次毫米波陣列望遠鏡之多重時期觀測原恆星噴流的噴流運動及團塊形成研究

本論文所研究的天體為雙極噴流 HH 211。HH 211 為臨近的年輕原恆星 (protostar) 所噴發而成，是一個高準直且具有團塊結構 (knotty structure)的噴流。而次毫米波陣列望遠鏡(SubmillimeterArrayorSMA)曾在四個時期 (2004、2008、2010 及 2013 年) 以一氧化矽 (SiO) J=8-7譜線觀測過 HH 211，我們整理這些觀測資料並進行分析研究。我們發現此噴流在每個時期都有擺動結構 (wigglestructure) 以及團塊結構。而針對噴流的自行運動 (proper motion) 做校正後，這些擺動結構都符合同一組環繞軌道運行噴流源模型 (orbiting source jet model)，確認了這些擺動結構是因為噴流源的軌道運動所造成的。另一方面，我們利用各個團塊在不同時期的位置，計算團塊的自行運動。而這些自行運動的大小幾乎一致，和與噴流源的距離無關。自行運動的平均大小為每年 0.087 角秒，相當於每秒 114 公里，比之前的測量結果少了 30 個百分點。接著我們選了 2 個結構非常清晰的團塊：BK2 和 BK3，來研究團塊的速度結構 (velocity structure)。我們發現他們的速度結構皆為線性分佈，且較快的物質都在較慢物質的後方。再者，當計算這些結構的速度梯度(velocity gradient) 後，我們發現這些梯度隨著時間和與噴流源的距離越來越小。這些結果可以推論出團塊內部其實包含了內衝擊波 (internalshock)，而這些內衝擊波或團塊結構是由於噴發速度上的微小週期變化所造成的。

關鍵字

恆星演化前期；赫比格-哈羅天體； HH 211 ；衝擊波；星際介質；團塊

並列摘要

HH 211 is a highly collimated jet with a chain of well-defined knots, powered by a nearby young Class 0 protostar. We have used 4 epochs(2004,2008, 2010, and 2013) of Submillimeter Array (SMA) archive data to study the properties of the HH 211 jet in SiO (J=8-7). The jet shows similar reflection symmetric wiggle structures in all epochs. The wiggle structures can all be fitted by an orbiting source jet model that includes a position shift due to proper motion of the jet, indicating that the wiggle propagates along the jet axis. Thus, this suggests the wiggle is indeed due to an orbital motion of the jet source. Proper motions of the knots are measured by using the peak positions of the knots in four epochs, and they are roughly the same and independent of the distance from the central source. The mean proper motion of the knots is ∼ 0".087 per year, resulting in a transverse velocity of ∼ 114 km/s, about 30% lower than that measured before. Knots BK2 and BK3 have a well-defined linear velocity structure, with the fast jet material upstream to the slow jet material. The gradient of the velocity structure decreases from knot BK2 to BK3. In addition, for each knot, the gradient decreases with time, as the knot propagates away from the central source. These results are both expected if the two knots trace internal shocks produced by a small periodical variation in ejection velocity of the jet.