National Astronomy Meeting Poster Exhibition

Binary star evolution can have a significant impact on the lifetime of massive stars, and on the manner in which they end their lives. We have explored an extensive grid of binary population synthesis models to evaluate whether supernova transient type ratios may provide an insight into the binary star fraction amongst both massive and low mass stars (Stanway et al 2020). LSST at the VRO has the potential to evaluate these type ratios with unprecedented precision, if the survey completeness and classification uncertainties can be robustly evaluated. In this poster we discuss possible constraints on stellar binarity that can be obtained from supernova surveys.

Space weather events cause disturbances of the Earth’s geomagnetic field. Rapid field fluctuations often result in the induction of quasi-direct currents, known as geomagnetically induced currents (GICs) in conductive structures on the Earth’s surface. Since GICs can be damaging to high-voltage power networks, pipelines or railways, a good forecasting capability is important in order to mitigate their impacts.
We used magnetohydrodynamic models of the magnetosphere and ionosphere, (SWMF/BATS-R-US, SWMF/BATS-R-US+RCM, GUMICS-4 and GORGON) to simulate ground magnetic field variations for the 7/8 September 2017 event, based on solar wind parameters propagated to the simulation domain. Modelled values of the northward and eastward magnetic field components show differences in both amplitude and temporal variability compared to the corresponding measurements from three UK observatories: Hartland, Eskdalemuir and Lerwick. The BATS-R-US model produces the closest agreement in terms of the northward component, whilst GORGON performs best in terms of the eastward component. The addition of Rice Convection Model (RCM) tend to overestimate the field values. Results indicate the accuracy of ground magnetic field forecast decreases with increasing latitude.
The resulting northward and eastward geoelectric field is calculated from the magnetic field using magnetotelluric transfer functions, which is then extrapolated to compute the GIC for a high-voltage UK power network. The GIC response to a uniform electric field of 1 V/km shows that substations (nodes) located near coastlines are affected the most. It is found that GICs computed from BATS-R-US modelled values are most accurate for nodes located at higher latitudes, whilst GUMICS-4 prediction performs best at lower latitudes.

Existing, commonly used, models of high-latitude electric fields and conductivities have been derived from ground-based radars and satellites since the 1970s. These have largely used measurements of plasma densities and velocities, or magnetic field measurements to derive the electric field, or the conductivity, individually and separately. These models are then used as drivers in coupled ionosphere-thermosphere models, which then calculate the response of the whole upper atmosphere system. However, the feedback contribution of the neutral atmosphere is not incorporated into these electric field and conductivity models. So each new model step uses an unmodified driver. For this preliminary study we will apply Machine Learning techniques to look for signatures of feedback between electric field and conductivities in EISCAT radar and satellite databases. We will also look at the contribution of the neutral atmosphere to the coupled system, in terms of neutral dynamics and temperatures, and, in particular, to the chemical changes due to upwelling of the neutral atmosphere measured by Fabry-Perot Interferometers co-located with the EISCAT radars.

One day after the discovery of the 2018 classical nova (CN) eruption of V392 Persei, a gamma-ray signal was detected from the position of V392 Per by the Fermi Gamma-Ray Space Telescope’s Large Area Telescope, sparking a panchromatic campaign of photometric and spectroscopic observations. As one of sixteen novae to date with detected gamma-ray emission, V392 Per provided an opportunity to probe the mechanism of the emission. This emission is thought to be due to particle acceleration by shocks between two or more different nova ejecta components, produced in multiple ejection episodes early in the eruption.

V392 Per, a known dwarf nova (DN), is the only DN whose subsequent CN eruption was detected in gamma-rays. It is one of only two DNe to later exhibit a CN eruption, and one of only nine cataclysmic variables to show clear evidence of both DN outbursts and a CN eruption. Archival observations available from the American Association of Variable Star Observers database, spanning over a decade, provide further information about the accretion history of the system.

A crucial component of the observing strategy was the use of the Neil Gehrels Swift Observatory, utilising its UV photometry and X-ray spectroscopy. I will present these observations, along with coordinated optical photometry and spectroscopy from ground based telescopes – spearheaded by the Liverpool Telescope – and discuss their significance.

Modern observations of astrophysical spectra are in many cases of higher quality than those observed within a laboratory setting. This can result in inaccurate conclusions being drawn. Accurate measurements of spectral line wavelengths and oscillator strengths are required particularly for use in stellar models and chemical abundance calculations, and in surveys such as Gaia-ESO or APOGEE and future surveys. Laboratory astrophysicists aim to measure and improve the atomic data most useful for astronomers, for light and heavy elements across the spectrum, from IR to vacuum-UV (VUV).

Atomic data of iron-group elements are important due to their high abundance and line-rich spectra. Lanthanides are under study as their line-rich spectra overwhelms at sites of r-process production. Our high-resolution Fourier Transform Spectrometry (FTS) group at Imperial College London has, supported by STFC, been providing accurate atomic data for use in astrophysics.

