本文選題：觀測 + 恒星大氣　； 參考：《河北師范大學(xué)》2011年碩士論文

【摘要】：鋇星是一類特殊的紅巨星,最初是由Bidelman和Keenan在1951年觀測得到[09],其光譜型為G2—K4,光譜中有非常強的BaⅡ4554A線,另外還有SrⅡ線、CH線、CN線,以及C2線(Burbidge et al.1957)。在隨后的觀測中,人們發(fā)現(xiàn)鋇星的光譜特征還表現(xiàn)為其他重元素的增豐,比如：Y、zr、La、Ce、Pr、Nd、Sm等。 在之后對鋇星的研究中,人們已經(jīng)得到了很多鋇星的演化歷史和物理屬性,但是還有很多問題沒有解決,例如造成鋇星重元素超豐的具體過程是什么,主要受哪些因素的影響,鋇星的運動學(xué)特征等等。以此為切入點,我們開展了對鋇星的研究工作。 Lu(1991)[60]搜集整理并列表給出了一個389顆鋇星的樣本表。并采用Warner et al.(1965)刪的方法依據(jù)BaⅡ4554 A譜線的強度,給出了每顆樣本星的鋇強度。具體值從1到5表明Ba強度逐漸增大,并定義Ba≥2的樣本為強鋇星,Ba2的樣本為弱鋇星。 另一方面,McClure(1980)[56]發(fā)現(xiàn)絕大部分鋇星(甚至可能是全部)都顯示視向速度的變化,表明它們有伴星的存在。之后的一些工作測得了大樣本鋇星的雙星軌道參數(shù)(Carquillat et al.1998[20], Udry et al.1998a[72],1998b[73], Jorissen et al.1998)。 雖然有了這些前期工作,但由于觀測限制,對于鋇星重元素的直接觀測分析還較少,而重元素豐度的分析是研究鋇星重元素超豐起源的重要而直接的方法。因而我們建立的研究課題是觀測獲得大樣本鋇星的高分辨率高信噪比光譜,進而獲得其重元素豐度。如果可能,并將詳細比較分析強、弱鋇星的特征,并探討其原因。 我們利用中國科學(xué)院國家天文臺興隆觀測站的2.16米天文望遠鏡進行了光譜觀測,并獲得了57顆鋇星的高分辨率、高信噪比光柵光譜。國家天文臺梁艷春研究員和劉國卿博士已經(jīng)分別處理和分析了其中的4顆和8顆樣本(Liang et al.2003[47], Liu et al.)。本文共處理和分析了其余的45顆樣本星。在處理光譜方面,我們用標準的MIDAS軟件包得到一維光譜并測量得到每顆目標源的視向速度和元素的等值寬度,然后用前人提出的經(jīng)驗方法迭代計算并得到可靠的大氣參數(shù)(有效溫度(Teff)、表面重力(1ogg)、金屬豐度[Fe/H]和微觀湍流速度((?))),然后將大氣參數(shù)及譜線的等值寬度輸入所采用的大氣模型中,從而得出了17種元素的豐度。 我們發(fā)現(xiàn)45顆樣本星里,除了HD 26是暈星,其它44顆都是盤星。它們的O,Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni等α、Na、Al及鐵族元素的豐度與太陽值類似,Y、Zr、Ba、La、Eu等中子俘獲元素表現(xiàn)出明顯增豐。例如[Ba/Fe], [La/Fe], [Eu/Fe]的中值分別是0.53,0.43,0.39。強鋇星的Y、Zr元素表現(xiàn)出第一個峰值,Ba、La、Eu等元素表現(xiàn)出第二個峰值,且比第一個峰值更高。而弱鋇星的Y、Zr元素看不出明顯增豐,甚至比太陽值還要低,Ba、La、Eu等元素依然能看出明顯的增豐。不過,應(yīng)該提到的是我們采用的是YⅠ、ZrⅠ線來計算得到Y(jié)、Zr元素的豐度。有研究表明,如果采用YⅡ、ZrⅡ線的話,豐度值會略有提高(0.1-0.3dex)。 然后,我們將樣本擴大,增加了Liang et al. (2003), Allen Barbuy (2006a), Smiljanic et al. (2007), Liu et al. (2009), Zacs(1994)工作的共69顆樣本星。這樣我們采用擴大后的樣本(114顆樣本星)來進一步分析鋇星的特征,特別是比較了強、弱鋇星的豐度特征,探討了可能影響其差別的主要參數(shù),包括金屬豐度,雙星軌道周期及中子輻照量。 我們基于高質(zhì)量光譜觀測獲得的樣本星的[Ba/Fe]值對鋇星進行了重新分類,我們把[Ba/Fe]≥0.69的鋇星劃分為強鋇星,把[Ba/Fe]0.69的鋇星劃分為弱鋇星。 因為之前的工作中絕大部分是強鋇星,而我們的45顆樣本星里很多是弱鋇星,這使得我們能夠?qū)�、弱鋇星的比較更加細致深入。我們發(fā)現(xiàn)對于強鋇星,隨著金屬豐度的增大,鋇元素豐度降低,對于弱鋇星沒有明顯趨勢。這可能意味著Ba超豐較強的那些星相比Ba超豐較弱的那些星屬于更老一些的盤族星。不過在較重(hs：Ba和La)與較輕(ls：Y和Zr)元素豐度比率[hs/ls]與[Fe/H]的關(guān)系中,卻沒有看到強、弱鋇星的明顯差別。 我們計算得到樣本星的空間速度U、V、W,證明這45顆樣本星里除了HD 26是暈星,其它的都是盤星。強、弱鋇星的空間速度U、V、W沒有明顯區(qū)別。 通過利用星風吸積模型擬合(Liang et al.2000, Zhang et al.1999),我們發(fā)現(xiàn)星風吸積模型能更好的解釋鋇星的重元素超豐：鋇星的重元素超豐是由于吸積了其伴星所拋射的重元素物質(zhì)造成的,而這顆伴星當時是一顆AGB星,現(xiàn)在已經(jīng)演化為一顆白矮星。 然后,我們進一步探討了另外兩個參數(shù)對強弱鋇星的影響,即雙星軌道周期P和其伴星在AGB階段發(fā)生中子俘獲過程時的中子輻照量。通過分析,我們發(fā)現(xiàn)軌道周期對于造成鋇星的重元素超豐有重要影響。一般來說,更短的軌道周期更有利于造成鋇星的超豐。而更強的中子輻照量會使得鋇星有更高的重元素超豐。不過,整體還是多個參量耦合在一起的復(fù)雜的過程。
[Abstract]:Barium star is a special kind of red giant star, which was first observed by Bidelman and Keenan in 1951, and its spectral type is G2 - K4. There are very strong Ba II 4554A lines in the spectrum. In addition, there are Sr II lines, CH lines, CN lines, and C2 lines (Burbidge). In the subsequent observation, the spectral characteristics of barium stars are also found to be other heavy elements. Zeng Feng, such as: Y, Zr, La, Ce, Pr, Nd, Sm and so on.
