A STUDY OF THE MOLECULAR MAKE UP OF SAKURAI'S OBJECT USING ALMA A thesis submitted to the University of Manchester for the degree of Master of Science in the Faculty of Science and Engineering November 2020 By Phoebe Stainton School of Physics and Astronomy Contents Abstract 11 Declaration 12 Copyright 13 Acknowledgements 15 1 Stellar Evolution 16 1.1 Motivation . 17 1.2 Overview of Evolution from the Main Sequence to the White Dwarf Phase . 18 1.2.1 Low Mass Stars . 18 1.2.2 Low and Middle Intermediate Mass Stars . 21 1.3 AGB Evolution . 23 1.3.1 Low Mass and Lower Intermediate Mass Stars . 24 1.3.2 Middle Intermediate Mass Stars . 25 1.4 Nuclear Reactions During Stellar Evolution . 27 1.4.1 Nucleosynthesis in Low Mass Stars . 27 1.4.2 Nucleosynthesis in Lower Intermediate Mass Stars . 29 1.4.3 Nucleosynthesis in Middle Intermediate Mass Stars . 33 2 1.5 Convection and Dredge Up . 35 1.5.1 Convection in Low Mass Stars . 35 1.5.2 Convection in Low and Middle Intermediate Mass Stars 35 1.5.3 Dredge Up Processes . 36 1.6 Post- AGB Evolution and Very Late Thermal Pulses . 40 1.6.1 Very Late Thermal Pulses . 40 1.6.2 Post-AGB Evolution in Low and Low Intermediate Mass Stars . 41 1.6.3 Post-AGB Evolution in Middle Intermediate Mass Stars . 43 1.7 Mass Loss . 44 1.7.1 Mass Loss Through Stellar Winds . 44 1.7.2 Mass Loss Through Superwinds . 46 1.7.3 Mass Loss Models . 47 1.8 Shaping of Nebulae . 49 1.9 Sakurai's Object . 51 2 Interferometry 56 2.1 Background to Interferometry . 57 2.2 The Process of Interferometry . 58 2.3 Deconvolution . 64 2.3.1 The H¨ogbom CLEAN Algorithm . 65 2.3.2 The Clark Algorithm . 67 2.3.3 Cotton-Schwab Algorithm . 68 2.4 Emission and Absorption from the Atmosphere . 70 2.5 The Effects of Baselines on Resolution . 71 2.6 The Effects of Baselines on Image Quality . 72 3 3 ALMA and Atomic Physics 73 3.1 ALMA . 74 3.1.1 Background to ALMA . 74 3.1.2 The Scientific Goals of ALMA . 75 3.1.3 The Effects of Baselines on ALMA . 76 3.2 Atomic Physics . 78 3.2.1 Fine Structure: Relativistic Correction . 78 3.2.2 Relativistic Energy Correction . 79 3.2.3 Fine Structure: The Spin-Orbit Interaction . 82 3.2.4 Fine Structure: Combining Relativistic Corrections and the Spin-Orbit Interaction . 85 3.2.5 Hyperfine Structure . 85 3.2.6 The Effects of Fine and Hyperfine Structure on this Research . 86 3.2.7 Example for Carbon . 87 4 Data Collection 89 4.1 Making Image Cubes . 91 4.1.1 The Continuum Images . 91 4.2 The Resolved Nature of Sakurai's Object . 96 4.3 Producing Spectra . 98 4.4 Identifying Spectral Lines . 100 4.5 Analysing the Spectral Lines . 106 4.6 Additional Line Searches . 116 4.6.1 HC5N.......................... 116 4.7 Final Identifications . 120 4 5 Astrochemistry 121 5.1 Environments in Space . 122 5.1.1 Diffuse Interstellar Medium . 122 5.1.2 Circumstellar Medium . 122 5.1.3 Giant Molecular Clouds . 122 5.2 Synthesis and Ionisation in Space . 124 5.2.1 Molecular Synthesis . 124 5.2.2 Ionization . 124 5.3 Gas Phase Chemical Reactions in Space . 126 5.3.1 Bond Formation Reactions: Radiative Association . 126 5.3.2 Bond Formation Reactions: Associative Detachment 127 5.3.3 Bond Formation Reactions: Dust-Grain-Catalysed Reaction . 127 5.3.4 Bond Breaking Reactions: Photodissociation and Col- lisional Dissociation . 128 5.3.5 Bond Breaking Reactions: Dissociative recombination 128 5.3.6 Rearrangement reactions: Charge transfer . 129 5.3.7 Rearrangement Reactions: Neutral reactions . 129 5.3.8 Rearrangement Reactions: Ion-molecule reactions . 129 5.4 Chemistry in Molecular Clouds . 131 5.5 Chemistry in Circumstellar Envelopes . 132 5.6 Astrochemical Modelling . 133 5.6.1 Background to the UMIST Database for Astrochem- istry . 133 5.6.2 Background to the Dark Cloud Chemical Model . 134 5.6.3 Using the Dark Cloud Chemical Model . 136 5 5.6.4 Testing Molecular Carbon . 139 5.6.5 Testing Ionic Carbon . 143 5.6.6 Testing the Visual Extinction and UV Radiation Field Scaling Factor . 145 5.6.7 Limits of the Dark Cloud Chemical Model . 147 5.7 RADEX . 149 5.8 The Online Version of RADEX . 150 5.8.1 Calculating Input Values for the Online Version of Radex . 150 5.8.2 Using the Online Version of RADEX . 152 5.8.3 Results from the Online Model . 153 5.9 The RADEX Source Code . 