本文選題：銀河系 + 星族��； 參考：《河北師范大學》2013年碩士論文

【摘要】：恒星元素豐度代表恒星大氣的化學組成，直接反映了恒星形成時所處的星系環(huán)境，是我們從觀測上追蹤恒星形成和星系化學演化的有效探針。由于不同元素的核合成過程和產(chǎn)生場所的演化時標不同，恒星中不同元素的豐度比在一定程度上反映了恒星形成和元素核合成的歷史，，可作為星系形成和演化的宇宙時鐘。特別是由于Ba元素的奇同位素(~(135)Ba和~(137)Ba)主要是r-過程核合成的產(chǎn)物，而偶同位素（~(134)Ba、~(136)Ba和~(138)Ba）主要是s-過程核合成的產(chǎn)物，因此其奇、偶同位素的豐度之比反映了r-過程~(和s-過程核合成對Ba豐度的相對貢獻，由此可以更好地追蹤r-過程和s-過程的核合成歷史，研究其可能的產(chǎn)生場所，為星系化學演化模型和元素核合成理論提供可靠的觀測約束。 我們分別用局部熱動平衡（LTE）和非局部熱動平衡（NLTE）模型分析了28顆恒星的Ba元素豐度，金屬豐度范圍為-2.41[Fe/H]+0.07，包括16顆薄盤星、3顆厚盤星、7顆暈星，以及2顆運動學特征介于厚盤和薄盤之間的過渡恒星。并利用BaII共振線455.4nm的超精細結(jié)構(gòu)和同位素結(jié)構(gòu)分裂，確定了不同奇、偶同位素比例的Ba元素豐度，以此來研究不同星族恒星中r-過程和s-過程核合成對Ba元素豐度的相對貢獻。 論文內(nèi)容包括6部分：(1)引言部分簡單介紹了元素核合成理論和元素豐度概念，綜述了對恒星Ba元素豐度的觀測研究；（2）觀測樣本和數(shù)據(jù)處理，樣本星的光譜數(shù)據(jù)取自歐洲南方天文臺（ESO）甚大望遠鏡（VLT）及其階梯光柵攝譜儀UVES公開釋放的一維譜，光譜分辨率R40000，光譜信噪比S/N200。一維譜的視向速度修正和歸一化是利用在IDL語言環(huán)境下開發(fā)的SIU程序包進行的；（3）確定恒星大氣參數(shù)，包括有效溫度T_(eff)、表面重力加速度logg、金屬豐度[Fe/H]和微觀湍流速度ξ，并建立恒星大氣模型，包括局部熱動平衡（LTE）和NLTE模型；（4）建立Ba原子模型，模型中考慮了Ba原子譜線的超精細結(jié)構(gòu)和同位素結(jié)構(gòu)分裂，包括BaII的35個束縛能級和BaIII基態(tài)能級；（5）Ba元素豐度分析和結(jié)果討論：利用光譜綜合方法，通過擬合觀測到的BaII原子的3條譜線455.4nm、585.3nm和649.6nm的譜線輪廓，確定了樣本星在LTE和NLTE模型下的Ba元素豐度，并且利用共振線455.4nm分析了幾種不同奇、偶同位素比例（偶:奇=82:18,70:30,65:35,54:46）的Ba同位素豐度；根據(jù)豐度分析結(jié)果，討論了不同星族包括暈星、厚盤恒星和薄盤恒星的[Ba/Fe]～[Fe/H]關(guān)系，以及不同星族恒星中r-過程和s-過程核合成對Ba元素豐度的相對貢獻，分析了Ba豐度NLTE效應(yīng)；（6）最后部分是論文的結(jié)論。 通過對28顆恒星的Ba元素豐度的分析和討論，我們得到以下重要結(jié)論： 1、不同譜線的NLTE效應(yīng)不同：次級譜線的NLTE豐度修正[Ba/Fe]_(NLTE-LTE)都是負的且與恒星金屬豐度無關(guān)，其中585.3nm的NLTE效應(yīng)較弱，其豐度修正[Ba/Fe]_(NLTE-LTE)平均為-0.03dex；649.6nm的NLTE效應(yīng)較強，其豐度修正[Ba/Fe]NLTE-LTE平均為-0.1dex，最大為-0.18dex。共振線BaII455.4nm的NLTE效應(yīng)也比較明顯，但其對豐度的修正依賴于恒星的金屬豐度，當[Fe/H]-1.8時，[Ba/Fe]_(NLTE-LTE)也是負的，平均為-0.1dex；而當[Fe/H]-1.8時，[Ba/Fe]_(NLTE-LTE)轉(zhuǎn)變?yōu)檎模骄?.1dex。 2、BaII譜線的NLTE效應(yīng)依賴于恒星的有效溫度，無論是共振線還是次級譜線，其豐度修正[Ba/Fe]_(NLTE-LTE)都有隨有效溫度的升高而變大的趨勢。尤其是次級譜線649.6nm的NLTE修正與有效溫度的相關(guān)性較強，當恒星的Teff從5600K升高到6600K時，其[Ba/Fe]_(NLTE-LTE)從-0.04dex增加到-0.15dex。 3、在樣本的整個金屬豐度范圍(-2.41[Fe/H]+0.07)內(nèi)恒星的[Ba/Fe]豐度并不依賴于恒星的金屬豐度且在平均值[Ba/Fe]=0附近變化，但卻與恒星的星族成分有密切的關(guān)系。薄盤恒星的[Ba/Fe]與太陽豐度一致，平均為0.0±0.02dex，而厚盤恒星的[Ba/Fe]明顯低于薄盤，平均為-0.1±0.02dex；運動學性質(zhì)處于厚盤和薄盤之間的過渡恒星，其[Ba/Fe]的豐度與厚盤一致；暈星恒星的[Ba/Fe]彌散較大，隨金屬豐度的變化比較復雜，[Fe/H]-1.0時暈星的[Ba/Fe]豐度值在0附近，而當[Fe/H]-1.0時[Ba/Fe]隨[Fe/H]的變低而由超豐變?yōu)榍坟S，當[Fe/H]-2.0時[Ba/Fe]有快速下降趨勢。 4、Ba的同位素豐度隨金屬豐度的變化與元素豐度[Ba/Fe]一致，而且也表現(xiàn)較強出的星族效應(yīng)，即不同星族恒星中偶-奇同位素對Ba元素豐度的貢獻比例不同。薄盤星中Ba元素偶-奇同位素的比并不是單一值，而是在82:18、70:30和65:35之間變化，表明薄盤恒星的Ba元素核合成過程比較復雜，多數(shù)薄盤恒星與太陽的Ba豐度一致且其奇偶核素比例也與太陽系混合比例相同，即s-過程的貢獻為主，但有些薄盤恒星的Ba豐度主要是r-過程的貢獻；對于厚盤星，Ba元素偶-奇同位素的比也不是單一的確定值，而是在65:35和54:46之間，這表明厚盤恒星的Ba元素核合成過程為r-過程占主要，低金屬豐度的厚盤恒星的Ba幾乎是純r-過程的產(chǎn)物，但s-過程的貢獻不能忽略；對于暈星，Ba元素偶-奇同位素之比為太陽系純r-過程54:46，表明暈星的Ba元素來自于純r-過程核合成，而且這與暈星的金屬豐度無關(guān)。
[Abstract]:The abundance ratio of different elements in a star reflects the relative contribution of the formation of stars and the evolution of the elements . The ratio of the abundance ratios of different elements in the stars reflects the relative contribution of the r - process and the s - process nuclear synthesis to Ba abundance .

