Durham E-Theses Optical polarimetry of bipolar planetary nebulae Booth, Paul Anthony How to cite: Booth, Paul Anthony (2001) Optical polarimetry of bipolar planetary nebulae, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/4237/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk Optical Polarimetry of Bipolar Planetary Nebulae Paul Anthony Booth B.Sc. The copyright of this thesis rests with the author. No quotation from it should be published in any form, including Electronic and the Internet, without the author's prior written consent. All information derived from this thesis must be acknowledged appropriately. A thesis submitted to the University of Durham for the degree of Master of Science The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Department of Physics July 2001 ABSTRACT Chapter 1 gives a brief review of the relevant aspects of stellar evolution leading to the formation of a planetary nebula. Included in this review is a discussion of the most important factors which appear to dictate the shaping and general characteristics of these nebulae. Chapter 2 follows with a review of polarization theory and its use in the study of planetary nebulae and the interstellar medium. This includes a description of the basic reduction procedures which are used to produce the polarization maps of later chapters. Discussion of the reduction process is accompanied by the analysis and interpretation of linear polarization data from the observation of an extragalactic source. Chapter 3 presents multicolour polarimetry data for the young bipolar planetary nebula M2-9. Much of the polarization data confirms previously gathered results and shows that extreme levels of polarization occur in the outer regions of the nebula. Polarization structure within the central regions of M2-9, however, appear to contradict a number of previously gathered results and suggest that the central illuminating source of the nebula is extended. The data conclusively proves that the mirror-symmetric condensations have changed position. An estimation of the rotation period of the condensations has been made using calculations which trace their lateral displacement. The result of these calculations agrees well with previously gathered results. Chapters 4 and 5 present new multicolour polarimetry data for the evolved bipolar planetary nebulae NGC 2440 and NGC 2818. Results provide evidence for the existence of bipolar rotating episodic jets in the evolved Type I bipolar nebulae. The data also shows that both nebulae possess low polarization levels and a lack of clear structure within the polarization pattern. Consequently, the dust distribution of planetary nebulae must become less favourable for the production of radiation scattering with age. i DECLARATION Work within this thesis deals with the study of bipolar planetary nebulae using the observing and analysis techniques of optical polarimetry. All data presented were recorded by the author using the Durham Imaging Polarimeter during observing time upon the 1.9m telescope at the South African Astronomical Observatory in September/October 1998, May 1999, and February/March 2000. Data reduction, analysis, and interpretation for all data has been carried out by the author. Results for M2-9 have already been published by Scarrott et al. (1993), but fresh analysis was made by the author. None of the material contained within this thesis has previously been submitted for a degree at the University of Durham or any other university. The data in this thesis were taken during telescope allocations made to Dr. S. M. Scarrott, Dr. R. D. Wolstencroft, and Mr. P. A. Booth and their permission must be obtained by anyone wishing to publish or use the results beyond this thesis. ii CONTENTS 1 Introduction to proto-planetary and planetary nebulae 1 1.1 The discovery of planetary nebulae 1 1.2 The classification of planetary nebulae 4 1.3 Stellar death and the formation of planetary nebulae 7 1.3.1 Life after the stellar nursery - Main sequence evolution 7 1.3.1.1 Low mass stellar evolution 9 1.3.1.2 Intermediate and high mass stellar evolution 9 1.3.2 Life after core hydrogen depletion - The post-main sequence 10 1.3.2.1 Low mass stellar evolution 10 1.3.2.2 Intermediate and high mass stellar evolution 12 1.3.2.3 Mass loss during the post-main sequence 13 1.4 The evolutionary effects