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Mid-Infrared Polarimetry: Insights Into Magnetic Fields and Dust Grain Properties in Young Stellar Objects and Protoplanetary Disks

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Mid-Infrared Polarimetry: Insights Into Magnetic Fields and Dust Grain Properties in Young Stellar Objects and Protoplanetary Disks MID-INFRARED POLARIMETRY: INSIGHTS INTO MAGNETIC FIELDS AND DUST GRAIN PROPERTIES IN YOUNG STELLAR OBJECTS AND PROTOPLANETARY DISKS By HAN ZHANG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2018 ⃝c 2018 Han Zhang When I look at your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is mankind that you are mindful of them, human beings that you care for them? { Psalm 8:3-4 ACKNOWLEDGMENTS Firstly, I would like to thank my advisor, Charles M. Telesco, for his patience, guidance, and generous financial supports for the past five years. It is a great privilege for me to work with Charlie and be part of the CanariCam science team. I want to thank all my collaborators, without your contributions, I can not finish the work presented in this thesis. I am particularly thankful to Dan Li, Eric Pantin, Aigen Li, Christopher M. Wright, Peter Barnes, and Naib´ıMari~nas.Thank you for your insightful discussions and comments. I thank my fellow graduate students here at University of Florida. My great classmates Rebecca, Nolan, Chen and Pekki, I remember the days we worked on the homework and projects together. I want to thank Jingzhe, my first-year roommate at UF, and Xiao, my driving coach. I want to thank Emily, Wenli, Chutipong, Shuo, Nahathai, Hanna, Tahlia, Yinan, Amanda, Rachel, Alan, Krittapas, Ben Wu, and Billy. Thank you all for your company and love. Go Gators! Finally, a special thanks to my parents for always believing in me and supporting me. I am grateful for all my church friends both in Gainesville and China. Thank you for your prayers, comfort and encouragement. We love because He first loved. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................... 4 LIST OF TABLES ...................................... 7 LIST OF FIGURES ..................................... 8 ABSTRACT ......................................... 10 CHAPTER 1 INTRODUCTION ................................... 12 1.1 Magnetic Fields in Star Formation ........................ 12 1.2 Protoplaneatry Disks ............................... 13 1.3 Polarimetry: An Important Technique to Study Magnetic Fields ........ 15 1.4 Challenges: Scattering, Radiative Grain Alignment ............... 17 1.5 Thesis Outline .................................. 19 2 OBSERVATIONS AND DATA REDUCTION ..................... 23 2.1 CanariCam .................................... 23 2.2 Stokes Parameters ................................ 23 2.3 Data Reduction ................................. 24 2.3.1 Polarimetric Imaging Data Reduction .................. 25 2.3.2 Spectropolarimetry Data Reduction ................... 27 3 THE MID-INFRARED POLARIZATION OF THE HERBIG AE STAR WL 16: AN INTERSTELLAR ORIGIN? .............................. 30 3.1 Introduction ................................... 30 3.2 Observation ................................... 32 3.3 Orign of the Polarization ............................. 34 3.3.1 Extinction toward WL 16 ......................... 34 3.3.2 Decomposition of Absorptive and Emissive Polarization ......... 40 3.3.3 Relationship of WL 16 and Regional Magnetic Fields .......... 43 3.3.4 Intrinsic Polarization ........................... 44 3.4 Discussions .................................... 45 3.4.1 PAHs in WL 16 .............................. 45 3.4.2 Disk Morphology ............................. 46 3.5 Summary ..................................... 48 4 DETECTION OF POLARIZED INFRARED EMISSION BY POLYCYCLIC AROMATIC HYDROCARBONS IN THE MWC 1080 NEBULA .................. 50 4.1 Introduction ................................... 50 4.2 Observation and Data Reduction ........................ 51 5 4.3 Results ...................................... 53 4.4 Discussion .................................... 54 4.4.1 Numerical Calculations using SD09 ................... 55 4.4.2 Alignment with Magnetic Fields ..................... 56 4.4.3 Relationship between Polarization Angles and the Ambient Magnetic Field ................................... 58 4.4.4 Marginally Detected 10.3 µm Polarization Feature ............ 59 4.5 Summary ..................................... 60 5 MODELING POLARIZATION OF YOUNG STELLAR OBJECTS AND PROTOPLANETARY DISKS AT MID-IR ................................... 64 5.1 Introduction ................................... 64 5.2 Theoretical Understanding of Dust Polarization ................. 65 5.2.1 Polarization from Dichnoic Emission and Absorption .......... 66 5.2.2 Dust Scattering .............................. 68 5.3 Model Description ................................ 