共查询到20条相似文献，搜索用时 62 毫秒
1.
长周期变星的演化和振动一直是引人入胜的课题。这不仅仅是因为在它们的变化过程中有丰富的物理内容，更重要的是可以用它们来做河外星系距离的定标者。在本文中详细的计算了在z=0.0005,z=0.001,z=0.005,z=0.01和z=0.02这样一个大的金属丰度跨度下，质量为15M⊙，20M⊙和30M⊙恒星的演化和振动。在计算中采用了最新的不透明度，考虑了星风损失对大质量星的影响，对于每一个模型都从零年龄主序演化到了中心氦燃烧结束。在文中仔细研讨了混合长参数以及中心对流核的对流超射对演化模型的影响，同时在中心氦燃烧阶段蓝超巨星和红超巨星的比值被用来限定模型的参数（尤其是混合长和对流超射）。尽管在文中并没有得到和观测一致的结论，即随着金属丰度的增加B／R增加。但是，通过在低金属丰度区采用对流超射，而在高金属丰度区放弃对流超射这一方法得到了与观测更相符合的比值。在新的演化模型的基础上，对于大质量星的振动进行了详细的计算。各项振动的性质用来和LMC，M33以及MW中的RSGs做比较。对于LMC和M33中长周期变星，理论的周光关系和观测在基频振动模式下很好的符合；而对于MW中长周期变星，它们更可能在一阶模式下振动。最终，得到了金属丰度和周光关系的之间的联系，即随着金属丰度的增加，有周期增加、光度下降的趋势。一个近似的改正δMbol-0.83δlgZ，对于决定河外星系的距离相信应该有所改善。 相似文献
2.
《天文学报》2014,(4)
捅姜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δScuti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δScuti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. 相似文献
3.
AGB长周期变星是中小质量恒星演化到晚期时形成的，由于它们存在强烈的振动和巨大的星风物质损失，研究这类变星对于了解恒星振动性质、星风产生机制及恒星晚期演化都有十分重要的意义。本文比较广泛地考查了最近十几年来国际上对于AGB长周期变星观测和理论研究工作的现状，讨论了AGB长周期变星的主要观测性质以及恒星振动和演化理论工作中所取得的进展，同时也分析了目前研究工作中存在的一些问题和困难，指出今后研究工作中需要逐步加以解决的一些问题。 相似文献
4.
ＡＧＢ长周期变星是中小质量恒星演化到晚期时形成的，由于它们存在强烈的振动和巨大的星风物质损失，研究这类变星对于了解恒星振动性质，星风产生机制及恒星晚期演化都有十分重要的意义，本文比较广泛地考查了最近十几年来国际上对于ＡＧＢ长周期变星观测和理论研究工作的现状，讨论了ＡＧＢ长周期变星的主要观测性质以及恒星振动和演化理论工作中所取得的进展，同时也分析了目前研究工作中存在的一些问题和困难，指出今后研究工作 相似文献
5.
银晕中天琴RR变星金属丰度的测定对于研究银河系晕的形成和演化具有重要的意义．在当前的技术条件下,高分辨光谱的方法难以测量银晕中较暗的天琴RR变星的金属丰度．高分辨光谱测定金属丰度的方法对恒星大气模型的依赖性较高,而恒星脉动引起的复杂大气状况对于建立正确的大气模型本身就是挑战．△S光谱方法、Caby测光方法和光变曲线的参数方法则弥补了高分辨光谱方法的不足,将能测量更远距离上的天琴RR变星的金属丰度．着重介绍了这3种方法发展的历史、具体的观测流程以及需要注意的问题。通过比较这3种方法的优劣,为实际观测时方法的选用提供借鉴。 相似文献
6.
本文根据依赖时间的对流统计理论,研究了对流同变星脉动的热力学耦合。对11种天琴座RR型变星模型序进行了线性非绝热脉动的计算,并探讨了脉动不稳定区红端边界对于恒星质量、光度、氦含量以及对流参数c_1=I_(el)/H_p的依赖关系. 相似文献
7.
本文采用国际上最新的辐射不透明度表，计算了有对流超射的两颗大中质量星从主序到中心氦燃烧结束阶段的演化，并和经典对流条件下的演化结果进行比较，发现恒星在赫罗图中的演化轨迹，中心氢、氦燃烧寿命，氢壳层源的特性都有明显变化，还注意到中等质量恒星的Tc-ρc关系对是否有对流超射较为敏感，并对这些变化进行了理论分析． 相似文献
8.
