UCL Astronomy Group PhD Projects

General information on UCL postgraduate admissions is available on the Web; note, in particular, the availability of an application form on-line. Students eligible for support from PPARC may wish to check their site. Finally, there are Web pages for the Department and for the Astronomy Group.

For general information on postgraduate admissions in the Department of Physics & Astronomy, contact Dr Alex Shluger ( a.shluger@ucl.ac.uk; phone +44 (0) 20 7679 1312, fax +44 (0) 20 7679 7145). It is also possible to submit enquiries on-line. Enquiries specifically concerning the astronomy programme, including arrangements for visits & interviews, should be directed to Professor Ian Howarth (idh@star.ucl.ac.uk) or Professor Mike Barlow (mjb@star.ucl.ac.uk).

The Department offers four postgraduate astronomy studentships funded by the Particle Physics and Astronomy Research Council (PPARC).Limited non-PPARC studentship funding may also be available - see below.

Notes for overseas applicants: PPARC rules do not permit the award to non-UK applicants of the maintenance allowance associated with a PPARC studentship (see the eligibility rules). Non-UK applicants seeking PPARC studentships to cover their fees should make clear their expected source of funds for maintenance.

The UCL Graduate School offers a small number of scholarships each year (College-wide), including `major' scholarships that cover both UK/EU fees and a maintenance allowance of £11,000 per year (2003 figures). General information about the UCL Graduate School scholarship scheme, including application forms and deadlines, can be found here.

Non-EU applicants, who are liable for a higher level of fees than EU students, can apply for Overseas Research Student (ORS) awards, which pay the difference between the fees levied for UK/EU applicants and those levied for applicants from the rest of the world. Applications for ORS awards are made via the Department to which the application for postgraduate study has been made. Applications for an ORS award to a given candidate cannot be made by more than one University in the UK. Please note that UCL's deadline for receipt of completed ORS applications is 7th April 2003. (More information on ORS awards.)

For information only, a selection of astronomy-related PhD projects that were offered in 2003 are listed below. Potential PhD projects with September 2004 start dates will be posted in mid-December 2003. For these projects, the normal minimum requirement for admission is a 2:i MSci, or equivalent (this is a mandatory requirement for PPARC studentships). The bulk of interviewing is expected to take place in late February to early March, so potential candidates are advised to submit their applications as soon as possible. Completed applications should be sent to Dr Alex Shluger, Dept. of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (and NOT to the College Admissions Office, as stated on the application form, as this can introduce unnecessary delays in processing).

Research topics on offer loosely fall into three broad (and inter-related) categories:

• Astrophysics;
• Atmospheric Physics (including planets and moons in our own Solar System and beyond);
• Astronomical Instrumentation.

Astrophysics

Star formation

Regions of high mass star formation: the aim of this project is to study the interaction of radiation and winds of newly formed stars on their environments. We use molecular emissions from transient remnants of dense gas left over from the star formation process to infer the properties of the pre-stellar gas, and hence learn something about the star-formation process for massive stars.

Regions of low mass star formation: we use observational data of molecular line emissions and continuum dust emissions from pre-stellar cores to infer the nature of the collapse process that leads to the formation of low mass stars. The aim is to distinguish between various models, and in particular to infor the role of magnetic fields.

Contact: Dr Jonathan Rawlings (jcr@star.ucl.ac.uk);
Dr Serena Viti (sv@star.ucl.ac.uk);
Professor David Williams (daw@star.ucl.ac.uk)

Extragalactic astrophysics

Emissions from molecules of various kinds and from dust are now detected from galaxies other than the Milky Way, even from galaxies at high redshift (z ~ 5). Evidently, nuclear chemistry was well advanced in the early Universe. However, conditions in these high redshift galaxies were quite different from those in the Milky Way: for example, the total and relative elemental abundances, the intensity and hardness of radiation fields, particle fluxes, interstellar gas densities may all be quite different. We can use the understanding we have Milky Way interstellar physics and chemistry to make models of the high redshift behaviour, and infer these basic galactic parameters. The aim of this study is to understand the history of star formation in the early Universe.

