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天体物理环境中的硅酸盐尘粒 总被引：1，自引：0，他引：1
硅酸盐尘粒是宇宙尘埃的主要成分之一,它广泛存在于许多天体物理环境中,其特性随环境而变化。由于近年来观测数据的不断增加和红外光谱质量的逐步提高,宇宙空间中的硅酸盐尘粒正受到越来越多的关注．该文详细地介绍了在各种天体环境(星际空间、演化晚期恒星的星周尘埃包层、绕年轻恒星和主序星的星周尘埃盘、彗星的彗发和行星际空间)中的硅酸盐尘粒的观测特征,并分别对其物理和化学性质进行了综合比较．观测已经证实在星际尘埃演化的前身(演化晚期恒星的星周尘埃包层)和其遗迹(彗星)均有可观数量的结晶硅酸盐存在。但是至今还没有在其中间态(弥散星际介质)找到结晶硅酸盐存在的证据。这一尚未解决的难题突出了结晶态硅酸盐在天体物理研究中的重要意义。 相似文献
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锂(Li)元素最初诞生于大爆炸核合成,是最重要的轻元素之一.但锂元素丰度在很多类天体中均表现出观测与理论不符的现象,这一问题困扰了天体物理学家数十年.富锂巨星就是这样的一类天体,它们大气中的Li丰度超过了标准恒星演化模型的理论值.虽然富锂巨星早在约四十年前就被发现,但其起源依然是未解之谜.随着以郭守敬望远镜(LAMOST)巡天等为代表的大型光谱巡天项目的开展、以开普勒(Kepler)卫星为代表的星震学观测数据的产出以及数据驱动类方法和技术的飞速发展,针对富锂巨星的研究取得了一系列重要的突破.在此将回顾富锂巨星近四十年来的研究进展,并总结对于富锂巨星最新的认知. 相似文献
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恒星的Al元素丰度可以为探索星团和星系的化学演化提供重要线索.通过系统分析银河系薄盘、厚盘、核球、银晕以及M4、M5等球状星团中恒星的[Al/Fe]随恒星金属丰度[Fe/H]的变化趋势,得出银河系薄盘、厚盘和核球恒星的[Al/Fe]随着[Fe/H]的增加而缓慢下降,而球状星团M4和M5恒星的[Al/Fe]随[Fe/H]增加没有下降趋势,这暗示Ia超新星对M4和M5恒星元素丰度的贡献比较小.详细研究了银河系恒星[Al/Fe]与[Mg/Fe]、[Na/Fe]的相关性,结果表明银河系场星的[Al/Fe]与[Mg/Fe]正相关,但在球状星团M4和M5恒星中未见此相关性;银河系盘星及M4和M5等球状星团恒星的[Al/Fe]与[Na/Fe]都存在正相关. 相似文献
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偏心率是描述天体运动轨道的重要参数之一, 能够为揭示天体的动力学演化提供重要线索, 进而帮助理解天体形成与演化的过程及背后的物理机制. 随着天文观测技术的不断发展, 人们对于天体运动轨道的研究已经走出太阳系, 包含的系统也从大质量端的恒星系统延伸到了低质量端的行星系统. 聚焦天体轨道偏心率研究, 回顾了目前在恒星系统(包括主序恒星、褐矮星以及致密星)和行星系统(包括太阳系外巨行星以及``超级地球''、``亚海王星''等小质量系外行星)方面取得的进展, 总结了不同尺度结构下偏心率研究的一些共同之处和待解决的问题. 并结合当下和未来的相关天文观测设备和项目, 对未来天体轨道偏心率方面的研究工作进行了展望. 相似文献
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HD 140283是一颗近邻极贫金属亚巨星,形成于宇宙大爆炸初期,被认为是迄今为止最古老的恒星之一,同时它也是一颗典型的弱r-过程星,对它的研究有助于深入理解宇宙早期演化、丰富元素核合成理论.将HD 140283从C到Zn的观测丰度与单个超新星(SN)事件元素理论产量进行拟合,得出HD 140283可能诞生于前身星质量为22.5 M⊙(下标"⊙"代表太阳)的超新星爆发污染的星云.基于同样的方法,研究了另外5颗典型弱r-过程星,分别得出了污染产生这些恒星的气体云的超新星前身星质量,进一步推测了弱r-过程可能发生的天体物理环境. 相似文献
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星际尘埃研究现状与进展 总被引：3，自引：0，他引：3
由于星际尘埃的广泛存在和其在恒星与行星系统的形成、星系以及整个宇宙演化中的重要作用,星际尘埃的研究成为当今天体物理领域的热点前沿课题。该文从尘埃与电磁场相互作用的观测证据出发,系统地介绍了星际消光(包括吸收和散射)、星际红外辐射、星际偏振等的研究现状,讨论了星际元素减损,以及行星际尘埃和陨石中的前太阳尘埃等问题。从相应的观测证据中,可以得到关于星际尘埃的丰度、化学组成、尺寸和形状的信息。该文还对当前比较流行的三种尘埃模型(硅酸盐-石墨-PAHs模型、硅酸盐核-碳有机耐熔质壳层模型和多孔尘埃模型)进行了讨论与比较,对该研究领域中待解决的问题也作了简要的概括。 相似文献
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题图说明：一个新发现的黑洞潜伏在一个年轻且拥有大量恒星的星系中心：美国宇航局斯必泽空间望远镜曾发现了两个类似的遥远天体。它们是周遭没有尘埃的类星体。 相似文献
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恒星形成区是研究恒星形成物理过程最重要的天体物理实验室. 猎户座分子云团是研究各种质量恒星形成和相关年轻恒星性质的一个著名天区. 通过对恒星形成区的光学光谱分析, 可以获取其内部热电离气体的运动学和化学性质. 基于国家大科学装置郭守敬望远镜(LAMOST)的光谱观测数据, 从LAMOST I期光谱巡天数据中筛选出8个指向猎户座分子云团的观测面板, 获取了1300多条针对猎户座分子云团内弥散电离介质的有效光谱. 选取不受星际介质污染的背景天光光谱构建超级天光, 对这些光谱数据做减天光处理, 并进一步测量其发射线性质,包括Ha、N Ⅱ] λ 6584、[S Ⅱ]λλ 6717和6731等发射线的中心波长和积分流量等.最后给出猎户座分子云团内弥散电离介质的视向速度和线强度比分布情况. 相似文献
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《Chinese Astronomy and Astrophysics》2006,30(3):235-242
Primitive meteorites contain microscopic pre-solar stardust grains that originated from stellar outflows and supernova ejecta. Identified phases include nano-diamond, graphite, silicon carbide, corundum, spinel, hibonite, nitride, and silicates. Their stellar origin was manifested by their enormous isotopic ratio variations compared to solar system materials. They are solid samples from various stellar sources, including red giant stars, AGB stars, novae, and supernovae. Laboratory isotopic analyses of these grains provide unique insights into stellar evolution, nucleosynthesis and mixing processes, dust formation in stellar envelopes, and galactic chemical evolution. Pre-solar grains open a new observational window for astrophysical researches. 相似文献
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B. E. J. Pagel & L. Portinari 《Monthly notices of the Royal Astronomical Society》1998,298(3):747-752
The slope Δ Y /Δ Z is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate Δ Y /Δ Z from fine structure in the main sequence of nearby stars from Hipparcos data for stars with Z ≤ Z⊙. We find a value of about 3, which is consistent with what has been found in extragalactic H II regions and with stellar models for suitable upper limits to the initial masses of supernovae according to the initial mass function slope adopted. 相似文献