of stellar wind processes 16 1.5 The evolutionary consequences of stellar binarity 21 1.6 Summary 23 2 Introduction to Polarization 25 2.1 Introduction 25 2.1.1 The use of polarimetry in the study of planetary nebulae 26 iii 2.2 The mathematical aspects of polarization theory 27 2.3 Measurement of polarization • • • • 32 2.3.1 The Durham Imaging Polarimeter 32 2.4 Polarimetric Observations • 36 2.5 Reduction, analysis, and interpretation of polarization data 37 2.6 Production of polarization 42 2.6.1 Processes leading to the production of polarization 42 2.7 Polarization in the astronomical environment 48 2.7.1 Polarization in the interstellar medium 48 2.7.2 Polarization in the circumstellar environment 51 2.7.3 Polarization in the nebular environment 52 3 M2-9 54 3.1 Introduction • 54 3.2 Previous studies of M2-9 55 3.3 Polarimetric Observations 65 3.3.1 Observational details 65 3.4 Results 67 3.4.1 Image details 67 3.4.2 The effects of interstellar polarization 68 3.4.3 Intensity images: V-band 73 3.4.4 Intensity images: R-band 74 3.4.5 Intensity images Ha 75 3.5 Polarization results 78 3.5.1 V-band, ISP uncorrected 78 3.5.2 V-band, ISP corrected 83 3.5.3 R-band, ISP uncorrected 89 3.5.4 R-band, ISP corrected 93 3.5.5 Ha, ISP uncorrected 99 3.5.6 Ha, ISP corrected 103 3.6 Discussion 109 3.6.1 General results 109 3.6.2 Evidence for a circumstellar disc 109 3.6.3 Inner lobe structures 110 3.6.4 Outer lobes structures HI 3.6.5 Nebular condensations 112 3.7 Summary 114 iv 4 NGC 2440 115 4.1 Introduction 115 4.2 Previous studies of NGC 2440 115 4.3 Polarimetric Observations 123 4.3.1 Observational details 123 4.4 Results 124 4.4.1 Image details 124 4.4.2 The effects of interstellar polarization 125 4.4.3 Intensity images: V-band 127 4.4.4 Intensity images: R-band 128 4.5 Polarization results 129 4.5.1 V-band, ISP uncorrected 129 4.5.2 V-band, ISP corrected 131 4.5.3 R-band, ISP uncorrected 140 4.5.4 R-band, ISP corrected 141 4.6 Discussion 149 4.6.1 Central torus 149 4.6.2 Bipolar lobes at P.A. 35 degrees 150 4.6.3 Bipolar lobes at P.A. 60 degrees 151 4.7 Summary 152 5 NGC 2818 153 5.1 Introduction 153 5.2 Previous studies of NGC 2818 •153 5.3 Polarimetric Observations 158 5.3.1 Observational details 158 5.4 Results 159 5.4.1 Image details 159 5.4.2 The effects of interstellar polarization 159 5.4.3 Intensity images: V-band 161 5.4.4 Intensity images: R-band 162 5.5 Polarization results 163 5.5.1 V-band, ISP uncorrected 163 5.5.2 V-band, ISP corrected 164 5.5.3 R-band, ISP uncorrected 172 5.5.4 R-band, ISP corrected 173 V 5.6 Discussion 181 5.6.1 Intensity distribution and morphological structure 181 5.6.2 Evidence for a circumstellar disc 182 5.6.3 The jet-like outflow 183 5.7 Summary 184 6 Summary and conclusion 185 7 List of abbreviations 189 Glossary 191 Bibliography 193 Acknowledgements 202 vi LIST OF FIGURES 1.1 Morphological classification of planetary nebulae 6 1.2 Hertzsprung-Russell diagram for the various stages of stellar evolution 8 2.1 Durham Imaging Polarimeter in its unmodified configuration 33 2.2 Durham Imaging Polarimeter in its modified configuration 34 2.3 Total intensity image of NGC 5253 with superposed contour and polarization data in the V-band..... 38 2.4 High resolution intensity images of NGC 5253 with superposed contour and polarization data. Data is shown in the V-band and Ha 40 2.5 Polarized intensity image of NGC 5253 with superposed polarized intensity contours 41 2.6 Production of polarization through dichroic extinction 43 2.7 Wavelength dependence of polarization. 45 2.8 Interstellar polarization throughout the milky way 49 3.1 Archival HST image of M2-9 at optical wavelengths 55 3.2 High resolution archival HST image of M2-9 showing the central regions of the nebula 56 3.3 Total intensity image of M2-9 with adjacent contour image in the V-band 84 3.4 Total intensity image of M2-9 with adjacent contour image and superposed polarization vectors in the V-band (ISP uncorrected) 85 3.5 Total intensity image of M2-9 with superposed contours and adjacent polarized intensity vii image with corresponding contours in the V-band (ISP uncorrected) 86 3.6 Total intensity image of M2-9with adjacent contour image and superposed polarization vectors in the V-band (ISP corrected) 87 3.7 ISP uncorrected polarized intensity image of M2-9 with superposed contours and adjacent