HONOURS THESIS Deep Learning for the Spectral Classification of Transient Astronomical Objects Author: Supervisors: Daniel MUTHUKRISHNA Dr. David PARKINSON Dr. Brad TUCKER A thesis submitted in partial fulfillment of the requirements for the degree of the Bachelor of Engineering in the discipline of Electrical and Aerospace Engineering November 25, 2016 iii Daniel Muthukrishna [email protected] 49 Foxmont Drive Carina, QLD 4152 November 25, 2016 Prof Michael Brünig Head of School School of Information Technology and Electrical Engineering The University of Queensland St Lucia, QLD 4072 Dear Professor Brünig, In accordance with the requirements of the Degree of Bachelor of Engineering in the School of Information Technology and Electrical Engineering, I submit the following thesis entitled: "Deep Learning for the Spectral Classification of Transient Astronomical Objects" The thesis was performed under the supervision of Dr David Parkinson. I declare that the work submitted in the thesis is my own, except as acknowledged in the text and footnotes, and that it has not previously been submitted for a degree at the University of Queensland or any other institution. Yours sincerely, Daniel Muthukrishna v Acknowledgments Firstly, I would like to thank my primary supervisor, Dr David Parkinson of the University of Queensland, for his continuous help, assistance, and guidance throughout this thesis. I would also like to thank my second supervisor, Dr Brad Tucker of the Australian National University, for his regular contact over email and video calls that guided the goals and direction of the project. I am indebted to both David and Brad for their generous support which expertly went above and beyond in responding to all of my questions over the course of the year. I am also very grateful to Mr Samuel Hinton, Prof Tamara Davis, and Dr Chris Lidman for their expertise and suggestions during this thesis. Their support has provided invaluable di- rection in the outcomes of the project. Finally, I’d like to thank several other members of the OzDES community including Dr Alex Kim, Dr Richard Kessler, Dr Jeffrey Silverman, Dr Anais Moller, Prof Mark Sullivan, Dr Michael Childress, and Prof Bob Nichol for their feedback and suggestions on the front-end requirements of the project. vii Abstract This thesis details the creation of a novel supernova spectral classification tool, DASH, that has been developed primarily for the OzDES collaboration as a replacement to current classi- fication tools. The main aim was to improve upon the speed and ease of classification while not compromising accuracy. DASH has used a completely new approach that does not rely on iterative template matching techniques like all previous software, but instead classifies based on the features of each supernova type and age bin. It has achieved this by employing a deep neural network to train a matching algorithm. This has enabled DASH to be over 100 times faster than Superfit while also being just as accurate. This has been tested using the latest OzDES ATEL data, where DASH has accurately classified each spectrum with a higher degree of certainty. The deep learning model was developed using Tensorflow, and has involved defining 306 dif- ferent classification bins made up of 17 supernova subtypes and 18 age bins. The model was trained using the Obelix Supercomputer at UQ and made use of nearly 4000 supernova tem- plates from SNID and the Berkeley SN Ia Program. The trained model is independent of the number of templates, which allows for DASH’s unprecedented speed. Two user interfaces available on GitHub and PyPI have been developed. These include a graphical interface for easy visual classification and analysis of supernovae, and a python library for the autonomous and quick classification of several supernova spectra. The speed, accuracy, user-friendliness, and versatility of DASH presents an advancement to existing spectral classification tools, and is a viable alternative for the astronomy community. ix Contents Acknowledgmentsv Abstract vii List of Figures xv List of Tables xix 1 Introduction 1 1.1 Motivation.........................................1 1.2 Scope............................................2 1.2.1 Wider Context...................................3 2 Background 5 2.1 Astronomical Objects...................................5 2.1.1 Flux, Luminosity, and Magnitude System...................5 2.1.2 Supernovae....................................6 Types........................................6 Age.........................................8 2.1.3 Galaxies......................................8 2.2 Astronomical Spectra...................................9 2.2.1 Spectroscopic Features.............................. 10 2.2.2 Redshift...................................... 