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Supernovae are the explosive death of stars. Massive stars (M>8M⊙) end their lives as core-collapse supernovae. A white dwarf that gains mass and reaches the Chandrasekhar mass (∼1.4M⊙) explodes as a thermonuclear supernova. Supernovae can be broadly split into two classes based on whether hydrogen is present in the spectrum. Type I supernovae lack hydrogen and type II supernovae exhibit hydrogen.Type IIn supernovae are a mysterious subclass, they are highly inhomogeneous and are characterised by complex Balmer line profiles with a narrow component which is interpreted as interaction between the SN ejecta and a dense, pre-existing hydrogen-rich circumstellar medium. The progenitor paths for type IIn supernovae are unclear, at least one transient, SN2005gl has pre-explosion imaging revealing the progenitor to be a luminous blue variable. These luminous blue variables are massive evolved stars that undergo episodic mass loss which may form the required circumstellar material for the type IIn phenomenon. However recent studies on the environments of type IIn supernovae reveal that these transients are not strongly associated with regions of ongoing star formation.These environmental studies are a powerful indirect method to constrain progenitor paths. In the first part of this thesis, I set out a classification scheme for type IIn supernovae and apply it to archival spectral data. Then using this sample with robust classifications, I observe the hosts of type IIn supernovae with the Liverpool Telescope, the Isaac Newton Telescope and the Las Cumbres Observatory Global Telescope Network 2m. Using these data, I create continuum subtracted Hα images and apply the novel pixel statistics technique, normalised cumulative ranking. This method is used to gauge the association of a SN position with the Hα emission in the host. There is a mass ladder in terms of this association, the more massive the progenitor, the better the supernovae follow the emission. I present the results of these pixel statistics as well as the radial distributions of type IIn supernovae in order to investigate possible progenitor routes.In the second part of this thesis, I investigate the environments of classical novae in the Andromeda galaxy, M31. Classical novae are a subset of cataclysmic variable where a white dwarf accretes hydrogen-rich material from a companion via Roche-lobe overflow, Once sufficient material has been accreted, a thermonuclear runaway occurs on the surface of the white dwarf and a portion of the accreted material is ejected. Generally, classical novae can be split into two spectral classes, Fe II and He/N, based on their characteristic non-Balmer lines.Previous work has suggested the existence of different populations of classical novae in terms of their radial distribution, or association to the bulge or disc of M31. I investigate the possibility that the spectral classes of classical novae can be separated based on their radial distributions. The progenitor systems of He/N classical novae may have a higher mass white dwarf and may be expected to be associate with the younger populations in the disc of M31. Firstly I present the largest spectroscopically confirmed M31 classical nova sample. Then as well as a radial analysis, for the first time, I will implement the normalised cumulative ranking method on classical novae. In this case with GALEX NUV and FUV. I compare the spectral classes to each other in terms of both their radial distributions and association to the UV emission.

We present pre-explosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST \\(R\\)-band to Spitzer 4.5 \\(\\mu\\)m. Fitting to blackbody and red supergiant (RSG) spectral-energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600 \\(R_{\\odot}\\) circumstellar shell of dusty material with a mass \\(\\sim\\)5\\(\\times10^{-5} M_{\\odot}\\) surrounding a \\(\\log(L/L_{\\odot})=4.74\\pm0.07\\) and \\(T_{\\rm eff}=3920\\substack{+200\\\-160}\\) K RSG. This luminosity is consistent with RSG models of initial mass 11 \\(M_{\\odot}\\), depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in pre-explosion Spitzer 3.6 \\(\\mu\\)m and 4.5 \\(\\mu\\)m imaging, exhibiting \\(\\sim\\)70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with \\(\\kappa\\)-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as \\(\\alpha\\) Orionis (Betelgeuse).

The nearby type II supernova, SN2023ixf in M101 exhibits signatures of early-time interaction with circumstellar material in the first week post-explosion. This material may be the consequence of prior mass loss suffered by the progenitor which possibly manifested in the form of a detectable pre-supernova outburst. We present an analysis of the long-baseline pre-explosion photometric data in \\(g\\), \\(w\\), \\(r\\), \\(i\\), \\(z\\) and \\(y\\) filters from Pan-STARRS as part of the Young Supernova Experiment, spanning \\(\\sim\\)5,000 days. We find no significant detections in the Pan-STARRS pre-explosion light curve. We train a multilayer perceptron neural network to classify pre-supernova outbursts. We find no evidence of eruptive pre-supernova activity to a limiting absolute magnitude of \\(-7\\). The limiting magnitudes from the full set of \\(gwrizy\\) (average absolute magnitude \\(\\approx\\)-8) data are consistent with previous pre-explosion studies. We use deep photometry from the literature to constrain the progenitor of SN2023ixf, finding that these data are consistent with a dusty red supergiant (RSG) progenitor with luminosity $\\log\\left(L/L_\\odot\\right)$$\\approx\\(5.12 and temperature \\)\\approx\\(3950K, corresponding to a mass of 14-20 M\\)_\\odot$

We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multi-peaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN 2022oqm was detected 13.1 kpc from its host galaxy, the face-on spiral galaxy NGC 5875. Extensive spectroscopic coverage reveals an early hot (T >= 40,000 K) continuum and carbon features observed \\(\\sim\\)1~day after discovery, SN Ic-like photospheric-phase spectra, and strong forbidden calcium emission starting 38 days after discovery. SN 2022oqm has a relatively high peak luminosity (MB = -17 mag) for (CaRTs), making it an outlier in the population. We determine that three power sources are necessary to explain the light curve (LC), with each corresponding to a distinct peak. The first peak is powered by an expanding blackbody with a power law luminosity, suggesting shock cooling by circumstellar material (CSM). Subsequent LC evolution is powered by a double radioactive decay model, consistent with two sources of photons diffusing through optically thick ejecta. From the LC, we derive an ejecta mass and 56Ni mass of ~0.6 solar masses and ~0.09 solar masses. Spectroscopic modeling suggests 0.6 solar masses of ejecta, and with well-mixed Fe-peak elements throughout. We discuss several physical origins for SN 2022oqm and find either a surprisingly massive white dwarf progenitor or a peculiar stripped envelope model could explain SN 2022oqm. A stripped envelope explosion inside a dense, hydrogen- and helium-poor CSM, akin to SNe Icn, but with a large 56Ni mass and small CSM mass could explain SN 2022oqm. Alternatively, helium detonation on an unexpectedly massive white dwarf could also explain SN 2022oqm.

A growing number of supernovae (SNe) are now known to exhibit evidence for significant interaction with a dense, pre-existing, circumstellar medium (CSM). SNe Ibn comprise one such class that can be characterised by both rapidly evolving light curves and persistent narrow He I lines. The origin of such a dense CSM in these systems remains a pressing question, specifically concerning the progenitor system and mass-loss mechanism. In this paper, we present multi-wavelength data of the Type Ibn SN 2020nxt, including \\(HST\\)/STIS ultraviolet spectra. We fit the data with recently updated CMFGEN models designed to handle configurations for SNe Ibn. The UV coverage yields strong constraints on the energetics and, when combined with the CMFGEN models, offer new insight on potential progenitor systems. We find the most successful model is a \\(\\lesssim4 {\\rm M}_\\odot\\) helium star that lost its \\(\\sim 1\\,{\\rm M}_\\odot\\) He-rich envelope in the years preceding core collapse. We also consider viable alternatives, such as a He white dwarf merger. Ultimately, we conclude at least some SNe Ibn do not arise from single, massive (\\(>30 {\\rm M}_\\odot\\)) Wolf-Rayet-like stars.