2023 Seminar Abstracts

Iain Hannah

Title: Focusing on faint solar X-rays

Solar flares impulsively release energy in the Sun’s atmosphere, with a substantial amount going into accelerating electrons, which subsequently heat the lower solar atmosphere material up to 10s MK. X-ray observations above a few keV (hard X-rays, HXR) are a crucial tool for understanding the properties of this thermal and non-thermal emission. NASA’s RHESSI mission did – and the STIX telescope on ESA’s Solar Orbiter does – study this in large flares and down to events many orders of magnitude smaller (microflares). Both instruments are indirect imagers, which use pairs of grids to block out the X-rays to encode spatial information, but this limits their sensitivity and dynamic range. This is problematic as one way to better understand the details of flare’s physical processes is to probe the faint emission from coronal energy release sites as well as the weak signatures from even smaller impulsive events (nanoflares). A focusing optics X-ray telescope would go beyond RHESSI/STIX to make such observations possible but unfortunately no solar-dedicated satellite exists to do this. Instead, we have been using NASA’s NuSTAR, an astrophysics mission launched in 2012, with X-ray focusing optics to directly observe faint sources with highly sensitive imaging spectroscopy. Most of NuSTAR’s time is spent on targets outside of the solar system but some is spent on the Sun. I will present some of the challenges of using an astrophysics telescope for solar work, as well as some of the results we have obtained from our NuSTAR solar campaigns, and prospects for the future.

John Stott

Title: Anisotropic quenching of satellite galaxies and novel galaxy cluster detection

A recent observational result finds that the quenching of satellites in galaxy groups at z = 0.1 has an angular dependence relative to the semi-major axis of the central galaxy. This observation is described as ‘anisotropic quenching’ or ‘angular conformity’. Here, I present the variation in the colour of a mass-limited sample of satellite galaxies relative to their angle from the major axis of the brightest cluster galaxy in the CLASH clusters up to z ~ 0.5, 4 Gyr further in lookback time. The same result is found: galaxies close to the major axis are more quenched than those along the minor axis. I also find that the star-forming galaxies tend to avoid a region +/- 45 degrees from the major axis. Simulations predict that this quenching signal is driven by AGN outflows along the minor axis, reducing the density of the intergalactic medium and thus the strength of ram pressure. I will discuss potential alternative mechanisms. In addition, I will describe 2 separate projects using quasars and machine learning in order to discover new galaxy clusters.

Licia Ray

Title: Neither here nor there: The coupling between giant planets and their surroundings

In this talk, I’ll focus on describing the interaction between Jupiter’s upper atmosphere and the surrounding plasma and magnetic environment. This rapidly rotating planet hosts the most volcanically active object in the solar system, Io. The interplay between the moon and the planet generates a vast magnetosphere that is ultimately coupled to the uppermost parts of the planetary atmosphere. I’ll describe the processes that generate Jupiter’s bright auroral emissions, discuss energy and angular momentum transport throughout the system, and touch on one of the Solar System’s biggest mysteries, the giant planet energy crisis.

Soumavo Ghosh

Title: Can (stellar) bars form in presence of hot thick discs?

Stellar bars are ubiquitous in disc galaxies (including the Milky Way) in the Local Universe, with about two-thirds of them harbouring a stellar bar. Bars are present in high redshift (z ~1) disc galaxies as well. Recent JWST observations further revealed the presence of conspicuous stellar bars even at a higher redshift (z ~ 2.3). At these high redshifts, the discs are known to be thick, kinematically hot (and turbulent), and more gas rich. A consensus about whether these bars are tidally-induced or formed due to the internal gravitational instability is still largely missing. In this talk, I will present results regarding the bar formation scenario in the presence of (kinematically-hot) thick discs using a suite of N-body models of (kinematically cold) thin and (kinematically hot) thick discs. I will further discuss the physical processes involved behind different bar formation scenarios as well as how the thick disc mass fraction impacts the properties and morphology of the resulting stellar bar.

Shih Ping Lai

Title: Exploring the Early Stages of Star Formation

he formation of stars remains a fundamental question in astrophysics. In this talk, I will discuss our ongoing research on the physical and chemical conditions that govern the early stages of star formation. Specifically, I will cover four projects:
1. Estimating the age of prestellar cores (Lin et al. 2020).
2. Investigating mass accretion towards protostellar disks (Thieme et al. 2022, Hsieh et al. 2020).
3. Analyzing magnetic fields in star-forming regions (Ko et al. 2020).
4. Modeling the density structure of first core candidates (Duan et al. 2023)
While our understanding of star formation is far from complete, these projects have enabled us to make some progress in unraveling the complexities of this intriguing process.

