大麥哲倫雲中年輕Ia 型超新星遺骸裡其前身系統的存活伴星尋覓

Abstract

Ia 型超新星常被用做標準燭光來探測宇宙中的距離。它們的光譜中沒有被偵測到氫，因此被認為其前身來自於雙星系統中的白矮星； 然而，到今日我們還是不確定一個Ia 型超新星的爆炸，是來自於一個從其非簡併伴星吸積至超過臨界質量的白矮星-單一蛻化，還是來自於兩個白矮星的合併-雙蛻化。在單一蛻化的情況,非簡併伴星可以在超新星爆炸後存活而且可被觀測到；在雙蛻化的情況， 兩個白矮星都會在爆炸後被毀滅，所以不會有星星的殘骸被觀測到。如果一個存活的非簡併伴星被觀測到，這個超新星是來自於單一蛻化的前身系統就可以被證實。 目前為止，在銀河系的Ia 型超新星遺骸中還沒有存活的非簡併伴星被找到及確認。另一方面，由於銀河面的消光影響，以及各個超新星殘骸的距離不確定性，讓拓展銀河系中存活非簡併伴星的尋覓變得非常艱難；相對的，大麥哲倫雲是一個理想的星系，讓我們能在其中尋覓超新星前身系統的存活非簡併伴星。大麥哲倫雲中不但有大量的超新星殘骸紀錄取樣被研究，而且它的距離非常確定，在約50千秒差距， 這個距離夠近讓我們能用哈伯太空望遠鏡直接看到超新星遺骸以及星星的影像；更好的是， 大麥哲倫雲幾乎是面向我們，減少了我們視線看過去可能因為角度而造成的困惑。 這本論文裡，我報告了五個大麥哲倫雲Ia 型超新星遺骸中的研究成果: 0509-68.7 (N103B)、0509-67.5、0519-69.0、0505-67.9 (DEML71)， 以及0548-70.4。我用哈伯望遠鏡以及其他多波段觀測超新星遺骸，分析物理結構，估計爆炸中心、計算存活非簡併伴星的可能自行，然後在靠近爆炸中心的一個區域間，把觀測到的恆星顏色和星等去跟模型模擬出恆星被超新星爆炸影響之後的結果做比較，用這個方法去尋找可能為存活非簡併伴星的恆星。針對這些可能是存活非簡併伴星 的恆星，我們將進一步用理論預期的可分辨特徵，諸如異常高的移動速度， 來檢查它們跟超新星前身系統關聯性。

Type Ia supernovae (SNe) have been used as standardizable candles for cosmological distances. They do not show any hydrogen in their spectra and are believed to originate from white dwarfs (WDs) in binary systems; however, it is still uncertain whether the explosion of a Type Ia SN is caused by a WD accreting too much mass from a non-degenerate stellar companion - the single-degenerate (SD) origin, or a merger of two WDs - the double-degenerate (DD) origin. In the SD case, the stellar companion can survive the SN explosion and may be bright enough to be detected. In the DD case, both WDs are destroyed and no stellar remnant is expected. If a surviving companion is detected, the SD origin can be a affirmed. Searches for surviving companions in Type Ia supernova remnants (SNRs) in the Milky Way have not yielded positive results. It is even difficult to extend the search of surviving companions to more Galactic Type Ia SNRs because of the confusion and extinction in the Galactic plane, compounded by the uncertain distances to the SNRs. The Large Magellanic Cloud (LMC), on the other hand, is an ideal galaxy to study SNRs and to search for surviving companions of SN progenitors because its large sample of SNRs are at a known moderate distance, 50 kpc, near enough for SNRs and stars to be easily resolved by the Hubble Space Telescope (HST); moreover, it has a nearly face-on orientation, limiting line-of-sight confusion. In this dissertation, I report our investigation of five LMC Type Ia SNRs: 0509-68.7 (N103B), 0509-67.5, 0519-69.0, 0505-67.9 (DEML71), and 0548-70.4. I have used HST images and multiwavelength observations of SNRs to analyze their physical structures, assess their explosion centers, estimate possible motions of surviving companions, and compare the observed colors and magnitudes of stars within the search radii with post-impact evolutionary models of companion to search for surviving companions. For candidates of surviving companions, we further use high translational velocities to investigate their association with the SN progenitors.