本文選題：熱亞矮星 + 雙星演化�。� 參考：《中國(guó)科學(xué)院大學(xué)(中國(guó)科學(xué)院云南天文臺(tái))》2017年碩士論文

【摘要】：熱亞矮星是在星團(tuán)的顏色-星等圖上位于水平分支的最藍(lán)端的恒星,因此也被稱(chēng)為極端水平分支星。它們一般被認(rèn)為是由燃燒的氦核以及很薄的包層所組成。熱亞矮星在以下幾個(gè)方面很重要:(1)對(duì)于熱亞矮星的形成與演化的研究可以提高天文學(xué)上對(duì)于恒星和雙星演化的認(rèn)識(shí)。(2)很多熱亞矮星表現(xiàn)出多周期脈動(dòng)現(xiàn)象(同時(shí)有p模式震動(dòng)與g模式震動(dòng)),因此它們是星震學(xué)上的重要研究對(duì)象。(3)熱亞矮星的形成和演化決定了球狀星團(tuán)水平分支的形狀。(4)熱亞矮星被認(rèn)為是早型星系中紫外反轉(zhuǎn)現(xiàn)象的一個(gè)重要來(lái)源。絕大部分熱亞矮星被發(fā)現(xiàn)在雙星系統(tǒng)中(對(duì)于場(chǎng)星大約2/3),因此雙星機(jī)制是目前熱亞矮星形成的主流解釋。本文首先對(duì)熱亞矮星的觀測(cè)性質(zhì)和形成模型進(jìn)行了綜述。然后,介紹了我們對(duì)公共包層拋射形成的熱亞矮星的性質(zhì)和相應(yīng)天體的研究情況。主要分為以下幾個(gè)方面。(1)公共包層拋射形成的熱亞矮星的性質(zhì)。我們對(duì)主星初始質(zhì)量分別為Mi=0.8M,1.0M,1.26M,和1.5M的情況進(jìn)行了研究。對(duì)每一個(gè)初始質(zhì)量,從最小氦核點(diǎn)燃質(zhì)量到第一巨星支頂端,每間隔0.002M取一個(gè)模型作為公共包層開(kāi)始的時(shí)刻。然后以10-3M yr-1的速率使恒星丟掉外包層,以此模擬公共包層拋射,直到恒星開(kāi)始收縮時(shí)停止丟失物質(zhì)。接著我們繼續(xù)跟蹤剩余恒星的演化,直至它演化成為碳氧白矮星。我們發(fā)現(xiàn)在有效溫度-表面重力加速度圖上,這些熱亞矮星被清楚地分為兩組:一組集中在極端水平分支的最藍(lán)端,另一組則均勻地覆蓋了經(jīng)典熱亞矮星的分布范圍,兩者之間存在明顯的空隙。集中在高溫端的那一組恒星在沿著白矮星冷卻線(xiàn)下降的過(guò)程中點(diǎn)燃氦閃過(guò)程,由此氦閃所驅(qū)動(dòng)的對(duì)流區(qū)將穿透富氫包層,從而將富氫物質(zhì)混入高溫氦燃燒區(qū),最終將這些物質(zhì)點(diǎn)燃并耗盡。因此,這組恒星集中在水平分支最高溫端。而另外一組氦點(diǎn)燃較早的恒星,由氦閃驅(qū)動(dòng)的對(duì)流區(qū)沒(méi)有穿透富氫包層。富氫物質(zhì)得以保留,這種方式產(chǎn)生的熱亞矮星根據(jù)包層質(zhì)量的不同可以覆蓋整個(gè)經(jīng)典熱亞矮星區(qū)域。但一些觀測(cè)到的短周期熱亞矮星位于兩組間的空隙中,并且它們的數(shù)密度遠(yuǎn)大于我們模擬中的理論值。公共包層拋射和對(duì)流的處理方式,可以很大的影響兩組的參數(shù)空間。公共包層拋射后的回落以及閃耀時(shí)的物質(zhì)損失可以分別使兩組恒星落入到空隙中,它們很可能可以解釋這個(gè)矛盾。(2)公共包層拋射通道生成的熱亞矮星的周期范圍。此結(jié)果和觀測(cè)對(duì)比可以用來(lái)約束公共包層拋射系數(shù),αCE。我們模擬了初始質(zhì)量從0.7到1.3M的七個(gè)恒星模型,并取出它們?cè)诮咏谝痪扌侵ы敹藭r(shí)的七組位置下的包層引力束縛能,Egr,和內(nèi)能,Eth。我們假設(shè)這些恒星在這些位置充滿(mǎn)洛希瓣并進(jìn)入公共包層階段,根據(jù)不同的伴星質(zhì)量,M2(人為設(shè)定),我們可以得到此時(shí)雙星系統(tǒng)的周期和者軌道間距。然后通過(guò)公共包層拋射的能量機(jī)制,給定一組αCE和αth,我們就可以得到熱亞矮星雙星的最終周期P。我們模擬得到的周期范圍大致與觀測(cè)和前人的工作相吻合,但是我們工作中的最大周期比Han et al.(2002)[1]得到的最大周期小了一個(gè)數(shù)量級(jí)。這種差別主要是由于核邊界定義不同產(chǎn)生的。(3)球狀星團(tuán)中的藍(lán)鉤星。藍(lán)鉤星在水平分支上非常高溫的位置,同時(shí)它們有高于一般極端水平分支星的氦豐度。兩種機(jī)制被提出以解釋藍(lán)鉤星的形成,氦自增豐機(jī)制和延遲氦閃機(jī)制。Lei et al.(2015,2016)[2,3]通過(guò)雙星中潮汐增強(qiáng)星風(fēng)研究了藍(lán)鉤星的形成。我們發(fā)現(xiàn),公共包層拋射通道形成的熱亞矮星由于延遲氦閃同樣可以產(chǎn)生藍(lán)鉤星。因?yàn)檠舆t氦閃是藍(lán)鉤星形成的物理原因,而與之前的物質(zhì)損失機(jī)制無(wú)關(guān),部分穩(wěn)定物質(zhì)轉(zhuǎn)移通道生成的極端水平分支星也可能是藍(lán)鉤星。
[Abstract]:The hot sub dwarfs are the bluest end stars located at the horizontal branch in the color star map of the cluster and are also known as extreme horizontal branching stars. They are generally considered to be composed of burning helium nuclei and very thin cladding. The hot dwarfs are important in the following aspects: (1) the study of the formation and evolution of the hot dwarf stars can be raised. The understanding of the evolution of stars and binary stars in high astronomy. (2) many hot sub dwarfs exhibit multi periodic pulsation (with P mode vibration and G mode vibration), so they are important research objects in the study of astrology. (3) the formation and evolution of the hot sub dwarfs determine the shape of the horizontal branch of the globular cluster. (4) the hot sub dwarf is considered to be early An important source of ultraviolet inversion in type galaxies. Most of the hot sub dwarfs are found in the binary system (about 2/3 of the field stars), so the double star mechanism is the mainstream interpretation of the current hot sub dwarf formation. This paper first reviewed the observation properties and the formation model of the hot sub dwarfs. The properties of the hot sub dwarfs and the research on the corresponding celestial bodies are mainly divided into the following aspects. (1) the properties of the hot sub dwarfs formed by the common cladding ejection. We have studied the initial mass of the main star Mi=0.8M, 1.0M, 1.26M, and 1.5M. At the top of the giant star branch, each 0.002M takes a model as the beginning of the