The RAS - Blackwell Prize 1999
A large part of my thesis was concerned with a very recent technique to analyze solar oscillations. Helioseismology investigates the internal structure of the Sun by studying the oscillations of the solar surface. A particularly interesting example is the study of waves that travel from the front side (the side facing the Earth) of the Sun to the back side, where they are reflected and return to the front side. When the waves reflect off a sunspot they suffer a time delay. In my thesis research I have developed a technique which could reveal active regions on the back side of the Sun that are not directly observable. A discovery of antipodal activity by seismic methods would be an exciting advance of the power of helioseismology and would have important applications, for instance, in space weather forecasts.
Other parts of my thesis dealt with atomic physics in the solar interior and with the interaction between sound waves in the Sun and convection.
After my PhD I went on to a postdoctoral position at the Max-Planck-Institut fur Astrophysik in Munich, Germany.
My current research revolves around issues in astrophysical and computational fluid mechanics. I am concerned with problems on a wide range of scales - from the propagation of waves in the Sun to the dynamics of flows in galaxies and clusters of galaxies.
My main fields of research are:
1. Mixing in stars and hydrodynamical simulations of fluid instabilities
2. MHD simulations of radio galaxies
3. Simulations of turbulent flames in supernovae
4. Propagation of sound waves in the Sun and other stars
Most of these problems are attacked using hydrodynamical simulations which have only become feasible with recent advances in computer technology.
Dr Claire Price (Huxley School of the Environment, Imperial College)
In many areas of the world, the continental lithospheric upper mantle contains bright, continuous regionally extensive, seismic reflectors. Despite the increasingly common observation of such mantle reflectors on deep seismic profiles, their geologic significance and origin remain obscure. During my PhD research at Imperial College in London I obtained results from a series of seismic experiments acquired across two of the brightest of these reflectors the so-called Flannan and W-reflectors near the Orkney Isles of Scotland. The primary objective was to constrain the thickness and composition of the reflectors; ultimately the data revealed regionally extensive dipping and sub-horizontal slabs of high velocity (> 8.4 km/s), high density (>3500 kg/m3) and of several kilometres thickness (> 3km) entrained within otherwise unremarkable mantle. A new technique for determining the polarity of the mantle reflectors was developed during my research, which provided independent evidence to infer a positive acoustic impedance contrast for the reflectors. Further insights were gained from studying another deep mantle reflector in the Bothnian Bay and the Aleutian islands active subduction zone. In conclusion the geometry, physical properties and geological setting of the Flannan and W-reflectors suggest they represent fragments of eclogitic oceanic crust - a relict of subduction now preserved within the lower continental lithosphere. There is an intriguing possibility that diligent mapping of relict subduction zones such as the Flannan and W-reflector may improve our understanding of past continental dynamics.
Since completing my PhD studies in 1998 I have been working for Shell International Ltd. After a period of basic training in the Hague I was posted to the Dutch operating company NAM in the N.E. Netherlands. The Netherlands boasts prolific reserves of natural gas both on and off-shore and NAM is the largest operating company exploiting these reserves. I work as a reservoir geophysicist to provide quantitative interpretation services to the asset teams. My role is to reduce prospect risk and increase field productivity through the quantitative assessment of seismic data. In particular the use of AVO, seismic attributes and seismic inversion are key techniques used to predict rock properties and better define reservoir volumetrics and ultimate recovery of reserves.
Anna Vickery undertook research at the University of Edinburgh for her doctorate on the development of geophysical methods for the investigation of contaminated land. Electrical and electromagnetic surveys were designed to locate contaminant sources, pathways and discharge zones at two ex-oil distribution terminals in West Granton, Edinburgh. Anna's thesis focussed on innovative methods of processing geophysical data to ease interpretation by geophysicists and non-geophysicists alike. The data processing methods include techniques for refining maps of electromagnetic data, locating and removing the dominating effect of subsurface linear conductors (e.g. pipes) from apparent resistivity pseudosections, and the construction of pseudo three-dimensional resistivity models that at the Granton site aided the understanding of geological and hydrological controls on contaminant migration.
The research was carried out during the tenure of a Natural Environment Research Council studentship and the field work was conducted under contract to Edinburgh City Council and Lothian and Edinburgh Enterprise Limited.
Subsequent to completing her PhD, Anna began employment as a member of the technical staff at Reynolds Geo-Sciences Ltd (RGSL), located near Mold in North Wales. RGSL is a geological consultancy specialising in natural hazards and in geophysical investigations of the shallow subsurface. Anna undertakes numerous duties within the Geophysics division of the company including the design and supervision of geophysical surveys and subsequent data analysis and interpretation of the resulting data. She is also becoming increasingly involved in the design of technical training seminars and geophysics awareness courses offered by RGSL to a variety of audiences ranging from geophysical contractors to engineering and environmental consultants and local authorities.
The main area I developed through my doctoral research was the application of covariant methods in cosmic microwave background (CMB) physics. The CMB is thermal relic radiation of the hot big bang, and has an almost uniform temperature of 2.7K in all directions. The departures from exact isotropy are at the level of one part in one-hundred thousand, but provide arguably the cleanest probe of conditions in the early universe available to cosmologists. The physical processes responsible for the CMB anisotropies --- general relativistic hydrodynamics and radiative transport theory --- have been understood for many years, although there have been bouts of confusion due to gauge issues associated with the relativistic, perturbative description of a universe which is close to being homogeneous and isotropic. In my research I developed covariant tools for CMB research, which avoid these gauge issues, and which give a physically transparent, but still exact, description of CMB physics. Applying these tools to universes which are only linearly perturbed from homogeneous and isotropic models, I provided a streamlined perturbation theory which allows seamless calculation of the anisotropies for all types of perturbation (i.e. from density perturbations, vortical motions, and gravitational waves) about backgrounds with open, flat, or closed spatial geometries. The methods I worked on also provide an ideal starting point for the qualitative description of non-linear effects in the CMB.