中等质量富金属AGB长周期变星的振动研究 总被引：1，自引：0，他引：1
本采用恒星演化计算与恒星振动计算相结合的方法，对中等质量富金属恒星演化到渐近巨星分支时的振动性质进行了分析研究，从理论上得出这类恒星的振动方式是处于一阶谐频振动，而振动的激发则是在氢电离区和氦的二次电离区由多种机制共同作用造成的，同时提出很长周期的ＡＧＢ长周期变星只能是由中等质量恒星演化到ＡＧＢ阶段形成的。我们的理论计算结果还比较支持在ＡＧＢ顶端存在巨大星风物质损失的观点，且这种星风物质损失很可 相似文献
9.
本采用国际上最新的辐射不透明度表，计算了有对流超射的两颗大中质量星从主序到中心氦燃烧结束阶段的演化，并和经典对流条件下的演化结果进行比较，发现恒星在赫罗图中的演化轨迹，中心氢、氦燃烧寿命，氢壳层源的特性都有明显变化，还注意到中等质量恒星的Ｔｃ－ρｃ关系对是否有对流超射较为敏感，并对这些变化进行了理论分析。 相似文献
10.
本文采用恒星演化计算与恒星振动计算相结合的方法，对中等质量富金属恒星演化到渐近巨星分支时的振动性质进行了分析研究，从理论上得出这类恒星的振动方式是处于一阶谐频振动，而振动的激发则是在氢电离区和氦的二次电离区由多种机制共同作用造成的，同时提出很长周期的ＡＧＢ长周期变星只能是由中等质量恒星演化到ＡＧＢ阶段形成的。我们的理论计算结果还比较支持在ＡＧＢ顶端存在巨大星风物质损失的观点，且这种星风物质损失很可能与恒星振动有关。 相似文献
11.
Laura Schaefer 《Icarus》2004,169(1):216-241
We modified the MAGMA chemical equilibrium code developed by Fegley and Cameron (1987, Earth Planet. Sci. Lett. 82, 207-222) and used it to model vaporization of high temperature silicate lavas on Io. The MAGMA code computes chemical equilibria in a melt, between melt and its equilibrium vapor, and in the gas phase. The good agreement of MAGMA code results with experimental data and with other computer codes is demonstrated. The temperature-dependent pressure and composition of vapor in equilibrium with lava is calculated from 1700 to 2400 K for 109 different silicate lavas in the ONaKFeSiMgCaAlTi system. Results for five lavas (tholeiitic basalt, alkali basalt, Barberton komatiite, dunite, and a molten type B1 Ca, Al-rich inclusion) are discussed in detail. The effects of continuous fractional vaporization on chemistry of these lavas and their equilibrium vapor are presented. The predicted abundances (relative to Na) of K, Fe, Si, Al, Ca, and Ti in the vapor equilibrated with lavas at 1900 K are lower than published upper limits for Io's atmosphere (which do not include Mg). We predict evaporative loss of alkalis, Fe, and Si during volcanic eruptions. Sodium is more volatile than K, and the Na/K ratio in the gas is decreased by fractional vaporization. This process can match Io's atmospheric Na/K ratio of 10±3 reported by Brown (2001, Icarus 151, 190-195). Silicon monoxide is an abundant species in the vapor above lavas. Spectroscopic searches are recommended for SiO at IR and mm wavelengths. Reactions of metallic vapors with S- and Cl-bearing volcanic gases may form other unusual gases including MgCl2, MgS, MgCl, FeCl2, FeS, FeCl, and SiS. 相似文献
12.
《中国天文和天体物理学报》2014,(9)
正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length 相似文献
13.
14.
《中国天文和天体物理学报》2014,(10)
正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work, 相似文献
15.
16.
Laura Schaefer 《Icarus》2005,173(2):454-468
We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10−6 to 10+1 bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I2 (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F. 相似文献
17.
18.
Li Xin-nan Zhang Hai-ying Cui Xiang-qun Jiang Zi-bo Zheng Yi Liu Xing-tao Ni Hou-kun 《Chinese Astronomy and Astrophysics》2012
A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope. 相似文献
19.
In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω
φ
∼−1, Ω
φ
=1, which avoid the “Big rip” problem and meets the current observations well.
相似文献
20.
In astronomical observations at optical wavelengths, a fast image tracking system can be adopted to reduce the effects of the atmospheric seeing and telescopic tracking error, and therefore improve the observing efficiency. Aiming at the need of astronomical observations, totally 5 kinds of algorithms in two categories were selected to make a comparative study on their accuracies and stabilities under different noise conditions by both numerical experiment and laboratory test. The results indicate that the normalized cross-correlation method and barycenter method have not only a higher accuracy but also a better reliability against interferences, they will be applied to the high-resolution spectrograph of the Xinglong 2.16 m telescope and the scienti?c instruments of the SONG (Stellar Observations Network Group) project, respectively. 相似文献