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The influences of convective overshooting and semiconvection on the chemical evolution of massive stars
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作者 Cai-Yun Ding Yan Li 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2014年第8期979-991,共13页
In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between ... In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between which are the radiative inter- mediate layers with uneven chemical abundances. Semiconvection would occur in the intermediate layers between the convective core and the homogeneous envelope in massive stars. We treat core convective overshooting and semiconvection together as a process. We found that when decreasing overshooting, the semiconvection is more pronounced. In these two processes, we introduce one diffusive parameter D, which is different from other authors who have introduced different parameters for these two zones. The influences of the turbulent diffusion process on chemical evolution and other quantities of the stellar structure are shown in the present paper. 展开更多
关键词 stars evolution -- stars abundances -- convection -- diffusion
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Influence of the convective mixing-length parameterαon the chemical abundances in the case of metal-poor giant HD 122563
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作者 Nan Song Sofya Alexeeval Gang Zhao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2020年第8期181-192,共12页
One-dimensional(1 D)model atmospheres are still the most commonly used tool for the determination of stellar chemical composition.Convection in the model is usually treated by mixing-length theory(MLT).The mixing-leng... One-dimensional(1 D)model atmospheres are still the most commonly used tool for the determination of stellar chemical composition.Convection in the model is usually treated by mixing-length theory(MLT).The mixing-length parameterαis generally calibrated from the Sun and applied to all other stars.The metal-poor giant,HD 122563,is an important benchmark star to test stellar atmosphere and interior physics.We investigate the influence of the convection mixing-length parameterαon the determination of chemical abundances of Na,Mg,Al,Si,Ca,Sc,Ti,Cr,Mn,Co,Ni,Sr,Y,Zr and Ba in the case of HD 122563,taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum.The abundance discrepanciesΔ[X/H]that occur due toαvariation rarely exceed 0.05 dex and most are less than 0.03 dex.We calculate the discrepancyΔ[X/H]using a line-by-line differential analysis.The abundance discrepancies do not have direct relation with either line strength or the excitation potential.For 1 D stellar atmospheric analysis of HD 122563,the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameterα(causing average discrepancies of<0.03 dex),while the uncertainties in the effective temperature and surface gravity play a more important role. 展开更多
关键词 stars:abundances convection stars:atmospheres line:profiles
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脉动稳定性对恒星对流包层氦丰度的依赖 被引量:1
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作者 熊大闰 邓李才 王坤 《天文学报》 CSCD 北大核心 2014年第4期279-287,共9页
利用一种非局部和非定常的恒星对流理论,计算了3种不同氦丰度(y=0.28,0.13,0.00)、太阳金属丰度(Z=0.02)、质量1.4~3.0 M⊙恒星演化模型的径向和低球谐阶F-p8模的线性非绝热脉动.数值计算结果表明,理论的δ Scuti变星脉动不稳定区... 利用一种非局部和非定常的恒星对流理论,计算了3种不同氦丰度(y=0.28,0.13,0.00)、太阳金属丰度(Z=0.02)、质量1.4~3.0 M⊙恒星演化模型的径向和低球谐阶F-p8模的线性非绝热脉动.数值计算结果表明,理论的δ Scuti变星脉动不稳定区红边界几乎不随氦丰度变化而改变.随着氦丰度降低,δScuti变星脉动不稳定区蓝边界向低温方向推移,脉动不稳定区中热方的高温星变得脉动更稳定;而冷方的低温星则变得脉动更不稳定.这似乎表明不大可能用氦弥散去解释δ Scuti脉动不稳定带中的不变星.然而脉动不稳定带热方和冷方中的不变星与变星的比例可能作为是否存在氦弥散的一种观测证据. 展开更多
关键词 恒星 变星 δScuti型星 恒星 脉动 恒星 丰度 对流
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太阳大气铍丰度的衰减
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作者 熊大闰 邓李才 《天文学报》 CSCD 北大核心 2003年第1期1-2,共2页
Li和Be轻元素在温度仅几百万度时就因核反应而遭毁坏,因此它们是恒星演化过程的外层对流混合延伸程度很好的一种示踪.基于这种考虑,我们曾计算过太阳包层模型Li的衰减,得到一个同时满足日震学太阳对流区深度和太阳Li丰度观测要求的非局... Li和Be轻元素在温度仅几百万度时就因核反应而遭毁坏,因此它们是恒星演化过程的外层对流混合延伸程度很好的一种示踪.基于这种考虑,我们曾计算过太阳包层模型Li的衰减,得到一个同时满足日震学太阳对流区深度和太阳Li丰度观测要求的非局部太阳对流包层模型[1].Li丰度给出了一个非局部对流混合延伸程度的上限. 展开更多
