利用鹿林前山一米望遠鏡對低質量X-射線雙星; XTE J1118+480 (KV UMa) 之光學波段時變研究 The Study of Optical Variations of LMXB with LOT – XTE J1118+480 (KV UMa)

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6030

Title:	利用鹿林前山一米望遠鏡對低質量X-射線雙星;XTE J1118+480 (KV UMa) 之光學波段時變研究 The Study of Optical Variations of LMXB with LOT – XTE J1118+480 (KV UMa)
Authors:	楊庭彰;Ting-Chang Yang
Contributors:	天文研究所
Keywords:	時間序列;雙星;LMXB;superhump;XTE J1118+480
Date:	2004-10-07
Issue Date:	2009-09-22 10:12:07 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	我們使用中大鹿林山天文台一米望遠鏡，對低質量 X-ray 雙星 (low mass X-ray binary (LMXB))-- XTE J1118+480 做光學波段的觀測，並藉此來研究其光學時變特性。由於 Zurita et al. 在 2001 年底觀測中，發現 XTE J1118+480 在接近寧靜狀態 (quiescent state) 時仍然會有 superhump 的現象產生。所以我們便想藉由 LOT 的觀測，來研究 XTE J1118+480 在完全寧靜狀態的時候是否也有 superhump 的現象，並判斷它為 permanent superhump 或是 late superhump 系統。我們使用並設立了一組光度資料處理流程來加速觀測資訊的解析，包括觀測資料約化 (data reduction)，及一套由 IRAF CL 命令稿 (script) 結合而成的標準測光程序。由於我們是使用較差測光 (differential photometry) 的方法來測量目標星光度的相對變化，所以適當比較星 (comparison stars) 的選擇也是很重要的。我們提出了一些對選擇適當標準星的建議，來避免光度資料因受到不必要的干擾而影響往後的時間序列分析。由於 XTE J1118+480 在可見光波段所看到的主要是伴星所發出來的光。再加上目標跟觀測者之間適當的幾何關係，所以在光變曲線上形成橢圓光變。由於橢圓光變等於直接的反應出雙星的軌道週期，所以藉由我們一年多的觀測資料，我們可以得到當時的軌道週期，並對可能的軌道週期演化做出一些推論。我們主要使用 Lomb-Scargle 功率譜 (power spectrum)，其頻率訊號在功率譜上的誤差我們藉由蒙地卡羅模擬法 (Monte Carlo simulation) 來獲得。在 2003 到 2004 年的觀測中，我們將觀測資料分成五小段，藉由相位分析的方法，我們可以得到最佳評估的軌道週期約為 0.16993349 +/- 0.00000090 天，與 Zurita et al. (2002) 所得到的軌道週期相一致。我們發現在 2001 年到 2004 年的觀測中， XTE J1118+480 的軌道週期並無明顯改變 (.P ~ 0)。此結論與一般低質量 X-ray 雙星系統所具有的典型極小變化量 (約 .P/ P= 10^-7 到 10^-8 yr^-1) 的結果相吻合。利用最佳估計的軌道週期，我們可以建立一套近似的光變模型來模擬其光變曲線。對原始的光變曲線減去模擬的軌道模型之後，得到的殘餘光變曲線便可能含有 superhump 的訊號。但是經由我們對功率譜的分析之後，發現在 Zurita et al. (2002)所發現的 superhump 頻率附近，並沒有明顯的峰值產生。所以利用鹿林一米望遠鏡在一年多來的觀測，並沒有辦法在 XTE J1118+480 完全靜止的時候偵測到有 superhump 的現象。由其光變曲線的形式看來，可能是觀測時的吸機盤在可見光波段貢獻太少，以致於無法偵測。至於 XTE J1118+480 是屬於 late superhump 抑或是 permanent superhump，目前我們仍無法下定論。可能需要更加優良的觀測儀器及分析方法，才有辦法改進。 We observed the low mass X-ray binary (LMXB) -- XTE J1118+480 in optical band with Lulin One-meter Telescope for its timing series properties. Zurita et al. (2002) found XTE J1118+480 still revealed superhump phenomenon near the quiescent state in 2001. We try to observe it with LOT to verify if there are superhumps in the fully quiescent state, and to distinguish if the source is a permanent superhump or late superhump system. We use and setup the standard procedures, including data reductions and the CL scripts for the photometry, to accelerate the processes for the photometric data. Differential photometry is applied to measure the intensity variations of the target star, so the selection for proper comparison stars is rather important. We propose some suggestions for selecting the comparison stars to avoid the disturbances for the timing series analysis. The companion star of LMXB is dominated in the optical observation. Because of proper geometry relation between the binary and observor, the light curve will show ellipsoidal modulation. Ellipsoidal modulation implies the orbital period of the binary system. We can derive the orbital period from our observation for about one and half years, and discuss about the evolution of the orbital period. We mainly use Lomb-Scargle (LS) power spectrum for the periodicity analysis, and derive the signal frequency error from Monte Carlo simulation. For the observation from 2003 to 2004, the observation data is divided into five data sets, and the best estimated orbital period is about 0.16993349 +/- 0.00000090 day by the phase analysis method. The result is consistent with that of Zurita et al. (2002). It is verified that there are no significant change for the orbital period (.P~ 0) during the 2001-2004 observation. The result is consistent with the small period change (.P/ P~ 10^-7 to 10^-8 yr^-1) of LMXB system. We can fit an first order approximated model of ellipsoidal modulation with the best estimated orbital period. Subtracting the modeled light curve from the origin one, there maybe superhump signals left in the residual light curves. But after our analysis of power spectrum, there is no significant detection near the superhump frequency and its harmonics of Zurita et al. (2002). Thus, we can not detect superhump signals with LOT from more than one year observations. From the variation shape of the light curves, we consider that the accretion disk of the system contributes too less intensity for the optical light curve, so the superhump signals can not be detected. We can not conclude that if XTE J1118+480 is a late superhump or permanent superhump system. It maybe need better instruments or analytical methods to improve this.
Appears in Collections:	[Graduate Institute of Astronomy] Electronic Thesis & Dissertation

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