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X-ray and Observational Astronomy Group

           Postgraduate Opportunities 2005

The X-ray and Observational Astronomy Group are now seeking applications for PhD studentships to begin in October 2005. These studentships will be fully funded by the Particle Physics and Astronomy Research Council. Applicants must meet PPARC's eligibility requirements. We also welcome applications from international students who have already arranged their own funding, and from self-funded students of all nationalities. For further information  on applying, and application forms, please visit the Departmental Postgraduate Admissions page. Please direct any questions to XROA's postgraduate admissions tutor, Dr. Matt Burleigh .

We are currently specifically seeking to hire students to work on the following projects:

The X-ray Properties of Normal Spiral Galaxies
The composition and structure of white dwarf stars
Exploiting the WASP data flow
Gamma Ray Bursts

Potential applicants, especially those who are able to support themselves, may also wish to review the other research areas within XROA. PhD students at Leicester typically have the opportunity to work on datasets from satellites such as XMM-Newton,Chandra, Swift , FUSE and HST, Galex, and Spitzer, and ground-based facilities such as Gemini , the ESO Very Large Telescope, WASP, the Isaac Newton Group of telescopes on La Palma, the Anglo-Australian Telescope (AAT), and the UK Infra-Red Telescope (UKIRT) on Hawaii.

The X-ray Properties of Normal Spiral  Galaxies

Supervisor: Prof. Bob Warwick

The X-ray band can provide crucial diagnostics in our quest to understand the structure, composition  and evolution of normal galaxies. Fortunately the new generation of X-ray missions, XMM-Newton and Chandra, provide highly appropriate tools for such studies.
The focus of this project is the study of the high energy properties of normal spiral galaxies. Since the 1970's we have known that discrete X-ray sources contribute significantly to the overall X-ray luminosity of spiral galaxies, along with hot diffuse gas, and in some cases an active galactic nucleus. The types of discrete X-ray source encountered in significant numbers in late-type galaxies include low-mass and high-mass X-ray binaries, supersoft sources, ultraluminous X-ray sources and supernova remnants. In the case of nearby galaxies there has been considerable recent progress in defining the form of the luminosity function of bright discrete sources and in the study the properties of individual highly luminous objects. However, much less is known about fainter source populations and the nature and origin of the hot diffuse emission which is invariably seen in the inner disk and central regions of spiral galaxies including our own Galaxy.
The initial task will be to carry out a comparative study of a sample of face-on spiral galaxies for which both XMM-Newton and Chandra are available. The objective will be to develop a coherent picture of the spatial distribution, nature and likely origin of the contributing X-ray components of nearby galaxies. In this context the properties of our own Galaxy will provide a useful template against which other galaxies can be compared.

The composition and structure of white dwarf atmospheres

Supervisor: Prof. Martin A. Barstow

White Dwarfs are among the oldest objects in the galaxy and are the remnants of the earliest phases of star formation. Study of the distribution and physical characteristics of the white dwarf population is an essential part of understanding the early history of the galaxy. In addition, observing white dwarfs allows us to address a number of problems concerning the latter stages of stellar evolution, particularly those of mass loss and cessation of nuclear fusion during the post Red Giant phases, and study the behaviour of matter under conditions of extreme temperature and pressure which cannot be reproduced in a laboratory.
An active and successful programme of research already exists in the department based on the use of optical, ultraviolet and extreme ultraviolet spectra to study the composition and structure of white dwarf atmospheres. In the recent past we have had extremely successful observational programmes with satellites such as EUVE , FUSE and HST, as well as with many ground-based telescopes. Analysis and interpretation of these datasets has relies on the ability to interpret the observational data with theoretical models. We generate synthetic spectra from state-of-the-art model atmosphere codes, and then compare the results with data from real stars. Gradually, it is possible to build up a self-consistent atmospheric model which describes all the spectral features observed in white dwarf atmospheres, allowing us to determine the composition and structure of the stellar envelopes. Our aim is to map out the dependence of element abundances on stellar temperature, mass and environment. Thus we will establish the routes through which white dwarfs are formed and understand their subsequent evolution. The majority of this work will be performed in the near future using new computational facilities available at Leicester. A ~£1M state-of-the art supercomputer, partly dedicated to the stellar atmosphere work, will become available early in 2005.
Recently, we have been awarded substantial amounts of observing time with NASA's Galex satellite to continue our UV studies of hot white dwarfs. The main aim of this PhD will be to analyse and interpret these datasets. In particular, we will be looking for white dwarfs hidden in binary systems with solar-like main sequence stars, analagous to the bright star Sirius and its white dwarf companion. These white dwarfs cannot be observed in the optical since they are hidden by the overwhelming brightness of their main sequence partners. But in the ultraviolet the white dwarfs are the brighter component of the binary system, and can be found, observed and studied. One of our Galex programmes is designed to show that the presence of such binaries will solve the problem of the "missing" white dwarfs in open clusters such as Praesepe. We are also looking for such binaries in the field, including in the large area surveys being undertaken by Galex.
Finally, we have also begun to extend our studies of white dwarfs into the infra-red and we plan to develop observational programmes for the Spitzer IR space telescope and, eventually, the James Webb Space Telescope (the replacement for Hubble). These telescopes may reveal the presence of brown dwarf and massive planetary companions to nearby white dwarfs.


