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Title: Luminosity distributions and abundance tomography modelling of Type Ia Supernovae
Author: Ashall, C. J.
ISNI:       0000 0004 6059 3653
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2017
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I present an investigation into Type Ia Supernovae (SNe Ia). The aim of this investigation is to explain the physics and diversity of SNe Ia, motivated by the fact that, although SNe Ia are known to come from a thermonuclear explosion of a C+O Chandrasekhar mass (Ch-mass) White Dwarf (WD), their exact explosion scenario is one of debate, and their full diversity is not fully understood. As SNe Ia are used as cosmological distance probes, understanding their explosions and progenitors systems in more detail could have important consequences. To examine the diversity of SNe Ia, I first present a large sample analysis of their B and V - band light curves, separated by host galaxy type. A new method for calculating host galaxy extinction is implemented and the width luminosity relation (WLR) is examined. After correction for host galaxy extinction, ‘normal’ SNe Ia (∆m15(B) < 1.6 mag) fill a larger parameter space in the WLR than previously suggested. Even excluding fast declining SNe, ‘normal’ (MB <−18mag) SNeIa from star forming(S- F) and passive galaxies are distinct. This may indicate that various progenitor channels are prevalent in different galaxy types. Furthermore, it was also confirmed that sub- luminous SNe Ia tend to favour passive galaxies, which implies that this subset of SNe Ia come from an older progenitor system. There was a lack of transition SNe Ia in the dataset used in this project. These are SNe Ia with a luminosity between normal and sub-luminous SNe Ia. Understanding transitional SNe Ia is important in determining whether sub-luminous SNe Ia are a totally different population. With the aim of understanding how normal SNe explode, I first turn my attention to SN 2014J. SN 2014J was the closest type Ia in the last 410 years, and it was a once in a life time opportunity to study. Therefore, a detailed spectroscopic and photometric analysis and abundance stratification modelling of SN 2014J is presented. SN 2014J is a spectroscopically normal type Ia SN with a B band decline rate of 0.95 mag, before correction for extinction. It was located in the dusty starburst galaxy M82, and does not follow the average Galactic extinction law of Rv = 3.1. With the knowledge about the diversity of SNe Ia and the ability to carry out de- tailed modelling, SN 1986G was next chosen to be modelled. SN 1986G sits in an interesting area of parameter space in the WLR. It is located in the ‘gap’ between normal and sub-luminous SNe Ia. It has been theorised that sub-luminous SNe Ia come from a different progenitor system than standard SNe Ia. Therefore, understanding SN properties in this ‘gap’ is important for determining at which point SNe Ia properties begin to diverge from the normal scenario. A full abundance tomography modelling of SN 1986G was carried out. It was found that this SN is a low energy Chandrasekhar mass explosion. It had 70% of the energy of a standard W7 model. These findings raise the possibility that only SNe Ia with very large decline rates deviate from a Chandrasekhar mass.
Supervisor: Mazzali, P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: QB Astronomy