本篇論文是討論利用掩星的方法來搜尋外太陽系天體（從 50 到 1000 天文單位）。在論文的第一部份，我針對利用中美掩星計畫視野內所有場星的光度曲線，來搜尋距離我們大約 100 到 1000 天文單位的外太陽系天體。我們使用一種特別的演算法來尋找這類天體遮蔽背景恆星後所形成的繞射陰影，在光度曲線上所造成一些連續而且些微變暗的訊號。我們在中美掩星計畫自 2005 年 2 月 7 日至 2006 年 12 月 31 日期間，由三座 50 公分廣角望遠鏡同時觀測所取得的 4.5×109 的資料量中搜尋可能的掩星事件。由於並沒有在這批資料中發現任何可能的事件，所以我們只能利用簡單的冪次分佈，針對這些外太陽系天體的大小以及距離來設定他們數量密度的上限。
在論文的第二部份，我將討論一些泛星計畫在正式啟動前的研究工作。我們預計利用泛星計畫 30 赫茲的導星視訊影像來搜尋位於 50 天文單位附近的外海王星天體。只要仔細地挑選位於泛星計畫 7 平方度的視野內可以利用的導星，我們就可以試著這些導星的光度曲線中尋找外海王星天體遮掩這些導星時所造成的繞射陰影。一般而言，選擇導星擁有比較好的訊噪比以及比較小的角直徑，是有利於我們在光度曲線中尋找繞射陰影。由於泛星計畫擁有比較好的時間解析度，所以我們也使用了不同於中美掩星計畫的演算法來尋找外海王星天體。偵測門檻的設定是在真實事件與偽真事件中取的平衡。預期的事件總數取決於不同的數量分佈模型。計算顯示，根據中美掩星計畫所設定的上限，在泛星計畫 3 年的巡天期間，我們預期可能有高達數百個事件將會被偵測到。泛星計畫的高時間解析度將有助於我們偵測到小至 400 公尺的外海王星天體，這將有助於我們來檢驗各種分佈模型的適用性，並有助於我們更進一步的瞭解外太陽系的結構與演化。

This thesis is the study of searching for outer Solar System objects (from 50 to 1000~AU) by methods of stellar occultation. In the first part, I present the results of a search for occultation events by objects at distances between 100 and 1000~AU in lightcurves from the Taiwanese-American Occultation Survey (TAOS). We utilize an algorithm capable of detecting consecutive, shallow flux reductions in the stellar lightcurvesobtained by our survey between 7 February 2005 and 31 December 2006 with a total of $sim$$4.5 imes10^{9}$ three-telescope simultaneous photometric measurements. No events were detected, allowing us to set upper limits on the number density as a function of size and distance of objects in Sedna-like orbits, using simple models.
In the second part, I present a pre-survey study of using Pan-STARRS 30~Hz video mode guide star images to search for TNOs near 50~AU. With careful selection of the guide stars in the Pan-STARRS 7 $m deg^{2}$ field of view, the light curves of these guide stars can be used to search for diffraction patterns by occultation of TNOs.
In principle, stars with higher signal to noise ratio and smaller angular size are best for our purpose. A detection method is outlined that can search for local fluctuation due to occultation events in the light curves. The detection threshold is set to compromise between real detection and false positive. Depending on the theoretical model been used, we expect to find up emph{a few hundred events} (upper limit set by TAOS survey) during 3 years life time of the Pan-STARRS survey. The high cadence of the survey facilitates detections of small objects (as small as 400m) and thus allows us to verify various models and further constrain our understanding of the structure in the outer reach of the Solar System.

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