10 2.2.3 Distortions..................................... 11 Interstellar Dust.................................. 12 x Sky lines...................................... 13 Noise........................................ 13 2.2.4 Equipment Miscalibration............................ 14 2.3 OzDES........................................... 14 2.3.1 Anglo-Australian Telescope........................... 15 3 Prior Methods 17 3.1 Current OzDES Approach................................ 17 3.2 Prior Software....................................... 17 3.2.1 SNID........................................ 18 3.2.2 MARZ....................................... 18 3.2.3 AUTOZ...................................... 18 3.2.4 Superfit...................................... 19 3.2.5 Summary of Previous Tools........................... 19 4 Requirements and Tool Decisions 21 4.1 Speed and Accuracy................................... 21 4.2 Installation and Updating................................ 22 4.3 Operating System..................................... 22 4.4 Online vs Offline..................................... 23 4.5 Language Decision.................................... 24 4.6 Integration......................................... 26 4.7 Libraries and Tools Used................................. 26 4.7.1 Libraries...................................... 26 4.7.2 Software Tools................................... 27 Git and GitHub.................................. 27 Resources..................................... 27 5 Data Description 29 5.1 Data Collection...................................... 29 5.1.1 SNID Templates.................................. 29 xi Templates-2.0................................... 30 5.1.2 Superfit...................................... 30 5.1.3 Increased SNID Templates............................ 31 Liu & Modjaz................................... 31 BSNIP....................................... 31 5.1.4 WISeREP...................................... 32 5.2 Deleting Templates.................................... 33 5.2.1 Unknown Ages.................................. 33 5.2.2 Ic-broad bias.................................... 33 5.3 Need for more templates................................. 34 5.3.1 Bias in all Supernova Classification Tools................... 34 5.4 Templates Description.................................. 34 5.4.1 Types and Ages.................................. 35 5.4.2 Number of Templates.............................. 36 Accounting for SNIa Bias............................ 36 5.5 Plot of Templates..................................... 37 5.6 File Types......................................... 38 5.6.1 lnw File...................................... 38 5.6.2 ASCII, data, Two-column Text Files...................... 40 5.6.3 FITS File...................................... 40 6 Initial Design and Major Decisions 43 6.1 Initial Design....................................... 43 6.1.1 Host Galaxy Subtraction............................. 45 6.1.2 Initial Classification Method.......................... 45 6.2 Changing Classification Method............................ 46 6.3 Deep Learning....................................... 48 6.3.1 Overview..................................... 48 6.3.2 Machine Learning in Astronomy........................ 49 6.3.3 Tensorflow..................................... 50 xii 7 Implementation 51 7.1 Processing Method.................................... 51 7.1.1 Filtering...................................... 52 7.1.2 Normalising and De-redshifting........................ 53 7.1.3 Log-wavelength Binning............................. 54 7.1.4 Continuum Modelling with Spline Interpolation............... 55 7.1.5 Cosine tapering edges.............................. 56 7.2 Preparing Training Data................................. 57 7.2.1 Label and Image Data.............................. 58 7.2.2 Template sample bias.............................. 58 7.3 Deep Learning Training................................. 59 7.3.1 Softmax Regressions............................... 59 7.3.2 Building Layers.................................. 61 7.4 Trained Models...................................... 61 7.4.1 Trained at zero redshift............................. 61 7.4.2 Agnostic Redshift................................. 63 7.5 Interfaces.......................................... 64 7.5.1 Graphical User Interface............................. 64 Label Guide:.................................... 66 7.5.2 DASH Python Library.............................. 69 8 Performance 71 8.1 Validation Set....................................... 71 8.1.1 Alternative Models................................ 73 8.2 Results with OzDES data................................. 74 9 Project Evaluation 79 9.1 Completion.......................................