National Astronomy Meeting Poster Exhibition

Carbon is essential for life, yet there remains uncertainties in when and where it is formed. The two main sources are massive stars and AGB stars. In this talk I will discuss how massive stars produce and eject carbon into the Universe. In single stars this can occur through wind mass loss and the ejection of the envelope in a core collapse supernovae. Using the MESA stellar evolution code I will show how the carbon yields vary between these different processes and thus varies over time. I will show how carbon yields vary between single and binary stars evolved up to core collapse as well their post supernovae explosive yields. I will discuss the role that a star being in a binary has on the production of carbon. Massive stars in binaries can be stripped by the companion, leading to additional mass loss. However I will show that it is the change in the core structure of the star, due to mass loss, that leads to an increase in the carbon yield and not the additional mass lost by itself.

The High-Resolution Coronal Imager (Hi-C) was launched for a third time on 29th May 2018, resulting in 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of approx. 4 s, and a plate scale of 0.129 arcsec^2/pixel. Using this data co-aligned with SDO/AIA 17.1nm observations, this presentation will outline results from investigating the widths of 49 coronal structures. Firstly, evidence of substructure within the loops that is not detected by AIA will be outlined. It is found that Hi-C 2.1 can resolve individual sub-loop strands as small as approx. 202 km, though the more typical strand widths seen are around 513 km. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss – this part of the corona is filled with ubiquitous, low emission, low density magnetic strands. Secondly, even at these superior spatial scales there may be evidence for further substructuring within the HiC strands themselves. Thus, the width profile intensity variations are reproduced by simultaneously fitting multiple Gaussian profiles using a nonlinear least-squares curve-fitting method. In total, 183 Gaussian profiles are examined and the full width at half maximum determined with most frequent structural widths about 450–575 km with 47% of the strand widths beneath SDO/AIA 17.1nm resolution. These appear to be the result of multiple strands along the integrated line of sight that can be resolved, rather than being the consequence of even finer sub-resolution elements. Finally, the change of strand width along strand length is examined – open fan magnetic strand structures display an observational width increase from the base while closed structures show little variation. The implications of these results on coronal loop modelling will be discussed.

The elusive low surface brightness components of galaxies – such as stellar halos and tidal features – are crucial components for understanding the way in which galaxies grow as well as for tracing their dark matter halos. I will present results from a state-of-the-art survey designed to probe low surface brightness structures in the nearby M81 Group. Using Hyper Suprime-Cam on the Subaru Telescope, our survey maps individual red giant branch stars over more than 11 square degrees. In this poster, I will present a giant tidal stream that we have discovered from the M81 Group dwarf galaxy F8D1, discussing its characteristics and the origin of its disruption. I will also discuss how this disruption might explain the properties of F8D1 itself, which is one of the closest known examples of the ultra-diffuse galaxy population.

Magnetopause reconnection drives magnetospheric dynamics, transferring energy from the solar wind into the Earth’s magnetosphere. During this process, we commonly observe helical magnetic field structures know as flux ropes. These structures are thought to play a role in the energy transfer processes taking place and in transporting magnetic flux from the magnetopause into the magnetotail. Previous studies have statistically investigated the properties of flux ropes observed on the magnetopause using various spacecraft, recently highlighting the importance of interactions between flux ropes. Here, we use Magnetospheric Multiscale (MMS) mission data to specifically investigate potentially recently-formed flux ropes observed near electron diffusion region (EDR) encounters. We characterise the properties of these ‘young’ flux ropes, including their size, core field strength, flux content and topology, as well as investigating if the properties of the EDR relate to the flux rope observations. We focus on what these properties can tell us about the formation mechanisms of the flux ropes and any flux rope interactions which may have taken place. We compare our observations to other studies to determine if such flux ropes have unique properties, forming a distinct category of flux ropes, or follow previously reported trends.

Dense stellar systems such as globular and nuclear star clusters have long been considered as environments ideally suited to harbour intermediate-mass black holes (IMBH). Still undetected, this class of astrophysical objects is a crucial missing link in the population of cosmic black holes. Current indirect observational searches for IMBHs inevitably rely on dynamical models, which are often unable to capture the true phase space complexity of the host stellar system.

In this contribution, we present a new family of self-consistent dynamical models describing a spherically symmetric, isotropic dense stellar system with a central black hole. The family is defined by a truncated isothermal distribution function in phase space, suitably modified to allow for the presence of a central point mass. We propose a novel treatment of the boundary conditions of the relevant Poisson equation, which is then solved approximately using matched asymptotics. Such an approach enables us to conduct a careful exploration of the parameter space of these models, which reveals the existence of a rapid change in the structure of the solution and the existence of two regimes, where the equilibria are dominated either by the mass of the black hole or the host system. This new class of models offers a fruitful playground for the study of the behaviour of the stars in the proximity of a central black hole within a realistic self-consistent potential.

The proposed prescription for the inclusion of the central point mass can be readily applied to more complex anisotropic, rotating, non-spherical equilibria, which will allow us to address a number of limitations of current modelling approaches and paves the way towards a more informative assessment of the presence of IMBHs in dense stellar systems.

