-Zel’dovich effect and its distance independence.

The effect of the atmosphere:  The atmosphere causes high-resolution images in both optical and radio (for different reasons) to jiggle about, limiting sensitivity as well as resolution.  The course considers these phase effects and ways that, without going into space, can overcome them.

Example 1:  Adaptive optics – methods of wavefront sensing, design of optimum systems.

Example 2:  Optical interferometry – the direct imaging of stars and nearby active galactic nuclei despite the jiggling phase.

BOOKS

Most of the material hasn’t entered textbooks yet, and certainly no book covers the course.  The course is therefore designed to be stand-alone, but references are given in the course where useful.

Course section:

Other Information

For more information, visit the Course WebsiteWeblink

Staff
Dr Richard SaundersLecturer