James Threlfall
What can test particles tell us about magnetic reconnection in the solar corona?
Solar flares are highly explosive events which release significant quantities of energy (up to 1032 ergs) from specific magnetic configurations in the solar atmosphere. As part of this process, flares produce unique signatures across the entire electromagnetic spectrum, from radio to ultra-violet (UV) and X-ray wavelengths, over extremely short length and timescales. Many of the observed signals are indicative of strong particle acceleration, where highly energised electron and proton populations rapidly achieve MeV/GeV energies and therefore form a significant fraction of the energy budget of each event. It is almost universally accepted that magnetic reconnection plays a fundamental role (on some level) in the acceleration of particles to such incredible energies.
In this talk, I will briefly summarise a series of recent experiments where test particles are introduced into a number of 3D magnetic reconnection configurations. I will discuss the particle population response to each configuration and what these responses might infer for both simulations and observations of magnetic reconnection in the flaring solar corona.
James Threlfall
What can test particles tell us about magnetic reconnection in the solar corona?
Solar flares are highly explosive events which release significant quantities of energy (up to 1032<\sup> ergs) from specific magnetic configurations in the solar atmosphere. As part of this process, flares produce unique signatures across the entire electromagnetic spectrum, from radio to ultra-violet (UV) and X-ray wavelengths, over extremely short length and timescales. Many of the observed signals are indicative of strong particle acceleration, where highly energised electron and proton populations rapidly achieve MeV/GeV energies and therefore form a significant fraction of the energy budget of each event. It is almost universally accepted that magnetic reconnection plays a fundamental role (on some level) in the acceleration of particles to such incredible energies.
In this talk, I will briefly summarise a series of recent experiments where test particles are introduced into a number of 3D magnetic reconnection configurations. I will discuss the particle population response to each configuration and what these responses might infer for both simulations and observations of magnetic reconnection in the flaring solar corona.
Yvonne Grunder
In situ studies of the atomic structure/charge distribution at the electrochemical interface
Electrochemical interfaces play a crucial role in many systems used for clean energy production, conversion and storage as well as for material processing. The structure of the electrode and electrolyte, as well as stability effects and charge transfer mechanism are the underlying properties and processes which can crucially affect reactivity and performance of electrochemical applications.
In-situ surface x-ray diffraction has enabled an atomic/molecular-level understanding of the interface under reactive conditions, including its potential and time dependence, to be developed. While information about the atomic structure of the electrode surface in electrochemical in-situ cells has been widely investigated, insight into the charge distribution and the structure of the electrolyte at the interface is still lacking. Advances in these directions offer possibilities in elucidating atomic scale models of the electrochemical interface and thus will help to establish structure-stability-reactivity relationships.
This is especially of importance as many energy storage and production devices employ non-aqueous electrolyte, which can crucially alter the electrochemical behaviour. Thus techniques elucidating changes in structure and the charge transfer mechanism are required.
Examples of how the use of surface x-ray scattering techniques can help to characterise electrochemical interfaces in-situ in order to link, structure, reactivity and stability will be presented. Examples will include monitoring the charge distribution and the structure of the electrolyte.
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Title
abstract
Jane Greaves
Seeing Planets Form
Extrasolar planetary systems are very diverse in their properties compared to the solar system. By observing and modelling the discs out of which the planets form, we can attempt to see how this diversity emerges, and start to look into implications such as the frequency of other habitable planets. I will show examples of unexpected phenomena in circumstellar discs, and present methods of high angular resolution astronomy looking at discs on few-AU scales. Our first results are appearing from the Planet Earth Building Blocks Legacy eMERLIN Survey (PEBBLeS), and I will discuss the discovery space of this project, and the future going into the SKA era.