69 5.3.1 Magnetic Fields Setup .......................... 69 5.3.2 Fiducial Model: Spherical Power-law Envelope ............. 70 5.3.3 Radiation Transfer with RADMC-3D ................... 70 5.3.4 Disk Model ................................ 72 5.3.5 Results .................................. 73 5.3.6 Example: AB Aur ............................ 75 5.3.7 Discussion ................................ 76 5.4 Summary ..................................... 77 6 UNDERSTANDING THE MAGNETIC FIELDS IN W51 IRS2 USING MID-IR POLARIMETRY 90 6.1 Introduction ................................... 90 6.2 Observation and Data Reduction ........................ 92 6.3 Discussion .................................... 93 6.3.1 Polarization Components { The Aitken Method ............. 93 6.3.2 Polarization Results of W51 IRS2 .................... 94 6.3.3 Magnetic Field Structure ......................... 96 6.3.4 Gas Emission from VLA ......................... 97 6.3.5 Magnetically Driven Gas Flow? ..................... 98 6.4 Summary ..................................... 99 7 CONCLUSIONS .................................... 106 7.1 Future Directions ................................. 108 APPENDIX: AITKEN'S METHOD ............................. 109 REFERENCES ........................................ 111 BIOGRAPHICAL SKETCH ................................. 119 6 LIST OF TABLES Table page 3-1 Basic Properties of WL 16 ............................... 32 3-2 Observing Log ..................................... 34 3-3 Polarization Measurements of WL 16 ......................... 43 3-4 Extinction and Polarization of WL 16 and Elias 29 .................. 44 4-1 Observing Log ..................................... 60 4-2 Different models and polarization at 11.3 µm ..................... 61 5-1 Model Parameters ................................... 78 6-1 Observation Log .................................... 100 6-2 Polarization and Flux Measurements ......................... 100 7 LIST OF FIGURES Figure page 1-1 The formation of a low mass star. ........................... 20 1-2 Illustration of the structures and physical processes in a protoplanetary disk. .... 21 1-3 Illustration of absorptive and emissive polarization in magnetically dust alignment theory. ......................................... 22 2-1 The frame of the object with o and e ray images. .................. 28 2-2 CanariCam wave-plate efficiency and Instrumental Correction. ............ 29 3-1 Total intensity maps of WL 16 at 8.7, 10.3, and 12.5 µm. .............. 35 3-2 The 8.7- µm linear polarization map of WL 16 superimposed on (total intensity) contours. ........................................ 36 3-3 The low-resolution (R≈50) spectrum of the brightest central 100.6 (21 pixels) region of WL 16. ....................................... 37 3-4 Polarization and emission/absorption decomposition results of WL 16. ....... 38 3-5 Polarization and emission/absorption decomposition results of Elias 29. ...... 39 3-6 The JHK color-color diagram. ............................ 41 3-7 Comparison of the polarization profiles of WL 16 (black) and Elias 29 (blue). .... 42 3-8 Intensity and charge state of PAHs at two sides of the disk. ............. 47 4-1 Intensity map (contours) of MWC 1080 system at 11.2 µm. ............. 61 4-2 Intensity and polarization spectra of NW nebula. ................... 62 4-3 Signal-to-noise (S/N) ratio of polarized intensity, Stokes u(U=I ), and Stokes q(Q=I ) of the NW nebula. .................................. 63 5-1 Ratio of the absorptive efficiency perpendicular and parallel to the shorter axis of the spheroid Qabs,?/Qabs,k covering wavelengths λ from 1.0 to 1000.0 µm. ..... 79 5-2 Ratio of the absorptive efficiency along two directions Q?/Qk vs changing grain radius a. ........................................ 80 5-3 Emissive polarization profiles vs wavelength. ..................... 81 5-4 The product of the degree of polarization at 90◦ due to single scattering (P) and the dust albedo (!) for dust size distributions with different values of amax (the value of amin is fixed at 0.01 µm). .............................. 82 8 5-5 Simulated linear polarization maps in a poloidal B-field configuration for a spherical envelope at λ=10.0 µm. ................................ 83 5-6 Simulated linear polarization map in a toroidal B-field configuration for a spherical envelop at λ=10.0 µm. ................................ 84 5-7 Dust scattering induced polarization map at λ=10.0 µm. .............. 84 5-8 Linear polarization map of a poloidal shape B-field configuration. .......... 85 5-9 Linear polarization map of a toroidal shape B-field configuration. .......... 86 5-10 Linear polarization map of an hour-glass shape B-field configuration. ........ 86 5-11 Linear polarization map of Aitken model IVa B-field configuration. .......... 87 5-12 Linear polarization map of Aitken
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