Investigating the presence and properties of circumstellar material in Type I Supernovae

Abstract

Understanding of the explosive deaths experienced by some stars in supernovae explosions has increased significantly over the last several decades, though many outstanding questions remain. The work presented here is comprised of two projects that seek to answer the role that circumstellar material plays in both core-collapse and thermonuclear supernovae, including its effects on single objects both in the generation of spectroscopic signatures and additional luminosity through interaction with supernova ejecta. As well as the information that can be obtained about the progenitor systems of interacting supernovae through analysis of the properties of the circumstellar material present. Interaction between circumstellar material and supernovae ejecta can have drastic impacts on the observed photometric and spectroscopic properties and evolutions of supernovae, with the full range of the resulting events yet to be fully understood.

The first project described is an analysis of one such object - LSQ13ddu. This supernova displayed rapid evolution, with large changes in both its light curve and spectra on timescales of a few days with these attributable to ejecta - circumstellar material interaction. This work includes photometric modelling of LSQ13ddu focusing on determining the powering mechanism of this unusual object as a combination of early time ejecta - circumstellar material interaction, with an underlying Ni decay powered core collapse event, which becomes dominant at later times. The work also puts LSQ13ddu in context with the broader transient population as a hybrid Ibn / Ic supernova with a small mass of residual He within its ejecta.

The second project explores the use of two probes of the progenitors of Type Ia supernovae to investigate using moderate resolution, near maximum spectroscopy to provide robust progenitor channel identification. Both probes, the statistical excess of narrow, blueshifted Na I D absorption features and the presence and strength of high velocity Ca II near infrared triplet absorption features, have been suggested to be produced as a result of interaction between the ejecta of the supernova with circumstellar material located within its progenitor system and are this linked to the single degenerate family of Ia explosion models. Whilst a clear relation between the two progenitor probes is not observed within the sample, tantalising evidence of a bimodality within the population of Type Ia supernovae is observed and discussed. The analysis also provided the opportunity to examine various other properties of Type Ia supernovae in differing host environments, with evidence that those hosted within irregular or dwarf galaxies may form a distinct group compared to the populations hosted by early or late type galaxies, which have been previously described in literature.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Department for Education
Supervisor	Kate Maguire (Supervisor) & Stephen Smartt (Supervisor)