Name
Title
abstract
Sarah Badman
Space Weather at Saturn
The gas giant Saturn has a rapid rotation period (~11 h) and is orbited by icy moons and rings, which are important sources of mass within its space environment. These features mean that the dynamics of its magnetosphere, the region containing the planetary magnetic field, are dominated by rotational processes and pick up of the icy material. However, despite its location nine times further from the Sun than the Earth, the Sun and solar wind also affect the transport of energy and mass through the vast Saturnian system. I will introduce how we can measure the space weather conditions at Saturn using solar wind propagation models and in situ spacecraft measurements, and how we can observe the magnetospheric response through auroral images. In particular I will show signatures of magnetic reconnection between the planetary and interplanetary magnetic fields, disruption of rotating phenomena, and the occurrence of auroral storms in response to compressions of the magnetosphere. These observations can help us understand how stellar winds interact with different planetary environments.
Name
Title
abstract
John Stott
KROSS: The KMOS Redshift One Spectroscopic Survey
KROSS is a major UK-led KMOS GTO survey, which targets the redshifted H-alpha emission in 800 star-forming galaxies at z=1. This constitutes the largest ever resolved H-alpha survey of distant galaxies. Selecting galaxies from the star-forming “main-sequence”, KROSS measures the resolved dynamics, chemistry and star formation in a statistical sample of galaxies in order to address: (i) How does the fraction of discs evolve as a function of z and environment? (ii) are major (and minor) mergers more prevalent at high-z ? (iii) How does the relation between the star-formation, stellar mass and dark halo evolve with z and environment? (iv) How does the angular momentum of galaxy disks evolve with z, stellar mass and environment; (v) Are chemical abundance gradients of early discs stronger or weaker than local spirals? These are critical issues for developing models of galaxy formation, in particular to determine if stellar mass assembly is dominated by secular or merger-induced growth. In this talk I will present the results from the first KROSS papers.
Name
Title
abstract
Del Atkinson
Physics at the Interface: Current research in thin-film ferromagnetic/non-magnetic systems for spintronics
Magnetism and magnetic phenomena in bulk ferromagnetic materials are generally well understood in physical terms. In contrast, in nanoscale thin-films and multilayered ferromagnetic/non-magnetic systems a range of exciting, non-trivial and potentially useful physics has emerged that is associated with the interfacing between ferromagnetic and non-magnetic materials. This is exemplified by giant magnetoresistance (GMR), for which the work of Albert Fert and Peter Grunberg in the late 1980s won the Nobel prize in 2007 and founded the burgeoning field of spintronics.
In the decades since the discovery of GMR, a range of interfacial physics has emerged in ferromagnetic/non-magnetic systems that opens up new avenues for physical understanding and offers potential for the creation of synthetic materials with designer properties for spintronic applications in current and future technology including data storage, logic and biomedical applications. Over the past decade several aspects of the fundamental spintronics physics, such as current-driven, rather than magnetic field driven, magnetization switching have been understood and applications developed.
However, there are many exciting areas of on-going research linked to interfacial effects such as interface spin-orbit interactions (SOI), spin-currents from the spin Hall effect (SHE), spin-orbit torques (SOT) and SOT switching, interfacial Dzyaloshinskii-Moriya (DMI) interaction, proximity magnetization of non-magnetic metals and effects such as anisotropic magnetoresistance (AMR) and ferromagnetic damping where interfacial effects with non-magnetic layers can yield new insights. These topics are being researched internationally and form some of the research activities in the Nanomagnetism and Spintronics research group at Durham University.
This talk will introduce some of these exciting physical phenomena, and discuss research progress with examples from our research work in the group at Durham University.
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Title
abstract
Tim Davis
The dark hearts of galaxies: molecules as dynamical probes of galaxy evolution
In this talk I will describe how mapping the dynamics of molecular clouds in the centre of galaxies can help us to constrain a wide range of astrophysical problems. From the enigmatic relation between galaxies and their supermassive black holes, the suppression of star-formation in dying galaxies, and the puzzling variation of the stellar initial mass function, molecules provide an ideal probe that can help us make progress. I will show how high resolution observations (with CARMA and ALMA) can be used to estimate the masses of supermassive black holes in galaxies across the Hubble sequence, and describe the WISDOM project, that aims to use this technique to constrain the importance of accreting SMBHs in galaxy quenching. I will show that the deep potential wells of massive galaxies can play an important role in quenching star-formation, transitioning galaxies as they grow from star-forming to “red and dead”. Finally I will show how one can use molecules to probe the controversial topic of variation in the stellar initial mass function.