154 5.9.1 Making RADEX Input Files . 156 5.9.2 Determining Parameters for Carbon Monoxide Input Files . 157 5.9.3 Determining Parameters for HC3N Input Files . 158 5.9.4 Using the RADEX Source Code . 158 5.9.5 Limits of the RADEX Source Code . 160 5.10 The Final Model and the Time Evolution of Sakurai's Object162 5.11 Discussion of the Model Results . 165 6 Conclusions 170 6.1 Further Work . 173 6 List of Tables 4.1 Details of the ALMA Data Sets . 90 4.2 Details of the Continuum Images Produced in CASA . 94 4.3 Details of the Bounding Ellipses used in CASA . 98 4.4 Initial Line Identifications . 103 4.5 Peak Flux ± 3σ, Noise, and Frequency Range Data for Initial Line Identifications . 104 4.6 Initial Line Identifications . 105 4.7 Additional CN Lines for Spectral Window 8 Band 7 . 115 4.8 Details of the Additional Lines for Spectral Window 5 Band 6117 4.9 Details of the Additional Lines for Spectral Window 16 Band 6118 5.1 Input abundances for the first test models . 136 5.2 Input values for test models with a constant C:O ratio . 138 5.3 Fractional Output Abundances for HC3N and HC5N..... 139 5.4 Input values for the molecular carbon models . 140 5.5 Output Fractional Abundances for Molecular Models . 141 5.6 Input values for the ionic carbon models . 144 5.7 HC3N and HC5N output abundances for ionic models . 144 5.8 Details of the Output Values at Different Times . 159 5.9 Details of the Input Values for the Final Model . 162 7 List of Figures 1.1 The interior of an AGB star showing the separation between the layers. (adapted from Lamers and M. Levesque (2017)) . 23 1.2 The three proton-proton chains used for nuclear fusion. PPI produces helium, and PPII and PPIII produce lithium and beryllium (Adelberger et al. (2011)) . 27 1.3 The NeNa cycle shown in context with the CNO cycle and MgAl cycle. Orange indicates short lived nuclei, whilst green nuclei are stable and long lived. 26Al is long lived in its ground state but will quickly decay in 26Mg when in its metastable state. (Boeltzig et al. (2016)) . 31 2.1 A schematic of a radio interferometer consisting of two dishes pointed at a source. 59 3.1 The Atomic Levels of Carbon with the Fine and Hyperfine Splitting . 88 4.1 A CASA FITS Image of the Continuum for the 2017 Data. The oval in the bottom left hand corner shows the beam size 92 4.2 A CASA FITS image of the continuum for band 6 from the 2014 data . 93 8 4.3 A CASA FITS image of the continuum band 7 from the 2014 data. This image does not include spectral windows 4 or 5 . 94 4.4 A UV Distance vs Amplitude Plot for all Spectral Windows in the 2017 Data Set . 97 4.5 Spectral Window 25 in velocity space with respect to the identified H13CN line . 106 4.6 Spectral Window 31 in velocity space with respect to the identified HNC line . 107 4.7 Spectral Window 31 in velocity space with respect to the identified HC3N line . 107 4.8 Spectral Window 2 Band 6 in velocity space with respect to the identified HC3N line . 108 4.9 Spectral Window 3 Band 6 in velocity space with respect to the identified CO line . 108 4.10 Spectral Window 5 Band 6 in velocity space with respect to the HC3N line . 109 4.11 Spectral Window 5 Band 6 in velocity space with respect to the 13CN line . 109 4.12 Spectral Window 10 Band 6 in velocity space with respect to the HC3N line . 110 4.13 Spectral Window 16 Band 6 in velocity space with respect to the CN line found in the absorption feature . 110 4.14 Spectral Window 1 Band 7 in velocity space with respect to the HC3N line . 111 4.15 Spectral Window 7 Band 7 in velocity space with respect to the 13CO line . 111 9 4.16 Spectral Window 8 Band 7 in velocity space with respect to the CN line . 112 4.17 Spectral Windows 31 and 5 Band 6 in velocity space with respect to HC3N........................ 117 5.1 Time Evolution of Sakurai's Object as Predicted by Model 10142 5.2 Time Evolution of Sakurai's Object as Predicted by Model 11143 5.3 Time Evolution of Sakurai's Object as Predicted by the Fi- nal Model . 162 5.4 Time Evolution of HCN, HNC, and CN . 163 10 Abstract This work will aim to use the abilities of ALMA, the UDfA Dark Cloud model, and RADEX to determine likely molecules in Sakurai's Object and attempt to predict a possible evolutionary path.