Recent results include new Fe I oscillator strengths for use in Galactic surveys (Belmonte et al. 2017), and 1130 wavelengths and transition probabilities of parity-forbidden Lines for Mn II (Liggins et al. 2021). The first high-resolution measurements of UV transition wavelengths of Cr III are being used as wavelength standards (Smillie et al. 2008). There has been an order of magnitude improvement in atomic data for Co III (Smillie et al. 2016) and in the accuracy of energy levels and transition wavelengths for Mn II (Liggins et al. 2021) and Ni II (Clear, PhD, Imperial College, 2018). Analysis of hyperfine structure of Co II lines has led to the determination of A constants for 292 levels (Ding and Pickering, 2020).

Using new spectra recorded, analysis is underway for accurate wavelengths and atomic energy levels in Mn I and Fe III. The investigation into the spectrum of Neodymium, with a focus on Nd III, has also begun. We welcome data requests!

We present the results of a study of the demographics of low-mass stellar systems at high redshift in a suite of cosmological simulations from the First Billion Years Project (FiBY). We have identified a population of objects at z=6 which we believe show characteristics to be early ancestors of local Universe globular clusters (GCs), which we dub “infant GC candidates”. These candidates are compact in size, have little dark matter and high gas content, thus they are likely to host further episodes of star formation. From their evolution until z=6, the process of star formation in these objects appears to be bursty in nature, which could be an early manifestation of the ‘multiple population phenomenon’ we currently observe in low-redshift GCs. In our simulations, these high-density GC ancestors tend to form in groups located within the disks of their host galaxies. We also propose a new link between present-day globulars and their high-redshift counterparts, which we have identified by studying the global properties of these infant GC candidates and the relationship with their large-scale environment. We find that the relation between the specific star formation rate of a host galaxy and the mass of the most massive GC holds across a large range of redshifts, thus providing a powerful way to probe both the early evolution of this class of stellar systems as well star formation across cosmic time.

Transverse oscillations are observed both in coronal loops (as standing waves) and in open magnetic tubes (as propagating waves).
In coronal loops, standing kink waves can be observed over a large number of periods, without showing any damping.
These decayless kink oscillations are interpreted as the result of a continuous driver at the footpoints of the loop.
However, analytical works predict that kink waves are subject to a cut-off frequency, that results from the atmospheric stratification.
As a result of this cutoff, only high-frequency waves can propagate through the transition region.
Current 3D MHD simulations of standing kink waves only take into account the coronal part of the loop (the driver is located at the top of the transition region), and thus are not sensitive to this cut-off effect.

We present a new numerical setup that allows to study the propagation of a kink wave through the transition region.
A magnetic tube is driven at the base of the chromosphere at different frequency, and we study the propagation of the resulting kink wave through the transition and into the corona.
We compare the resulting behaviour to several analytical formulas that predict the cut-off frequency of kink waves.

The interplay of galaxy components shapes their evolution and the resulting output energy distribution. By comparison of observations of their integrated light to stellar population synthesis models, valuable information about the galaxy's properties can be inferred. This comparison is complicated by the severe and poorly understood impact of dust absorption and reemission - an issue which will become particularly important in the Webb Era. We investigate the impact of various dust parameter assumptions on model galaxy spectra associated with Binary Population and Spectral Synthesis (BPASS) models. Grids of models will be produced through an investigation of the extent to which dust emission models can be associated with individual galactic stellar populations, using comparisons with archival data. The study then informs a preliminary release of dust absorption and reemission models as part of the BPASS project. Such models will inform and accommodate the wide variety of dust grain size distributions and compositions which are likely to vary between galactic environments.

Binary stars evolve into chemically-peculiar objects or binary compact objects, releasing significant amounts of enriched gas, making them the main driver of the Galactic enrichment in heavy elements (and for some of those, the only driver). During their evolution, they go through a series of interactions, among which tides are the most common kind.

To pin down tidal interactions and the evolution of binary stars, we implement an updated prescription in the stellar population code binary_c. Relying on Zahn's theory of tides, and on grids of MESA main-sequence models covering an extensive mass range (0.1 to 320Msun), we use detailed structural quantities to derive the parameters lambda and E2 that rule equilibrium and dynamical tides respectively. We augment the ubiquitous BSE implementation by adding those parameters in the binary_c code.

I will present a few applications of this new determination of circularisation and synchronisation timescales: rates of stellar mergers, gamma-ray bursts and gravitational wave progenitors are updated, while the comparison between the derived and observed period-eccentricity diagrams for clusters provides an accurate estimate of their ages.

We present first a brief overview of an ongoing multi-wavelength
campaign to study the evolution of microflares in active region cores.
The primary new instrument is the Solar X-ray Monitor
(XSM) on board the Chandrayaan-2 mission, which has been providing
since 2019 X-ray spectra with a greater sensitivity than
previous instruments. We then present an analysis of AR12759 as it
crossed the disk in Apr 2020. Using a new Hinode EIS calibration, we
find that the AR core chemical abundances are constant over time,
with the coronal values of Del Zanna (2013). XSM clearly shows
that the abundances of the flare loops are close to photospheric
values, providing new constraints on the chemical fractionation
process. We also present the evolution of the temperature of the
flare loops as obtained from XSM, SDO AIA and Hinode XRT,
and briefly discuss the limitations of current instrumentation
to study the hot (4-12 MK) emission in flares.