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.
Top
The composition and structure of white
dwarf atmospheres
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.
Top
Exploiting
the WASP data flow
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.
Top
Gamma-Ray Bursts
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.
Top
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