Very High Angular Resolution Imaging

Author by : J.G. Robertson
Languange : en
Publisher by : Springer Science & Business Media
Format Available : PDF, ePub, Mobi
Total Read : 28
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Description : The 1990s are proving to be a very exciting p&iod for high angular resolution astronomy. At radio wavelengths a combination of new array instruments and pow erful imaging algorithms have generated images of unprecedented resolution and quality. In the optical and infrared, the great technical difficulties associated with constructing separated-aperture interferometers have been largely overcome, and many new instruments are now operating or are being developed. As these pro grams start to produce observational results they will be able to draw extensively on the experience gained by the radio-interferometry community. Thus it seemed that the time was ripe for a meeting which would bring together workers from all wavelength ranges to discuss the details of the science and art of "Very High Angular Resolution Imaging" . While the main emphasis of Symposium No. 158 was on high resolution tech niques from the radio, mm-wave, infrared and optical bands, it also provided an opportunity for presentation of astronomical results from these techniques. As well as giving our colleagues from the Northern Hemisphere a break from midwinter, the location of the Symposium in Australia recognised the continuing development of astronomical interferometry in this country, especially the recent completion of the Australia Telescope radio array, and the progress toward com missioning of the Sydney University Stellar Interferometer. A number of the par ticipants visited these instruments during the post-symposium tour.


Astronomy At High Angular Resolution

Author by : Henri M. J. Boffin
Languange : en
Publisher by : Springer
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Total Read : 16
Total Download : 279
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Description : This book offers an essential compendium of astronomical high-resolution techniques. Recent years have seen considerable developments in such techniques, which are critical to advances in many areas of astronomy. As reflected in the book, these techniques can be divided into direct methods, interferometry, and reconstruction methods, and can be applied to a huge variety of astrophysical systems, ranging from planets, single stars and binaries to active galactic nuclei, providing angular resolution in the micro- to tens of milliarcsecond scales. Written by experts in their fields, the chapters cover adaptive optics, aperture masking imaging, spectra disentangling, interferometry, lucky imaging, Roche tomography, imaging with interferometry, interferometry of AGN, AGN reverberation mapping, Doppler- and magnetic imaging of stellar surfaces, Doppler tomography, eclipse mapping, Stokes imaging, and stellar tomography. This book is intended to enable a next generation of astronomers to apply high-resolution techniques. It informs readers on how to achieve the best angular resolution in the visible and near-infrared regimes from diffraction-limited to micro-arcsecond scales.


Astronomy At High Angular Resolution

Author by : Henri M. J. Boffin
Languange : en
Publisher by : Springer
Format Available : PDF, ePub, Mobi
Total Read : 66
Total Download : 358
File Size : 44,9 Mb
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Description : This book offers an essential compendium of astronomical high-resolution techniques. Recent years have seen considerable developments in such techniques, which are critical to advances in many areas of astronomy. As reflected in the book, these techniques can be divided into direct methods, interferometry, and reconstruction methods, and can be applied to a huge variety of astrophysical systems, ranging from planets, single stars and binaries to active galactic nuclei, providing angular resolution in the micro- to tens of milliarcsecond scales. Written by experts in their fields, the chapters cover adaptive optics, aperture masking imaging, spectra disentangling, interferometry, lucky imaging, Roche tomography, imaging with interferometry, interferometry of AGN, AGN reverberation mapping, Doppler- and magnetic imaging of stellar surfaces, Doppler tomography, eclipse mapping, Stokes imaging, and stellar tomography. This book is intended to enable a next generation of astronomers to apply high-resolution techniques. It informs readers on how to achieve the best angular resolution in the visible and near-infrared regimes from diffraction-limited to micro-arcsecond scales.


High Angular Resolution In Astrophysics

Author by : A. Lagrange
Languange : en
Publisher by : Springer Science & Business Media
Format Available : PDF, ePub, Mobi
Total Read : 93
Total Download : 213
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Description : Over the last decade many efforts have been made to develop high angular resolution techniques in astrophysics. Combined with imaging facilities, they have rapidly proved their efficiency and have already led to major astrophysical results. During the decade to come, astronomers will be offered new, even more sophisticated high angular resolution tools, especially in the IR and optical domains, coupled with much bigger telescopes, either on the ground or in space. In such a context of rapidly evolving techniques and a growing need for higher angular resolution to test theories or discover new objects, the present book reviews both instrumental and scientific aspects. The main questions addressed are: what kind of science will benefit from high angular resolution techniques? How can they best be used? Audience: The book is accessible to students and research workers in both instrumental and astrophysical aspects.