Name
Title
abstract
Juntai Shen
Gas inflow patterns and nuclear rings in barred galaxies
Nuclear rings, dust lanes, and nuclear spirals are common structures in the inner region of barred galaxies, with their shapes and properties linked to the physical parameters of the galaxies. We use high-resolution hydro-dynamical simulations to study gas inflow patterns in barred galaxies, with special attention on the nuclear rings. The location and thickness of nuclear rings are tightly correlated with galactic properties, such as the bar pattern speed and bulge central density, within certain ranges. We identify the backbone of nuclear rings with a major orbital family of bars. The rings form exactly at the radius where the residual angular momentum of inflowing gas balances the centrifugal force. We propose a new simple method to predict the bar pattern speed for barred galaxies possessing a nuclear ring, without actually doing simulations. We apply this method to some real galaxies and find that our predicted bar pattern speed compare reasonably well with other estimates. Our study may have important implications for using nuclear rings to measure the parameters of barred galaxies with detailed gas kinematics. I will also briefly discuss the new results of extending current hydro-dynamical simulations to understand the gas features in the Milky Way.
Name
Title
abstract
Gary Fuller
From Dark to Light: Molecular Clouds to Massive Protostars & Clusters
Stars are the fundamental building blocks of the Universe and most stars in our Galaxy form in clusters, some of which also produce high mass stars. Although relatively rare, from their birth to their ultimate death as supernovae, these high mass stars dominate the chemical and mechanical evolution of the interstellar medium of galaxies. Despite their importance for understanding phenomena ranging from the dispersal of molecular clouds to the origin of gamma ray bursts and black holes, the formation and early evolution of these massive stars are poorly understood. Key issues include understanding how gas accumulates into highly condensed clumps, the precursors to clusters, and how these then fragment in to cores, the precursors of individual stars, as well as how massive protostars evolve. Studies of regions which are not yet dominated by star formation and effects of stellar feedback are essential for understanding these processes. In this colloquium I will discuss our recent work on such regions selected from the Spitzer Dark Cloud catalogue and the insights they provide into how clusters and massive stars form.
Name
Title
abstract
Sven Friedemann
Correlated Electrons at the Border of Charge and Magnetic Order in d-Metals
In this talk I will present results on the magnetic and charge order of the two d-metal compounds NbFe2 and NiS2. These rather different systems are prototypes of correlated electronic materials.
In NbFe2 we studied the suppression of 2nd order ferromagnetic order. This allows to unravel the physics at the quantum critical point where the ferromagnetic transition is suppressed to zero temperature. In fact, for systems with effective dimension d>1 like NbFe2 the ferromagnetic quantum critical point is predicted to be avoided. Indeed, the ferromagnetic quantum critical point is preempted by spin-density-wave order. We identify the underlying avoided ferromagnetic quantum critical point. Moreover, we discovered novel quantum tricritical points associated with the suppression of both the ferromagnetic and spin-density-wave order.
In NiS2 we study the faith of the Fermi surface on the approach of the Mott metal-to-insulator transition. The Mott transition at half-filling of the Hubbard model is controlled by the ratio of Coulomb repulsion and kinetic energy of the electrons. It underlies many important systems including the cuprate superconductors. Luttinger theorem dictates that electrons localize via a divergence of the effective mass as the kinetic energy is reduced [1] while further theoretical work suggests variations for 1st order transitions naturally arising for systems with lattice coupling [2]. NiS2 marks the first clear example of a transition metal compound as originally in the focus of Mott and Hubbard. We are able – for the first time – to detect the Fermi surface with quantum oscillation techniques as we tune NiS2 through the metal-insulator transition [3]. Our results confirm the expectation of a correlation driven enhanced effective mass and show signatures of the 1st order character of the metal-insulator transition as well as of the magnetic state in the metallic phase.
[1]W. F. Brinkman and T. M. Rice, Phys. Rev. B 2, 4302 (1970).
[2]A. Georges, W. Krauth, and M. J. Rozenberg, Rev. Mod. Phys. 68, 13 (1996).
