| 摘要: | 根據目前的行星形成理論及模型，主帶小行星是由早期太陽系中行星碰撞過程及受行星的重力擾動後的產物，遺留至今保留著許多早期太陽系當時的物質與化學訊息，因此被視為解開太陽系形成與演化的重要線索之一。為了瞭解位於主帶小行星的結構與表面物質等細節，我們使用鹿林天文台的一米可見光望遠鏡(Lulin One-meter Telescope, LOT)，搭配三色成像偏振儀（Triple Range Imager and Polarimeter, TRIPOL）、光度儀器和LISA光譜儀來進行小行星的偏振、光度和光譜觀測。
在論文的第一部份，為了校正及確認三色成像偏振儀在觀測小行星的可靠性，我們利用偏振量與軌道相位角（太陽－小行星－地球之間形成的夾角）的特徵曲線，針對已知分類的小行星做觀測分析，例如富含矽化合物的S型、富含碳質化合物的C型（與相似物質組成的Ch型、B型）、富含鎳鐵金屬的Ｍ型、與富含鈣鋁包裹體的L型。從觀測結果中，我們的結果與前人的偏振觀測成果一致，並且印證三色成像偏振儀可應用於小行星偏振觀測的準確性。接著，我們也利用偏振儀來針對金屬含量高的小行星編號16的賽姬小行星（16 Psyche）做觀測。在雙色指數圖（color-color diagram, g′-r′和r′-i′）和偏振光變曲線的分析結果中，我們發現賽姬小行星的偏振光變曲線較為平坦，因此較不容易將光變曲線與偏振特徵曲線做關聯性。最後，三色成像偏振也可以藉由偏振光變曲線及相位角來找尋，帶有太陽系發現最古老礦物的L型小行星—Barbarians。
論文的第二部分，根據小行星的瓦礫堆模型，我們藉由小行星光變曲線資料庫（Lightcurve Database）、廣角紅外線尋天觀測計畫中的NEOWISE、和小行星家族成員資料庫（Hierachical Clustering Method, HCM），用統計分析比較了S型與C型小行星家族成員的大小、形狀和週期分佈，來研究小行星的組成與結構。在S型和C型小行星的週期分佈比較中，我們的結果顯示S型小行星的自轉週期與先前的研究相符為2.2小時，而C型的小行星的自轉週期極限應修正約為3小時，此結果可以支持兩者不同分類的小行星物質密度不同。此外，我們也觀測了在C型司理小行星家族（Themis family）中的巴索夫小行星（3599 Basov），不同於之前研究C型的小行星的自轉週期極限為3小時，該小行星的自轉週期為2.157±0.037小時，其光譜分析結果，與典型C型小行星的光譜特徵相似，可以作為C型超快自旋小行星的候選者。;The main-belt asteroids provide valuable information for us to study the general history of the solar system since they are considered the leftover planetesimals during the formation and evolution of the planetary disk. In order to understand the role-play of asteroids in planetary system formation, tracing the physical parameters to figure out the actual structures and compositions is one important way. We aim to investigate the albedo, which is related to the composition and structure of asteroids, by multi-method such as 1)polarimetry using the Triple Range Imager and Polarimeter (TRIPOL) instrument, 2) photometry of Charge-coupled device (CCD) instrument, and 3) a spectrum of LISA spectrograph, observations on the Lulin One-meter Telescope (LOT).
In the first part of this thesis, we demonstrated the technical properties and capability of TRIPOL instrument. We observed a number of bright asteroids with known taxonomic classifications at different phase angles, including B-type, C-type, Ch-type, M-type, S-type, and L-type. By measuring polarization degree with phase angle tracing, We confirmed the validity and reliability of the TRIPOL instrument were working. Furthermore, to study the surface texture of a single asteroid, we also measured rotationally resolved photo-polarimetric variation of a metal-rich object (16) Psyche. Our measurements showed no change in the $g′$-$r′$ and $r′$-$i′$ colors of the rotationally resolved photometry and the intriguing variability in the polarization degree as a function of the rotational phase. The TRIPOL instrument can also be used to measure the polarization of the Barbarians with higher phase angles.
In the second part of this thesis, utilizing the Lightcurve database, NEOWISE, and Hierarchical Clustering Method (HCM) datasets, we analyzed to investigate the differences in size, shape, and rotation period distributions among two S-type and C-type asteroid families based on the compositions and the rubble-pile structure model. From the rotation period distributions, we found that the S-type and C-type asteroids have different spin limits, with the S-type period P$_s$ = 2 hours and the C-type period P$_c$ = 3 hours, respectively. That implies the difference in their bulk densities. In addition, we analyzed a sizable C-type super-fast rotator candidate, asteroid (3599) Basov, to look into the rotation period and taxonomic classification through photometry and spectroscopy using the Lulin One-meter Telescope (LOT) at the Lulin Observatory. The rotation period of asterid (3599) Basov was 2.157$\pm0.037$ hours, and the result of reflectance spectrum result was similar to typical C-type asteroids. |
