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title page
Acknowledgements
Contents
Abstract 16
Chapter 1. Introduction 18
1.1. Kuiper belts: knowns and unknowns 18
1.2. TAOS essentials: method and expected capabilities 20
1.3. Goals and scope of this work 23
1.4. Thesis outline 23
Chapter 2. Observations and data properties 26
2.1. TAOS robotic telescopes 26
2.2. Zipper data and its characteristics 27
2.2.1. Zipper mode observation 27
2.2.2. Properties of zipper data 28
2.3. Zipper observation of the predicted occultation event by asteroid iclea 31
Chapter 3. Photometric measurement of zipper data 34
3.1. Data preparation 34
3.1.1. Fields selection 34
3.1.2. Preliminary catalogs 35
3.1.3. Flagging poor data 39
3.2. Sky and streak removal 41
3.3. Temporal correction terms and flagging data 44
3.3.1. Image motion and centroiding strategy 44
3.3.2. PSF variation and aperture correction 45
3.3.3. Removal of clouds effect and poor data flagging 45
3.4. Pipelined aperture photometry and light curve extraction 50
Chapter 4. Detection of occultation candidates 52
4.1. Data archive description 52
4.2. Candidates detection with single telescope 53
4.3. Coincidence check of detected occultation candidates 56
4.4. Detected event candidates and contaminations 56
Chapter 5. Conclusion and discussion 63
Chapter 6. Work in progress 65
Chapter 7. References 67
국문요약 70
AppendiX 71
Table 4.1. Total observation time of analyzed zipper data 54
Figure 1.1. Conceptually. KBO detection by stellar occultation survey is straightforward One can detect KBOs by monitoring field stars and finding out the brief blinking of one of them when KBOs occult those stars. Typically, the occultation by a 1 ~ 2km KBO lasts... 21
Figure 1.2. A simulated diffraction pattern (dash curve) through a stellar center and a light curve (solid curve) when a 1.5 km KBO occulted a A0 star(T = 9790 K) at 43 AU where shadow velocity is 25.24 km/s (King et al. 2005) A solid curve is the normalized... 22
Figure 1.3. Diffraction effect as a obstacle for detecting small KBOs (Alcock et al. 2003) Target stars of TAOS, the greater part of them have 10 ~ 14 magnitude, mostly suffer from diffraction (dotted line). To detect KBOs affected by diffraction, blue stars... 24
Figure 2.1. Conceptual illustration of the shutterless zipper operation (King 2005). the process of shifting charges until the row block reaches steady state can be seen through (a), (b), (c) and (d). After fourth cycle, all eight stars in the field are squeezed into a... 29
Figure 2.2. Section of the real zipper image. Every star repeats themselves at each row block. There are many streaks (not shown in the illustration of figure 2.1) occurred during the shifting of each row block, which takes several tens of milliseconds, due to... 30
Figure 2.3. The working telescopes of TAOS (A, B and D) detected the stellar occultation by asteroid (286) Iclea. This event was predicted by Dr. Sato (Nakano Star Gaxers Club). Clear Magnitude drop about 2 ~ 2.5 during ~ 6 sec can be seen in the... 32
Figure 2.4. 9 row blocks when the occultation begins by asteroid Iclea. Three telescopes (A, B and D) among the four TAOS telescopes operated. Each row block is cropped and rearranged horizontally, so it looks different from typical zipper image. Time interval... 33
Figure 3.1. Every TAOS candidate field are shown (from TAOS internal document, Schwamb 2004). Red curve is the ecliptic plane. The almost candidate fields locate near the ecliptic 36
Figure 3.2. Procedure of TAOS catalog construction. In order to make TAOS catalogs, at least one stare mode image per one TAOS field is needed. The resulting catalogs are saved to local hard drive as text files. The catalogs is used to check the coincidence... 37
Figure 3.3. Distortion map before (left) and after (right) correction. Pixel differences are exaggerated by 30 times. Left diagram shows a typical pattern of distortion. The distortion is removed well after the correction 38
Figure 3.4. Variation of sky background of zipper data under stable sky (left) and unstable sky (right). Every ADU counts along the x-axis of the plot are averaged pixel values of each column in a given row block. When sky is unsteady, the background... 42
Figure 3.5. Zipper image before and after background removal. Clear passage of cloud across FOV can be seen in (a), which causes significant sky variation as illustrated in figure 3.4 (right). However, the sky variation is removed after our sky treatment as... 43
Figure 3.6. Light curves of a single faint star which has a neighboring bright star. Three telescopes worked synchronously under cloudy sky. Top diagrams are made with center calculation performed repeatedly for each row block, while bottom diagrams are... 46
Figure 3.7. Light curve of a single star obtained with three telescopes at the same time under cloudy condition. Top diagrams are made with conventional aperture photometry, and bottom diagrams are with our "aperture correction" photometry. All false positives... 47
Figure 3.8. A light curves of single star from one telescope. Top diagram is the "aperture corrected" light curve of the star, and middle diagram is "cloud corrected" light curve. Even after the cloud correction, there still remains a lot of significant magnitude fluctuation... 49
Figure 3.9. Procedure of Automated Photometry Pipeline. Among the above process, selection of bright stars is most important procedure. We choose isolated and un-saturated bright stars which are not placed at the edge of FOV and row block either. Those stars... 51
Figure 4.1. Light curve of a single bright star after applying all corection terms described in this thesis (top) and histogram (bottom). Best gaussian fit is also shown. Rapid PSF variation created significant magnitude fluctuation at the beginning of the light curve 55
Figure 4.2. Light curves of the first possible occultation candidate observed at Feb. 7th 2005. Arrows indicate where the occultation occurred. Duration of the event is one row block ( ~ 0.25s). Drops of telescope A, B and D have statistical significance of 3.13,...st 58
Figure 4.3. Light curves of the second possible occultation candidate observed at Apr. 4th 2005. Arrows indicate where the occultation occurred. Duration of the event is one row block ( ~ 0.25s). Drops of telescope A, B and D have statistical significance of 2.89,... 59
Figure 4.4. Light curves of the third possible occultation candidate observed at Apr. 7th 2005. Arrows indicate where the occultation occurred. Duration of the event is one row block ( ~ 0.25s). Drops of telescope A, B and D have statistical significance of 2.09,... 60
Figure 4.5. Satellite passes across the zipper image. Such trace of satellites along the y-axis can cause the increasing of the background level, yielding the reduction of ADU count neighboring stars. As a result, sudden magnitude drop appears as shown at... 61
Figure 4.6. Magnitude drop caused by the artificial satellite shown in the figure 4.5. Two telescopes operated in synchronous mode. At the center of both light curves, there are clear magnitude drop which resembles real occultation events. To distinguish such... 62
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