common cladding. Then the star loses the outer layer at the rate of 10-3M yr-1 to simulate the common cladding, until the star begins to shrink and stops losing the material. Then we continue to track the evolution of the remaining stars until it evolves into the carbon oxygen white dwarf. It is found that the hot sub dwarfs are clearly divided into two groups in the effective temperature surface gravity acceleration map: one is concentrated at the bluest end of the extreme horizontal branch, and the other is evenly covered by the distribution range of the classic hot sub dwarfs. There is a clear gap between the two groups. The group of stars in Gao Wenduan is cooled down the white dwarf. In the process of line descent, the helium flash process is ignited, thus the convection zone driven by the helium flash will penetrate the hydrogen rich cladding, thus mixing the rich hydrogen into the high temperature helium combustion area, and eventually igniting and exhausting these substances. Therefore, this group of stars is concentrated at the highest temperature end of the horizontal branch. The hydrogen rich material is not penetrated. The hydrogen rich material is retained. The hot sub dwarfs produced in this way can cover the whole classic hot sub dwarf region based on the mass of the cladding. However, some observed short periodic thermo dwarfs are located in the gap between the two groups, and their number density is far greater than the theoretical value in our simulation. The treatment of radiation and convection can greatly affect the parameter space of the two groups. The fall of the common cladding and the material loss of the blazed can make two groups of stars fall into the gap, respectively. They are likely to explain the contradiction. (2) the periodic range of the hot sub dwarf produced by the common cladding channel. The contrast can be used to constrain the common cladding ejection coefficient. Alpha CE. we simulated seven stellar models with initial mass from 0.7 to 1.3M, and removed the cladding gravitational binding energy, Egr, and internal energy at the seven sets of positions near the top of the first giant star branch, and Eth. we assumed that these stars were filled with Loch flaps and entered public packets at these positions. In the layer phase, according to the mass of the companion stars, M2 (artificially set), we can get the cycle and the distance between the two stars at this time. Then, by the energy mechanism of the common cladding, we give a set of alpha CE and alpha th, we can get the final cycle of the P. of the hot sub dwarf star. Human work is consistent, but the maximum period in our work is one order of magnitude smaller than the maximum period obtained by Han et al. (2002) [1]. This difference is mainly due to the difference in the definition of the nuclear boundary. (3) the blue hook star in the globular cluster. The blue hook star is very high temperature in the horizontal branch, and they are higher than the ordinary extreme water. The two mechanism is proposed to explain the formation of the blue hook star, the helium self augmented mechanism and the delayed helium flash mechanism.Lei et al. (20152016) [2,3] study the formation of the blue hook star through the tidal enhanced star wind in the double stars. We found that the hot sub dwarf of the common cladding channel can also produce blue because of the delay of helium flash. Because the delayed helium flicker is the physical cause of the formation of the blue hook star, it is not related to the prior material loss mechanism, and the extreme horizontal branch star formed by the partial stable material transfer channel may also be the blue hook star.
【學(xué)位授予單位】：中國(guó)科學(xué)院大學(xué)(中國(guó)科學(xué)院云南天文臺(tái))
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：P144

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