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Doppler Imaging of Active Young G Stars

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Doppler Imaging of Active Young G Stars UNIVERSITY OF SOUTHERN QUEENSLAND DOPPLER IMAGING OF ACTIVE YOUNG G STARS A Dissertation submitted by Carolyn Jane Brown B.Sc. (Hons) For the award of Doctor of Philosophy Department of Biological and Physical Sciences University of Southern Queensland July 2011 © Copyright Carolyn Jane Brown 2011 i Abstract This thesis investigates the activity of three young solar analogues, R58, LQ Lup, and RX J0850.1-7554, using Doppler imaging, as a way to investigate the early history of solar activity by proxy. The spot distributions of the targeted stars have been mapped and differential rotation measurements obtained from the drift of spot features over the course of the observations. A large polar spot is present on all targets examined within this thesis, as well as the simultaneous presence of mid and low latitude features. Comparison of differential rotation results for R58 and LQ Lup to previous work suggests these stars can undergo changes in differential rotation over time. Furthermore, a differential rotation measurement for RX J0850.1-7554 suggests this star is the first known example of a G-type star with solid body rotation. Overall, the results presented suggest the young Sun was a star with a major polar spot feature and some smaller spots at lower latitudes, and most likely possessed a fundamentally different dynamo to today‟s Sun. ii Certification of Dissertation I certify that the ideas, experimental work, results, analyses, software and conclusions reported in this dissertation are entirely my own effort, except where otherwise acknowledged. I also certify that the work is original and has not been previously submitted for any other award, except where otherwise acknowledged. ______________________________ ________________________ Signature of Candidate Date ENDORSEMENT ______________________________ ________________________ Signature of Supervisor Date iii Acknowledgements Thank you to the following people for whom without, this project and thesis would not have come to fruition. To my principal supervisor, Dr. Bradley Carter, I thank for everything... especially for putting up with me throughout this trying time and saving my behind in the final hours. This thesis would not have been possible without him. Also to my associate supervisor Dr. Stephen Marsden, for all of his wisdom, patience, and invaluable lessons in the black art of ZDICAM. I thank Mr. Ian Waite for all of his help with the period determination of „Fred‟ and for taking over in the 11th hour of my thesis perusal in Stephen‟s absence. To various USQ staff, especially Dr. Rhodes Hart and Prof. Grant Daggard, for their support, kind words, and understanding. Also to Dr. Harry Bulter for all of his technical support in getting my data analysis software working on my laptop. I would also like to thank the USQ Astronomy Group for their constant support and friendship. I extend my gratitude to the USQ Office of Research and Higher Degrees staff, especially Mrs Annmaree Jackson, for all of their support and for being able to make sense of how the system works (and how to get around it). To my family and friends, I would like to say a big thank you for all of their love and support, and for being accepting of my constant absence from their lives during this project. I would especially like to thank Mr. Stephen Mihaljcevic for his love and support over the years no matter what happened. I will never forget his 3 words of advice... „Tudy tudy tudy‟. iv A special thanks to Mr. Jack Daniels and Mr. Peter Jackson for being there for me when I needed them and helped to keep me sane throughout the entire PhD process. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, which can be accessed at http://adsabs.harvard.edu/; and the Astrophysics Data System (ADS) Data Services, operated by the Smithsonian Astrophysical Observatory (SAO), which can be currently accessed at http://simbad.u-strasbg.fr/simbad/ And finally I say, thank you for the music. v Contents Abstract ................................................................................................................... i Certification ........................................................................................................... ii Acknowledgements ............................................................................................... iii List of Figures ..................................................................................................... viii List of Tables ...................................................................................................... xiv Introduction ........................................................................................................... 1 1.1 The Sun ............................................................................................................... 1 1.1.1 Basic Properties........................................................................................... 2 1.1.1 Solar Magnetic Activity .............................................................................. 2 1.2 Activity of Solar-Type Stars ............................................................................. 17 1.3 Doppler Imaging of Active Solar-Type Stars ................................................... 18 1.4 Stellar Dynamo Theory & Observations ........................................................... 21 1.5 The Dynamos of Young Solar Analogues ........................................................ 24 Instrumentation and Methodologies ................................................................. 28 2.1 Introduction ....................................................................................................... 28 2.2 High Resolution AAT Spectra .......................................................................... 31 2.3 Data Reduction .................................................................................................. 33 2.4 Least Squares Deconvolution............................................................................ 34 2.5 Maximum Entropy Image Reconstruction ........................................................ 36 2.5.1 Limitations of Doppler Imaging ............................................................... 42 2.5.2 Process of Determining Stellar Parameters Using Maximum Entropy Reconstruction .......................................................................................................... 44 Doppler Imaging of R58 ..................................................................................... 47 3.1 Observations ..................................................................................................... 47 3.2 Fundamental Parameters ................................................................................... 50 3.3 Surface Features ................................................................................................ 56 vi 3.4 Surface Differential Rotation ............................................................................ 77 3.5 Discussion ......................................................................................................... 83 Doppler Imaging of LQ Lup ............................................................................... 92 4.1 Observations ...................................................................................................... 92 4.2 Fundamental Parameters ................................................................................... 93 4.3 Surface Features ................................................................................................ 98 4.4 Surface Differential Rotation .......................................................................... 112 4.5 Discussion ....................................................................................................... 115 Doppler Imaging of RX J0850.1-7554.............................................................. 120 5.1 Observations .................................................................................................... 121 5.2 Fundamental Parameters ................................................................................. 122 5.3 Period Determination ...................................................................................... 126 5.4 Surface Features .............................................................................................. 129 5.5 Surface Differential Rotation .......................................................................... 139 5.6 Discussion ....................................................................................................... 142 Discussions and Conclusions ............................................................................ 147 6.1 Introduction ..................................................................................................... 147 6.2 Discussion of the Surface Features of Young Solar Analogues ...................... 148 6.3 Discussion of the Differential Rotation of Young Solar Analogues ............... 158 6.4 Conclusions ..................................................................................................... 164 Future Directions ............................................................................................... 166 7.1 Future Directions ............................................................................................. 166 7.1.1 Further Doppler Imaging Observations for RX J0850.1-7554 ................ 168 7.1.2 Extending the
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