The VLT Interferometer - ESO

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5.3. INCREASE OF SENSITIVITY BY ADAPTIVE OPTICS 105 the adaptive correction. Each telescope would require its own laser source. In case this techniques would become available in the future it could be considered to be added to the interferonetric mode of the VLT in a later phase. 5.3 Increase of Sensitivity by Adaptive Optics The use of telescopes with a size larger than the atmospheric coherence length ro is of value only if the pupil can be phased with adaptive optics. A significant gain in sensitivity over smaller pupils is the obtained. This has been described in detail in Chapter 2.1. When adaptive optics is applied the signal to noise ratio becomes independent of roo Nevertheless, seeing quality remains mandatory for the following reasons: • the better the seeing the easier is the adaptive correction • the better r 0 the smaller is the RMS phase difference between the various pupils, which allows to increase the integration time • at the shorter wavelengths, where only partial correction is possible the signal to noise ratio varies as a high power of r o' 5.4 Partial Adaptive Correction Even if the the adaptive optics systems is not suited for a full correction of the wavefront aberration due to spatial and temporal undersampling of the system it improves the image quality. It corrects the lower order aberrations which are associated with lower spatial and temporal frequency. In atmospheric turbulence induced wavefront distortions the amplitudes of the aberrations have to decrease with increasing order. Therefore a correction with an undersampling system leads to a partial correction with high frequency residual wavefront errors. As a result modelling shows a nearly diffraction limited image is obtained surrounded by a "halo" which is left over from the residual errors (figure 5.3) . . For pupil plane interferometry the would mean that the fringes will be straight lines with some remaining high frequency components.
106 CHAPTER 5. ADAPTIVE OPTICS FOR INTERFEROMETRY Figure 5.2: Images of ,2 AND (AO spectral type at air mass = 1.08) in the K-band on October 22, 1989. UT = 1h40, integration time = 4 sec. Upper left: uncorrected image. The separation of this binary star is 0.55 arcsec. Upper right: corrected image, with ,I AND at 9.6 arcsec used for the wavefront sensing. The two figures below are the contour lines of the images shown above
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FOREWORD In November 1988 I propose
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INTRODUCTORY COMMENTS This document
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3.6.2.1 Spectral Dispersion in Imag
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9.4 Remote Observing . . . . . . .
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7.1 Lay-out of the 8 meter telescop
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Chapter 1 Introduction 1.1 General
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1.2. PREMISES AND ASSUMPTIONS 3 and
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8 CHAPTER 1. INTRODUCTION being rou
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Chapter 2 Scientific Aspects of Int
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14 CHAPTER 2. SCIENTIFIC ASPECTS Ta
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18 CHAPTER 2. SCIENTIFIC ASPECTS Ta
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22 CHAPTER 2. SCIENTIFIC ASPECTS ra
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24 CHAPTER 2. SCIENTIFIC ASPECTS an
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26 CHAPTER 2. SCIENTIFIC ASPECTS [H
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28 CHAPTER 2. SCIENTIFIC ASPECTS ti
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32 CHAPTER 2. SCIENTIFIC ASPECTS LM
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34 CHAPTER 2. SCIENTIFIC ASPECTS fo
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2.3. DERIVED DESIRED PROPERTIES FOR
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2.3. DERIVED DESIRED PROPERTIES FOR
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42 CHAPTER 2. SCIENTIFIC ASPECTS li
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52 CHAPTER 3. OPTO-MECHANICAL ASPEC
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Page 76: 3.3. FIELD-OF-VIEW EFFECTS IN INTER
Page 81: 68 CHAPTER 3. OPTO-MECHANICAL ASPEC
Page 86 and 87: 3.6. FRINGE ACQUISITION AND TRACKIN
Page 89 and 90: 76 FRINGE DETECTION CHAPTER 3. OPTO
Page 98 and 99: 3.7. "BLIND FRINGE ACQUISITION AND
Page 100 and 101: 4.1. COMPUTER SIMULATIONS OF MULTIS
Page 102: 4.2. REDUNDANT VS. NON-REDUNDANT AR
Page 107 and 108: 94 CHAPTER 4. IMAGE FORMATION ASPEC
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Page 115 and 116: Chapter 5 Adaptive Optics for Inter
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Page 121 and 122: Chapter 6 VLT Site Considerations 6
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Page 132 and 133: 7.1. SUMMARY OF BASIC REQUIREMENTS
Page 134 and 135: 7.2. THE 8M TELESCOPES 121 Ml M 11
Page 137 and 138: 124 CHAPTER 7. DEFINITION OF THE VL
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Page 155 and 156: Chapter 8 Implementation Plan 8.1 I
Page 158: 8.2. DESCRIPTION OF THE ADVANCED AR
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B.B. ADDITIONAL SUPPORT NEEDED 157
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9.2. OPERATION OF THE VLTI/ADVANCED
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9.5. OTHER OPERATIONAL ASPECTS OF T
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Bibliography [Afanas'jev et al1988]
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BIBLIOGRAPHY [Foy 1988] [Forbes 198
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BIBLIOGRAPHY [Reinheimer et al 1988
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Chapter 11 Appendices List of Appen
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171 6. encourage the funding and co
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3.2 Koechlin's 12T Results I derive
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Appendix C Polarization effects in
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in Table I for incidence angles 9 e
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186 3. W. A. Traub, "Polarization E
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7. REFERENCES 1. J. M. Beckers, "Fi
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telescope diameter d. That conclusi
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The VLT Interferometer - ESO

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