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E. Caffau M. Steffen P. Bonifacio H.‐G. Ludwig L. Monaco G. Lo Curto I. Kamp 《Astronomische Nachrichten》2014,335(1):59-64
The measurement of isotopic ratios provides a privileged insight both into nucleosynthesis and into the mechanisms operating in stellar envelopes, such as gravitational settling. In this article, we give a few examples of how isotopic ratios can be determined from high‐resolution, high‐quality stellar spectra. We consider examples of the lightest elements, H and He, for which the isotopic shifts are very large and easily measurable, and examples of heavier elements for which the determination of isotopic ratios is more difficult. The presence of 6Li in the stellar atmospheres causes a subtle extra depression in the red wing of the 7Li 670.7 nm doublet which can only be detected in spectra of the highest quality. But even with the best spectra, the derived 6Li abundance can only be as good as the synthetic spectra used for their interpretation. It is now known that 3D non‐LTE modelling of the lithium spectral line profiles is necessary to account properly for the intrinsic line asymmetry, which is produced by convective flows in the atmospheres of cool stars, and can mimic the presence of 6Li. We also discuss briefly the case of the carbon isotopic ratio in metal‐poor stars, and provide a new determination of the nickel isotopic ratios in the solar atmosphere. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Lynnette M. Dray † Christopher A. Tout 《Monthly notices of the Royal Astronomical Society》2007,376(1):61-70
We introduce a set of stellar models for massive stars whose evolution has been affected by mass transfer in a binary system, at a range of metallicities. As noted by other authors, the effect of such mass transfer is frequently more than just rejuvenation. We find that, whilst stars with convective cores which have accreted only H-rich matter rejuvenate as expected, those stars which have accreted He-rich matter (e.g. at the end stages of conservative mass transfer) evolve in a way that is qualitatively similar to rejuvenated stars of much higher metallicity. Thus, the effects of non-conservative evolution depend strongly on whether He-rich matter is amongst the portion accreted or ejected. This may lead to a significant divergence in binary evolution paths with only a small difference in initial assumptions. We compare our models to observed systems and find approximate formulae for the effect of mass accretion on the effective age and metallicity of the resulting star. 相似文献
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E. Caffau A. Mott M. Steffen P. Bonifacio K. G. Strassmeier A. Gallagher R. Faraggiana L. Sbordone 《Astronomische Nachrichten》2015,336(10):968-980
We present a detailed analysis of seven young stars observed with the spectrograph SOPHIE at the Observatoire de Haute‐Provence for which the chemical composition was incomplete or absent in the literature. For five stars, we derived the stellar parameters and chemical compositions using our automatic pipeline optimized for F, G, and K stars, while for the other two stars with high rotational velocity, we derived the stellar parameters by using other information (parallax), and performed a line‐by‐line analysis. Chromospheric emission‐line fluxes from Caii are obtained for all targets. The stellar parameters we derive are generally in good agreement with what is available in the literature. We provide a chemical analysis of two of the stars for the first time. The star HIP 80124 shows a strong Li feature at 670.8 nm implying a high lithium abundance. Its chemical pattern is not consistent with it being a solar sibling, as has been suggested. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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A. Frebel 《Astronomische Nachrichten》2010,331(5):474-488