Contact: Dr Jonathan Rawlings (jcr@star.ucl.ac.uk);
Professor David Williams (daw@star.ucl.ac.uk)

The diffuse interstellar medium of the Milky Way Galaxy

The role of the diffuse neutral gas in the evolution of the Milky Way Galaxy is unclear. Is it a diluted remnant of denser molecular clouds, or is it gas in the process of contraction from a very tenuous intercloud state? What is the origin of the very small scale structure (~ 10 AU) now found along some lines of sight in diffuse clouds? We aim to use molecular astrophysics to address these questions. In addition, the extent of the population of very small dust grains or large molecules (polycyclic aromatic hydrocarbons) is unclear. A comprehensive model of the diffuse regions of our Galaxy is required; that is the aim of this study.

Contact: Dr Jonathan Rawlings (jcr@star.ucl.ac.uk);
Professor David Williams (daw@star.ucl.ac.uk)

ISO Studentship: A high spectral resolution far-infrared study of the Orion star formation region

The Infrared Space Observatory (ISO) was an ESA satellite mission designed to observe the Universe at wavelengths from 2.4 to 200 microns that cannot be observed from the ground. It operated from 1995 until 1998 when the liquid helium used to cool the telescope and instruments ran out. One of the four instruments on board was the Long Wavelength Spectrometer (LWS) which took spectra over the 45 to 200 micron band at medium (R~200) and high (R~10000) spectral resolution. The high spectral resolution measurements were made using a Fabry-Perot (F-P) interferometer designed and built at UCL. The spectra taken with this instrument are, and will remain for the foreseeable future, unique in their combination of wavelength coverage, sensitivity and spectral resolution.

Of particular interest are the very large spectral surveys covering the 47-190 micron wavelength region that were taken with the LWS F-P of the massive star formation regions in the Galactic Centre (GC) region (Sgr B2 and Sgr A) and the Orion Nebula. The data for the GC have now been reduced and published but those for the Orion Nebula have not yet been analysed. This project will be concerned with the analysis and interpretation of the LWS high resolution data from the Orion Nebula scans. The Sgr B2 F-P data revealed many new spectral features that had not been seen before, and it is anticipated that the Orion Nebula data (which are of higher quality) will also yield discoveries and lead to a greater understanding of the physical conditions in this massive star formation region and the astrochemistry of the region.

This project is sponsored by the Rutherford Appleton Laboratory (RAL) in Oxfordshire and will be jointly supervised by Dr. Tanya Lim at RAL and Prof. Mike Barlow at UCL. The student will be expected to spend a substantial fraction of time each year at RAL working on the analysis of the spectra. The studentship, which will be funded at the normal London rate of 11000 pounds/annum, is open to both UK and EU applicants. Funds of up to 2000 pounds/annum will be available for travel between London and RAL.

Contact: Professor Mike Barlow (mjb@star.ucl.ac.uk);
Dr Tanya Lim (T.L.Lim@rl.ac.uk)

Chemically Peculiar Stars

Among the stars of the upper main sequence, approximately between A0 and B0 spectral classes, there are a surprisingly large number of objects with bizarre compositions totally unlike those of the Sun and normal stars of Population I. They include the magnetic Ap stars, the Mercury-Manganese Stars, and the Silicon stars. All of these types tend to rotate very slowly compared to normal stars.

Research on these objects at UCL has concentrated on the study of Hg-Mn stars, the abundances of the elements in their photospheres, and the mechanisms of radiative diffusion and gravitational settling in the absence of rotational mixing that are the likely cause of these strange abundances. Some recent topics include:

Radiative acceleration of Neon;

Neon abundances in HgMn stars;

Gallium abundances in HgMn stars;

Manganese abundances in HgMn stars.

Current work in progress includes a study of He abundances in HgMn stars. There are opportunities for prospective PhD students to do research in abundance analysis of HgMn stars and in further theoretical work on radiative diffusion and gravitational settling mechanisms with increasingly realistic models that may include non-LTE effects.