In the later study of barium stars, many barium stars have been obtained the evolution history and physical properties, but there are many problems that have not been solved, for example, what is the specific process of barium star heavy elements, which is mainly influenced by the factors, the kinematic characteristics of barium stars and so on. Research work.
Lu (1991) [60] collects and lists a sample table of 389 barium stars. Using the method of Warner et al. (1965) deletion, the barium strength of each sample star is given according to the intensity of Ba II 4554 A spectrum. From 1 to 5, the strength of Ba is increased gradually, and the sample of Ba > 2 is a strong barium star, and the sample of Ba2 is a weak barium star.
On the other hand, McClure (1980) [56] found that the vast majority of barium stars (or even all) showed changes in the apparent velocity, indicating the presence of the companion stars. Some of the subsequent work measured the double star orbital parameters of the large sample barium stars (Carquillat et al.1998[20], Udry et al.1998a[72], 1998b[73], Jorissen et al.1998).
In spite of these previous work, the observation and analysis of the barium star heavy elements are less and less due to the observation restrictions, and the analysis of the abundance of heavy elements is an important and direct method to study the super abundant origin of barium stars. Therefore, the study of the high resolution and high signal to noise ratio spectra of large sample barium stars is observed. The heavy element abundance can be obtained. If possible, the characteristics of strong and weak barium stars will be compared and analyzed in detail.
We used the 2.16 meter telescope of the 2.16 meter telescope at the National Astronomical Observatory of the National Astronomical Observatory of the Chinese Academy of Sciences. We obtained the high resolution and high signal to noise ratio raster spectra of 57 barium stars. The National Observatory Liang Yanchun and Dr. Liu Guoqing have processed and analyzed 4 and 8 samples (Liang et al.2003[47], L). IU et al.). This paper deals with and analyzes the remaining 45 sample stars. In the spectrum of processing, we use the standard MIDAS package to obtain the one-dimensional spectrum and measure the apparent velocity of each target source and the equivalent width of the element. Then the reliable atmospheric parameters (effective temperature (Tef) are calculated and obtained by the previous empirical methods. F), the surface gravity (1ogg), the metallicity [Fe/H] and the microscopic turbulence velocity ((?))), and then input the equivalent width of the atmospheric parameters and the spectral lines into the atmospheric model adopted, thus obtaining the abundance of the 17 elements.
We found that in 45 sample stars, except that HD 26 is a halo star, the other 44 are disc stars. Their O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, and so on are similar to the sun value. 9. strong barium star Y, Zr element shows the first peak, Ba, La, Eu and other elements show second peaks, and higher than the first peak. And the weak barium star Y, Zr element can not see obvious increase, even lower than the sun value, Ba, La, Eu and other elements can still see obvious enhancement. However, it should be mentioned that we used Y I, Zr I line The abundance of Y and Zr elements is calculated. Studies show that if the Y II and Zr II lines are used, the abundance will increase slightly (0.1-0.3dex).
