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Observational Aspects of Globular Cluster and Halo Stars in the GALAH Survey

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Observational Aspects of Globular Cluster and Halo Stars in the GALAH Survey THE UNIVERSITY OF NEW SOUTH WALES DOCTORAL THESIS Observational aspects of globular cluster and halo stars in the GALAH survey Student: Supervisor: Mohd Hafiz MOHD SAADON Associate Professor Sarah MARTELL A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Physics Faculty of Science The University of New South Wales 12 March 2021 i ii iii iv Declaration of Authorship I, Mohd Hafiz MOHD SAADON, declare that this thesis titled, “Observational aspects of globular cluster and halo stars in the GALAH survey” and the work presented in it are my own. I confirm that: • This work was done wholly or mainly while in candidature for a research degree at this University. • Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated. • Where I have consulted the published work of others, this is always clearly at- tributed. • Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work. • I have acknowledged all main sources of help. Signed: Date: v “In loving memory of my grandmothers, Ramlah and Halijah, who wished to see me this far but could not be here anymore.” – your grandson. “To Amani, my sweet little angel, this thesis is your sibling.” – your father. vi THE UNIVERSITY OF NEW SOUTH WALES Abstract Doctor of Philosophy Observational aspects of globular cluster and halo stars in the GALAH survey by Mohd Hafiz MOHD SAADON This thesis is a study of the observational aspects of globular cluster and halo stars in the Galactic Archaeology with HERMES (GALAH) survey. GALAH is a major astronomical survey project that derives stellar parameters (Teff, log g, [Fe/H]) and up to 30 elemen- tal abundances for a very large sample of stars in the Milky Way from high-resolution spectroscopy. This thesis uses the third GALAH internal data release, which includes over 600 000 stars, to test the validity of GALAH’s reported quantities, especially for cool metal-poor globular clusters and halo stars. We also examine the light-element abun- dance patterns of stars in globular clusters, which have known peculiarities, to search for stars in the Galactic halo with globular cluster-like abundance patterns, and to chart the age-abundance relation in halo stars using elements that have been reported as particu- larly useful age indicators. In this first application of GALAH data to globular clusters and halo chemodynamics, we explore the behaviour of 30 elemental abundances for 340 stars in four globular clusters, which are NGC 104, NGC 5139, NGC 6397 and NGC 7099, which we found inconsisten- cies in the light-element abundances. We also discover that approximately 1% (4/445) of metal-poor halo giants in the sample are likely globular cluster escapees with enhanced [Al/Fe] and depleted [Mg/Fe]. Finally, we chart the age-abundance relations of metal- poor halo giants and identify stars with likely extragalactic origins using their kinematics and abundances. vii Acknowledgements Praise be to the Lord of this magnificent universe. Before anything else, I would like to thank my funder for granting me the SLAB fel- lowship under the University of Malaya (UM) and the Ministry of Higher Education Malaysia so that I would be able to pursue my study. Most importantly, no words can truly express how thankful I am to my wonderful su- pervisor and mentor, Associate Professor Sarah Martell, for her guidance, support and especially patience throughout my PhD, who have taught me about the Galactic archae- ology and make me enjoy the topic that still amazes me. She is always making time to read, edit, and comment on my works and tirelessly provide feedback whenever possi- ble. I am incredibly thankful that she took me under her wings when I was lost, desperate and had nowhere to go. I am also grateful for her wisdom, selfless time, positivity and passion that kept me moving even through the most challenging times. I pray that all good things will always be bestowed upon her. I am also grateful to Dr Jeffrey Simpson, Nicholas Borsato, Kirsten Banks, Aditya Gu- dalur Balasubramaniam, and other UNSW Milky Way Group members, for their helpful insights and discussions during our weekly meetings. I would also like to thank Prof. Chris Tinney for helping me by overseeing my progress reviews. A special thanks to my postgraduate coordinators Assoc. Prof. Kim Vy-Tran and Prof. Richard Newbury, and also Prof. Michael Ashley and Prof. Jeremy Bailey. They became my panels for the progress review meetings during my candidature, and gave a lot of suggestions and en- couragement so that I can stay on track, be realistic on my milestones and finish my PhD. I want to thank other postgraduate students and the staff of School of Physics, GRS and UNSW for their assistance in the campus and faculty. For Johannes Böttcher, thank you for providing me this thesis template. I also thank my former supervisors who welcomed me when I first arrived in Australia, Prof. Rob Wittenmyer and Assoc. Prof. Dennis