Our research themes
Our research in astrophysics is wide-ranging and covers observational and computational work on stars, planets, interstellar matter and galaxies. Below is a brief outline but further information is available on the Astrophysics Group website.
Wide Angle Search for Planets
Searching for planetary transits is a demonstrated technique for the discovery of new planets beyond the solar system. The Wide Angle Search for Planets (WASP) is undertaking a comprehensive, wide-field sky survey to detect planetary transits in stars down to 18th magnitude. With greatly increased numbers of known extra-solar planets we will investigate the accretion processes that lead to planet formation, and thus better understand the origin of our own home. WASP will also provide a wealth of data on all classes of variable stars, allowing the systematic analysis of large samples and the discovery of new and rare variable types.
For further information see our https://wasp-planets.net/
Stellar Hydrodynamics, Evolution and Nucleosynthesis (SHEN)
The SHEN group, led by Prof Raphael Hirschi, studies stars and related topics like supernovae, black holes and the origin of elements by performing numerical simulations. Simulations include both large-scale multi-D hydrodynamics simulations using UK (www.DiRAC.ac.uk) and EU (www.PRACE.eu) HPC facilities and standard 1D stellar evolution models. Models are being computed at metallicities ranging from solar down to very low metallicities and from the main sequence until the pre-supernova stage. These models are able to predict the properties of the stars during their evolution (mass, surface composition and position in the HR diagram), as well as black hole masses and supernova types coming from single stars and the production of chemical elements in massive stars. The main focus of the group is to improve the theory of convection using 3D hydrodynamic simulations as well as to use chemical elements as tracers of the evolution of the cosmos (ChETEC COST Action, see www.chetec.eu for details).
For further information see Professor Raphael Hirschi's homepage.
High-precision stellar astrophysics
Rendering of PLATO (PLAnetary Transits and Oscillations of stars), ESA program. Copyright: TAS
Accurate stellar models are an essential tool in our exploration of the Universe. A new generation of stellar models is now needed to interpret the exquisite data that are being provided for stars and planets throughout the Galaxy by space missions such as Kepler, TESS and GAIA. The astrophysics group at Keele is playing a leading role in characterising stars in binary star systems to high precision in order to calibrate the next generation of stellar models. Data from exoplanet transit surveys such as WASP, Kepler K2 and TESS are used to identify suitable eclipsing binary star systems. Follow-up observations are obtained with high-resolution planet-finding spectrographs such as HARPS that enable is to measure the masses of stars to ±0.1%. Accurate binary star models developed at Keele are then used to model the eclipses of these binary systems so that we can also measure the size of the stars to similar precision. To ensure that these results are accurate we will observe the light curve at multiple wavelengths using the new Xamidimura telescopes that have recently been installed at the Keele observatory site in South Africa. New techniques are currently being developed so that we can also measure the luminosity and composition of the stars in these binary precisely and accurately. This work is being coordinated with collaborators throughout Europe within the framework of PLATO mission stellar science group work package WP125500 “Benchmark stars”.
The Large and Small Magellanic Clouds are the nearest templates for the detailed study of star formation under metal-poor conditions. These galaxies mirror the conditions typical of galaxies during the early phases of their assembly, providing a stepping stone to understand star formation at high redshift where such processes can not be directly observed. Furthermore, they provide the exciting new opportunity of bridging the gap between star formation processes on large galactic-wide scales and on the small scales of individual young stellar objects (YSOs).
The advent of the Spitzer Space Telescope finally allowed the identification of sizable samples of early-type YSOs across the whole MCs. The Spitzer Legacy Programs (SAGE and SAGE-SMC) have photometrically identified 1000s of previously unknown YSOs, while the Herschel Legacy program (HERITAGE) is revealing the youngest, most embedded YSOs, that are only accessible at longer wavelengths Using Spitzer, Herschel and ground-based spectroscopic facilities we investigate the detailed properties of gas- and solid-state chemistry at sub-solar metallicity. Any variations on the gas and ice phase chemistries could imply significant variations in gas-phase abundances of oxygen, carbon, water and CO, that consequently impact the ability of the YSO envelopes to cool and its early evolution. We use galaxy-wide photometric surveys to constrain the Initial mass function and star formation rates across the whole system in order to link the environmental conditions to the star formation outcomes.
For further information contact Joana Oliveira
Atmospheric parameters of stars
The stellar atmospheric parameters of effective temperature and surface gravity are of fundamental astrophysical importance. They are the prerequisites to any detailed abundance analysis. As well as defining the physical conditions in the stellar atmosphere, these parameters are directly related to the physical properties of the star; mass, radius and luminosity. Model atmospheres are our analytical link between the physical properties and the observables - flux distributions and spectral line profiles. We can obtain effective temperature and surface gravity from suitable observations, assuming of course that the models we use are adequate and appropriate.
