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球状星团是银河系中最年老的天体之一,是储存着银河系早期演化珍贵信息的“化石”.球状星团的天体测量,主要包括球状星因天区内恒星相对自行的测定,并由这些相对自行数据采用适当方法定出星团的绝对自行,或者直接测定绝对自行.利用这些自行数据,或者进一步与测光和视向速度数据结合,可以开展与球状星团的距离、运动、动力学状况、质量、年龄、演化等等以及银河系的结构和演化等有关的一系列重要的研究.在本文中对本世纪70年代中期以来在球状星团相对自行测定和成员概率估计、内部运动检测、绝对自行测定和空间运动研究这三方面取得的成果和进展以及存在的问题作了评述. 相似文献
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确定银河系的年龄是现代天体物理学的一项基本任务。其方法之一是核纪年法,即通过恒星中某一长寿命放射性元素的丰度随时间的变化来确定恒星的年龄,并以此作为银河系年龄的下限,其中目前的观测丰度来自恒星的光谱分析,恒星形成时的初始丰度来自理论模型的预言。这种方法最初是利用元素对Th/Nd来确定G矮星的年龄,近年来开始利用元素对Th/Eu和U/Th来确定晕族场星和球状星团内恒星的年龄。简要介绍了核纪年法确定银河系年龄的原理,回顾了恒星中Th和U的观测研究,其中着重介绍了极贫金属星的研究。详细讨论了用核纪年法估计银河系年龄的不确定性。作为与核纪年法的比较,简单介绍了确定银河系年龄的其他方法。提出了今后需要进一步研究的几项工作。 相似文献
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朱紫 《紫金山天文台台刊》2003,(1)
针对地面FK5和空间依巴谷自行系统 ,采用银河系运动学分析方法发现 ,即使考虑了岁差改正的影响 ,两种自行系统之间仍存在很大差异。用建立在FK5系统上的PPM和ACRS自行与依巴谷自行比较 ,发现FK5自行系统内部存在非刚性运动 ;同时无法用VLBI及LLR所测定的岁差改正值来解释FK5与依巴谷自行系统的关系。 相似文献
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银河系厚盘的发现,对于研究银河系以至星系的结构和演化具有重要意义。在简单回顾银河系结构研究史和厚盘发现过程的基础上,综合介绍了人们对银河系厚盘各方面性质认识的现状,并对迄今为止所提出的几种厚盘形成机制作了比较详细的说明和讨论。就目前来看,与伴星系的并合可能是形成厚盘最为可能的机制。 相似文献
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N. R. Deacon N. C. Hambly R. R. King M. J. McCaughrean 《Monthly notices of the Royal Astronomical Society》2009,394(2):857-871
The UK Infrared Telescope Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of infrared surveys. Here, we combine the data from two UKIDSS components, the Large Area Survey (LAS) and the Galactic Cluster Survey (GCS), with Two-Micron All-Sky Survey (2MASS) data to produce an infrared proper motion survey for low-mass stars and brown dwarfs. In total, we detect 267 low-mass stars and brown dwarfs with significant proper motions. We recover all 10 known single L dwarfs and the one known T dwarf above the 2MASS detection limit in our LAS survey area and identify eight additional new candidate L dwarfs. We also find one new candidate L dwarf in our GCS sample. Our sample also contains objects from 11 potential common proper motion binaries. Finally, we test our proper motions and find that while the LAS objects have proper motions consistent with absolute proper motions, the GCS stars may have proper motions which are significantly underestimated. This is possibly due to the bulk motion of some of the local astrometric reference stars used in the proper motion determination. 相似文献
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Based on the Ogorodnikov-Milne model, we analyze the proper motions of Tycho-2 and UCAC2 stars. We have established that the model component that describes the rotation of all stars under consideration around the Galactic y axis differs significantly from zero at various magnitudes. We interpret this rotation found using the most distant stars as a residual rotation of the ICRS/Tycho-2 system relative to the inertial reference frame. For the most distant (d≈900 pc) Tycho-2 and UCAC2 stars, the mean rotation around the Galactic y axis has been found to be M 13 ? =?0.37±0.04 mas yr?1. The proper motions of UCAC2 stars with magnitudes in the range 12–15m are shown to be distorted appreciably by the magnitude equation in μα cos δ, which has the strongest effect for northern-sky stars with a coefficient of ?0.60±0.05 mas yr?1 mag?1. We have detected no significant effect of the magnitude equation in the proper motions of UCAC2 stars brighter than ≈11m. 相似文献
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Zhen-Yu Wu Jia-Ji Wang Li ChenShanghai Astronomical Observatory Chinese Academy of Sciences Shanghai National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(3):216-225
We examine 14 plates of the globular cluster M3 (NGC 5272) taken with the 40 cm refractor at the Sheshan station of Shanghai Astronomical Observatory. The plates span over a period of about 77 years. The positions and absolute proper motions of eight stars in the Hipparcos Catalogue and of 49 stars in the Tycho-2 Catalogue are used as the reference frame. The astrometric reduction is made with the central overlapping principle. The absolute proper motions of 534 stars in a region of about 100' × 100' around the cluster are measured. With the new proper motion data the membership probabilities of the stars are determined. The average absolute proper motion obtained for the cluster is -0.06@0.30 mas yr-1 in R.A. and -2.6@0.30 mas yr-1 in Decl. By combining this result with the known distance and radial velocity of the cluster, we also obtained the Galactic orbit of M3 for a chosen three-component Galactic potential. 相似文献
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P. N. Fedorov A. A. Myznikov V. S. Akhmetov 《Monthly notices of the Royal Astronomical Society》2009,393(1):133-138
We combined data from the Two-Micron All Sky Survey (2MASS) and USNO-A2.0 catalogues in order to derive the absolute proper motions of about 280 million stars distributed all over the sky excluding a small region near the Galactic Centre, in the magnitude range 12 < B < 19 mag . The proper motions were derived from the 2MASS Point Sources and USNO-A2.0 catalogue positions with a mean epoch difference of about 45 years for the Northern hemisphere and about 17 years for the Southern one. The zero-point of the absolute proper motion frame (the 'absolute calibration') was specified with the use of about 1.45 million galaxies from 2MASS. Most of the systematic zonal errors inherent in the USNO-A2.0 catalogue were eliminated before the calculation of proper motions. The mean formal error of absolute calibration is less than 1 mas yr−1 . The XPM Catalogue will be available via CDS in Strasbourg during 2010. The generated catalogue contains the International Celestial Reference System positions of stars for the J2000 epoch, original absolute proper motions, as well as B , R , J , H and K magnitudes. A comparison of the proper motions obtained in this work with the data of other recent catalogues of quasars was fulfilled. 相似文献