[3]S. Friedemann, H. Chang, M. B. Gamża, P. Reiss, X. Chen, P. Alireza, W. A. Coniglio, D. Graf, S. Tozer, and F. M. Grosche, Sci. Rep. 6, 25335 (2016).
Name
Title
abstract
Danielle Fenech
The e-MERLIN Legacy Cyg OB2 Radio Survey: Constraining mass-loss and other stories
The Cygnus OB2 association is located in the Galactic Cygnus X region at a
distance of 1.4 kpc, making it one of the closest young massive stellar
clusters. Cyg OB2 is not only very rich in stellar density but also in its
diversity. It is known to contain a rich population of massive stars
including almost 2600 OB stars, a large number of binaries and a
considerable number of pre-main sequence stars.
I’ll report on the first results from The Cyg OB2 Radio Survey (COBRaS),
an e-MERLIN legacy project to provide a deep-field radio map of the Cygnus
OB2 association. The project aims to enhance our understanding of stellar
mass-loss and binary interactions and has been awarded a total allocation
of 252 hrs at C-band (5 GHz) and 42 hrs at L-band (1.6 GHz) to image the
core of the cluster. I will present our key findings from the completed
L-band observations and some of the unexpected surprises.
Name
Title
abstract
Nick Wrigley
Using e-MERLIN to measure the star-formation rate history of the Universe
The Great Observatories Origins Deep Survey North (GOODS-N) field, first surveyed by the HST, has been observed across numerous wavebands revealing populations of both Star- Forming Galaxies (SFG) and Active Galactic Nuclei (AGN) over wide ranges of luminosities. It has been surmised that the evolution in the star forming population appears to diverge from that in the AGN population leading to a domination of SFGs at low flux densities. The number of these starbursts can only be disentangled from the entire population if each source can be classified individually, which usually requires high angular resolution imaging. This is the motivation behind the e-MERlin Galaxy Evolution survey, e-MERGE, which expands the depth of high resolution radio imaging in the GOODS-N field to increase the number of potentially classifiable sources. By use of wide-field imaging techniques, together with a new semi-empirical primary beam-shape model for the e-MERLIN array, a deep wide-field hi-resolution map can be derived. This is the widest and deepest contiguous imaging yet obtained from e-MERLIN observations, and yet contains less than 25% of the e-MERLIN data so far observed.
Name
Title
abstract
Viktor Tóth
Star formation and the interstellar medium from sub-pc to kpc scales
I will review our results on star formation and interstellar medium in nearby Galactic star forming regions, galaxies of the Local Universe, and extragalaxies beyond a redshift of z=2. I will briefly talk about:
- some of the coldest star forming interstellar cloud cores
- young stellar objects discovered with applied statistics
- attempts to classify local galaxies
- estimations on the interstellar medium in gamma-ray burst host galaxies.
Viktor Toth
Title
abstract
Rob Kennicutt
Unveiling the Birth of Stars and Galaxies
Understanding the birth of stars is one of grand challenges of
21st century astrophysics, with impacts extending from the
formation of planets to the birth and shaping of galaxies themselves.
The challenge has been all the more difficult because the most
active birth sites are largely hidden in visible light. Thanks
to a new generation of infrared and submillimetre space telescopes
this veil has been lifted, and a complete picture of starbirth in
the Universe is emerging. They reveal an extraordinary diversity
of activities in galaxies, and an emerging history of star formation
cosmic time, extending back to some of the first stars and seeds of
galaxies. This talk will summarise what we have learned about
starbirth on cosmic scales, and highlight the challenges and
opportunities which lie ahead.
Name
Title
abstract
Richard Alexander
Building Planetary Systems
The last few years have seen an explosion in our knowledge of extra-solar planetary systems. We now know that exoplanets have an extraordinary range of properties, and almost every conceivable planetary architecture seems to exist in nature. Planets form in cold discs of dust and gas around young, newly-formed stars, and in this talk I will discuss how these protoplanetary discs shape the formation and evolution of planetary systems. I will first review the physics of protoplanetary disc evolution, and discuss new developments in both theory and observations which allow us to test our understanding of how protoplanetary discs evolve. I will then consider how these evolving disc shape the architectures of young planetary systems, with a particular focus on the new class of compact planetary systems discovered by Kepler. I will show how these tightly-packed systems can be assembled, and how mean-motion resonances between planets can be broken. Finally I will discuss how we can apply these results more broadly, and what we can hope to learn in the coming years.
