A survey of radial velocities in the zodiacal dust cloud : thesis accepted for the degree of Doctor of Philosophy by the Imperial College of Science, Technology and Medicine London 2007

The Zodiacal Light, that misty diffuse cone of light seen in the West after Sunset and the East before Sunrise, is a beautiful and intriguing phenomenon. Even though everyone can enjoy the sight from a suitably dark location, it is poorly understood, and has been the subject of relatively little research. Brian May began his research into the subject in 1970, and was finally awarded his PhD in 2007, after a hiatus of more than 30 years pursuing his other career as guitarist with his rock band Queen. This book is Brian’s thesis, and as such presents the results of his research for astronomers. This thesis documents the building of a pressure-scanned Fabry-Perot Spectrometer, equipped with a photomultiplier and pulse-counting electronics, and its deployment at the Observatorio del Teide at Iza?a in Tenerife, at an altitude of 7,700 feet (2,567 m), to record high-resolution spectra of the Zodiacal Light. The aim was to achieve the first systematic mapping of the Magnesium I (MgI) absorption line in the night sky. More than 250 scans of both morning and evening Zodiacal Light were obtained, in two observing periods in 1971 and 1972. The scans showed profiles modified by various Doppler-shifted components with respect to the unshifted shape seen in daylight. The set of spectra obtained is compared with predictions made from a number of different models of a dust cloud, assuming various distributions of dust density as a function of position and particle size, and differing assumptions about their speed and direction. The observations fit predominantly prograde models fairly well, but show a morning-evening asymmetry, different in the two observing periods. Models are investigated containing various components, including prograde and retrograde orbiting dust around the Sun, a drift of interstellar material though the Solar System, and light from distant emitting matter. The implications for possible asymmetries of the Zodiacal Cloud are discussed. Other researches on the Zodiacal Dust Cloud are reviewed, including recent insights into its structure, orientation, and evolution. Brian’s observations are evaluated in this context. Cover......Page 1 A SURVEY OF RADIAL VELOCITIES IN THE ZODIACAL DUST CLOUD......Page 2 ISBN 9780387777054 (HB)......Page 3 Foreword......Page 6 Preface and Acknowledgements......Page 8 Contents......Page 12 Abstract......Page 16 List of Figures......Page 18 Abbreviations and Acronyms......Page 22 1.1 The Zodiacal Light – the phenomenon......Page 24 1.2 Review of observations of the ZL prior to 1970......Page 25 1.3 Review of the period of my observations of the ZL, 1970–1974......Page 43 1.4 Review of recent developments in ZL research, 1974–2007......Page 44 2.2 Choice of resolving power......Page 64 2.3 The site......Page 67 2.4 The ZL building......Page 68 2.5 Instrumental details......Page 70 2.6 New features of the instrument......Page 75 2.7 Optimisation of the system......Page 95 2.8 How the observations were made......Page 96 3.1 Intensity calibration......Page 99 3.2 Wavelength calibration......Page 103 3.3 Treatment of a single scan......Page 108 3.5 MgI emission......Page 109 3.7 Polynomial fits......Page 117 3.8 Gaussian curve fitting (Program GAUSSN)......Page 123 4.1 Gallery of Spectra......Page 128 4.3 Information obtainable from the Gaussian fits......Page 139 4.4 Accuracy of the fits......Page 142 4.5 Evidence from line widths and depths......Page 143 4.6 Analysis of the wavelength shift versus elongation data......Page 144 4.7 Forces experienced by particles in the Zodiacal Cloud......Page 145 4.8 Rotating dust cloud models......Page 146 4.9 Other considerations in rotating models......Page 147 4.10 Geocentric Dust Cloud (GDC) model......Page 150 4.11 A uniform dust flow model......Page 151 4.12 Estimation of the effect of a contribution to the Zodiacal Light from sources distant from the Solar System......Page 159 4.13 Further analysis of the data by comparison with new radialvelocity data and model theory available in 2007......Page 163 4.14 ʻBinningʼ of the HMR data......Page 167 4.15 Variations with time......Page 169 4.16 Summary of the implications of the 1970–4 work, and pointers for the future ......Page 170 5.1 Current Zodiacal Light research......Page 172 5.2 Objectives of our proposed new work in Zodiacal Light......Page 174 5.3 Concluding remarks......Page 176 Appendix 1 Program ZLPLT......Page 184 Appendix 2 Programs which fit curves to the fully reduced data points......Page 188 Appendix 3 Programs which draw the fitted curves and extract parameters from the fits......Page 198 Appendix 4 STREAM and CONVL......Page 202 Appendix 5 Hicks, May and Reay NATURE paper 1972 ......Page 207 Appendix 6 Hicks, May and Reay MNRAS paper 1974 ......Page 212 Appendix 7 Derivation of the Airy Summation for a Fabry- Perot Interferometer......Page 224 References......Page 228 In the summer and autumn of 2006 I read several interviews with Brian May in which he mentioned his desire to complete the PhD that he had abandoned in 1974. I looked up the papers he had published while a PhD student, which were on spectroscopic studies of the motion of the dust responsible for the zodiacal light, and felt that there was a basis for a thesis. Since he had been a student at Imperial, I knew, as Head of the Astrophysics Group at Imperial, that it would be good for the Group if he came and worked with us. I got in touch with him by email and suggested he come and talk about it. He replied enthusiastically and said that he was working on typing up what he had completed by 1974. I gradually realized that I was the only staff member at Imperial who had previously worked on zodiacal dust, so that I would have to act as his supervisor. Eventually we met and I tried to assess whether he would be able to find time for the huge amount of work that finishing off a thesis involves, particularly if it has not been touched for over 30 years. Since some of Brian's emails were coming from the recording studio I knew there was strong competition for his time. Introduction -- Preparations And Experimental Details 1971-1974 -- Reduction Of The Data -- Interpretation Of Results In Terms Of Physical Models -- Current Developments And Future Plans. Brian Harold May. Brian Harold May's Thesis (doctoral)--imperial College Of Science, Technology And Medicine, London, 2007. Includes Bibliographical References (p. [205]-215).