This page describes astrophysics experiments available to Third Year students studying physics at the University of Oxford. All experiments are computer based and carried out individually using a Mac OS-X personal computer in the Astrophysics Laboratory which is situated on Level 2 of the Denys Wilkinson Building. Space is currently available for twenty or more students to carry out practicals.
Four different experiments are currently available. Additional experiments are planned and will be announced as they become available. Experiments making use of the Phillip Wetton Telescope (PWT) are also planned and are to be announced on this page once the telescope, now moved to its new location on the Denys Wilkinson Building Lift Shaft, has some further correcions made to its polar axis alignment.
One or two of the available experiments should be performed during Michaelmas Term or during the first four weeks of Trinity Term. Each experiment is expected to take two days to complete. The scheduled hours during which experiments may be carried out are 10:00 - 17:00 on Mondays and Tuesdays, although facilities of the Astrophysics Laboratory may be used on other days and at other times (during Michaelmas Term and Trinity Term only) by prior arrangement. In Hilary Term, all computers in the Astrophysics Laboratory are reserved for those doing Fourth Year Projects.
Mac OS-X machines are available in the Astrophysics Laboratory for the use, on a first come first served basis, of those performing experiments. Astrophysics Laboratory machines may also be accessed, with a secure shell, using computers elsewhere in the University and Colleges. If you do not need to discuss your progress with a demonstrator, you are encouraged to work elsewhere so that Astrophysics Laboratory facilities can be used by your colleagues requiring the services of a demonstrator.
It will be necessary to familiarise yourself with UNIX using the locally produced tutorial at least to the point where you can manipulate files and directories. An alternative tutorial is also available and the CERN UNIX User Guide has proved to be very useful. Learning UNIX will help you to make a good start with your astrophysics Fourth Year Project should you choose to do one.
It will also be necessary to create and modify text files, a task usually accomplished with an editor. The editor of choice in Astrophysics is emacs which is an extraordinarily powerful editor, well worth learning to use if you intent to undertake research in astrophysics.
There are a number of pages on the World Wide Web (WWW) that will help you carry out experiments listed here. Most of the important astronomical literature, dating back to the Nineteenth Century, has been scanned and made available for reading and downloading at the NASA Astrophysics Data System. References and data for all stellar (and a few non-stellar) objects studied can be obtained from the SIMBAD Astronomical Database. The Los Alamos National Laboratory hosts a preprint server from which the latest research results can be obtained; copies of papers are often deposited here so that they are available to the community before publication.
A large variety of astronomical software is available on the WWW although all
programs that are needed for experiments described here are supplied and ready
for use. Nonetheless, the sites hosted by the
Space Telescope Science Institute
and the
Berkeley Illinois Maryland Association
are well worth looking at for future reference.
A program needed for several of the experiments listed below is DIPSO, for which
an online
User Guide
is available.
Experiments available for the Academic Year 2007/8 are as listed below:
A specific intensity or integrated flux solar spectrum is supplied along with an interactive spectrum synthesis code and model stellar atmosphere. The element whose abundance is required is obtained by matching observed and synthetic line profiles, calculated on the basis of chosen atomic data, microturbulent velocity and lines to be fitted. The classical spectrum synthesis method makes certain assumptions which limits the accuracy of determined abundances and these need to be considered in making an assessment of the results obtained. Atomic data will be needed for this experiment and the site hosted by Harvard is a good place to start looking. An excellent introduction to radiation transfer in stellar atmospheres is given in Rob Rutten's lecture notes which forms the basis of his thirty lecture course given at the University of Utrecht. Click here for a copy of the script describing this experiment.
An Hertzsprung-Russell (HR) Diagram of a globular cluster having a well-defined Main Sequence turn-off is supplied. With theoretical isochrones the age of the cluster, its distance, interstellar reddening and metallicity are determined from a fit to the Main Sequence turn-off and shape of the Giant Branch. A stellar evolution code is then used to compute an evolution track for a star of the appropriate mass and metallicity, in order to verify the age estimate. Comparison of the Globular Cluster age with possible ages of the Universe for assumed geometries, enables the plausibility of those geometries to be considered. Click here for further details.
Radial velocity and light curves (in two different filters) are supplied for an eclipsing binary star. After determining the period, a light and radial velocity curve synthesis program is used to determine masses, radii and temperatures of both stars in the binary; these are refinements to preliminary estimates made by hand using the assumption of a circular orbit whose plane lies in the line of sight. The final part of the practical is to compare results obtained with those found in the literature and to discuss the past and future evolution of both stars. Click here for further details.
The luminous red galaxy SDSS J094656+100652.8 is a never-before-seen optical alignment, in space discovered by the Hubble Space Telescope; two distant galaxies are strung directly behind a foreground massive galaxy which gravitationally deflects their light towards an observer on Earth who sees two almost complete Einstein Rings. The aim of the experiment here is to measure the angular radii of both Einstein rings and obtain two independent mass estimates for the lensing luminous red galaxy in the foreground. Click here for further details.
The aim of this experiment is to determine constraints on the values of cosmological parameters by statistical analysis of the "Hubble diagram" for a sample of type Ia supernovae. This analysis is one of the key pieces of evidence in favour of a non-zero "cosmological constant" or "dark energy", which leads to an acceleration of the expansion of the universe. We will use the latest publicly-available data to derive the best-fitting values of the energy density in matter and in "dark energy", together with the statistical uncertainties on those values. Click here for further details.
There is some overlap with material provided in lectures. The overlap is not complete, however, and this is regarded as a healthy state of affairs provided the balance is about right. Having attempted one or more of the experiments, any thoughts that you may have are welcome; these can be given anonymously if you prefer.
Last update: 2012 October 22nd @ 17:18 BST