Cyg X-3是一個高質量X光雙星系統，由一個大質量恆星演化晚期的沃夫瑞葉星（Wolf-Rayet stars，WR stars）及一個緻密天體（中子星或黑洞）組成，藉由吸積WR星的強烈恆星風物質而放出的X光會依雙星互繞的4.8小時軌道週期規律變化，並呈現特殊的波形。本論文使用公開的X光光變曲線資料，分析RXTE/ASM 1996～2011年、MAXI 2009～2015年、Swift/BAT 2005～2015年三架全天監測X光望遠鏡多年觀測的Cyg X-3的數據，探求其軌道週期演化情形。我們以固定時距將之分成數個區間並製成疊合光變曲線後，與之前已設定之標準軌道光變模式比對得到的相位差，再結合前人資料，用O-C方法發現了其軌道週期有三階之變化，其軌道週期各階變化率分別為P ̇=(1.29±0.18)〖"×" 10〗^(-9) 〖yr yr〗^(-1)、P ̈=(-6.13±1.41)〖"×" 10〗^(-11) 〖yr〗^(-1)、P ⃛=(2.31±0.96)〖"×" 10〗^(-12) 〖 yr〗^(-2)。軌道週期的高階變化眾說紛紜，我們嘗試針對質量流失及階級式三星系統的影響解釋，目前仍傾向是由質量流失的變化所造成。

Cyg X-3 is a high-mass X-ray binary system composed by a Wolf-Rayet star and a compact object. Its 4.8 hr orbital modulation profile is caused by the strong stellar wind from companion with a specific form. We analyzed the light curve collected by the all sky monitor (ASM) on broad Rossi X-ray Timing Explorer (RXTE), the Monitor of All-sky X-ray Image (MAXI) and The Burst Alert Telescope (BAT) on broad Swift. To make clear orbital modulation profiles, the light curve from each observation was divided into several segments and folded by a linear ephemeris, then cross-correlated with a standard template. Combined with previous results, we discovered the significant third order orbital period derivative and obtained the orbital period derivatives of P ̇=(1.29±0.18)〖"×" 10〗^(-9) 〖yr yr〗^(-1)、P ̈=(-6.13±1.41)〖"×" 10〗^(-11) 〖yr〗^(-1)、P ⃛=(2.31±0.96)〖"×" 10〗^(-12) 〖 yr〗^(-2) using O-C method. These high order orbital period derivatives are likely due to the variation of mass outflow. We also considered that the orbital derivatives are caused by that Cyg X-3 is in a hieratical triple system but found that this model can hardly fit into our observation result.

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