PhD Projects 2011

There are a number of PhD opportunities available in Astrophysics, for projects starting in October 2011. Below is a list of possible projects suggested by academics involved in the theme.

Exo-climatology: The study of atmospheric dynamics of exoplanets

Supervisor: Prof. Isabelle Baraffe

This project is devoted to the study of exoplanet atmosphere dynamics based on numerical simulations of global circulation flow characterising the surface of exoplanets, and in particular of strongly irradiated transiting planets. The development of atmospheric circulation models is a crucial step required to understand exoplanet properties. Atmospheric dynamics, indeed, affect heat redistribution over the surface of the planet and its spectroscopic signatures (i.e transmission and emission spectra as is now observed on several known extrasolar planets). Atmospheric circulation is also expected to affect the planet’s internal structure and evolutionary properties. The goal is to adapt models based on the so-called General Circulation Model (GCM) approach, which is used for climate studies on Earth and on solar system planets, to the conditions appropriate for the description of exoplanet atmospheres.  For this project, we are using a sophisticated GCM code which has been developed at the Met Office of Exeter.

Multi-dimensional stellar evolution: very early phases of evolution of low mass stars and brown dwarfs

Supervisor: Prof. Isabelle Baraffe

The general context of this project is the study of the very early phases of evolution of low mass stars and brown dwarfs, following the dynamical phase of gravitational collapse and fragmentation of a molecular cloud which produces a pre-stellar core and an accretion disk. The physical properties of the newly born protostar/proto-brown dwarf crucially depend on two physical processes: accretion from the disk and internal convection which is the most important energy transport in the protostellar interior. To describe these processes, our team is developing a multi-dimensional, time implicit, hydrodynamical code. Time implicit simulations are required for the description of characteristic stellar evolution processes which proceed on timescales much longer than the dynamical timescale. The main goal of this project is to participate to the development of the implicit hydrodynamical code and to study the properties of interior convection in accreting objects.

Astrometric companion search with PRIMA - from stars to planets

Supervisor: Dr. Jenny Patience

By combining the signal from two telescopes in an interferometer, it is possible to measure small angular motions on the sky very precisely, down to tens of micro-arcseconds. This project will employ the astrometric search technique with the newly-commissioned PRIMA interferometer to detect the small motion of a star caused by an unseen companion, ranging from stellar companions to planetary companions. In addition to detecting the presence of a planet, it is also possible to measure the planet mass. For students interested in instrumentation experience, this project also has the possibility of working with the instrument development at the ESO observatory in Chile or the ESO headquarters in Germany.

Star formation in local molecular clouds

Supervisor: Dr. Jenny Hatchell

Star formation is the fundamental building process of galaxies and an ongoing process during planet formation.  Yet we cannot yet look at an interstellar cloud and predict how many stars will form, where, or how their masses are determined.  This is a golden age for star formation studies with an unprecedented amount of data currently being returned from an array of largearea survey instruments at infrared and submillimetre wavelengths (Spitzer and Herschel space telescopes, SCUBA-2 on JCMT).  These surveys will be followed in quick succession by high-resolution probes of the individual collapse and accretion processes (ALMA, e-MERLIN).  For your PhD, you will address these fundamental questions of star formation using observations of nearby molecular clouds, where we have the spatial resolution to resolve individual star-forming events and study the inner workings of the star-formation process.

The turbulent structure and dynamics of molecular clouds

Supervisor: Dr. Chris Brunt

Molecular clouds are enormous, massive structures - tens of parsecs across and containing up to millions of solar masses of material. Their internal structure and dynamics are controlled by the combined action of self-gravity and magnetohydrodynamic turbulence. To understand the processes that lead to the formation of stars within these clouds, we will analyse their spatial and dynamic structure through a variety of advanced statistical methods. This PhD project is primarily observational, but will include work on supercomputer simulations of star-forming clouds.

Mapping the progression of star formation throughout the local region of our Galaxy

Supervisor: Prof. Tim Naylor

Whilst the basic idea of star formation is well understood (gas collapses to form stars), the environment in which this happens, including how the gas is collected why it collapses is not. It is clear that spiral arms are the major factories which change the gas into stars, but to understand them in detail one needs to follow the gas through the arms, and then follow the stars as they flow away from the arms. We have developed techniques for measuring the ages and distances to groups of stars which now need to be applied to the new-born stars emerging from the spiral arms, so we can construct a "movie" of the progress of star formation, and compare it to spiral arm models. The work will involve data from large surveys, and from new observations.

One of the strengths of this project is that it several members of the group are working in areas which support the project's aims. So the student would be expected to interact with Chris Brunt who works on radio surveys of the gas from which the stars form, Clare Dobbs who performs simulations of spiral arms, and Matthew Bate who simulates the collapse of molecular clouds to form stars.

Determining the properties of stellar clusters

Supervisor: Prof. Tim Naylor

In the last ten years observational work has clearly answered the question as to WHETHER planets exist around other stars, now we must move onto the question of WHY they exist, addressing the physics of planet formation itself. Whilst there has been a great deal of theoretical activity in the area, the observational constraints are poor, in part because it there are at present no good techniques for following the planet formation itself in detail. The best way to constrain the theories, therefore, is to study the environments in which the planets form, following the evolution of the planetary discs, stellar rotation and related properties. Studying a single young cluster will yield a large sample of stars with homogenous properties. Studying many clusters allows us to study variation of planet formation as a function of those properties. Such meta-studies have now been made possible by the new generation of sky surveys, which yield homogeneous data for large numbers of clusters. The PhD will involve us- ing these, in combination with new techniques developed in Exeter for determining ages of the clusters, new data from large telescopes and interaction with Exeter theorists to learn from observations what controls planet formation.

The interaction between a young star and its accretion disc

Supervisor: Prof. Tim Harries

The environment close to a typical protostar contains gas and dust that is rotating around the star in a disc, as well as outflowing in a wind and plummeting down magnetic field lines onto the protostar itself. This gas and dust is adding to the protostar's mass, is injecting energy into the interstellar medium (perhaps inducing further star formation) and is also clumping together to form planets. Although rich in physics, this environment is on a scale that is far too small to be observed using traditional imaging, and we must turn to other methods, such as spectroscopy, polarimetry and interferometry to probe the geometry, dynamics and physical conditions of the gas.This PhD project involves using a combination of numerical modelling and observations obtained on international facilities (such as the VLT and WHT) to examine the processes that occur within a few radii of protostars, with the aim of measuring the accretion rates onto protostars and how the magnetic field interacts with the planet-forming disc.This project would be suitable for a student with an interest in both observations (particularly infrared spectroscopy and interferometry) and computer modelling.