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The study of extraterrestrial magnetic fields is a relatively new one, confirmation of the existance of the first such field (that of our Sun) having come a s late as 1908. In the past 30 years a great ammount of knowledge has been accumulated on Cosmic Magnetism, which has turned out to be a truly fascinating topic for study. Percy Seymour's book is the first to deal with the topic in a non-mathematical way, and he offers a fine introduction to his subject. The first three chapters consolidate our knowledge on magnetism in general and the magnetic field of the Earth, as well as discussing the reasons for studying astronomy and cosmic magnetism in particular. The remainder of the book is devoted to the main areas of cosmic magnetism - solar, plantetary and interplanetary fields, fields in stars and pulsars, fields of the milky way and fields in other galaxies. Cosmic Magnetism in an ideal book for sixth-formers and undergraduates studying physics or astronomy and will also appeal to amateur astronomers. as previous work on this topic has been 'hidden' in specialised academic journals.
This book focuses on observing magnetic fields in order to understand their role in star and planet formation. Polarimetry observers will gain a better understanding of all the various techniques, especially those beyond what they themselves use. Theorists will gain an understanding of exactly what one can infer from the observational data, including both the limitations and the power of the different techniques. Readers not actively involved in star formation research will gain a clear understanding of the possible roles played by magnetic fields and the current state of the observational field. The book provides a foundation for future research in this field.
IAU Symposium 259 presents the first interdisciplinary, comprehensive review of the role of cosmic magnetic fields, involving astronomers and physicists from across the community. Offering both theoretical and observational topics ranging from Earth's habitability to the origin of the universe, this is an invaluable summary for researchers and graduate students.
Star formation is a fundamental process in the evolution of the cosmos. Yet given the abundance of stellar constituents, it remains prescient as to why the number of stars is not correspondingly large. If we cannot satisfactorily explain how stars are formed, then many further avenues of research are hindered. This thesis makes claims about one of the foremost theories as to the relative lack of stars, interstellar magnetic fields. These fields have been observationally verified on multiple scales. I will use the most direct method to probe magnetic fields in known star-forming regions, polarization, at millimetre/submillimetre wavelengths. In particular I will focus on the effect that magnetic fields have on the emission produced by rotational molecular transitions. Much of the background behind the study of magnetic fields, and their deduction through submillimetre polarimetry, will be developed in Chapter 1. Here I provide an overview of not only the role that magnetic fields may play in star formation, but also the competing theories of turbulence and magnetohydrodynamic waves. The various manifestations of polarization will also be covered, including polarized molecular transitions. Chapter 2 will look at one of the most well-studied star-forming regions, Orion KL, through observations of a newly discovered water maser transition at 620.701 GHz. Interstellar masers allow different environments to be probed, regions where more complex activity has created a population imbalance between rotational energy levels. The remaining two chapters will present methods and data from the Four-Stokes-Parameter Spectral-Line Polarimeter at the Caltech Submillimeter Observatory. I will look at considerations that must be made when a small map is collected by way of quantifying the amount of instrumental polarization. Spurious polarization signals may pervade the outer edges of the telescope beam, leading to a misrepresentation of the true amount of source polarization. Chapter 3 details the methods involved in removing sidelobes plus the other sources of instrumental polarization, while Chapter 4 goes on to present the actual data to which these techniques have been applied. The data itself is of the molecular transition 12CO (J = 2 ⇢1), prominent within the protostellar source OMC-2 FIR 4.
Abstract: Astronomers have a limited understanding of the large-scale structure of the Galactic magnetic field and its role in the evolution of the interstellar medium (ISM). This understanding derives primarily from Faraday rotation and synchrotron observations which do not probe the cool, dusty ISM. To advance our knowledge of the Galactic magnetic field, this dissertation reports on the application of a different method, near-infrared (NIR) polarization of background starlight, to place new observational constraints on the nature of the Galactic magnetic field and to study the field's role in the evolution of interstellar material.A radiative transfer computer code was developed to predict all-sky starlight polarization observations. Starlight polarimetry predictions were made for several different dynamo-driven magnetic field geometries, assuming that magnetically-aligned interstellar dust grains polarize background starlight. New NIR starlight polarimetry measurements in the outer Galaxy were tested against these predictions. These observations favor disk-symmetric magnetic fields while rejecting disk-antisymmetric magnetic fields. This result contradicts some previous interpretations of all-sky, radio Faraday rotation measurements. The Galactic magnetic pitch angle is constrained to p = -6 ± 2°.The physical orientations of Galactic HII regions, traced by mid-infrared emission, are compared to the large-scale, disk-symmetric Galactic magnetic field geometry derived above. Hydrogen recombination line spectra towards these same objects revealed that many possessed turbulent linewidths. If fluid turbulence decays with time, then it may be used as a relative age indicator. A trend is seen between magnetic alignment and the degree of turbulence in the HII region. This result leads to the development of an observationally-driven HII region magnetic evolutionary sequence.Resolved polarimetry across the face of the galaxy M51 was measured for comparison with the internal, edge-on view of the Milky Way seen from Earth. Strong upper limits (
Magnetic Fields play a key role in the physics of star formation on all scales: from the formation of the large complexes of molecular clouds to the formation of solar-like planetary systems. The plasma physics involved is non-linear and very complex, which requires the development of large numerical codes. An additional difficulty is that the detection and study of magnetic fields is not easy from an observational point of view, and therefore theoretical models cannot easily be constrained. In the week from April 21st to 25th in 2003, a meeting was held on the Campus of the Universidad Complutense de Madrid (Spain) to join theoretical and observational efforts to address these issues. The objective was to define a set of relevant problems for the physics of star formation that can be properly addressed with the current or near-future instruments. This book summarizes the results of this intensive week of work. The book is written in a comprehensive manner and reviews our current knowledge of the subject. It also represents an updated account of the ideas and thoughts of the scientists working in the field of Star Formation. The contributions are presented in six chapters which correspond to the six fundamental issues (sessions) on which the discussion was focused during the workshop: the physics of turbulence in the Interstellar Medium (ISM), the formation of structure in the ISM, the formation of stars within dense cores of molecular gas, the physics of accretion disks, the physics of outflows and their interaction with the ISM, and the interaction between the stellar magnetosphere and accretion disk. Each chapter starts with a comprehensive summary written by one of the editors, which includes input from the contributions as well as the editor's own thoughts on the subject. For all these reasons the book is well-suited as a primer to introduce graduate students in the richness of this field of research.