Infrared Spectroscopy of Super Novae
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Infrared Spectroscopy of Super novae by Jason Spyromilio Astrophysics Group Blackett Laboratory Imperial College of Science, Technology and Medicine London SW7 A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Membership of the Imperial College August 1989 1 Abstract Infrared spectroscopic observations of snpernovae 1986G and 1987A are presented and discussed. Late-time observations of SN 1986G at CTIO show no evidence for any spectral features. Contemporary observations at the AAT show a low S/N feature at 1.64 fim. The observations of SN 1987A are unique both in spectral and temporal coverage. The spectra exhibit forbidden lines of iron group elements believed to arise from the radioactive decay of 56Ni and of silicon. In addition allowed lines of hydrogen, oxygen, silicon, sodium, magnesium and calcium are identified. Models for the interpretation of these spectra are presented. Modelling of hydrogen lines in the early-time spectra of SN 1987A suggests that large deviations from Boltzmann populations are present in the envelope. A late-time model for Type la supernovae is also presented. The energy deposition of the 7-rays resulting from the radioactive decay of 56Ni is calculated through the use of Monte Carlo techniques and a self-consistent temperature and ionisation structure is calculated. A model spectrum is compared with the spectra of SN 1986G. Finally we discuss the molecular emission present in the spectra of SN 1987A and present models of the vibrational-rotational spectra of carbon monoxide and singly ionised carbon monoxide and compare them with the data. 2 Acknowledgements I would like to thank the many people who helped me during the course of the work described in this thesis. My thanks go to Peter Meikle under whose careful supervision this work was under taken. He provided a constant source of enthusiasm, essential help and advice. I would also like to thank him and John Quenby for dealing with the bureaucratic problems arising from my non-SERC student status. Special thanks are due to David Allen for educating me in the techniques of infrared spectroscopy and for his constant enthusiasm during observing runs. Without his help and advice the quality of data presented here would certainly be much poorer. Also special thanks are due to Dick Learner for his patience in our regular tutorials on molecular and atomic physics and for convincing me that modelling the molecular emission in SN 1987A was ‘straightforward’. I would also like to thank my friends and colleagues for stimulating and helpful discus sions. Thanks go to Phil Andrews, Chris Bell, Rene Doyon, James Graham, Phil James, Bob Joseph, Steve Matcher, Robert Renton, Sunil Sidher, Tim Sumner, Gian Varani and Martyn Wells. Finally I would like to thank my parents for their support and encouragement during my student years. 3 Contents 1 Introduction 11 1.1 Observed characteristics of supernovae .................................................................12 1.1.1 Spectroscopic classification of supernovae...............................................12 1.1.2 Electromagnetic emission properties of supernovae................................15 1.2 Explosion mechanisms............................................................................................ 19 1.3 The importance of infrared observations.............................................................. 22 1.3.1 Early time observations.............................................................................22 1.3.2 Late time observations t > 150 d a y s........................................................23 1.4 Conclusions...............................................................................................................24 2 Techniques of Infrared spectroscopy of Supernovae 25 2.1 Introduction.............................................................................................................. 25 2.2 Devices .....................................................................................................................26 2.2.1 Circular Variable Filter (C V F ).................................................................26 2.2.2 Cooled Grating spectrometers (CGS)........................................................27 4 2.3 Observing techniques...............................................................................................27 2.4 Factors influencing the quality of the d a ta ...........................................................28 2.5 Flux calibration and removal of Telluric features...............................................29 2.6 Wavelength calibration............................................................................................30 3 Infrared spectroscopy of Supernovae 1986G and 1987A 31 3.1 Supernova 1986G..................................................................................................... 31 3.1.1 The early time observations.......................................................................32 3.1.2 The late time observations ................................. 32 3.2 Supernova 1987A..................................................................................................... 43 3.2.1 The observations ......................................................... 43 3.2.2 Results ........................................................................................................ 46 3.3 Conclusions...............................................................................................................65 4 Interpretation of the Infrared spectra of supernovae 79 4.1 Early time spectra...................................................................................................79 4.1.1 Theory of continuum formation.................................................................80 4.1.2 Theory of P-Cygni profile formation........................................................81 4.1.3 Modelling the early time spectra of SN 1987A......................................... 86 4.2 Late time spectra............................................................... 91 4.2.1 The 7 rays .................................................................................................. 91 4.2.2 Non-thermal electron energy deposition..................................................92 5 4.2.3 The thermal and ionisation balance 95 4.2.4 The final spectrum....................................................................................100 4.2.5 Comparison with observations ..................................................................100 4.3 Conculsions............................................................................................................102 5 Molecules in Supernovae 103 5.1 The infrared spectra of diatomic molecules.........................................................103 5.1.1 Energy level structure..............................................................................103 5.1.2 Selection rules and band structure.........................................................107 5.1.3 Radiative rates .......................................................................................... 108 5.2 Carbon monoxide emission in SN 1987A............................................................109 5.2.1 The discovery of emission bands ..........................................................109 5.2.2 The location of the emitting C O ............................................................110 5.2.3 Modelling the emission from C O ............................................................ 110 5.2.4 Interpretation of the CO emission .........................................................114 5.3 Other molecules in SN 1987A ..............................................................................116 5.4 Molecular formation in SN 1987A ........................................................................117 6 Conclusions and further work 119 References 122 A Publications 129 6 List of Figures 3.1 Spectrum of SN 1986G AAT March 1987 ....................................................... 38 3.2 Spectrum of SN 1986G CTIO 4m March 14th 1987 ........................................ 38 3.3 Spectrum of SN 1986G CTIO 4m March 16th 1987 ........................................ 39 3.4 Spectrum of SN 1986G AAT April 1987 .......................................................... 39 3.5 Spectrum of SN 1986G AAT May 1987 ............................................................. 40 3.6 Spectrum of SN 1986G CTIO 4m June 21st 1987 ........................................... 40 3.7 Spectrum of SN 1986G AAT March 1988 ....................................................... 41 3.8 Binned spectrum of SN 1986G AAT April 1987 .............................................. 41 3.9 Binned spectrum of SN 1986G AAT May 1987 .............................................. 42 3.10 March 1987 J window spectrum of SN 1987A....................................................... 66 3.11 March 1987 H window spectrum of SN 1987A...................................................... 66 3.12 March 1987 K window spectrum of SN 1987A ......................................................67 3.13 March 1987 L window spectrum of SN 1987A.......................................................67 3.14 June 1987 J window spectrum of SN 1987A.......................................................... 68 3.15 June 1987 H window spectrum of SN 1987A......................................................... 68 7 3.16 June 1987 K window spectrum