Name
Title
abstract
Phil Armitage
Protoplanetary disks and the first stages of planet formation
Observations of protoplanetary disks at sub-mm wavelengths are providing
dramatically improved glimpses of the earliest phases of planet formation,
as dust grows into the first asteroid or comet-sized planetesimals. I will
discuss some of the surprising ways in which magnetic fields are predicted
to affect disk evolution, and show results from new simulations of how
pebble-sized solids may collapse to form planetesimals. The theoretical
predictions provide clues to the origin of the observed large-scale
structure in disks, but I will highlight the many open questions that
remain.
Name
Title
abstract
Lyndsay Fletcher
Solar Flares – How the Sun relaxes
The outer atmosphere of the Sun is a magnetically-dominated environment.
The magnetic field determines the transport, storage and dissipation of
energy, particularly in abrupt and impulsive events called solar flares.
Solar flares represent the rapid conversion of energy as the
magnetically stressed corona relaxes, with magnetic energy going into
plasma heating, the KE of accelerated particles and mass motions. Flares
are now observed in exquisite detail with imaging and spectroscopy
across the electromagnetic spectrum, allowing increasingly meaningful
comparisons with detailed theory. In this talk I will give a general
overview of recent flare observations and the framework in which they
are interpreted, before focusing on one aspect of flare physics, namely
the need to rapidly transport energy through the corona and accelerate
particles, and discuss recent work on models motivated in part by
processes in the Earth’s magnetosphere.
Name
Title
abstract
Johannes Courtial
Pixellated optics: from invisibility cloaks to medical eyeglasses
What does the world look like when viewed through an array of tiny telescopes? Such an array is a (relatively) novel optical component, and the telescopes are its pixels. My group investigates the optics of such pixellated devices, usually starting with the theory of the complex imaging in such devices, then working towards physical realisations.
Pixellated optical components introduce, at the boundaries between neighbouring pixels, discontinuities in the wave front of the transmitted light beams. They therefore remove the global continuity of the wavefronts, which in turn is assumed in the derivation of a number of properties (and therefore limitations) of light-ray fields. If the pixel size is chosen appropriately, the pixellation can be almost unnoticeable. The vision of our work is that, by replacing globally continuous wave fronts with piecewise continuous wave fronts, the possibilities of optics can be significantly extended.
I will give an overview of our work on pixellated optics. I will explain how pixellated surfaces can perform very general imaging, and how — at least in principle — this can be harnessed to build transformation-optics devices such as invisibility cloaks and medical low-vision aids aimed at helping patients who have lost vision in the central part of the retina.
Name
Title
abstract
Giovanni Natale
The Development of DART-Ray
In this talk I will speak about DART-Ray, the 3D dust radiative transfer code that I have been developing almost from scratch since I joined UCLan in 2011. The talk will start with general considerations about the process of development (in a wider sense not only software development), a common theme underlying almost all activities in the UCLan campus. Then, I will make a brief introduction to the 3D dust radiative transfer problem. Following that, I will summarize the long history of successes and failures that led to the current version of DART-Ray. In particular, I will point out which, in my opinion, are the dos and don’ts when involved in similar long-term projects.
Name
Title
abstract
David Armstrong
Variability in Exoplanet Atmospheres
The study of exoplanets is moving from a phase of discovery to one of detailed characterisation. Here I will look at one aspect of this: the study of exoplanet atmospheres, and in particular their variability over time. Weather is common on all planets in the Solar System; but is this also true in the unusual exoplanets now known? I will study this topic from the perspective of planetary phase curves, introducing them and exoplanet variability before showing the first detection of variability in a giant exoplanet, HAT-P-7b. This planet has a strong superrotating equatorial jet. I will show how changes in the speed of this jet, driven by either instabilities or directly by a magnetic dynamo, can cause observable shifts in the planetary phase curve and allow us to place limits on the planet’s magnetic field.