Imaging At High Angular Resolution Of Stellar Surfaces And Close Environment

Author by : Nicolas Nardetto
Languange : en
Publisher by : EDP Sciences
Format Available : PDF, ePub, Mobi
Total Read : 79
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Description : Imaging at high angular resolution (HRA) is a flourishing discipline. High performance instruments like the spectro-polarimeter SPHERE at VLT/ESO has recently been implemented. A harvest of splendid results is continuously coming from interferometry with PIONIER, MATISSE, and now GRAVITY (all at VLTI/ESO), VEGA and JouFlu (CHARA), and at longer wavelengths with ALMA at VLTI/ESO and NOEMA/IRAM. The future is already underway with the very close launch of JWST/NASA, and the development of ELT at ESO. HRA provides a unique way to study regions of stellar formation, proto-planetary discs as well as the surfaces of stars and their environments. This volume offers lectures given by world experts in the field during the EvrySchatzman School on Stellar Physics (EES 2017) held in Roscoff, France. The addressed topics include a course of introduction to optical/IR interferometry covering the history and basic principles, a course on diffraction-dominated observational astronomy, and a course presenting the principles and instrumentation of optical long baseline interferometry. This book will be a valuable reference for researchers and students in the coming years.


Jets From Young Stars Ii

Author by : Francesca Bacciotti
Languange : en
Publisher by : Springer
Format Available : PDF, ePub, Mobi
Total Read : 94
Total Download : 992
File Size : 55,7 Mb
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Description : This volume offers a background in modern high spatial resolution techniques, illustrating how such methods have impacted on our understanding of young stars. It provides hands-on insight into observing from space as well as the ground, the use of interferometers at millimeter and infrared wavelengths, image analysis and spectral diagnostic techniques, and High Angular Resolution studies of the inner regions of circumstellar disks that play a fundamental role in jet launching.


Very High Angular Resolution Imaging

Author by : J.G. Robertson
Languange : en
Publisher by : Springer
Format Available : PDF, ePub, Mobi
Total Read : 51
Total Download : 186
File Size : 48,8 Mb
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Description : The 1990s are proving to be a very exciting p&iod for high angular resolution astronomy. At radio wavelengths a combination of new array instruments and pow erful imaging algorithms have generated images of unprecedented resolution and quality. In the optical and infrared, the great technical difficulties associated with constructing separated-aperture interferometers have been largely overcome, and many new instruments are now operating or are being developed. As these pro grams start to produce observational results they will be able to draw extensively on the experience gained by the radio-interferometry community. Thus it seemed that the time was ripe for a meeting which would bring together workers from all wavelength ranges to discuss the details of the science and art of "Very High Angular Resolution Imaging" . While the main emphasis of Symposium No. 158 was on high resolution tech niques from the radio, mm-wave, infrared and optical bands, it also provided an opportunity for presentation of astronomical results from these techniques. As well as giving our colleagues from the Northern Hemisphere a break from midwinter, the location of the Symposium in Australia recognised the continuing development of astronomical interferometry in this country, especially the recent completion of the Australia Telescope radio array, and the progress toward com missioning of the Sydney University Stellar Interferometer. A number of the par ticipants visited these instruments during the post-symposium tour.


Jets From Young Stars Ii

Author by : Francesca Bacciotti
Languange : en
Publisher by : Springer
Format Available : PDF, ePub, Mobi
Total Read : 64
Total Download : 348
File Size : 47,5 Mb
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Description : This volume offers a background in modern high spatial resolution techniques, illustrating how such methods have impacted on our understanding of young stars. It provides hands-on insight into observing from space as well as the ground, the use of interferometers at millimeter and infrared wavelengths, image analysis and spectral diagnostic techniques, and High Angular Resolution studies of the inner regions of circumstellar disks that play a fundamental role in jet launching.


Diffraction Limited Imaging With Very Large Telescopes

Author by : D.M. Alloin
Languange : en
Publisher by : Springer Science & Business Media
Format Available : PDF, ePub, Mobi
Total Read : 64
Total Download : 868
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Description : A few years ago, a real break-through happened in observational astronomy: the un derstanding of the effect of atmospheric turbulence on the structure of stellar images, and of ways to overcome this dramatic degradation. This opened a route to diffraction-limited observations with large telescopes in the optical domain. Soon, the first applications of this new technique led to some outstanding astrophysical results, both at visible and infrared wavelengths. Yet, the potential of interferometric observations is not fully foreseeable as the first long-baseline arrays of large optical telescopes are being built or cOIIllnissioned right now. In this respect a comparison with the evolution of radio-astronomy is tempting. From a situation where, in spite of the construction of giant antennas, low angular resolution was prevailing, the introduction of long baseline and very long baseline interferometry and the rapid mastering of sophisticated image reconstruction techniques, have brought on a nearly routine basis high dynamic range images with milliarcseconds resolution. This, of course, has completely changed our views of the radio sky.