The Ba element abundance of 28 stars is analyzed by means of local thermal equilibrium ( LTE ) and non - local thermal equilibrium ( NLTE ) models . The range of metal abundance is - 2.41 擄 Fe / H ~ + 0.07 , including 16 thin plate stars , 3 thick disk stars , 7 halo stars , and 2 kinematic features between thick disk and thin disc .

The contents of this paper include 6 parts : ( 1 ) Introduction section simply introduces the theory of element nuclear synthesis and the concept of element abundance , and summarizes the observation and research on the abundance of Ba elements of stars ;
( 2 ) The spectral data of the sample star is taken from the one - dimensional spectrum , the spectral resolution R40,000 , the spectral signal - to - noise ratio S / N200 , which is released by the European Southern Observatory ( VLT ) and its step - grating spectrograph UVES , and the spectral data of the sample star is carried out by using the SIU package developed under the IDL language environment ;
( 3 ) determining stellar atmosphere parameters , including effective temperature T _ ( eff ) , surface gravity acceleration , metal abundance , Fe / H and micro turbulence velocity , and establishing stellar atmosphere model , including local thermal dynamic balance ( LTE ) and NLTE model ;
( 4 ) Ba atom model is established , and the hyperfine structure and isotope structure splitting of Ba atomic spectrum line are considered in the model , including 35 binding energy level and BaIII ground state energy level of BaII ;
( 5 ) The Ba element abundance analysis and the results are discussed . The Ba element abundance in the LTE and NLTE models is determined by fitting the spectral lines of 450.4nm , 585.3 nm and 649.6 nm of the observed BaII atom , and the Ba isotope abundance of several odd and even isotope ratios ( even : odd = 82 : 18 , 70 : 30 , 65 : 35 , 54 : 46 ) is analyzed by using the resonance line 450.4nm .
Based on the results of abundance analysis , the relative contributions of different stars including halo stars , thick disk stars and thin disk stars , and the relative contribution of r - process and s - process nuclear synthesis on the abundance of Ba elements are discussed , and the effects of Ba abundance NLTE are analyzed .
( 6 ) The last part is the conclusion of the paper .