Theoretical models of different possible MHD equilibria and wave propagation are required to better explain the ever increasing number of hi-resolution solar observations thanks to modern ground- and space-based instruments (SDO, Hinode, Solar Orbiter, DST, SST, DKIST). In this work (Skirvin et. al, MNRAS 2021), a numerical approach has been used to obtain the dispersion diagrams and eigenfunctions of any arbitrarily-symmetric inhomogeneous equilibrium. The proposed technique implements the shooting method to match necessary boundary conditions on continuity of displacement and total pressure of the slab or cylindrical waveguide. This approach was tested against well-known analytical solutions for MHD waves in uniform waveguides. This work is then extended further by investigating the dispersion diagrams and eigenfunctions when the equilibrium plasma density and background flow are radially inhomogeneous modelled as a Gaussian and sinc(x) profile. The resulting eigenfunctions of perturbed total pressure and displacement in an inhomogeneous plasma are compared with the uniform model and the physical differences in spatial structure are discussed which have implications for observers. This developed numerical technique can be used to analyse the MHD wave generation by small scale photospheric vortices under equilibria which are routinely observed in the solar atmosphere. The Solar Orbiter and DKIST era will provide observational data at much greater spatial resolution such that this new tool can be used in parallel to gain a better understanding of the waves which are observed.

New deep learning analyses are a promising new method of background rejection and event reconstruction for Imaging Atmospheric Cherenkov Telescopes (IACTs), particularly in the context of the next generation Cherenkov Telescope Array (CTA). This is as they allow for sensitive analysis of complete camera images at high speed. Unlike other fields of astrophysics where deep learning is being used to characterise astronomical sources, deep learning use in IACT astronomy is comparatively unique in that the analysis targets are Extended Air Showers in Earth's atmosphere. As such, we have access to large datasets of highly complex Monte Carlo simulations of both the air shower particle physics and our detectors. However, this in turn leads to a highly non-trivial domain gap problem when attempting to apply deep learning methods trained on simulations to real data. I will present state of the art results displaying the combined effects of custom simulations, Bayesian optimisation and graph-based network architectures to attack this problem.

The relativistic (MeV) electron population in the outer Van Allen radiation belt is highly dynamic and strongly coupled to geomagnetic activity such as storms and substorms driven by the interaction of the magnetosphere with the solar wind. Electron content and energy within the outer belt can vary on timescales of hours to days, dictated by the continuously evolving influence of simultaneously occurring acceleration and loss processes. The exact nature and relative significance of each of these processes is highly complex and far from fully understood. Using a continuous 12-year dataset from the Proton Electron Telescope (PET) on board the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX), we statistically examine the relative variation of electron flux in the bounce loss cone in relation to trapped flux. We find that during storm main phase and early recovery phase, there is a proportional increase in flux entering the bounce loss cone outside the plasmapause. Dawn-side loss enhancement is sustained throughout the recovery phase while the post-noon sector is enhanced around minimum Sym-H and quickly diminishes. The detailed MLT-variation of loss is also examined and compared with wave power maps where a possible causal relationship is discussed. These new results reveal important changes in the balance of radiation belt acceleration and loss processes with geomagnetic activity.

γ-ray bursts (GRBs) are transient cataclysmic events, whose role became central in the new multi-messenger era. In the present work I propose a novel investigation of the GRB emission mechanism, via time-resolved spectral analysis of the X-ray tails of bright GRB pulses observed with the XRT instrument onboard the Neil Gehrels Swift Observatory, discovering a unique relation between the spectral index and the flux. The investigation of the spectral evolution during the GRB tail is an ideal diagnostic to understand the connection between the emission processes, the cooling processes and the outflow environment. I thoroughly discuss possible interpretations in relation to current available models and I show the incompatibility of our results with the standard high latitude emission. Our results for the first time strongly suggest evidence of adiabatic cooling of the emitting particles, shedding light on fundamental physics of relativistic outflows in GRBs. Finally I discuss the crucial role of future wide-field X-ray telescopes, such as the mission concept Theseus, for the characterisation of the GRB tail emission, highlighting also its importance in the multi-messenger context.

Active regions often show S-shaped structures in the corona called sigmoids. These are highly sheared and twisted loops formed along the polarity inversion line. They are considered to be one of the best pre-eruption signatures for CMEs. Here, we investigate the thermodynamic evolution of an on-disk sigmoid observed during December 24-28, 2015. For this purpose, we have employed Emission Measure (EM) and filter-ratio techniques on the observations recorded by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and X-ray Telescope (XRT) onboard Hinode. The EM analysis showed multi-thermal plasma along the sigmoid and provided a peak temperature of 10-12.5 MK for all observed flares. The sigmoidal structure showed emission from Fe XVIII (93.93 Å) and Fe XXI 128.75 Å) lines in the AIA 94 and 131 Å channels, respectively. Our results show that the hot plasma is often confined to very hot strands. The temperature obtained from the EM analysis was found to be in good agreement with that obtained using the XRT, AIA, and GOES filter-ratio methods. These results provide important constraints for the thermodynamic modeling of sigmoidal structures in the core of active regions. Moreover, this study also benchmarks different techniques available for temperature estimation in solar coronal structures.