McDonald, S (2024) The Evolution of Red Supergiants in Local Group Galaxies. Doctoral thesis, Liverpool John Moores University.

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Abstract

The luminosities and mass loss rates of Red supergiants are important factors for understanding the evolution of massive stars. The empirical upper limit to Red Supergiant (RSG) luminosity, known as the Humphreys-Davidson (HD) limit, has been commonly explained as being caused by the stripping of stellar envelopes by metallicity-dependent, line-driven winds. As such, the theoretical expectation is that the HD limit should be higher at lower metallicity, where weaker mass-loss rates mean that higher initial masses are required for an envelope to be stripped. The HD limit is investigated in this thesis using a large sample of M31 RSGs in a galaxy-wide study to measure where the HD limit sits and to observe whether it has a metallicity dependence.

Using a large homogeneous sample provides a great test bed for mass loss rates of RSGs. Recent prescriptions for RSG mass loss have seen a downward revision, showing that quiescent mass-loss during the RSG phase is not effective at removing a significant fraction of the Hydrogen envelope, prior to core-collapse. This places extra emphasis on potential short-lived high mass loss phases, which have been suggested to remove several solar masses of material in short periods of time. We investigate the mass-loss rates of RSGs at high metallicity, with the aim of obtaining an unbiased sample that catches RSGs in all mass loss phases, even the very brief ones, such that we can then ascertain in which phase most of the mass is lost.

The overall aim of this thesis is to address these unresolved problems in massive stellar evolution and help bridge the gap between the RSG phase and supernova explosion. Having a better understanding of RSG luminosity and mass loss rates will enhance the accuracy of predictions from stellar evolution models, strengthening our understanding of massive stellar evolution.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	Massive stars; Evolution; Stellar physics
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
SWORD Depositor:	A Symplectic
Date Deposited:	05 Mar 2024 15:43
Last Modified:	05 Mar 2024 15:43
DOI or ID number:	10.24377/LJMU.t.00022742
Supervisors:	Davies, B
URI:	https://researchonline.ljmu.ac.uk/id/eprint/22742

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