Ian Sherrington

Title: Tribology for Beginners

Tribology is the study of interacting surfaces in relative motion and concerns the related phenomena of friction and wear, both of which have placed challenges on engineers throughout history. Lubrication remains the main tool for controlling these effects and the presentation will briefly describe how effective lubrication is achieved in different circumstances. It will also explain how the science of tribology, originally only relevant in relation to the economic landscape, now has a fundamental role to play in supporting sustainable engineering systems. The presentation will close by describing how research in tribology at the Jost Institute is making pioneering efforts to extend the traditional limitations in the operation of machine elements through the sub-topic of “tribotronics”.

Ant Whitworth

Title: Massive cloud/cloud collisions and their aftermath

Interstellar clouds regularly collide with one another at mildly supersonic velocities. When they do, they produce a shock-compressed layer of gas, star formation is triggered in this layer, and feedback from the most massive stars excites an HII region which breaks out of the cloud and disperses the residual gas. I will present numerical simulations of this process, and discuss the morphological and kinematic features that characterise it, including monolithic filaments, hub-and-filament systems and filamentary networks; approximately spherical and bipolar HII regions; second generations of stars; and what one can infer analytically about (a) the parameters of the original collision (velocity and impact parameter), (b) the density and linear extent of the layers and filaments), (c) the net ionising output of the massive stars, and (d) the amount of ionising radiation that escapes into the surroundings.

Rob Wicks

Title: The radial scaling of the magnetic field spectrum in the near Sun solar wind; Parker Solar Probe and aims for a map of the structure of the inner heliosphere with MeerKAT.

The solar wind flows out from the Sun, expanding to fill interplanetary space and forming the medium through which coronal mass ejections and energetic particles travel. The magnetic field of the Sun is entrained within the solar wind. On the largest scales the classic Parker spiral shape is formed, but close to the Sun the field is a complex mix of open and closed field lines. The magnetic field and plasma on open field over expands to form the majority of the solar wind. This means that understanding how energetic particles made by flares and CMEs will escape into the heliosphere and where they will end up is difficult. Building a clearer picture of how the solar wind escapes the corona and the magnetic field structure that forms is one of the science goals for two current spacecraft missions, the ESA Solar Orbiter and the NASA Parker Solar Probe (PSP). These missions provide in-situ measurements of the magnetic field and plasma in the inner heliosphere.
Another way to investigate the near-sun plasma and magnetic field structure is through the scintillation of radio signals from distant compact objects. As radio waves pass through the inner heliosphere they are scattered and polarised by structures in the plasma electron density. The structure of the magnetic field can be inferred from the alignment of electron structures, which (theoretically) align along the magnetic field direction and imprint that into the anisotropy of the scintillation of the radio waves.
In this talk I will present results from Lotz, Nel, Wicks et al., ApJ 2023 where we show that the magnetic field spectrum measured by PSP has a characteristic ‘spectral break’ close to the ion cyclotron wave resonant scale, and including a comparison with previous results from spacecraft at further distances from the Sun, that this persists and scales with distance in the same way from 0.1 au to 5 au. This is the scale at which electron density structures form and align with the magnetic field. At the same time that this measurement was made by PSP, the team that authored this paper also coordinated radio scintillation observations by the MeerKAT radio telescope in South Africa. These images are still under analysis, but I will describe how the combination of PSP and MeerKAT data may be able to provide a map of the near-Sun solar wind magnetic field structure.

Beth Biller

Title: Partly Cloudy with Molten Iron Rain: Characterising Exoplanet Atmospheres via Direct Imaging

Direct detection and direct spectroscopy have great potential for advancing our understanding of extrasolar planets, in particular, the dynamics, composition, and cloud chemistry of their atmospheres. I will discuss JWST early release science results on directly imaged exoplanet atmospheres. I will present both the first >10 um image of any exoplanet and the first direct spectrum of an exoplanet with JWST. These datasets reveal dynamic and turbulent atmospheres for these objects, via spectral features deriving from both silicate clouds and non-equilibrium chemistry. Variability attributed to this cloud structure already appears to be a persistent feature in free-floating planetary mass objects, potentially due to the breakup of thick silicate and iron condensate clouds during the L to T spectral type transition. Directly imaged planetary companions are likely to be equally variable. I will also discuss the prospects for detecting and characterising exoplanet weather patterns through monitoring the intrinsic photometric variability of these objects.

Kate Pattle

Title: Interstellar Magnetic Fields: From Star Formation to Galaxy Evolution

Recent advances in submillimetre dust emission polarimetry are revolutionizing our understanding of the magnetic fields which thread the interstellar media of the Milky Way and other galaxies. In this talk I will discuss the insights which we are gaining into the energy balance, dynamics and evolution of the magnetized interstellar medium from recent observations made with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). These observations span size scales ranging from nearby star-forming regions, observed as part of the JCMT BISTRO Survey, to the disc and superwind of the starburst galaxy M82. I will particularly discuss how we can infer the dynamic importance of magnetic fields from observations of magnetic field geometries in the dense interstellar medium, and the emerging evidence for how the interaction between magnetic fields, outflows and feedback may influence star formation efficiency on both small and large scales.