For further information see Barry Smalley's homepage
Quick tours of the H-R diagram
When a star like the Sun exhausts its fuel its internal structure undergoes major changes and it moves away from the main sequence of the Hertzsprung Russell diagram. During this phase of evolution it seeds the interstellar medium with dust and gas in the form of a wind, providing the raw materials for the formation of new stars. This research involves using infrared and sub-millimeter telescopes to probe the latter stages of stellar evolution, particularly those stars that evolve on the timescale of a human lifetime. These include not only the 'born-again' stars, which re-ignite some of their fuel as they head towards the white dwarf region of the H-R diagram, but also the explosions of novae, in which thermonuclear runaway occurs on the surface of a white dwarf in a close binary system.
For further information see the Nye Evans' homepage
Accretion is one of the most widespread and important phenomena in the universe. It is the dominant source of X-rays in the universe, powering X-ray sources from black-hole binaries to active galaxies. Accretion discs are also crucial in the formation of stars and contain the material out of which planets grow. Close binary stars provide the best opportunities for studying the physical processes of accretion. Keele's programme investigates accretion onto neutron stars and white-dwarf stars, using satellites such as XMM, Chandra and HST, complemented by ground-based telescopes. A particular strength is the understanding of magnetically channelled accretion, where the accretion process interacts with a strong magnetic field on the compact star.
For further information see Coel Hellier's homepage.
Low-mass stars in clusters and associations
Stars like the Sun or of even lower mass are born in clusters and associations. We search for young Suns, low-mass stars and brown dwarfs in star forming regions and clusters in order to find how common they are in a variety of environments and follow the temporal evolution of their discs, rotation rates, magnetic activity and chemical abundances. Our goals are to understand the way in which birth environment influences the development of low-mass stars (and their planetary systems) and to investigate the astrophysics, such as mixing, convection and magnetic fields, that are incorporated into pre main sequence evolutionary models.
Observations of close binary stars
Many stars are found in pairs (binaries) and orbit around each other with orbital periods of years, weeks, days or even every few hours. These stars have often interacted very strongly and may have exchanged mass or thrown their outer layers out of the binary system. This can produce some of the most dramatic objects in the sky, e.g., black hole X-ray binaries and Type-Ia supernovae. It is difficult to predict how stars behave when they interact strongly, so research at Keele uses surveys to find simpler examples of close binary stars which have interacted in the past, and may do again, but are currently not exchanging mass. We then study these binaries in more detail to measure their properties, e.g., the number in the galaxy, their distribution of orbital periods or the masses and sizes of the stars. This research gives information which is being used to understand the properties of many types of interacting binary stars.
For further information see Pierre Maxted's homepage.
Stellar and interstellar physics as drivers of galaxy evolution
Galaxies evolve because stars form and die within them. This cycle depends on the dynamics of the interstellar medium... and affects it. Galaxies are also stirred by external disturbances such as galaxy-galaxy encounters. The ecology in which stars and galaxies take part is subject of a diverse range of observational programmes at Keele. These include the physics of molecular clouds and star formation, stellar feedback and supernova remnants, and the structure and dynamics of the interstellar medium from the smallest, au scales to the largest, global galactic scales. We study these processes in the Milky Way and other nearby galaxies such as the Magellanic Clouds and spiral galaxies within about 7 Mpc distance, where we can still study the individual red supergiant progenitors of supernovae.
For further information see Jacco van Loon's homepage.
Since their birth at high redshift, activity in galaxies has had a profound effect on their evolution as well as the reionization of the Universe. The activity is either due to the accretion onto a supermassive black hole, or a starburst. Both are affected by galaxy encounters. At Keele we focus on understanding the relation between nuclear activity, star formation and the circumgalactic environment. We find extreme examples, as well as finding out what is common. Our work makes use of multi-wavelength surveys, from the ultraviolet and optical, through the infrared and radio.
For further information see Jacco van Loon's homepage.
All we know about the Universe is underpinned by laboratory measurements. This project replicates Solar System materials, such as ices and minerals, in the laboratory, and studies their solid state properties (such as crystal structure and thermal expansion) using X-Ray powder diffraction using beam-line I11 at the Diamond Light Source, the UK’s world-leading synchrotron radiation facility. Our work is relevant to the oceans of Europa and Enceladus, the lakes on Titan, and the Martian regolith.
For further information see the Nye Evans' homepage.
Low-mass stars in clusters and associations
The majority of stars and planets are born in groups or clusters of some sort. While some of these clusters survive to maturity as long-lived Open Clusters, the majority rapidly disperse into the galaxy. These dispersing groups of young stars are briefly visible as associations. At Keele we study the structure and dynamics of both clusters and associations to understand how these groups form, how they evolve and influence the stars and planets within them, and why most groups disperse. We use data from space telescopes such as Gaia, as well as ground-based photometry and spectroscopy.
For further information see Nick Wright’s homepage