Exoplanets and stellar physics

Supervisor: Katherine Blundell

In recent years the existence and significance of circumbinary discs, orbiting outside of pairs of binary stars in orbit around one another, has emerged. Not only are these purported to have significant dynamical back-reactions on their inner binary stars (and hence their evolution) and in the development of nova explosions but they are in some cases likely to be the breeding ground of Tatooine-like circumbinary planets. The goal is to explore and understand the nature of binary star systems that host such circumbinary structures, using data from the Global Jet Watch telescopes (PI K Blundell; www.GlobalJetWatch.net).

Supervisor: Katherine Blundell

Nova explosions occur much more frequently than supernova events and arise as the result of a thermonuclear runaway on the surface of a white dwarf. The recent discovery of jets being ejected at the onset of a nova explosion, which have speeds of a few thousand km/s, suggests an important means by which the inter-stellar medium can be enriched by the products of nucleosynthesis that take place on the surface of the white dwarf.  The goal is to investigate the mechanisms by which these processes take place, and the efficacy of enrichment of the ISM by jets from nova explosions, using time-lapse data from the Global Jet Watch (PI K Blundell; www.GlobalJetWatch.net).

Supervisor: Gavin Dalton

WEAVE is a new spectroscopy facility at the William Herschel Telescope, led from Oxford and now in the commissioning phase. Over the next few years, WEAVE will deliver more than 12,000,000 high quality calibrated spectra for 8 diverse surveys ranging from the structure and evolution of the Milky Way to the formation of the earliest galaxies. Working with the WEAVE PI within a diverse science team spanning 6 countries, this project provides unique access to all aspects of the WEAVE surveys, with possible avenues of exploration including a WEAVE-based calibration of the Hobby-Eberly Telescope Dark Energy Experiment, analyses to search for rare objects within the Milky Way, or spectroscopic identification of gravitationally lensed galaxies.

Supervisors: Ray Pierrehumbert, Jayne Birkby

Technosignature gases are gases that have no known significant natural sources (including metabolisms of non-technological life), but which are produced by industrial processes that are not mimicked by any natural geological processes. Technosignature gases with long atmospheric lifetimes are of particular interest, since even weak sources can lead to significant accumulation in the atmosphere. SF6 is a good example of a long-lived technosignature gas on Earth. This project seeks to evaluate the concentrations at which various technosignature gases could be detected on exoplanets using either the James Webb Space Telescope or ground-based high resolution spectroscopy. Allied questions include atmospheric lifetime of technosignature gases in non-Earthlike atmospheres of planets orbiting stars of various spectral types, identification of need for more spectroscopic data, and concepts for generalization of the list of technosignature gases beyond those that have so far been produced by Earth's industries.

Supervisor: Caroline Terquem

A large proportion of stars are found in binary systems.  When the distance between the two stars in such systems is small enough, oscillations are excited in each of the stars by the tidal potential of its companion.  These tidal waves are dissipated in the convective regions of the stars.  Such dissipation of energy leads to circularisation of the orbits.  Observations show that close orbits are circular whereas wider orbits have eccentricities.  The period at which the transition occurs for a type of stars is called the 'circularisation period'.  Until now,  theoretical studies, which have relied on mixing length theory to model convection, have predicted circularisation periods significantly smaller than the observed ones.   We have developed  a new description of the interaction between tides and convection that yields the observed values of the circularisation period.  This new formalism is also able to account for the rate of tidal energy dissipation which is needed in giant planets to explain the orbital evolution of their satellites, and which had been a puzzle for the last 50 years.  There is a large number of problems that should be revisited using this new description, and this is the aim of the project.  These studies can be applied to a variety of systems, including binary systems with two stars, or with one star and a giant planet, or with a giant planet and a satellite.   The project will use analytical and numerical tools. 

Supervisors: Matthias Tecza, Niranjan Thatte

One of the E-ELT's highest scientific priorities is to characterise exo-planets and to take images of Earth-like planets.  For this purpose the E-ELT will be equiped with a dedicated planetary camera and spectrograph, called PCS, to be commissioned in the 2030s. The overriding factor in directly imaging exo-planets is the contrast ratio between the faint planet and the bright star it orbits.

In Oxford we are leading the R&D effort to establish which spectrograph design offers the best performance. Using a bench mounted spectrograph we will measure the achievable contrast ratio of an image-slicer based and a lenslet-array based spectrograph.

We are looking for motivated D.Phil student who has a keen interest in state-of-the-art instrumentation. She/he will be involved in the design and set-up of the experiment, including opto-mechanical design, and data acquisition using CCD detectors.  The student will also reduce, process, and analyse the data collected to determine and optimise the achievable contrast, including applying and/or developing novel algorithms to exploit the advantages of image-slicer or lenslet-array based spectrographs.

Supervisor: Jayne Birkby

When we observe exoplanets in high resolution, be it via direct imaging or by spectroscopy, a wealth of information about the exoplanetary atmosphere awaits us. These powerful high resolution techniques can reveal the composition, structure, and dynamics of exoplanets atmospheres, including their global winds patterns and rotation, alongside their variability over time that may indicate their appearance or even presence of exomoons. This project seeks a student eager to explore exoplanet atmospheres in detail through observational and simulated data, with input from theoretical modelling. The goal is to explore the properties of a range of different planets, from gas giants, to mini-Neptunes and super-Earths, in a goal to understand the incredible diversity of exoplanet atmospheres. The DPhil timeline aligns with the final stages of preparation for the first light of the Extremely Large Telescope (ELT), which will host instruments highly suited to survey small rocky planets in our local neighbourhood and mapping giant planet atmospheres using the techniques learnt during this DPhil. The student will join Prof Birkby’s group working on exoplanet atmospheres at Oxford Astro, and will be encouraged to engage with the broader exoplanet community within Oxford, including the Atmospheric, Oceanic and Planetary science department, and the Earth Science department.