Interferometric observations of pre-main sequence disks - Caltech ...

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32 Introduction to interferometry Figure 2.3: Modified from Monnier (2003). The figure explain the principle behind the closure phase analysis. As described in the text, phase errors introduced at any telescopes causes equal but opposite phase shifts, cancelling out if the closure phase is calculated on a close loop of three or more telescopes. where, for each pair (i, j), the observed phase can be expressed by the relation φi j=φ0,i j+θi−θ j, (2.8) whereφ0,i j is the intrinsic source phase andθi,θ j are the phase shifts introduced by atmospheric variations and/or instrumental errors at each antenna. Defining the closure phase as the sum of the observed phases,β123=φ12+φ23+φ31, the Eq. 2.8 implies that the termsθi cancel each other out with the result that the closure phase is equal to the sum of the intrinsic phases: β123=φ12+φ23+φ31=φ0,12+φ0,23+φ0,31. (2.9) Closure phase measurements can be used to obtain information on the single Fourier phasesφ0,i j, which are required to reconstruct the source image, with complex methods
2.3 Optical versus millimeter interferometry 33 whose description is out of the aim of this thesis (see Monnier, 2003). Nevertheless, closure phase has an important property that gives information on the morphology of the source: if the source has a centro-symmetric brightness distribution, the closure phases is 0 ◦ for every choice of the telescopes configuration. It is easy to prove this by imaging the centro-symmetric brightness exactly at the center of the image: in this case every single phaseφ0,i j is indeed zero. Fixed the three telescopes array configuration, the closure phase increases with the asymmetry of the surface brightness of the source; a practical application of this method to the study of the structure of the inner regions of circumstellar disks is shown in Chapters 5 and 9. A third difference between radio and optical interferometry comes from the type of detection and beam combination. In the radio domain, the signal detection occurs at the antenna level thanks to the heterodyne technique: the signal is coupled with a reference signal of high coherence and therefore one records the amplitude and the phase of the coming electric field. The signals from each antenna are then digitized and the combination takes place in the correlator. An electronic phase delay is applied to take into account the difference in path length between the two arms. In the optical domain, the heterodyne technique can not be applied and the interferometry is obtained by direct detection of interference fringes. The light beams are propagated to a central lab where the optical paths are equalized using delay lines, and are combined to form interference fringes which are recorded. Sensitivity of optical interferometers is strongly limited by the low throughput due to the large number of reflections between the telescopes and the final detector. Taking into account also the light loss in filters, dichroics and along the beam transport, the visible-light transmission results to be generally between 1% and 10%. The direct consequence of all these differences is that while images are routinely produced by radio interferometers, this is not the case in the optical domain. Although optical interferometers have made enormous progress in the last few years, in most of cases we are still limited to the interpretation of visibility measurements.
Page 1: Università degli Studi di Milano F
Page 5 and 6: CONTENTS I Introduction 1 1 Scienti
Page 7 and 8: CONTENTS v 4.5 Comparison with prev
Page 9: Part I Introduction
Page 12 and 13: 4 Scientific overview the critical
Page 14 and 15: 6 Scientific overview Log νFν Log
Page 16 and 17: 8 Scientific overview are the subje
Page 18 and 19: 10 Scientific overview disk regions
Page 20 and 21: 12 Scientific overview Figure 1.2:
Page 22 and 23: 14 Scientific overview depleted inn
Page 24 and 25: 16 Scientific overview the gas and
Page 26 and 27: 18 Scientific overview Figure 1.3:
Page 28 and 29: 20 Scientific overview We propose a
Page 31 and 32: CHAPTER 2 2.1 A bit of history Intr
Page 33 and 34: 2.1 A bit of history 25 measure ste
Page 35 and 36: 2.2 Basic principle of astronomical
Page 37 and 38: 2.3 Optical versus millimeter inter
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Page 43 and 44: 2.4 Introduction to modelling techn
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Page 49 and 50: CHAPTER 3 The shape of the inner ri
Page 51 and 52: 3.1 Introduction 43 Tauri stars (Ei
Page 53 and 54: 3.2 Model description 45 adapt the
Page 55 and 56: 3.2 Model description 47 log(δR/R
Page 57 and 58: 3.2 Model description 49 the pressu
Page 59 and 60: 3.3 Results 51 Photospherical heigh
Page 61 and 62: 3.3 Results 53 ever, is sufficientl
Page 63 and 64: 3.3 Results 55 Sec. 3.3.1 (see Fig.
Page 65 and 66: 3.4 Discussion 57 the value ofǫ, t
Page 67 and 68: 3.4 Discussion 59 sample of Fig. 3.
Page 69 and 70: 3.5 Summary and conclusions 61 R in
Page 71 and 72: 3.6 Appendix 63 However, the bright
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Page 76 and 77: 68 Large dust grains in the inner r
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82 Large dust grains in the inner r
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Face-on disk image Baseline (m) V 2
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V 2 1 0.8 0.6 0.4 0.2 0 0 50 100 15
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V 2 1 0.8 0.6 0.4 0.2 0 0 50 100 15
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CHAPTER 5 More on the “puffed-up
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5.1 Fuzzy and sharp rims 97 opacity
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5.2 New shapes for the rim 99 grain
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5.3 New observational results 101 (
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5.3 New observational results 103 w
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CHAPTER 6 Constraining the wind lau
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6.1 Introduction 109 λ Fλ (erg cm
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6.2 Observations and data reduction
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6.3 Results and discussions 113 V V
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6.4 Conclusions 115 note however th
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Part IV The structure of the outer
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120 The keplerian disk of HD 163296
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Part V Conclusions and future prosp
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152 Summary and Conclusions ∼1 an
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154 Summary and Conclusions disk in
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CHAPTER 9 Future developments As my
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9.1 Gas in the inner disk of Herbig
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9.2 Probing planet formation throug
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Published papers • Isella, A.; Te
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172 BIBLIOGRAPHY [2000] Bodenheimer
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174 BIBLIOGRAPHY [2004] Gail H.-P.,
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176 BIBLIOGRAPHY Arizona Press, Tuc
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178 BIBLIOGRAPHY [2001] Thompson A.
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