Stello. I am also grateful to GALAH researchers and collaborators, especially Dr Sven Buder, Dr Sanjib Sharma, Jane Lin, and Prof. Martin Asplund for sharing their knowledge about the GALAH survey. My sincere thanks also go to Dr Chris Lidman, Dr Tayyaba Zafar and Dr Lee Spitler and other as- tronomers, engineers and technicians of AAT and AAO during my observation nights. I will always remember those Christmas and New Year’s Eve. I am also indebted to Dr Muhammadin for his advice and guidance on being a sane human when I was so down, and his reminders and tips to be humble but wise. Another sincere thank to the alumni of the late Prof. Rahim for their motivational supports and viii prayers. Also not to be ignored, to the members of Facilitator Alumni Club KMJ, thank you for being my platform to have a laugh and gossip about our silly past. Also, I am thankful to the Heads of Department of Fiqh and Usul UM, Dr Ridzwan, Dr Luqman and Assoc. Prof. Sa’adan; Directors of the Academy of Islamic Studies UM, Prof. Mohd Yakub @ Zulkifli and Prof. Raihanah; and to the program coordinator of Is- lamic Astronomy UM, Dr Sailful Nawawi and Dr Raihana. Thank you for offering me the fellowship and checking on me. Even not to be forgotten, to my comrades of House Sec- retaries of Malaysia Hall Sydney, Azmilnidzam, Yow Hun Yen, Nur Iman, Noor Alyssa, Muhammad Haris, Chng See Yi, Rabiatul Adawiyah, Lo Sin Kuang and Ezwan Shah. Thank you for your cooperation, your understanding, your eyes and ears, your energy and efforts. I also want to thank my housemate, Chng Zhi Yee; the Directors and the At- taches of Education Malaysia Australia; and the residents of Malaysia Hall. They make me feel like home during my time in Australia. More recently, I also would like to thank Assoc. Prof Andrew Cole and Professor Renee James for being the thesis reviewers and giving a lot of helpful insights and recommen- dations to improve the thesis. Finally, I want to express my heartfelt gratitude and love to my parents, Mohd Saadon and Siti Hajar; my wife, Nur Liyana Atikah; and my big family for their unconditional love and support (even financially) despite me being so far away. Thank you for being so patient and understanding during this whole journey. And to my dear little daughter, Nur Nasirah Amani, daddy is home. ix Contents Declaration of Authorship iv Acknowledgements vii List of Figures xii List of Tables xviii List of Abbreviations xix List of Symbols xx 1 Introduction1 1.1 Galactic archaeology...............................1 1.1.1 Chemical tagging.............................2 1.1.2 Halo stars and halo streams.......................4 1.1.3 Globular clusters.............................6 1.1.4 Age-abundance relations and metal-poor stars............8 1.1.5 The [α/Fe] ratio..............................9 1.2 Large-scale surveys................................ 11 1.2.1 Galactic Archaeology with HERMES.................. 12 GALAH in comparison with other surveys.............. 12 1.2.2 Gaia ..................................... 13 1.3 Stellar abundances................................ 14 1.3.1 Metallicity................................. 15 1.3.2 Spectroscopic analysis.......................... 16 1.4 Research objectives................................ 19 1.5 Thesis structure.................................. 21 2 Globular clusters in GALAH 22 2.1 The role of globular clusters in Galactic archaeology............. 22 2.2 Stellar abundances in globular clusters..................... 27 2.2.1 Light-element abundance variations.................. 27 x Mg-Al anticorrelation.......................... 29 2.2.2 Metallicity variations........................... 29 2.2.3 Neutron-capture abundance variations................ 30 2.3 Globular clusters observed by the GALAH survey.............. 32 2.3.1 Determining cluster membership.................... 33 Position cut................................ 33 Radial velocity cut............................ 34 Proper motion cut............................ 34 Parallax cut................................ 34 Other criteria............................... 37 2.4 Globular cluster abundances in the GALAH survey............. 40 2.4.1 Metallicity................................. 42 2.4.2 Light elements.............................. 48 2.4.3 An extension to silicon.......................... 52 2.4.4 Neutron-capture elements........................ 55 2.4.5 Lithium.................................. 56 2.4.6 The clusters in detail........................... 62 NGC 104.................................. 62 NGC 5139................................. 70 NGC 6397................................. 77 NGC 7099................................. 83 2.5 Summary and conclusion............................ 89 3 Globular cluster stars in the halo 91 3.1 The role of halo stars in Galactic archaeology................. 91 3.1.1 Kinematics of halo stars......................... 92 3.1.2 The chemical compositions of halo stars................ 93 3.2 Selecting halo stars in the GALAH data set.................. 95 3.3 Abundance patterns of the GALAH halo giant stars............
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