Context. Classical novae are eruptions on the surface of a white dwarf in a binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell of gas and dust around the system. The three-dimensional structure of these shells is difficult to untangle when viewed on the plane of the sky. In this work a geometrical model is developed to explain new observations of the 2015 nova V5668 Sagittarii. Aims. We aim to better understand the early evolution of classical nova shells in the context of the relationship between polarisation, photometry and spectroscopy in the optical regime. To understand the ionisation structure in terms of the nova shell morphology and estimate the emission distribution directly following the light-curve's dust-dip. Methods. High-cadence optical polarimetry and spectroscopy observations of a nova are presented. The ejecta is modelled in terms of morpho-kinematics and photoionisation structure. Results. Initially observational results are presented, including broadband polarimetry and spectroscopy of V5668 Sgr nova during eruption. Variability over these observations provides clues towards the evolving structure of the nova shell. The position angle of the shell is derived from polarimetry, which is attributed to scattering from small dust grains. Shocks in the nova outflow are suggested in the photometry and the effect of these on the nova shell are illustrated with various physical diagnostics. Changes in density and temperature as the super soft source phase of the nova began are discussed. Gas densities are found to be of the order of 10 9 cm −3 for the nova in its auroral phase. The blackbody temperature of the central stellar system is estimated to be around 2.2 × 10 5 K at times coincident with the super soft source turn-on. It was found that the blend around 4640 Å commonly called 'nitrogen flaring' is more naturally explained as flaring of the O ii multiplet (V1) from 4638 -4696 Å, i.e. 'oxygen flaring'. Conclusions. V5668 Sgr (2015) was a remarkable nova of the DQ Her class. Changes in absolute polarimetric and spectroscopic multi-epoch observations lead to interpretations of physical characteristics of the nova's evolving outflow. The high densities that were found early-on combined with knowledge of the system's behaviour at other wavelengths and polarimetric measurements strongly suggest that the visual 'cusps' are due to radiative shocks between fast and slow ejecta that destroy and create dust seed nuclei cyclically.

A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of $0.5\substack{+1.4 \\-0.2}$ kpc for V4362 Sgr and 6.7 ± 3.5 kpc for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07″/year for DO Aql and 0.32″/year for V4362 Sgr. A preliminary investigation into the ionisation structure of the nova shell associated with V4362 Sgr is presented. The observed ionisation structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects.

Research into the processes of photoionised nebulae plays a significant part in our understanding of stellar evolution. It is extremely difficult to visually represent or model ionised nebula, requiring astronomers to employ sophisticated modelling code to derive temperature, density and chemical composition. Existing codes are available that often require steep learning curves and produce models derived from mathematical functions. In this article we will introduce PyCross: PyCloudy Rendering Of Shape Software. This is a pseudo 3D modelling application that generates photoionisation models of optically thin nebulae, created using the Shape software. Currently PyCross has been used for novae and planetary nebulae, and it can be extended to Active Galactic Nuclei or any other type of photoionised axisymmetric nebulae. Functionality, an operational overview, and a scientific pipeline will be described with scenarios where PyCross has been adopted for novae (V5668 Sagittarii (2015) & V4362 Sagittarii (1994) and a planetary nebula (LoTr1). Unlike the aforementioned photoionised codes this application neither requires any coding experience, nor the need to derive complex mathematical models, instead utilising the select features from Cloudy / PyCloudy and Shape. The software was developed using a formal software development lifecycle, written in Python and will work without the need to install any development environments or additional python packages. This application, Shape models and PyCross archive examples are freely available to students, academics and research community on GitHub for download.

A computer vision system for measuring the displacement and bending angle of ionic polymer–metal composites (IPMC) was proposed in this study. The logical progression of measuring IPMC displacement and bending angle was laid out. This study used Python (version 3.10) in conjunction with OpenCV (version 4.5.5.64) for the development of the vision system. The coding functions and the mathematical formulas used were elaborated on. IPMC contour detection was discussed in detail, along with appropriate camera and lighting setups. Measurements generated from the vision system were compared to approximated values via a manual calculation method. Good agreement was found between the results produced by the two methods. The mean absolute error (MAE) and root mean squared error (RMSE) for the displacement values are 0.068080668 and 0.088160652, respectively, and 0.081544205 and 0.103880163, respectively, for the bending angle values. The proposed vision system can accurately approximate the displacement and bending angle of IPMCs.