DOCTOR OF PHILOSOPHY Massive stars in low metallicity environments Higgins, Erin Award date: 2020 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. If you believe this document breaches copyright, or there is sufficient cause to take down, please contact us, citing details. Email: [email protected] Supplementary materials Where possible, we endeavour to provide supplementary materials to theses. This may include video, audio and other types of files. We endeavour to capture all content and upload as part of the Pure record for each thesis. Note, it may not be possible in all instances to convert analogue formats to usable digital formats for some supplementary materials. We exercise best efforts on our behalf and, in such instances, encourage the individual to consult the physical thesis for further information. Download date: 08. Oct. 2021 Massive stars in low metallicity environments Erin Rose Higgins BSc PGCE PhD Queen’s University of Belfast & Dublin Institute for Advanced Studies & Armagh Observatory & Planetarium June 2020 To the strong women in my life, for their eternal inspiration. Declaration I declare that the work contained in this thesis has not been submitted for any other award and that it is all my own work. I also confirm that this work fully acknowledges opinions, ideas and contributions from the work of others. The work was done in col- laboration with Jorick Vink. I declare that the Word Count of this thesis is less than 80,000 words. Name: Erin Rose Higgins Signature: 4 June 2020 External Examiner: Prof. Jose Groh Director of Astrophysics and Tenured Assistant Professor Trinity College Dublin, Ireland Internal Examiner: Dr. Gavin Ramsay Armagh Observatory and Planetarium Armagh, UK Principal Supervisor: Prof. Jorick Vink Armagh Observatory and Planetarium Armagh, UK Ph.D Candidate: Erin Rose Higgins Student identification number : 40080963 Armagh Observatory and Planetarium, Dublin Institute for Advanced Studies, Queen’s University Belfast ii Acknowledgements To my supervisor Jorick Vink, thank you for your guidance and encouragement through- out my PhD. For moulding me into a better astrophysicist and giving me the best ex- periences, I am indebted to you. To Andreas Sander for your continued motivation and feedback, thank you for the pleasure of your collaboration. To my childhood sweetheart, Jamie, for our endless discussions on life, the Universe, and even semiconvection. For teaching me to be spontaneous, for growing up beside me, and for supporting me throughout my PhD, I am perpetually thankful for our life together, and for exploring the cosmos with you, my closet-physicist. To my Mammy, for teaching me how powerful a young woman can be, and for always knowing how to fix anything on our long walks on the beach. You will forever be my inspiration and my best friend, for I am only here because of your immeasurable strength and love. To my Daddy, for being the origin of my motivation and curiosity, for the years of graphs and for shaping my future, I owe my scientific nature to you. Thank you for your unwavering determination to get me to where I needed to be and supporting me through everything. To Kate, watching you become the woman you hope to be brings me so much pride and inspiration that I often forget who the little sister is, thank you for being you. To my grandparents, for my Grandma’s limitless belief in me and my Granda’s heartfelt pride. Thank you for making me believe I could do anything. For my Nana, who showed me the value of education, though I wish you could be here, a part of you will always remain in me. For my Granda-Jo, who always supported me. To my PhD-partner Lauren, thank you for making this journey one of laughter and friendship. To all the students and staff at Armagh Observatory, thank you for your support over the years. iii Abstract The evolution of massive stars has been a key field of research for many decades, as it has significant effects on a variety of astrophysical disciplines, Langer (2012). Nonetheless, it is still widely uncertain due to a deficit of observational evidence to verify theoretical models. Recent surveys of the galaxy and Magellanic clouds (Evans et al., 2011) in