关键词 太阳 丰度 衰减机制 对流包层模型 太阳大气
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低部主序恒星锂和铍的衰减
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作者 熊大闰 邓李才 《天文学报》 CSCD 北大核心 2007年第2期165-180,共16页
根据化学非均匀恒星的非局部对流理论,计算了质量为0.7-1.15M(?)恒星主序演化模型锂和铍的衰减,并将理论和不同年龄疏散星团锂丰度的观测进行了比较.结果表明,贯穿对流混合能重现温度低于6400 K的晚型主序星锂丰度观测的一般性质.... 根据化学非均匀恒星的非局部对流理论,计算了质量为0.7-1.15M(?)恒星主序演化模型锂和铍的衰减,并将理论和不同年龄疏散星团锂丰度的观测进行了比较.结果表明,贯穿对流混合能重现温度低于6400 K的晚型主序星锂丰度观测的一般性质.贯穿对流混合可能是晚型矮星锂衰减的一种重要机制. 展开更多
关键词 物理数据与过程 对流 恒星 元素丰度 恒星 晚型 恒星 演化 银河系 疏散星团和星协
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Contributions of type II and Ib/c supernovae to Galactic chemical evolution
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作者 Sandeep Sahijpal 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2014年第6期693-704,共12页
Type II and Ib/c supernovae (SNe II and Ib/c) have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here w... Type II and Ib/c supernovae (SNe II and Ib/c) have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here with the help of recently developed numerical simulations of Galactic chemical evolution in the solar neighborhood to un- derstand the contributions of SNe II and Ib/c by comparing the stellar nucleosynthetic yields obtained by two leading groups in this field. These stellar nucleosynthetic yields differ in terms of their treatment of stellar evolution and nucleosynthesis. The formu- lation describing Galactic chemical evolution is developed with the recently revised solar metallicity of -0.014. Furthermore, the recent nucleosynthetic yields of stellar models based on the revised solar metallicity are also used. The analysis suggests that it could be difficult to explain, in a self-consistent manner, the various features asso- ciated with the elemental evolutionary trends over Galactic timescales by any single adopted stellar nucleosynthetic model that incorporates SNe II and Ib/c. 展开更多
关键词 sun abundances - stars evolution - stars supernovae - Galaxy:abundance - Galaxy: formation - Galaxy: evolution - nucleosynthesis
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Spectral analysis of two solar twins and the colors of the Sun
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作者 ZHAO ZhengShi1,2, CHEN YuQin1, ZHAO JingKun1 & ZHAO Gang1 1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China 2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China 《Science China(Physics,Mechanics & Astronomy)》 SCIE EI CAS 2010年第3期579-585,共7页
High resolution (R^40,000) and high signal-to-noise ratio (】150) spectra of two solar twins, HD146233 and HD195034, are obtained with the Coude Echelle Spectrograph at the 2.16 m telescope of the National Astronomica... High resolution (R^40,000) and high signal-to-noise ratio (】150) spectra of two solar twins, HD146233 and HD195034, are obtained with the Coude Echelle Spectrograph at the 2.16 m telescope of the National Astronomical Observatories of Chinese Academy of Sciences (Xinglong, China). Based on the detailed spectrum match, comparisons of chemical composition and chromospheric activity, HD146233 and HD195034 are confirmed that they are similar to the Sun except for lithium abundance, which is higher than the solar value. Moreover, among nine solar twin candidates (including HD146233 and HD195034) found in the previous works, we have picked out six good solar twin candidates based on newly-derived homogenous parameters, and collected their colors in the Johnson/Cousins, Tycho, 2MASS and Strmgren system from the literature. The average color are (B-V)⊙=0.644 mag, (V-Ic)⊙=0.707 mag, (BT-VT)⊙=0.725 mag, (J-H)⊙=0.288 mag, (H-K)⊙=0.066 mag, (v-y)⊙=1.028 mag, (v-b)⊙=0.619 mag, (u-v)⊙=0.954 mag and (b-y)⊙=0.409 mag, which represent the solar colors with higher precision than previous works. 展开更多
关键词 sun-colors Star-atmospheres abundances fundamental parameters
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