In related work, I derived the first analytic results for the spectral distortions induced in the CMB by photons Compton scattering off relativistically moving electrons in galaxy clusters. These results now allow observers to take into account the effects of high electron temperatures and large bulk motions in a routine manner, without recourse to numerical techniques.
My doctoral research was carried out in the Astrophysics Group of the Department of Physics in the University of Cambridge, under the supervision of Dr Anthony Lasenby.
For my postdoctoral work I have stayed in the Astrophysics Group of the Department of Physics, University of Cambridge since completing my doctorate. I was awarded a three-year Research Fellowship from Queens' College, Cambridge starting in October 1998. In October 1999, I was appointed a lecturer on a fixed-term one year contract to cover the absence of Dr Anthony Lasenby who was awarded a Royal Society/Leverhulme Senior Fellowship. In October 2000 I was awarded a PPARC Postdoctoral Research Fellowship for three years. As well as conducting my own research and teaching, I supervised an M.Phil. student last year, and took on my first Ph.D. student this autumn.
My postdoctoral work has concentrated on the polarization of the CMB. The CMB is expected to be linearly polarized at the level of one part in one billion, but this is too small to have been detected to date (only upper limits exist). CMB polarization contains a wealth of additional cosmological information which is complementary to that contained in the temperature anisotropies. I have extended the methods developed in my doctoral thesis to provide a very convenient, covariant description of CMB polarization, and more generally of the transfer of polarized radiation in arbitrary spacetime geometries. In collaboration with Antony Lewis, then a graduate student in the Astrophysics Group, Cambridge, we implemented the formalism at the level of linear perturbation theory in an efficient, publicly available code, based on the widely-used CMBFAST code of Seljak and Zaldarriaga. Our code was the first to compute efficiently the temperature and polarization anisotropies in all possible almost-homogeneous and isotropic cosmological models. The code was downloaded by many groups, and has since been used in the headline-making analyses of the BOOMERanG and MAXIMA-1 balloon experiments.
As an outgrowth of the work on CMB polarization, I applied the exact, covariant methods to compute the polarization induced in the CMB by scattering of photons off electrons in galaxy clusters. The analytic expressions I derived were the first to allow for relativistic thermal and bulk motions, and to fully include the effects of the (primordial) temperature anisotropy of the CMB radiation incident on the cluster.
I am also actively involved in the construction of analysis and simulation algorithms for the ESA Planck satellite. The Planck mission will measure the CMB temperature and polarization anisotropies with unprecedented precision. I am an Associate of the Planck project and a member of the Cambridge Planck Analysis Centre (CPAC), which will be responsible for producing maps of the various astrophysical components that Planck will be sensitive to. In an international collaboration, I have worked on efficient techniques for computing the instrument response to incident polarized radiation, including the effects of stray-light in the side lobes of the instrument. I have also been actively involved in the development of a fully harmonic model for the analysis of Planck data (with several members of CPAC), which offers significant advantages over existing map-based techniques. Currently, I am working on assessing the impact of instrument systematics on the measurement of CMB polarization with Planck.
Understanding galaxy formation and evolution is one of present-day astronomy's greatest challenges. In my thesis research, carried out at the University of Durham, UK, I explored how observations of both local and very distant galaxies can be used to gain a better understanding of galaxy formation and evolution. In particular, I used optical and near-infrared luminosities in conjunction with state-of-the-art models to constrain the ages and chemical compositions of local spiral galaxies. I find that most of their properties are consistent with the proposition that the star formation rate is regulated primarily by the supply of gas, and is affected little by the mass of the galaxy.
In my subsequent research, carried out at Steward Observatory, in Tucson, Arizona, USA, I have extended this work in two directions. I have used our understanding of spiral galaxy evolution to limit the mass of stars in nearby spiral galaxies. These stellar mass estimates are combined with the observed dynamical mass estimates to place strong constraints on the mass of dark matter in these galaxies, which in turn powerfully constrains theories of galaxy formation. Another aspect of my research is the use of archival data to explore the effects of interstellar dust on indicators of recent star formation. When these data are combined with the optical and near-infrared brightnesses of galaxies as outlined above, this will provide powerful insight into galaxy evolution.
Dr Harald Kuntschner (University of Durham) Physics Dept., University of Durham, UK
In my Ph.D. thesis I investigated the ages and metal content of early-type galaxies in the nearby Fornax cluster. Using a high precision analysis of carefully selected absorption features in the optical wavelength range I found that: (1) elliptical galaxies were created early on in the history of the universe and their metallicities scale with their mass; (2) galaxies with a disk component show stellar populations with younger ages and a wide range of metallicities.
Following on from my Ph.D. research I stayed at Durham to investigate currently the stellar populations and dynamical make-up of early-type galaxies in different environments. One of my main projects here is the search for isolated elliptical galaxies. The analysis of their properties promises to give tight constraints on the type of cosmological models which are able to describe the general properties of our universe. Another main research interest of mine is focusing on the dynamics of individual galaxies. This type of research will give us insight into the underlying reasons of why galaxies have different shapes.