Contact: Dr Michael Dworetsky (mmd@star.ucl.ac.uk)

Brown Dwarfs

About 8 out of 10 stars in our stellar neighbourhood are low-mass stars (LMSs). The astrophysical importance of identifying a large number of brown dwarfs and low-mass stars comes from the fields of cosmology (are some of these stars primordial?) and Galactic dynamics (how much mass is stored in faint, low-mass stars?), from the field of star formation (does the initial mass function vary among star formation regions, and is there a lower mass limit below which no "stars" form?) as well as from an area of great current interest, that of extrasolar planets (what distinguishes a brown dwarf from a low-mass star, and an extrasolar planet from a brown dwarf?). Their spectra are extremely rich in structure, with atmospheric opacity made up of many molecular and atomic absorbers, each with hundreds of thousands to millions of spectral lines. Their spectra can therefore be used as a tool to determine fundamental parameters of these stars, such as the effective temperature: for example, it is well known that water vapour is extremely sensitive to effective temperature, and could therefore potentially be used as a tool to derive an effective-temperature scale. This project involves the use of near- and mid-infrared data for water (and other molecular) to determine properties of low-mass stars and brown dwarfs.

Contact: Dr Serena Viti (sv@star.ucl.ac.uk)
Professor Jonathan Tennyson (j.tennyson@ucl.ac.uk

Young massive clusters

The aim of this PhD project is to investigate the stellar content and global properties of clusters of young massive stars. This will focus on two primary goals - the characterisation of the post MS evolution of massive stars and their influence on their environment, with particular emphasis on their impact on the formation of lower (solar) mass stars.

Particular reference will be made to the cluster Westerlund 1; potentially the first example of a `Super Star Cluster' in the Local Group of galaxies, for which comprehensive photometric and spectroscopic datasets already exist. It is anticipated that the project will also encompass analysis of data from the Faulkes Telescope Cluster Project, an ambitious program to survey all the known open clusters from the optical - near IR to construct a detailed picture of star formation in the galaxy.

Contact: Dr Simon Clark (jsc@star.ucl.ac.uk);
Dr Raman Prinja (rkp@star.ucl.ac.uk)

Line-profile studies of Luminous Hot Stars

High-resolution spectra of hot, luminous stars show that the absorption-line profiles do not exhibit the detailed shapes expected from classical theory. The discrepancies offer important insights into the physics of the stars and their atmospheres, and the broad aims of this project would be to investigate some aspects of this physics. Specific examples include:
• Line profiles of Be-type stars. Modelling of these line profiles should yield the projected rotational velocities and the inclination (hence the true equatorial rotation velocities). The determination of these quantities is of importance in understanding the mechanisms responsible for the Be process (still unknown a century after discovery).
• Line profiles of O-type stars. We are ignorant of the processes responsible for line broadening in the hottest 'normal' stars. Phenomenological modelling should constrain the possibilities.
• Variability in OB supergiants. A number of stars show periodic variability in their absorption profiles, tentatively attributed to stellar pulsation. Characterizing and modelling these variations would be a first step towards asteroseismology of these objects.

Contact: Professor Ian Howarth (idh@star.ucl.ac.uk)

Young massive stars in starburst galaxies

Starburst galaxies are defined as galaxies which are undergoing enormous bursts of star formation. In the nearby Universe, at least one-quarter of the entire high mass star formation is produced in only a handful of starburst galaxies. The starburst event itself is usually characterised by the formation of "super star clusters" with masses of a few million solar masses. The stellar winds and subsequent supernovae from the young massive star population drive galactic-scale winds which eject enriched material into the intergalactic medium.

The study of these objects is an exciting and developing field. Much quantitative work remains to be done in, for example, defining the properties of the young clusters, and the importance of the mass and energy return to the interstellar/intergalactic medium. The aim therefore of this project will be to put young starburst galaxies on a more quantitative footing by examining and defining their massive star content. The overall goal will be to use the results of this study as a means to understanding young star-forming galaxies in the early Universe. The project will start with the analysis of images and spectra from the Hubble Space Telescope. Ground-based optical spectra will be obtained and modelled to deduce the ages, stellar content and metallicities of the starburst regions. Since the cores of many starburst galaxies are obscured in the optical, data will also be obtained at infra-red wavelengths. The observations will be modelled using population synthesis codes, which have recently been extensively up-dated and improved at UCL.