Through analysis and discussion of the abundance of Ba elements of 28 stars , we have the following important conclusions :

1 . The NLTE effect of different spectral lines is different : the NLTE abundance modification of the secondary spectrum line is negative and independent of the abundance of the star metal , of which the NLTE effect of 585.3 nm is weak , and the abundance correction of the NLTE - LTE is - 0.03dex ;
The NLTE effect of 649.6 nm is stronger than that of NLTE - LTE - LTE with an average of - 0.1dex , and the maximum is - 0.18dex . The NLTE effect of the resonance line BaII450.4nm is also obvious , but its correction to abundance depends on the metal abundance of the star . When Fe / H reaches - 1.8 , the NLTE - LTE is also negative , and the average is - 0.1dex ;
However , when Fe / H alloy - 1.8 was added , Ba / Fe alloy _ ( NLTE - LTE ) was changed to positive , and the average was 0.1dex .

2 . The NLTE effect of the BaII spectral line depends on the effective temperature of the star , whether the resonant line or the secondary spectrum line , the abundance correction of the NLTE - LTE has a tendency to increase with the increase of the effective temperature . Especially the NLTE correction at 649.6 nm of the secondary spectrum line has a strong correlation with the effective temperature , and when the Teff of the star rises from 5600K to 6600K , it increases from - 0.04 dex to - 0.15dex when Teff of the star rises from 5600K to 6600K .

3 . The abundance of the stars in the whole metal abundance range of the sample ( - 2.41 擄 Fe / H ~ + 0.07 ) does not depend on the metal abundance of the star and varies around the average value of Ba / Fe isotope = 0 , but it is closely related to the star component of the star . The stellar Ba / Fe isotope of the thin disc star is consistent with the solar abundance , the average is 0.0 鹵 0.02dex , while the thick disc star has a significantly lower Ba / Fe isotope than the thin plate , with an average of - 0.1 鹵 0.02dex ;
The kinematic property is a transition star between thick disk and thin plate , and its abundance is consistent with thick disc .
When Fe / H becomes - 1.0 , Ba / Fe alloy has a higher value of Ba / Fe alloy . When Fe / H becomes - 1.0 , Ba / Fe alloys change from ultra - feng to underabundance . When Fe / H becomes - 2.0 , Ba / Fe alloy has a tendency to decrease rapidly .

The ratio of Ba element even - odd isotopes in thin plate stars is not a single value , but also varies between 82 : 18 , 70 : 30 and 65 : 35 , indicating that the Ba element nuclear synthesis process of thin disk stars is complex , and that the ratio of Ba element even - odd isotopes in thin plate stars is the same as that of the solar system , that is , the contribution of the s - process is dominant , but the Ba abundance of some thin disk stars is mainly the contribution of r - process ;
For thick - disc stars , the ratio of Ba element even - odd isotopes is not a single definite value , but between 65 : 35 and 54 : 46 , which indicates that the Ba element nucleus synthesis process of thick disc stars is r - process , Ba of thick disc stars with low metal abundance is almost the product of pure r - process , but the contribution of s - process cannot be ignored ;
For halo , the ratio of the Ba element to the odd isotope is the pure r - process 54 : 46 of the solar system , indicating that the Ba element of the halo is derived from the pure r - process nuclear synthesis , and this is independent of the metal abundance of the halo .

【學位授予單位】：河北師范大學
【學位級別】：碩士
【學位授予年份】：2013
【分類號】：P144

【參考文獻】

相關(guān)期刊論文 前1條

1 張波,李冀,張彥霞,彭秋和;貧金屬星中子俘獲元素豐度[J];天文學進展;2000年03期

本文編號：1891039