Exploiting the WASP data flow

Supervisor: Dr. Peter Wheatley

Leicester XROA is a partner in the Wide Angle Search for Planets (WASP) project, which is building wide-field robotic telescopes in La Palma and South Africa. The primary science goal is to discover hundreds of hot extra-solar planets using the transit method. WASP will also be sensitive to variable and transient objects over most of the sky (to V~15).
The first instrument (SuperWASP-1) was operated for six months during 2004 collecting ~10TB of imaging data with five CCD cameras. Release of the production version of the SuperWASP pipeline is scheduled for Jan 2005, and the full set of processed data will be available by April 2005. From Spring/Summer 2005, both instruments will be operated with a total of sixteen cameras.
The only complete copy of the processed WASP data will be stored at Leicester. This puts us in a strong position to take the lead in mining the WASP dataset.
A WASP PhD student at Leicester could work in a number of different science areas. Here I list the most important topics. The precise balance of the programme will depend on the strengths and interests of the student and our science priorities one year from now.

Planet Hunting. Finding and confirming extra-solar planet transits is a mammoth task that is being organised on a cooperative basis by the WASP consortium. The allocation of a Leicester PhD student to this area will allow us to play a full role in this high profile area. With local access to the WASP archive, we would expect our student to search for transits by applying established transit-search algorithms to the full data set. This experience might also lead us to develop new algorithms.With our e-science student, David Brett, we have already pioneered the use of neural networks for the analysis of time series data. Our WASP student could build on this to apply neural networks to the automated classification of transit candidates. This would allow the WASP consortium to prioritise the follow-up of individual transit candidates, thereby increasing the efficiency of planet discoveries. Our student could also contribute to the programme of follow-up observations of transit candidates with larger telescopes. Imaging and spectroscopy is required to weed out eclipsing binary stars that can mimic transits under certain circumstances. Photometry is required to confirm transits and measure their precise profile. WHT time has already been allocated to this programme, and we are currently negotiating access to 1m-class telescopes around the world.

Swift GRB follow up. The SuperWASP instruments will respond to Swift GRB alerts ~3 times faster than the Liverpool and Faulkes Telescopes, thereby making important early observations. Our WASP student could contribute to the timely analysis of these data, possibly linking into parallel GRB follow-up work in XROA.

Optical Transients. WASP will be sensitive to very rare optical transients. These might include orphan afterglows of GRBs, shock-breakout in supernovae, and accretion flares from supermassive black holes in normal galaxies (a more detailed document is available on request). At present, WASP detections that cannot be associated with known objects are read into a separate large database, also held only at Leicester. Local access to this rich resource presents an opportunity to take the science lead in this area. Our student could work to mine this database for coherent transients, separating real events from artefacts of the automated processing. Once the data are sufficiently well understood, we could automate this process, allowing a real-time search for optical transients at the telescope.

Gamma-Ray Bursts

Supervisors: Dr. Paul O'Brien, Dr. Richard Willingale, Dr. Julian Osborne

Gamma-ray bursts (GRBs) are among the most intriguing objects in the Universe. Thought to be powered by the death of a star, a GRB can for a brief moment outshine an entire galaxy (and the entire Universe in gamma rays). To understand GRBs requires high-quality data for a large sample. In particular, we need to probe the X-ray emission which provide unique astrophysical information on both the progenitor and the surroundings. The advent of the Swift GRB mission (launched 2004 November 20) provides an ideal opportunity for the XROA group to expand its activities in the GRB area. The group also has unique access to ground-based data through the provision of optical spectrographs for the Faulkes Telescopes and is heavily involved in ground-based follow-up using a number of telescopes (e.g. ESO, La Palma, UKIRT etc.).
The student will work on GRB data from Swift, XMM-Newton, the Faulkes Telescopes and other ground-based facilities. The student would concentrate on analysis of ground-based data working with the Leicester Swift team and taking advantage of the local theoretical expertise. Their prime task would be to develop a comprehensive understanding of the optical/UV properties of the entire Swift GRB sample, including both long and short bursts.

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Last updated: 2004 Dec 13th by Matt Burleigh mbu |at| star.le.ac.uk