Multi Compartment Model Estimation And Analysis In High Angular Resolution Diffusion Imaging

Author by : Xinghua Zhu
Languange : en
Publisher by : Open Dissertation Press
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Description : This dissertation, "Multi-compartment Model Estimation and Analysis in High Angular Resolution Diffusion Imaging" by Xinghua, Zhu, 朱星华, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Diffusion weighted magnetic resonance images offer unique insights into the neural networks of in vivo human brain. In this study, we investigate estimation and statistical analysis of multi-compartment models in high angular resolution diffusion imaging (HARDI) involving the Rician noise model. In particular, we address four important issues in multi-compartment diffusion model estimation, namely, the modelling of Rician noise in diffusion weighted (DW) images, the automatic determination of the number of compartments in the diffusion signal, the application of spatial prior on multi-compartment models, and the evaluation of parameter indeterminacy in diffusion models. We propose an expectation maximization (EM) algorithm to estimate the parameters of a multi-compartment model by maximizing the Rician likelihood of the diffusion signal. We introduce a novel scheme for automatically selecting the number of compartments, via a sparsity-inducing prior on the compartment weights. A non-local weighted maximum likelihood estimator is proposed to improve estimation accuracy utilizing repetitive patterns in the image. Experimental results show that the proposed algorithm improves estimation accuracy in low signal-to-noise-ratio scenarios, and it provides better model selection than several alternative strategies. In addition, we derive the Cramer-Rao Lower Bound (CRLB) of the maximum Rician likelihood estimator for the balland-stick model and general differentiable diffusion models. The CRLB provides a general theoretical tool for comparing diffusion models and examining parameter indeterminacy in the maximum likelihood estimation problem. DOI: 10.5353/th_b5223987 Subjects: Diffusion magnetic resonance imaging


Quantifying Stellar Mass Loss With High Angular Resolution Imaging

Author by : Anonim
Languange : en
Publisher by : Unknown
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Total Read : 15
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Description : Mass is constantly being recycled in the universe. One of the most powerful recycling paths is via stellar mass-loss. All stars exhibit mass loss with rates ranging from approximately 10( -14) to 10( -4) solar mass yr( -1), depending on spectral type, luminosity class, rotation rate, companion proximity, and evolutionary stage. The first generation of stars consisted mostly of hydrogen and helium. These shed material - via massive winds, planetary nebulae and supernova explosions - seeding the interstellar medium with heavier elements. Subsequent generations of stars incorporated this material, changing how stars burn and providing material for planet formation. An understanding of mass loss is critical for modeling individual stars as well as answering larger astrophysical questions. Understanding mass loss is essential for following the evolution of single stars, binaries, star clusters, and galaxies. Mass loss is one of our weakest areas in the modeling of fundamental stellar processes. In large part this is owing to lack of confrontation with detailed observations of stellar photospheres and the mass-loss process. High resolution optical imagery with telescope arrays is beginning to provide these data and, combined with spectroscopy and broad infrared and sub-mm coverage, supporting more sophisticated models on fast computers and promising a new era in mass-loss studies.


A Hard X Ray Spectrometer For High Angular Resolution Observations Of Cosmic Sources

Author by : Anonim
Languange : en
Publisher by : Unknown
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Total Read : 88
Total Download : 239
File Size : 55,8 Mb
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Description : LAXRIS (large area x-ray imaging spectrometer) is an experimental, balloon-borne, hard x-ray telescope that consists of a coaligned array of x-ray imaging spectrometer modules capable of obtaining high angular resolution (1--3 arcminutes) with moderate energy resolution in the 20- to 300-keV region. Each spectrometer module consists of a CsI(Na) crystal coupled to a position-sensitive phototube with a crossed-wire, resistive readout. Imaging is provided by a coded aperture mask with a 4-m focal length. The high angular resolution is coupled with rather large area ((approximately)800 cm2) to provide good sensitivity. Results are presented on performance and overall design. Sensitivity estimates are derived from a Monte-Carlo code developed to model the LAXRIS response to background encountered at balloon altitudes. We discuss a variety of observations made feasible by high angular resolution. For instance, spatially resolving the nonthermal x-ray emission from clusters of galaxies is suggested as an ideal program for LAXRIS. 15 refs., 5 figs.


