大型EKBO(Quaoar, Ixion, 2004DW)的自轉週期和表面顏色的測量;The rotation period and surface colors of the large EKBOs(Quaoar, Ixion, 2004DW)

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6020

Title:	大型EKBO(Quaoar, Ixion, 2004DW)的自轉週期和表面顏色的測量;The rotation period and surface colors of the large EKBOs(Quaoar, Ixion, 2004DW)
Authors:	吳宇立;Yu-Li Wu
Contributors:	天文研究所
Keywords:	古伯帶;週期;顏色;似彗結構;EKBO;KBO;period;color;cometary activity
Date:	2005-01-07
Issue Date:	2009-09-22 10:11:59 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	我們使用鹿林天文台的LOT（Lulin One-meter Telescope）一米望遠鏡，於2003年和2004年進行古伯帶天體Quaoar、Ixion、2004DW的觀測工作。觀測共使用兩種CCD，分別為AP8及PI1300B，視野範圍約10角分平方，所使用的濾鏡為標準的Johnson UBVRI濾鏡組。我們嘗試了兩個不同的方法來從光變曲線中找出Quaoar的自轉周期，分別為Lomb Normalized Periodgram（LNP）和Phase Dispersion Minimization（PDM）。由PDM法對Quaoar的2003年R波段資料求得的週期為0.381天。J.L. Ortiz et al. (2003)也利用位在西班牙的Sierra Neveda天文台對Quaoar進行觀測，他們找到Quaoar的自轉周期為0.368308±0.000001天。雖然我們的觀測精度較低，資料點也比較少，但是由2003年6月份資料所求得的週期0.381天來看，仍然和J.L. Ortiz的結果相近。測量KBO的顏色可以知道它的表面特性和它的來源。我們以兩種方法來測量KBO的顏色。第一種是用標準星校正求得。我們在不同仰角對標準星進行觀測，將所得的標準星星等對大氣質量做圖，求出不同波段的消光曲線來修正。另一種則為在拍攝時選擇一系列R-V-R-B-R的拍攝方式，在計算顏色時我們將兩個相鄰的V-R值平均來除去光變曲線的影響，而將整個晚上所求得的V-R和B-V值加以平均則可求得Quaoar的平均顏色，最後再用公式將儀器星等求得的色指數換為標準色指數。以序列拍攝法得到Quaoar的B-V=1.095±0.037，V-R=0.612±0.028。Ixion為B-V=1.299±0.219，V-R=0.723±0.157。2004DW為B-V=0.789±0.033，V-R=0.427±0.028。我們也試著利用現有的觀測資料來檢驗可能的似彗活躍。我們在個別單張的影像中並沒有發現異狀，但似彗結構很容易為背景的雜訊所覆蓋，所以第一步便是增加資料的訊噪比。我們選擇天氣良好的觀測夜的資料加以疊加，並選擇星場中和KBO相鄰且星等相近的星為參考星，將KBO和參考星的流量歸一化後，可由兩者的徑向數值曲線（radial profile）看出似彗活躍的可能性。但正如我們所預期的，我們無法在Quaoar、Ixion、2004DW的資料中找出似彗活躍或氣體包暈的可能。 We have observed three bright Kuiper-belt objects (KBOs), Quaoar, Ixion, and 2004DW, with the 1-meter telescope at Lulin Observatory. Two kinds of CCDs, Ap8 and PI1300B, and standard Johnson BVR ﬁlters as the broad-band photometry are used for the observations. The exposure time is 300 seconds in the R ﬁlter, 420 seconds in the V ﬁlter and 600 seconds in the B ﬁlter. Data reduction and calibration are carried out with standard IRAF processes and aperture photometry. The lightcurves of the objects are obtained by using diﬀerential photometry. We adopt two methods to determine the rotation period of Quaoar. One is Lomb normalized periodogram (LNP) and the other is phase dispersion minimization (PDM). The period of Quaoar is 0.381 days determined from the PDM method. Using the 1.5-meter telescope at Sierra Neved Observatory, Ortiz et al. (2003) also observed Quaoar with no ﬁlter. They had observed Quaoar for 14 days and found that the period of Quaoar is 0.36831±0.00001 days. Although our data points are just a few and possess larger errors than theirs, our result is still in agreement with Ortiz’s value. For determining the surface color of our objects, we also adopt two methods: (1) using standard star correction to obtain the extinction coﬃcient of each ﬁlter to correct the airmass eﬀect and (2) R-V-R-B-R series exposure. In series exposure, adjacent B-V and V-R values are averaged to avoid the rotation eﬀect and translation fomulae are used to transfer insturment colors to standard colors. With the series exposure method, we have determined the surface colors of Quaoar are BV= 1.095±0.037 and V-R=0.612±0.028. The results for Ixion are B-V=1.299±0.219 and V-R=0.723±0.157; those for 2004DW are 0.789±0.033 and V-R=0.427±0.028. We have investigated the cometary activity of the objects. To obtain the radial proﬁles of the objects, we ﬁrst add their images together to imporve the S/N ratio and then subtract the averaged sky background from them. We ﬁnd no faint coma in our objects, Quaoar, Ixion and 2004DW.
Appears in Collections:	[Graduate Institute of Astronomy] Electronic Thesis & Dissertation

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