addition to continuous development of stellar evolution codes (Paxton et al., 2015) are, however, replenishing the domain of massive stars so that we may probe the characteristics of their evolution to better understand the early stages of their life. The evolution of massive stars is highly heterogeneous, sensitive to mass loss, internal mixing, metallicity, rotation, binarity, and magnetic fields. In this thesis, I have probed the evolution of massive stars for a range of metallicities, including our Milky Way galaxy and the Magellanic Clouds. This work provides an insight into the evolutionary models conducted in an endeavour to understand the dominant physical processes act- ing on massive stars, chapters 3 and 4. Theoretical predictions of the upper luminosity limit of red supergiants and constraints on internal mixing processes such as convective overshooting and semiconvection are presented in chapter 5. Chapters 1 and 2 provide an introduction to the central research chapters 3-5, with conclusions and future work outlined in chapter 6. iv List of Publications A list of publications resulting from the work presented in this thesis are provided below. Erin R. Higgins & Jorick S. Vink, Massive star evolution: rotation, winds, and overshooting vectors in the mass-luminosity plane. I. A calibrated grid of rotating single star models, 2019, A&A, 622, A50 Erin R. Higgins & Jorick S. Vink, Massive star evolution revealed in the Mass- Luminosity plane, 2019, IAUS, 346, 480H Erin R. Higgins & Jorick S. Vink, A theoretical investigation of the Humphreys- Davidson limit at high and low metallicity, 2020, A&A, 635 Erin R. Higgins & Jorick S. Vink, Stellar age determination and mass discrepancies in the Mass-Luminosity Plane. II. A grid of rotating single star models with LMC metallicity, 2020, to be submitted to A&A Erin R. Higgins, Andreas S. Sander, Jorick S. Vink, Raphael Hirschi, Evolution of Wolf-Rayet stars as black hole progenitors, with a new locally consistent mass-loss recipe, 2020, in prep. v Contents Declaration ii Acknowledgements iii Abstract iv List of Publications v 1 Introduction 1 1.1 Stellar classification and evolution . 2 1.1.1 Massive stars . 2 1.1.2 Evolutionary channels . 5 1.1.3 Final fates . 6 1.2 Massive stars throughout the Universe . 9 1.2.1 Low metallicity environments . 11 1.2.2 Mass Loss as a function of Metallicity . 14 1.2.3 Most massive stars in the Universe . 14 1.3 Thesis overview . 16 2 Theoretical modelling of massive stars 18 2.1 Stellar structure and evolution . 18 2.2 1-dimensional stellar evolution . 21 2.2.1 MESA v8845 . 23 2.2.2 Basic input parameters . 23 2.3 Physical processes . 25 2.3.1 Convection . 25 2.3.2 Rotation . 28 2.3.3 Stellar winds . 30 2.3.4 Summary . 32 3 Galactic evolution in the Mass-Luminosity Plane 34 vi 3.1 Introduction . 35 3.2 Method . 40 3.2.1 The detached, eclipsing binary HD 166734 : A test-bed for massive star evolution . 42 3.3 Mixing and mass loss . 46 3.3.1 Envelope stripping and nitrogen enrichment. 46 3.3.2 Rotationally induced mass loss . 49 3.4 Mass - Luminosity Plane . 51 3.5 Observational constraints . 60 3.5.1 Galactic observational sample . 63 3.6 Grid analysis . 65 3.6.1 Red supergiant upper luminosity limit . 67 3.6.2 Compactness parameter . 68 3.7 Discussion and conclusions . 71 4 The Magellanic Clouds and determining stellar age 73 4.1 Introduction . 74 4.2 Methodology . 76 4.2.1 MESA . 76 4.2.2 Mass - Luminosity Plane . 77 4.3 Evolution models for detached binaries in VFTS . 77 4.3.1 R139 : the most massive binary test-bed . 79 4.3.2 VFTS063 . 80 4.3.3 VFTS116 . 80 4.4 Stellar age determination in the M-L plane . 81 4.4.1 VFTS age estimates . 81 4.5 Grid comparison with observations of O and B supergiants from the VFTS sample . 86 4.5.1 Main sequence objects . 86 4.5.2 Mass discrepancy . 87 vii 4.6 Conclusions . 91 5 Post-Main Sequence Evolution to Red Supergiants 93 5.1 Introduction . 94 5.2 Method . 97 5.2.1 MESA Stellar evolution models . 97 5.2.2 Mixing processes . 98 5.2.3 Observations in the HRD . 99 5.3 Results . 100 5.3.1 Evolutionary channels . 102 5.3.2 The HD limit . 104 5.3.3 Unified theory of the HD limit at all Z . 109 5.3.4 Implications for the B/R ratio .