Contact: Dr Linda Smith (ljs@star.ucl.ac.uk)

Studies of main sequence stars with debris dust disks

Many main sequence stars are known to be surrounded by infrared-emitting dust disks. These so-called debris dust disks are preferentially found around younger main sequence stars and may currently be forming planetesimals and planets within the disks. This project will involve the analysis of high spectral resolution echelle spectra of main sequence Vega-like stars and their circumstellar disks, obtained at the Anglo-Australian Observatory and Mt Stromlo Observatory. Spectra of two samples will be analysed; the first group comprising A-F type Vega-like stars (some of which may have characteristics similar to those of young Herbig Ae/Be stars) and the second group being G-K type stars (some of which which may have characteristics similar to those of T Tauri stars). Both samples are drawn from the Mannings & Barlow 1998 list of southern hemisphere main sequence stars whose far-infrared properties indicate that they possess debris dust disks.

There will be two stages of analysis: (a) the stellar spectra will be analysed to determine the properties (e.g. age, mass, chemical composition) of the stars, which are potentially surrounded by planet-forming disks, in order to understand to what extent these disks depend on the properties of their central stars; (b) the circumstellar emission and absorption lines in the spectra will be analysed in order to determine the physical conditions prevailing in the disks of gas and dust which surround the stars, in order to gauge the extent to which they may be in the process of forming planetary systems.

Contact: Professor Mike Barlow (mjb@star.ucl.ac.uk)

Cold plasmas in nebulae

Much of our knowledge of elemental abundances in our own and other galaxies is based on the analysis of the emission line spectra of ionized nebulae. The strongest forbidden lines from HII regions, which are associated with the formation of massive stars in galaxies, can be observed to great distances and the analysis of these lines has yielded abundances for a wide range of elements in the Milky Way and elsewhere. The strength of these forbidden lines has an exponential dependence upon the nebular electron temperature - they are efficiently excited at typical nebular temperatures of 10,000K but they will be strongly enhanced in regions of a nebula where the electron temperature fluctuates significantly above the mean value. Conversely, any regions in a nebula with temperatures less than a few thousand K will not emit these very temperature sensitive lines.

Recently, with the aid of large telescopes and efficient detector systems, it has become possible to measure accurate strengths for the much weaker recombination lines that originate from the same ions that emit the classical strong forbidden lines. These optical recombination lines have a much weaker dependence upon nebular temperature than do the forbidden lines - in fact their strength rises inversely with temperature in the same way as for the strong Balmer lines from recombining hydrogen, the element to which abundances are usually referenced. A number of studies that our group has published recently for heavy element (e.g. C, N, O, Ne, etc) optical recombination lines in the spectra of HII regions and planetary nebulae have found that these lines are much stronger than expected. At first this seemed to indicate that the classical forbidden line method had grossly underestimated elemental abundances, but detailed analysis of UV, optical and IR spectra now indicates that the more likely explanation is that there are ionized regions within both HII regions and planetary nebulae that have electron temperatures below 1000K, qualifying these regions to be called `cold plasmas'. The aim of this project is to obtain and analyse optical, ultraviolet and infrared spectra of selected nebulae in our own and other galaxies, in order to elucidate the nature and origin of this previously unsuspected but significant component of photoionized nebulae.

Contact: Professor Mike Barlow (mjb@star.ucl.ac.uk)

Electron impact excitation of molecules

Stars cooler than the Sun are substantially molecular. Solar astronomers and modellers have problems in interpreting molecular spectra which correspond to rotational transitions between different electronic states. There is an urgent need for data on collisions which might help to understand the observed emissions. As electrons are abundant where the molecules are (conditions similar to photodissociation regions - PDRs), it important to have electron-impact electronic-rotational excitation rates for molecules such as hydrogen. Such data are particularly needed to interpret recent results obtained with the telescope THEMIS. In fact similar data, are also needed to interpret spectra observed from the edge of fusion plasmas produced on earth. The UCL TAMPA group uses the R-matrix method to study electron molecule collision processes and has already completed a number of studies important for PDRs. A student would be asked to work initially on electron collisions with H₂ although molecules, such as CO, might be considered at a later stage.

