模擬雙極行星狀星雲

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題名:	模擬雙極行星狀星雲
作者:	卓宛嫺;Cho, Wan-Hsien
貢獻者:	天文研究所
關鍵詞:	(原)行星狀星雲;數值模擬;磁流體力學;雙極形;(proto-)planetary nebula;simulation;MHD;FLASH;bipolar
日期:	2020-01-18
上傳時間:	2020-06-05 17:05:06 (UTC+8)
出版者:	國立中央大學
摘要:	行星狀星雲的形狀分類可以分成：圓形的行星狀星雲、橢圓形的行星狀星雲、雙極形的行星狀星雲、不規則的行星狀星雲。而我們對於雙極形的行星狀星雲特別感興趣。想像中恆星末期吹出的恆星風應該要是球形的，但是觀測上以雙極形的行星狀星雲居多，理論上有兩種可能造成雙極形的行星狀星雲的形成原因，分別是磁場與雙星系統。我們想要了解雙極形的行星狀星雲的形成原因，因此我們利用數值模擬的方法來研究行星狀星雲的演化，我們利用磁流體模擬程式FLASH進行我們的研究。我們認為雙星系統是造成雙極形的原行星狀星雲的主因。我們假設恆星演化到末期會與伴星形成甜甜圈結構在恆星外圍，而恆星外圍的甜甜圈結構會阻止恆星風，使恆星風無法往赤道方向移動，只能往雙極的方向移動，造成雙極的形狀。我們設計有一個甜甜圈結構在恆星周圍，恆星會穩定發出脈衝，而外界為星際介質，我們想模擬當恆星風撞上甜甜圈結構時，會有如何的交互作用，藉以印證甜甜圈結構會造成行星狀星雲呈現雙極形，證實雙星系統會造成雙極形的行星狀星雲。從我們模擬的結果上來看，甜甜圈結構可以阻止恆星風的行進，形成雙極形的行星狀星雲，且我們試著改變甜甜圈結構的密度，隨著甜甜圈結構的密度降低，越來越無法阻止恆星風，甜甜圈就會被破壞。因此我們成功驗證甜甜圈結構是造成行星狀星雲形成雙極結構的因素之一。 ;Planetary nebulae can be classified into round, elliptical, bipolar, and irregular. We are especially interested in bipolar planetary nebula. It is conceivable that the stellar wind from the star should be spherical. However, from observations the morphology of most planetary nebulae is bipolar not spherical. There are two main reasons for planetary nebula to have bipolar structure: one is binary system, and the other is magnetic field. We would like to understand the formation of bipolar planetary nebula, and we use numerical simulation for our study. We choose the magnetohydrodynamic simulation code FLASH as our main tool. In this thesis, we focus on binary system as the major cause of bipolar structure in planetary nebula (in particular in proto-planetary nebula). We assume that at the end of stellar evolution, the interaction of the stellar wind from the star with the companion star would form a torus around the star. The torus impedes outflow in the equatorial direction. Thus subsequent stellar wind prefers polar direction. As a result, bipolar planetary nebula (proto-planetary nebula) is formed. Our model involves a gas torus surrounding the central star. The star pulsate periodically and stellar wind bursts at each pulsation. The whole system is embedded in a low density uniform interstellar medium. We study the interaction of the stellar wind with the torus using numerical simulations, and examine the proposition that torus in the binary system is the cause of bipolar (proto-)planetary nebula. From our simulation result, the gas torus is able to impede the stellar wind, and the shape of the (proto-)planetary nebula is bipolar. We also investigate the effect of the density of the gas torus on the result. As expected, when the density of the tours is lower, it becomes more difficult to hinder the stellar wind, and it may be totally disrupted if its density is low enough. With these simulations, we successfully confirm that gas torus can be one of the main reasons for the formation of bipolar morphology of (proto-)planetary nebulae.
顯示於類別:	[天文研究所] 博碩士論文

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