Then, we expand the sample, add the Liang et al. (2003), Allen Barbuy (2006a), Smiljanic et al. (2007), Liu et al. (2009), and 69 sample stars working (1994). So we use an expanded sample (114 sample stars) to further analyze the characteristics of the barium star, especially the comparison of the strong, weak barium star abundances. The main parameters that may affect the difference are discussed, including metallicity, double orbit period and neutron exposure.
We reclassified barium stars based on the [Ba/Fe] values of the sample stars obtained by high mass spectroscopic observations. We divide the barium stars of [Ba/Fe] > 0.69 into strong barium stars and divide the barium star of [Ba/Fe]0.69 into weak barium stars.
Because most of the previous work is strong barium, and many of our 45 sample stars are weak barium stars, which makes it possible for us to compare the strong, weak barium stars more carefully. We found that for strong barium stars, as the abundance of metal increases, the abundance of barium decreases, and there is no obvious trend to the weak barium star. This may mean Ba super. Those stars in the stronger and stronger than those with the Ba superabundance are older, but in the relation of heavier (hs:Ba and La) to the lighter (ls:Y and Zr) element abundances [hs/ls] and [Fe/H], there is no obvious difference between strong and weak barium stars.
We calculate the space velocity of the sample star U, V, W, which proves that the 45 star sample stars except HD 26 are halo stars, the other are all disc stars. Strong, weak barium star space velocity U, V, W has no obvious difference.
By using the Liang et al.2000 model (Zhang et al.1999), we found that the stellar wind accretion model can better explain the heavy element super abundance of barium Star: the barium star's heavy element overabundance is caused by the heavy element material that accretion of its companion star, and the companion star was a AGB star at the time, and now it has evolved into one. A white dwarf.
Then, we further discuss the effect of the other two parameters on the barium star, that is, the double star orbit period P and the neutron irradiation amount of its companion star during the neutron capture process at the AGB stage. By analysis, we find that the orbit period has an important effect on the heavy element of the barium star. Generally, the shorter orbit period is more favorable. The barium star is caused by the super abundance of the barium star, and the stronger neutron radiation will make the barium star have a higher weight of heavy elements. However, the whole process is a complex process coupled with a number of parameters.

【學(xué)位授予單位】：河北師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2011
【分類號】：P144

【共引文獻】

相關(guān)博士學(xué)位論文 前2條

1 呂國梁;共生星的理論研究[D];中國科學(xué)院研究生院（云南天文臺）;2006年

2 楊家艷;恒星對流的Reynolds應(yīng)力模型及其日震學(xué)檢驗[D];中國科學(xué)院研究生院（云南天文臺）;2006年

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本文編號：1813804