Studies in Atmospheric Physics

Thermosphere-Mesosphere Coupling Study

The Atmospheric Physics Laboratory has a network of Fabry-Perot Interferometers in northern Scandinavia to study the upper atmosphere in the region of auroral activity called the auroral oval. This is a highly dynamic region of the upper atmosphere since it is directly coupled with the solar wind from the Sun, via the Earth's magnetosphere. Our major experimental work has been with the dominant red and green line auroral and airglow emissions of the thermosphere, which cover an altitude region of between 100-300km. We are proposing an investigation of the coupling of the energetics between the thermosphere and mesosphere regions by simultaneous observations of auroral and airglow emissions from around 90km, 110km and 240km. The transfer of energy is very complex, involving winds, tides, gravity waves, turbulence, radiative processes and chemistry. Coupling between the middle and upper atmosphere is new territory and the experimental work will be augmented by theoretical models that are also part of the expertise of the APL.

Energetics of the High-Latitude Magnetosphere-Ionosphere-Thermosphere System

The ionosphere responds almost immediately to changes in the electric field near the north and south poles. These changes can be highly dynamic and derive from the way that the solar wind interacts with the Earth's magnetic field. However, the neutral atmosphere, which is the vast bulk of the upper atmospheric composition, can take a few hours before such changes feed through to the large- scale motion via ion-neutral interactions. This inertia has major consequences for the ionosphere-thermosphere system, in particular the currents and energy dissipation. Studies of the energetics of the upper atmosphere at high- latitudes may be achieved through a combination of ground- based observations by Fabry-Perot Interferometers (built by this group), coherent/incoherent scatter radars, ionospheric tomography and satellite measurements. These are then compared with model simulations, in particular with the UCL/Sheffield/SEL three-dimensional Coupled Thermosphere-Ionosphere- Plasmasphere model. There is plenty of scope here for an instrumental PhD through to a modelling PhD and any combination in-between.

Astronomical Instrumentation

The Optical Science Laboratory has exciting opportunities for PhD studentships in research areas related to the next generation of extremely large telescopes, space telescopes, industrial optics and medical physics. As current 8m telescopes reach maturity, worldwide attention is turning to the next generation of 30-100 metre telescopes. The UK's position is strengthened by its involvement in the European Southern Observatory, which has an extremely large telescope ('ELT') project already up and running.

These telescopes are providing new challenges in many areas of instrumentation science. The Optical Science Laboratory is in a strong position to contribute to some key areas - and indeed is already contributing. Examples include the automated manufacturing and metrology of the primary mirror segments using computer controlled techniques, the adaptive control of large mirror surfaces, and the development of novel instrumentation concepts to be deployed on these enormous telescopes. These developments will be closely related to the astronomical case for the telescope as it develops over the coming years, and will be conducted in partnership with several external organisations.

The programme includes the development of state-of-the-art methods to produce mirror segments for ELTs, in collaboration with a UCL spin-out company Zeeko Ltd (www.zeeko.co.uk) and other members of a UK-based consortium. Another highlight is the development of adaptive mirror systems and light-weight mirrors in collaboration with QinetiQ, with potential for both ground and space-based telescopes. The programme also embraces developments in the metrology of surfaces in collaboration with Heriot-Watt University and the National Physical Laboratory.

The control and metrology of complex surface forms is being researched not only in support of optics fabrication, but also for improving the lifetimes of prosthetic knee and hip joints. This grant-funded project is a collaboration with the Royal National Orthopaedic hospital and Huddersfield University.

PhD projects can be tailored around the particular skills and interests of candidates. Typical projects can range from highly experimental (optics, electronics, process-development etc) at one extreme, to theoretical and computer simulation at the other. There is also considerable scope for software development, particularly in C++ and MATLAB. There is great opportunity for enthusiastic and capable students to make real contributions to these extremely large telscope projects. Students who can participate in both experimental and theoretical/computing work are particularly valued.