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Title: The progenitors of type IIP supernovae
Author: Beasor, Emma R.
ISNI:       0000 0004 7964 3112
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2019
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Mass-loss prior to core collapse is arguably the most important factor affecting the evolution of a massive star across the Hertzsprung-Russel (HR) diagram, making it the key to understanding what mass-range of stars produce supernova (SN), and how these explosions will appear. It is thought that most of the mass-loss occurs during the red supergiant (RSG) phase, when strong winds dictate the onward evolutionary path of the star and potentially remove the entire H-rich envelope. Uncertainty in the driving mechanism for RSG winds means the mass-loss rate (Ṁ) cannot be determined from first principles, and instead, stellar evolution models rely on empirical recipes to inform their calculations. At present, the most commonly used Ṁ-prescription comes from a literature study, whereby many measurements of mass-loss were compiled. The sample sizes are small (< 10 stars), highly heterogeneous in terms of mass and metallicity, and have very uncertain distances from observations and analysis techniques that at best provide order-of-magnitude estimates compared to what is possible today. The relation itself contains large internal scatter, which could be the difference between a star losing its entire H-envelope, or none of it at all. More modern efforts to update the RSG mass-loss rate prescription rely on samples which suffer from statistical biases, for example by selecting objects based on mid-IR brightness or circumstellar maser emission, and hence are inevitably biased towards higher mass-loss rate objects. It is the aim of this thesis to overhaul our understanding of RSG mass-loss. By selecting RSGs in clusters, where the initial mass and metallicity are known, I will be able to observe how mass-loss changes as the star approaches SN and compare this to what is currently implemented in stellar evolutionary models. Ultimately, I will measure Ṁ values and luminosities for RSGs in 5 different clusters of varying ages, thus targeting RSGs of different initial masses. I will then combine these mass-loss rate-luminosity relations to derive a new initial mass-dependent mass-loss rate, which can be implemented into stellar evolutionary models.
Supervisor: Davies, B. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: QB Astronomy ; QC Physics