Photonic Integrated Circuits For Compact High Resolution Imaging And High Capacity Communication Utility

Author by : Tiehui Su
Languange : en
Publisher by : Unknown
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Description : “Integrated photonics” refers to the integration of multiple photonic components on a common substrate. Examples of photonic components include waveguides, gratings, couplers, polarizers, interferometers, beam splitters, light sources, and detectors. In turn, these components can then be used as building blocks to realize more complex planar photonic circuits, capable of performing a wide range of functions with applications in optical sensors and communication systems. The development of integrated photonics is the confluence of waveguide technology and photonic disciplines, which deals with the control of light by electrons and vice versa. The optical waveguide technology is the fundamental of integrated photonics which enables light guiding, coupling, splitting, multiplexing and demultiplexing of optical signals. In the first three chapters of this dissertation, we will discuss the main characteristics of integrated photonics and show relevant aspects of material and fabrication technologies. We will also briefly describe some basic components used in integrated photonics, emphasizing the difference in their design concepts in contrast to conventional bulk optics. Some examples of photonic integrated circuits (PICs) are presented to highlight photonic integration as an elegant solution to realizing multifunctional chip-scale module. Chapter 4 discusses the arrayed waveguide grating (AWG) as another example of PIC. The AWGs are widely used as optical (de)multiplexers in wavelength division multiplexer (WDM) systems. These devices are capable of multiplexing a large number of wavelength channels into a single optical fiber, thereby increasing the aggregate transmission capacity of the single-mode fiber. We will explain the working principle of AWG devices, and then address several design techniques. Eventually, we will demonstrate a large channel spacing AWG (an 18 channel 3.3 THz channel spacing AWG centered around 1310 nm) and a high channel count AWG (a 512 channel 25 GHz channel spacing AWG centered around 1550 nm). Chapter 5 investigates the use of PICs in interferometric imaging. In astronomy, optical interferometric imaging is a technique that brings the light of many telescopes together to create images with high angular resolution. While these interferomic telescopes based on PICs achieve the same spatial resolution as the conventional telescopes, they offer much more compact and robust platforms. This chapter further proposes and demonstrates a small-scale interferometric imager based on PIC technology. The PIC interferometer has the potential to become an alternative to conventional telescope interferometer, but with significantly reduced size, weight and power consumption. Chapter 6 discusses the use of PICs in orbital angular momentum (OAM) communication system. OAM can be understood as characterizing the “twist” of a helical phase front of the light beam. A set of OAM mode forms an orthogonal modal basis set that can be used in a mode-division-multiplexing system, which increases the capacity of optical communication in addition to WDM and polarization division multiplexing (PDM) techniques. This chapter demonstrates the first silicon PIC that is capable of demultiplexing free-space optical beams with multiple OAM states near 1550 nm into the single-mode waveguides. The device is easily connected to high-speed telecommunication components like modulators and photodetectors and is comparable with the CMOS silicon fabrication process. Chapter 7 summarizes this dissertation and projects possible future research directions.


Phase Retrieval With Application To Intensity Correlation Interferometers

Author by : Russell Edward Trahan
Languange : en
Publisher by : Unknown
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Description : As astronomers and astrophysicists seek to view ever-increasingly distant celestial objects, the desired angular resolution of telescopes is constantly being increased. Classical optics, however, has shown a proportional relationship between the size of an optical telescope and the possible angular resolution. Experience has also shown that prohibitive cost accompanies large optical systems. With these limitations on classical optical systems and with the drastic increase in computational power over the past decade, intensity correlation interferometry (ICI) has seen renewed interest since the 1950's and 60's when it was initially conceived by Hanbury Brown and Twiss. Intensity correlation interferometry has the advantage of less stringent equipment precision and less equipment cost when compared to most other forms of interferometry. ICI is thus attractive as a solution to the desire for high angular resolution imaging especially in space based imaging systems. Optical interferometry works by gathering information about the Fourier transform of the geometry of an optical source. An ICI system, however, can only detect the magnitude of the Fourier components. The phase of the Fourier components must be recovered through some computational means and typically some a priori knowledge of the optical source. This thesis gives the physics and mathematical basis of the intensity correlation interferometer. Since the ICI system cannot detect the phase of an optical source's Fourier transform, some known methods for recovering the phase information are discussed. The primary method of interest here is the error-reduction algorithm by Gerchberg-Saxton which was adapted by Fienup to phase retrieval. This algorithm works by using known qualities of the image as constraints; however, sometimes it can be difficult to know what these constraints are supposed to be. A method of adaptively discovering these constraints is presented, and its performance is evaluated in the presence of noise. Additionally, an algorithm is presented to adapt to the presence of noise in the Fourier modulus data. Finally, the effects of the initial condition of the error-reduction algorithm are shown and a method of mitigating its effect by averaging several independent solutions together is shown. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148155


