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PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/197982 Please be advised that this information was generated on 2021-10-09 and may be subject to change. Optical Variability with the Palomar Transient Factory Proefschrift ter verkrijging van de graad van doctor aan de Radboud Universiteit Nijmegen op gezag van de rector magnificus prof. dr. J.H.J.M. van Krieken, volgens besluit van het college van decanen in het openbaar te verdedigen op dinsdag 27 november 2018 om 10.30 uur precies door Joannes Christiaan Josephus van Roestel geboren op 2 april 1990 te Tilburg 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 1 Promotoren: Prof. dr. Paul Groot Prof. dr. Tom Prince (California Institute of Technology, VS) Manuscriptcommissie: Prof. dr. Bas van de Meerakker Prof. dr. Rudy Wijnands (Universiteit van Amsterdam) Prof. dr. Frank Verbunt Prof. dr. Peter Jonker Dr. Raffaella Margutti (Northwestern University, VS) © 2018, Jan van Roestel Optical Variability with the Palomar Transient Factory Thesis, Radboud University Nijmegen Illustrated; with bibliographic information and Dutch summary Cover design: Femke Boezen Front cover image: Binary stars Image credit: Casey Reed/NASA ISBN: 978-94-028-1279-4 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 2 Contents 1 Introduction 1 1.1 The optical variable sky ................................. 1 1.2 Stellar evolution; the life and death of stars . ................... 3 1.3 Binary star evolution ................................... 4 1.4 The transient zoo ..................................... 5 1.4.1 Classical transients ................................ 5 1.4.2 New transients .................................. 6 1.5Telescopes......................................... 9 1.5.1 The Palomar Transient Factory ........................ 9 1.5.2 Spectroscopic followup of PTF sources . .................... 10 1.6Methods.......................................... 10 1.6.1 Measuring binary star parameter ........................ 10 1.6.2 Fitting data . .................................. 14 1.6.3 Machine learning and its applications in astronomy .............. 15 1.7Thisthesis......................................... 16 2 PTF-Sky2Night 17 2.1 Introduction ........................................ 17 2.2 Survey design ....................................... 21 2.3 Observations ....................................... 21 2.4Results........................................... 24 2.4.1 Survey characteristics .............................. 24 2.4.2 Transients ..................................... 27 2.4.3 Observed transient rates . .......................... 33 2.5 Discussion ......................................... 34 2.5.1 Expected number of transients ......................... 34 2.5.2 Upper limit for fast optical transients ..................... 36 2.5.3 False positives in the search for kilonovae ................... 38 2.6 Summary and conclusions . ............................... 41 i 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 3 Contents 2.A Additional Figures and Tables .............................. 42 3 PTF-Sky2Night II 53 3.1 Introduction ........................................ 53 3.2 Observations ....................................... 54 3.2.1 Survey design ................................... 54 3.2.2 Execution ..................................... 55 3.2.3 Transient classification .............................. 56 3.3Results........................................... 56 3.3.1 Survey characteristics .............................. 56 3.3.2 Transients in the 2015 campaign ........................ 58 3.3.3 Transients in the 2016 campaign ........................ 68 3.3.4 Rates ....................................... 70 3.4 Discussion ......................................... 73 3.4.1 Unusual transients ................................ 73 3.4.2 Observed rates of transients ........................... 74 3.4.3 Kilonova follow up ................................ 75 3.5 Summary and conclusions ................................ 76 3.A Additional figures and tables . ............................. 77 4 PTF1 J085713+331843 95 4.1 Introduction ........................................ 96 4.2 Observations ....................................... 97 4.2.1 SDSS photometry ................................ 97 4.2.2 Palomar Transient Factory photometry .................... 97 4.2.3 Catalina Sky Survey photometry ........................ 99 4.2.4 ULTRACAM high cadence photometry .................... 99 4.2.5 Spectroscopy . ................................ 99 4.3 Analysis ..........................................100 4.3.1 Magnitudes ....................................100 4.3.2 Orbital period ..................................102 4.3.3 Spectral type and temperature .........................102 4.3.4 Radial velocities .................................105 4.3.5 Light curves ....................................108 4.3.6 System parameters ................................109 4.4 Discussion .........................................112 4.4.1 Mass, Radius and Temperature .........................112 4.4.2 Surface gravity, spectral type, and distance ..................112 4.5 System evolution .....................................114 4.6 Summary . ........................................116 4.A Centre of light offset ...................................118 ii 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 4 Contents 5 EL CVn-type binaries in PTF 121 5.1 Introduction ........................................122 5.2 Target selection ......................................123 5.2.1 The Palomar Transient Factory .........................123 5.2.2 Data ........................................123 5.2.3 Machine Learning Classification .........................123 5.2.4 EL CVn identification ..............................126 5.3 Spectroscopy .......................................127 5.4 Methods and analysis ..................................129 5.4.1 Lightcurve .....................................129 5.4.2 Effective temperature .............................. 131 5.4.3 Radial velocity .................................. 131 5.4.4 Galactic kinematics ...............................132 5.4.5 Masses and radii .................................135 5.5Results...........................................139 5.6 Discussion .........................................140 5.6.1 Co-rotation ....................................140 5.6.2 Binary evolution and stellar parameters .................... 141 5.6.3 Galactic population and space density .....................145 5.6.4 Comparison with the SWASP sample .....................146 5.6.5 Pulsations .....................................148 5.7 Summary and conclusion ................................149 5.AAdditionaltablesandfigures.............................. 151 Bibliography 169 Summary 181 Transients............................................182 Eclipsing binary stars .....................................182 Samenvatting 185 Astrofysische explosies .....................................186 Eclipserende dubbelsterren . ...............................186 Curriculum vitæ 189 List of publications 191 Acknowledgments 193 iii 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 5 525927-L-bw-van Roestel Processed on: 7-11-2018 PDF page: 6 Chapter 1 Introduction 1.1 The optical variable sky Even though it may seem so to the naked eye and on human time scales, stars are not eternal and static but vary on all time scales and energy scales. Variability is either intrinsic to the source, in which case the energy output varies as a function of time, or extrinsic, in which case the environment is the cause of changes in the observed luminosity. This means that by studying the variability in the luminosity of objects, we can learn more about the physics that is involved in the generation or transport of energy (typically gravitational energy or nuclear energy) and/or learn more about the immediate environment of the objects. The nuclear fusion processes in the cores of stars change over the course of time as the reservoir of hydrogen gets depleted, leading to secular variability. If the hydrostatic equilibrium that keeps stars in balance is disturbed the structure of a star changes, sometimes on cataclysmic ways, on timescales of seconds, as in a supernova explosion at the end of the lives of stars with masses exceeding eight times that of the Sun (8 Solar Masses, 8 M). In the outer layers of stars, the intricate interplay between radiation and plasma can cause large-scale instabilities leading to stellar pulsations, and the interaction with magnetic fields can lead to eruptive events. Solar flares are an extremely low-energy and mild example of these magnetic reconnection events. In lower mass stars the luminosity of the star can be increased by >500 times over the course of an hour, thereby posing a real obstacle for the habitability of planets around these stars. As many stars are part of a binary system, interactions between the two components can lead to a different type of eruptive variability, induced by accretion, the mass overflow from one star to another. Next to these intrinsic changes, extrinsic variability can be induced, in particular in binary systems when the orbital plane of the binary is favourably oriented towards our line of sight and the two stars are eclipsing each other in their orbit. The regularity