Name
Title
abstract
Derek Ward-Thompson, Don Kurtz and Robert Walsh
The Great Eclipse of 2017
Three JHI Professors recount their various adventures chasing the great eclipse of 2017. They explain how eclipses occur and the cycles of eclipses. They show various of their results from observing the 2017 eclipse, and they describe some of the remaining unsolved problems in solar physics.
Name
Title
abstract
Richard Booth
The link between planet formation and disc evolution
How and when giant planets form is a key challenge which planet
formation theories struggle to resolve, with core accretion appearing to
require longer than the typical life time of protoplanetary discs. A
variant of core accretion, in which the planet’s core grows by accreting
cm sized pebbles may overcome the time scale problem. These two
scenarios make differing predictions for the late accretion of solids,
because pebble accretion must stop before the planet accretes its
envelope, while the accretion of planetesimals is thought to continue.
This provides a way to constrain how they might have formed is through
their chemical compositions. Jupiter, being carbon rich (C/H ~ 4x
solar), provides a useful benchmark case because a high C/H ratio
produced by the late accretion of planetesimals, which are oxygen rich,
would produce a low C/O ratio. Here I will show that a high C/H ratio
can also be achieved via the radial transport of volatiles in icy dust
grains. I will discuss how this evolution appears to be reflected in the
signatures of gas being accreted onto T Tauri stars. Thus Jupiter might
have acquired its high C/H ratio through the accretion of metal rich gas,
resulting in a high C/O ratio. Juno’s imminent measurement of Jupiter’s
oxygen abundance will place constraints on how Jupiter acquired its
metals, and thus the importance of pebble versus planetesimal accretion
in forming its core.
Name
Title
abstract
Sargam Mulay
Active region jets in the Solar atmosphere
Solar jet are the ubiquitous transient events in the solar
atmosphere. They have been observed to originate from the edge of active
regions and were named as active region jets. These events are mostly
associated with sunspot regions and their signatures have been observed
in H-alpha, at UV/EUV and X-ray wavelengths. I’ll be presenting
multiwavelength observations obtained from the AIA/SDO, XRT/Hinode,
EIS/Hinode and IRIS instruments. I’ll be discussing about a study of
active region jets and their associated phenomena such as nonthermal
type III radio burst, hard x-ray emission and photospheric magnetic
activity. Plasma parameters, such as differential emission measure
(DEM), doppler velocities, electron densities, nonthermal velocities and
filling factor will be discussed using imaging and spectroscopic
instruments.
Name
Title
abstract
Claire Esau
Measuring mass segregation in young star clusters and the effects of 2D projection
The early dynamical evolution of star clusters is dependent on the initial conditions of the cluster at the time of formation. In mass segregated clusters, the most massive stars are concentrated together rather than being evenly distributed throughout the cluster. This may be either primordial, consistent with a competitive accretion-like formation scenario, or dynamical, the result of two-body interactions. In this talk, I will review how mass segregation is quantified, and will present how the degree of mass segregation in simulated clusters changes over the first few Myr of cluster evolution. I will also discuss how the degree of apparent mass segregation can vary when considering two-dimensional projections of clusters rather than three-dimensional stellar distributions.
Name
Title
abstract
Darren Graham
Developing terahertz radiation sources for particle acceleration: A route to future table-top accelerators
Radio-frequency (RF) accelerating cavities used in current particle accelerators are
typically limited to accelerating gradients of 100 MV/m. To achieve the desired increase in
acceleration gradient for future particle accelerators while enabling a reduction in the size
and cost requires a fundamentally new approach. Free-space acceleration with ultrafast
laser driven terahertz radiation sources offer a promising alternative. Such terahertz
radiation sources have a number of characteristics that makes them ideal for the
acceleration of relativistic particles within accelerators. They can provide electromagnetic
pulses with electric field strengths in excess of 100 MV/m and they have an oscillation
period which matches the particle bunch lengths that are produced in conventional RF
accelerators.