High Resolution Imaging With Aeos

Author by : Anonim
Languange : en
Publisher by : Unknown
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Total Read : 17
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Description : The U.S. Air Force Advanced Electro-Optical System (AEOS) which includes a 941 actuator adaptive optics system on a 3.7m telescope has recently been made available for astronomical programs. Operating at a wavelength of 750 nm, the diffraction-limited angular resolution of the system is 0.04 inches; currently, the magnitude limit is V (almost equal to) 7 mag. At the distances of nearby open clusters, diffraction-limited images should resolve companions with separations as small as 4-6 AU--comparable to the Sun-Jupiter distance. The ability to study such close separations is critical, since most companions are expected to have separations in the few AU to tens of AU range. With the exceptional angular resolution of the current AEOS setup, but restricted target magnitude range, we are conducting a companion search of a large, well-defined sample of bright early-type stars in nearby open clusters and in the field. Our data set will both characterize this relatively new adaptive optics system and answer questions in binary star formation and stellar X-ray activity. We will discuss our experience using AEOS, the data analysis involved, and our initial results.


Development Of High Resolution Imaging Detectors For X Ray Astronomy

Author by : National Aeronautics and Space Administration (NASA)
Languange : en
Publisher by : Createspace Independent Publishing Platform
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Total Read : 18
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Description : This final report summarizes our past activities and discusses the work performed over the period of 1 April 1990 through 1 April 1991 on x-ray optics, soft x-ray (0.1 - 10 KeV) imaging detectors, and hard x-ray (10 - 300 KeV) imaging detectors. If microchannel plates (MCPs) can be used to focus x-rays with a high efficiency and good angular resolution, they will revolutionize the field of x-ray optics. An x-ray image of a point source through an array of square MCP pores compared favorably with our ray tracing model for the MCP. Initial analysis of this image demonstrates the feasibility of MCPs for soft x-rays. Our work continues with optimizing the performance of our soft x-ray MCP imaging detectors. This work involves readout technology that should provide improved MCP readout devices (thin film crossed grid, curved, and resistive sheets), defect removal in MCPs, and photocathode optimization. In the area of hard x-ray detector development we have developed two different techniques for producing a CsI photocathode thickness of 10 to 100 microns, such that it is thick enough to absorb the high energy x-rays and still allow the photoelectrons to escape to the top MCP of a modified soft x-ray imaging detector. The methods involve vacuum depositing a thick film of CsI on a strong back, and producing a converter device that takes the place of the photocathode. Murray, S. S. and Schwartz, D. A. Unspecified Center NASA-CR-193653, NAS 1.26:193653 NAG5-605...


High Resolution Optical Imaging Through The Atmosphere

Author by : Robert W. Noyes
Languange : en
Publisher by : Unknown
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Description : This program has concentrated on three major areas: the application of high angular resolution image reconstruction techniques to the reconstruction of solar surface features; speckle imaging of a wide range of astronomical sources; and the implementation of adaptive optics for faint object imaging. In this project, we have made substantial modifications to a technique for reconstruction of high resolution images from single short exposure solar frames, blind iterative deconvolution (IDC). We have been testing these improvements using numerical simulation data. Analysis of speckle data of the supernova SN1987A has detected a new bright source, 0.9 arcseconds south of the SN, as well as substantial structure in the region surrounding the SN. We also have new results on several Young Stellar Objects and supergiants. In the area of adaptive optics, an AOA wavefront sensor has been set up and tested using an image intensifier which increases its sensitivity by three orders of magnitude. Faint object image active tilt correction has also been tested with some important enhancements, including new highly linear and sensitive CCD quad cells developed by Cal Tech and Tektronix, and an off-the-shelf high speed 2-D tilting mirror with greatly improved specifications. The effects of only partially correcting atmospheric turbulence have been theoretically analyzed and numerically simulated.