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Durham E-Theses A polarimetric study of the reection nebulae NGC 2068 and NGC 2023 in the Orion R1 association Mannion, Michael David How to cite: Mannion, Michael David (1987) A polarimetric study of the reection nebulae NGC 2068 and NGC 2023 in the Orion R1 association, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/6892/ 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 2 A polarimetric study of the reflection nebulae NGC 2068 and NGC 2023 in the Orion R1 association 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. Michael David Mannion Department of Physics University of Durham Science Laboratories South Road Durham DH1 3LE A thesis subrnitted to the University of Durham for the degree of Doctor of Philosophy 30 January 1987 A polarimetric study of the reflection nebulae NGC 2068 and NGC 2023 in the Orion R1 association Michael David Mannion ABSTRACT Polarimetry studies of two reflection nebulae in the Orion R1 association are used to determine the nature of the dust in which recently formed stars are embedded in, and show the geometry of the surrounding dust cloud. The data reductions presented are on NGC 2068 and NGC 2023, which are centres of recent low-mass star formation and are embedded on the nearside of 11630. In the case of NGC 2068, it appears that there is a single illuminating star which illuminates a foreground tilted slab of varying dust density from the rear. A simple tilted slab model assuming single Mie scattering from homogeneous spherical grains was used to fit visual data of traces of polarization, polarized intensity and total intensity through HD 38563N in a north-south direction. The model favoured metallic grains; the best fit being for iron grains and a slab 0.5 parsecs in front of HD 38563N tilted at an angle 55 degrees to the line-of-sight. In the case of NGC 2023, multicolour polarimetry is presented in B,V,R,I and z. The star HD 37903 was found to be the sole illuminating star. A model to fit the spectral dependence of polarization gave low refractive index grains assuming a power law size distribution. Associated with NGC 2023 are Herbig-Haro objects HH-1, 4, which were found not to be polarized. Ph.D. Thesis PAGE i January 1987 PREFACE The work undertaken for this doctoral thesis was done while the author was a postgraduate member of the Astronany Group in the Department of Physics at Durham University under the supervision of Dr. S.M. Scarrott between February 1983 and January 1987. During this time the author reduced and analysed electronographic polarimetry data on NGC 2068 in the V waveband, and electronographic (B,V,R) and CCD (R,I,Z) data on NGC 2023. Mcdels were devised to fit a) the observations of visual polarization in NGC 2068 as a function of offset distance and b) the observed wavelength dependence of polarization in NGC 2023. No part of this thesis has previously been submitted for a degree in this or any other university and all work is due to the author unless otherwise acknowledged. The copyright of this thesis rests with the author. No quotation fran it should be published without his prior written consent and information derived from it should be acknowledged. Michael David Mannion Ph.D. Thesis PAGE ii January 1 987 Cl)NTENTS Page ABSTRACI' i PREFACE ii TABLES viii LIST OF FIGURES X LIST OF PLATES xiii Chapter 1 Intrcrluction 1 1 01 Observations 1 1o2 Star fonnation 3 1o3 The Orion Complex 8 1o4 Reflection nebulae 14 . 1 oS Interstellar dust grains 19 1o6 Polarimetry 20 1o7 Aims 26 PhoDo Thesis PAGE iii January 1987 CDNT.ENTS Page Chapter 2 Interstellar Dust Grains 28 2.1 Introduction 28 2.2 Data on dust grains 33 2.2 a Extinction 35 2.2 b Polarization 39 2.2 c Spectroscopy 43 2.2 d Scattering 44 2.2 e Distribution 46 2.2 f Dust-to-gas ratio 46 2.2 g Physical properties 48 2.3 Grain models 50 2.4 Fonnation, growth and destruction 54 2.5 Dust interactions in the interstellar medium 57 2.6 Conclusions 58 Chapter 3 Star Fonnation 62 3.1 Theories of star fonnation 62 3.2 Signposts of star fonnation 79 3.3 Star fonnation in the 84 Orion Molecular Cloud Complex Ph.D. Thesis PAGE iv January 1987 <X>NTENTS Page Chapter 4 