The challenge in using freely propagating electromagnetic radiation for particle
acceleration is in maximising the interaction length between the radiation and the particle
beam. The phase slippage of the radiation with respect to the particle bunch velocity, v, can
limit the effective interaction length as v < c. In comparison to using optical frequencies, the
use of terahertz frequency radiation is attractive because the particle bunches and radiation
pulses can remain in phase over longer distances.
In this talk I will present our work on developing ultrafast laser-driven terahertz
radiation sources suitable for the acceleration of charged particles and our initial work in
realising a proof-of-principle terahertz acceleration experiment. This will include a
discussion of our work on developing sources which can be focused to produce radiation
with a novel polarisation state aligned along the direction of beam propagation [1,2] and
our more recent work on developing a terahertz source with a sub-luminal phase velocity
that can be tuned to match the velocity of the particle beam [3].
[1] M. J. Cliffe et al. Generation of longitudinally polarized terahertz pulses with field amplitudes
exceeding 2 kV/cm, Applied Physics Letters. 105, 10 (2014).
[2] M. J. Cliffe et al. Longitudinally polarized single-cycle terahertz pulses generated with high
electric field strengths, Applied Physics Letters. 108, 221102 (2016).
[3] D. A. Walsh et al. Demonstration of sub-luminal propagation of single-cycle terahertz pulses for
particle acceleration, Nature Communications 8, 421 (2017).
Name
Title
abstract
David Eden
Star formation scales and efficiency in Galactic spiral arms
The role of spiral arms in the star-formation process is unclear but the production of a quantitative relationship between changes in the star-formation efficiency, and stellar initial mass function and the star-forming environment, as pertaining to the large-scale Galactic structure, is required as the basis to a predictive model of star formation.
The process of star formation is evolutionary from the atomic gas down to the stars themselves and the stages in between have associated efficiencies, and any changes to these efficiencies on the scales of Galactic structure features would hint at the stage upon which Galactic structure and spiral arms have the strongest effect. By combining the results of other studies and Galaxy-wide surveys, I will discuss each efficiency stage to try and pinpoint the scale at which star formation occurs as a result of a triggering mechanism, whether that be the large-scale structure or local feedback processes.
Name
Title
abstract
Barry Smalley
The Am stars: peculiarities, pulsations and planets
The metallic-line (Am) stars are a sub-class of peculiar A-type stars which exhibit strong Fe lines and weakening of Ca lines, but lack any strong magnetic fields. Slow rotation is thought to be a prerequisite for element separation processes, leading to observed peculiarities, and most Am stars appear to be members of relatively short period binary systems. Pulsating Am stars, found by Kepler and SuperWASP, are at odds with theory. Currently, there are only a handful of A-type stars known to host transiting short-period hot Jupiters, but finding them around Am stars poses a challenge to our understanding of their formation mechanism. In this talk I will review the Am stars, the interaction between peculiarities, pulsations and planets.
Barry Smalley
The Am stars: peculiarities, pulsations and planets
The metallic-line (Am) stars are a sub-class of peculiar A-type stars which exhibit strong Fe lines and weakening of Ca lines, but lack any strong magnetic fields. Slow rotation is thought to be a prerequisite for element separation processes, leading to observed peculiarities, and most Am stars appear to be members of relatively short period binary systems. Pulsating Am stars, found by Kepler and SuperWASP, are add odds with theory. Currently, there are only a handful of A-type stars known to host transiting short-period hot Jupiters, but finding them around Am stars poses a challenge to our understanding of their formation mechanism. In this talk I will review the Am stars, the interaction between peculiarities, pulsations and planets.