The abundance patterns of the most metal‐poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, these old survivors allow us to study the nature of the first stars and supernovae, the relevant nucleosynthesis processes responsible for the formation and evolution of the elements, early star‐ and galaxy formation processes, as well as the assembly process of the stellar halo from dwarf galaxies a long time ago. This review presents the current state of the field of “stellar archaeology” – the diverse use of metal‐poor stars to explore the high‐redshift Universe and its constituents. In particular, the conditions for early star formation are discussed, how these ultimately led to a chemical evolution, and what the role of the most iron‐poor stars is for learning about Population III supernovae yields. Rapid neutron‐capture signatures found in metal‐poor stars can be used to obtain stellar ages, but also to constrain this complex nucleosynthesis process with observational measurements. Moreover, chemical abundances of extremely metal‐poor stars in different types of dwarf galaxies can be used to infer details on the formation scenario of the halo and the role of dwarf galaxies as Galactic building blocks. I conclude with an outlook as to where this field may be heading within the next decade. A table of ~ 1000 metal‐poor stars and their abundances as collected from the literature is provided in electronic format (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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贫金属富碳恒星(Carbon-Enhanced Metal-Poor, CEMP)是研究宇宙早期恒星性质和化学演化的极佳样本,通常认为来自双星.目前发现的贫金属富碳星中有9颗天琴RR变星(RR Lyrae star, RRL),其中至少7颗未表现出任何双星特征.传统双星物质转移模型不足以充分解释贫金属富碳天琴RR变星(CEMP-RR Lyrae)单星的形成.之前研究表明氦白矮星和赫氏空隙星(HG)的并合模型可以解释部分富碳红巨星单星的碳增丰现象,因此贫金属富碳星单星也可能来自氦白矮星和赫氏空隙星的并合模型渠道.通过详细计算的氦白矮星和赫氏空隙星并合模型来检验这一演化渠道,结果表明:该并合模型在后续的演化过程中,其重力加速度、温度、表面碳丰度均能与观测符合较好.由此,氦白矮星和赫氏空隙星并合模型极有可能是贫金属富碳天琴RR变星的形成渠道之一. 相似文献
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《Chinese Astronomy and Astrophysics》2020,44(1):61-69
Carbon-enhanced metal-poor (CEMP) stars are considered to be related to the first generation of stars, and responsible for the chemical evolution of the early Galaxy. More than half of them are in binaries, and could be explained by the binary evolution, but the formation channel of them is still not fully understood. Among the hundreds of CEMP stars, there are nine CEMP RR Lyrae stars identified, and at least seven of which are very likely not binaries. The usual binary star evolution channel is difficult to produce such a single star, particularly that of carbon enrichment. One way in which such a single star might be produced is the merger of a helium white dwarf with a Hertzsprung gap (HG) star. We use a stellar evolution program to calculate the models of the merger remnants, and find that the models can reproduce the observed distribution of these CEMP single RR Lyrae stars in terms of surface temperature, gravity, and carbon abundance. Hence, it is extremely possible that the helium white dwarf and HG star merger model is one of the formation channels of the metal-poor carbon-rich RR Lyrae stars. 相似文献
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A. Marcolini A. D'Ercole G. Battaglia B. K. Gibson 《Monthly notices of the Royal Astronomical Society》2008,386(4):2173-2180
Using three-dimensional hydrodynamical simulations of isolated dwarf spheroidal galaxies (dSphs), we undertake an analysis of the chemical properties of their inner regions, identifying the respective roles played by Type Ia supernovae (SNe Ia) and Type II supernovae (SNe II). The effect of inhomogeneous pollution from SNe Ia is shown to be prominent within two core radii, with the stars forming therein amounting to ∼20 per cent of the total. These stars are relatively iron-rich and α-element depleted compared to the stars forming in the rest of the galaxy. At odds with the projected stellar velocity dispersion radial profile, the actual three-dimensional one shows a depression in the central region, where the most metal-rich (i.e. [Fe/H]-rich) stars are partly segregated. This naturally results in two different stellar populations, with an anticorrelation between [Fe/H] and velocity dispersion, in the same sense as that observed in the Sculptor and Fornax dSphs. Because the most iron-rich stars in our model are also the most α depleted, a natural prediction and test of our model is that the same radial segregation effects should exist between [α/Fe] and velocity dispersion. 相似文献