Polarimetry of NGC 2068 89 4a1 Introduction 89 4 a2 Summary of previous work 92 4a3 New observations 96 4a4 The polarimetry data 97 4a5 Discussion 114 Chapter 5 A Model of NGC 2068 120 5a1 Tilted slab 120 5a2 Immediate enviroment in NGC 2068 131 5a3 Discussion 138 Chapter 6 Polarimetry of NGC 2023 139 6a 1 Optical and near-infrared 139 polarimetry of NGC 2023 6a1 a Electronographic data 145 6o 1 b CCD data 152 PhaDo Thesis PAGE V January 1987 CDNTENTS Page 6.2 Comparison of C<D and Electronographic 160 data on NGC 2023 6.3 Wavelength dependence of polarization 164 6.4 IRAS data 170 6.5 The optical filament and HH-1 173 6.6 Discussion 175 Chapter 7 Analysis of NGC 2023 180 7.1 Physical conditions in NGC 2023 180 7.2 Morphology and structure of NGC 2023 187 7.3 The star S1 08 and HH-1 190 7.4 Extended emission 195 7.5 Inferences on dust 195 Chapter 8 Conclusions 202 8.1 Interpreting the main observations of 202 NGC 2068 and NGC 2023 Ph.D. Thesis PAGE vi January 1987 CDNTENTS Page Summary 206 ACKNOWLEDGEMENTS 208 LIST OF SYMBOLS 209 REFERENCES 210 APPENDICES 230 A An optical polarization study of NGC 2068 230 B A comparison of data reductions of NGC 2068 243 C Linear traces through HD 37903 244 Ph.D. Thesis PAGE vii January 1987 TABLES Page Table 1.1 The Orion R1 association 16 1 • 2 A cx:mparison of CCD and electronographic detectors 25 2. 1 The interstellar medium 30 2. 2 Infrared features of dust grains 44 2.3 Reflection nebula models 51-52 2.4 Interstellar dust grains 61 4.1 r::ata on the stars associated with NGC 2068 90 4. 2 Previous polarimetry of NGC 2068 94-96 4. 3 Infrared stars associated with NGC 2068 102 4.4 Polarization of selected regions of NGC 2068 106 5.1 Grain materials 123 5.2 Grid of models 130 5. 3 Physical parameters of NGC 2068 137 Ph.D. Thesis PAGE viii January 1987 TABLES Page Table 6.1 Filter characteristics 140 6.2 Data on the stars associated with NGC 2023 143 6.3 Identification of stars on Electronographic data 147 6.4 Identification of stars from CCD data 154 6.5a Multicolour polarimetry of NGC 2023 162 6.5b Multicolour polarimetry of NGC 2023 163 6.6 Stars common to COD and Electronographic data 164 6.7a Multicolour polarimetry of NGC 2023 168 6.7b Multicolour polarimetry of NGC 2023 169 6.8 Polarimetry of regions close to S108 175 7. 1 Physical parameters of NGC 2023 186 7.2 Best fits to the wavelength dependence of polarization 197 8.1 Summary of reflection nebula observations 207 Ph.D. Thesis PAGE ix January 1987 LIST OF FIGURES Page Figure 1 • 1 The Orion molecular canplexes 10 1 .2 The dark dust cloud - Lynds 1630 12 1 • 3 Manifestations of star fonna.tion near the M78 canplex 13 1.4 Galactic distribution of Rand OB associations 15 2.1 The interstellar extinction curve 38 2.2 Interstellar polarization 41 3.1 Sequential star fonna.tion in OB associations 68 3.2 Evolutionary tracks of collapsing protostars 73 4.1 A visual polarization map of NGC 2068 100 4.2 A map of the region of NGC 2068 103 4.3 Polarization trace through HD 38563N 110 in a north-south direction 4.4 Polarized intensity trace through HD 38563N 111 in a north-south direction 4.5 'Ibtal intensity trace through HD 38563N 112 in a north-south direction 4.6 Arc traces about HD 38563N 113 Ph.D. Thesis PAGE x January 1987 LIST OF FIGURES Page Figure 4.7 Tilted slab model 119 5.1 Geometry of the tilted slab model 122 5. 2 Mie scattering curves 126-129 5.3a Model fits to the data - Polarization 132 5.3b Model fits to the data - Polarized intensity 133 5.3c Model fits to the data - Total intensity 134 6. 1 A map of the stars in the region of NGC 2023 144 6.2 Polarization of NGC 2023 using a B filter 149 6.3 Polarization of NGC 2023 using a V filter 150 6.4 Polarization of NGC 2023 using an R filter 151 6.5 Polarization of NGC 2023 using an R filter 157 6.6 Polarization of NGC 2023 using an I filter 158 6.7 Polarization of NGC 2023 using a z filter 159 6.8a Wavelength dependence of polarization 166 6.8b Wavelength dependence of polarization 167 6.9a Wavelength dependence of position angle 171 6.9b Wavelength dependence of position angle 172 6.10 A polarization and contour map of the S108 region 176 Ph.D.
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