Elizabeth Stanway
Exploring the properties of distant star formation with observations and models
Observations of star-forming galaxies in the distant Universe (z > 2) are starting to confirm the importance of massive stars in shaping galaxy emission and evolution. The intense starbursts common at high redshift, and rare but identifable in local analogue populations, boast a very high specific star formation rate and are physically compact, leading to a similarly high star formation volume density. Understanding these populations, and their evolution with age and metallicity is likely to be key to interpreting processes such as supernova and gamma-ray burst rates, cosmic reionization and the chemical enrichment of the Universe through galaxy-scale winds. One avenue of exploring these populations is through the study of local galaxies which share the star formation properties of the distant Universe. A second, overlapping, approach is through modelling. Inevitably, distant stellar populations are unresolved, and the limited data available must be interpreted in the context of stellar population synthesis models. With the imminent launch of JWST and the prospect of spectral observations of galaxies within a gigayear of the Big Bang, the uncertainties in modelling of massive stars are becoming increasingly important to our interpretation of the high redshift Universe. In turn, these observations of distant stellar populations will provide ever stronger tests against which to gauge the success of, and flaws in, current massive star models.
Name
Title
abstract
Aidan Hindmarch
Spintronics: understanding pure spin currents for future applications in computing
Spintronics aims to utilise the intrinsic ‘spin’ of the electron, in addition to or instead of its charge, as a state variable to process, convey, and store digital information. This can lead to higher data storage densities, non-volatile storage & memory, radiation hardness, and encourage development of novel processing architectures. One of the primary ‘problems’ in spintronics is understanding the role of interfaces between the dissimilar classes of materials required for different device functionalities; particularly the passage of spin-polarised current, or more recently pure spin-currents, across these interfaces. After an introduction to spintronics, the basic physics of how these various devices operate, and how they compare with the current state-of-the-art in conventional electronics I will discuss some of our recent related work investigating the passage of spin-currents across interfaces. I will show how we have used neutron and synchrotron x-ray scattering techniques to assist in understanding details of the physics underpinning spintronic device functionalities.
Name
Title
abstract
David Burgess
Linking astrophysical and space plasmas with the Earth’s bow shock
Shocks in collisionless plasmas are ubiquitous, and widely invoked in astrophysics as regions of particle acceleration. The level of detailed observation in space experiments makes it possible to probe some aspects of particle acceleration that are central to commonly accepted theories. Here we discuss two examples. First we report on detailed comparisons between observations from the Cluster spacecraft and two-dimensional hybrid shock simulations. We identify characteristics in the ion velocity space distribution that match with simulations and validate a model of injection from the thermal population into a diffusive acceleration process. Secondly, we discuss observations of unusually high Mach number shocks at the Earth, similar to those seen at Saturn, which allow us further insight into their structure. In addition we discuss the relevance of these observations as analogues for shocks at supernova remnants.
Name
Title
abstract
Name
Weighing the Initial Mass Function with gravitational lenses in the backyard
To infer physical properties of a distant galaxy (e.g. its stellar mass or star-formation rate), it is almost always necessary to assume some form for the IMF, i.e. the distribution of the birth-masses of its constituent stars. Since the IMF can only be directly measured in the Milky Way and its satellites, we usually resort to assuming that it is universal and unvarying. In recent years, several studies have argued that the IMF in the cores of giant elliptical galaxies may differ from that in the Milky Way, harbouring a larger population of cool low-mass stars. The question remains controversial, however. In this talk, I will review the evidence for non-standard IMFs in ellipticals, and show how gravitational lensing by low-redshift galaxies can provide robust and powerful constraints on any variation. I will describe the latest results from our ongoing studies of the few nearby lenses known to date, and our continued efforts to enlarge the sample through novel lens-search programmes.
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Adam Avison
Uncovering the evolution of high-mass protostars with ALMA
The formation mechanism of high-mass stars still lacks a coherent evolutionary timeline comparable to the well studied mechanism observed for low-mass stars. To address this we have performed an ALMA survey toward 38 colour-luminosity selected sample (L* > 3×103 L☉) of nearby (< 5 kpc) young high mass embedded protostellar sources which will eventually go on to form high-mass stars. The survey aims to study the properties of both the thermal dust and selected organic molecular species in the protostellar objects as they begin to heat their surroundings allowing us to identify evolutionary trends.
We will present the results of the dust continuum emission from the sources, including analysis of the protocluster populations, the clustering within the observed systems, and observed spectral energy distribution properties of all protostellar sources. We will also address methods of observing continuum emission in line-dominated regions and describe some of the chemical properties of the sample.
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