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Data from our compiled catalog of spectroscopically determined magnesium abundances in dwarfs and subgiants with accurate parallaxes are used to select Galactic halo stars according to kinematic criteria and to identify presumably accreted stars among them. Accreted stars are shown to constitute the majority in the Galactic halo. They came into the Galaxy from disrupted dwarf satellite galaxies. We analyze the relations between the relative magnesium abundances, metallicities, and Galactic orbital elements for protodisk and accreted halo stars. We show that the relative magnesium abundances in protodisk halo stars are virtually independent of metallicity and lie within a fairly narrow range, while presumably accreted stars demonstrate a large spread in relative magnesium abundances up to negative [Mg/Fe]. This behavior of protodisk halo stars suggests that the interstellar matter in the early Galaxy mixed well at the halo formation phase. The mean metallicity of magnesium-poor ([Mg/Fe] < 0.2 dex) accreted stars has been found to be displaced toward the negative values when passing from stars with low azimuthal velocities (|Θ| < 50 km s?1) to those with high ones at Δ[Fe/H] ≈ ?0.5 dex. The mean apogalactic radii and inclinations of the orbits also increase with increasing absolute value of |Θ|, while their eccentricities decrease. As a result, negative radial and vertical gradients in relative magnesium abundances are observed in the accreted halo in the absence of correlations between the [Mg/Fe] ratios and other orbital elements, while these correlations are found at a high significance level for genetically related Galactic stars. Based on the above properties of accreted stars and our additional arguments, we surmise that as the masses of dwarf galaxies decrease, the maximum SN II masses and, hence, the yield of α-elements in them also decrease. In this case, the relation between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of accreted stars is in complete agreement with numerical simulations of dynamical processes during the interaction of galaxies. Thus, the behavior of the magnesium abundance in accreted stars suggests that the satellite galaxies are disrupted and lose their stars en masse only after dynamical friction reduces significantly the sizes of their orbits and drags them into the Galactic plane. Less massive satellite galaxies are disrupted even before their orbits change appreciably under tidal forces. 相似文献
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Photometric detection of high proper motions in dense stellar fields using difference image analysis
The difference image analysis (DIA) of the images obtained by the Optical Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artefact in the sample of stars proposed as variable by Woźniak in one of the Galactic bulge fields: the occurrence of pairs of candidate variables showing anti-correlated light curves monotonic over a period of 3 yr. This effect can be understood, quantified and related to the stellar proper motions. DIA photometry supplemented with a simple model offers an effective and easy way to detect high proper motion stars in very dense stellar fields, where conventional astrometric searches are extremely inefficient. 相似文献
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N. V. Kharchenko V. S. Kislyuk S. F. Rybka A. I. Yatsenko 《Astrophysics and Space Science》1991,177(1-2):65-71
The works of the Goloseevo Observatory (Kiev, U.S.S.R.) on the compilation of catalogues of absolute proper motions measured with respect to faint galaxies are discussed. Using these catalogues, some astrometric and stellar characteristics have been obtained. Particular attention is paid to the problem of improving the accuracy of stellar position and proper motion determinations. The optimum procedure for compiling the consolidated catalogue intended for the improvement of fundamental reference frame, kinematic characteristics of stars as well as for the solution of applied problems is developed. 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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We present a catalogue of radial velocities of Galactic stars with high precision astrometric data CRVAD which is the result of the cross‐identification of star lists from the General Catalog of Average Radial Velocities (GCRV) and from the homogeneous All‐sky Compiled Catalogue of 2.5Million Stars (ASCC‐2.5). The CRVAD includes accurate J2000 equatorial coordinates, proper motions and trigonometric parallaxes in the Hipparcos system, Johnson's BV photometric data, spectral types, multiplicity and variability flags from the ASCC‐2.5, and radial velocities, stellar magnitudes and spectral types from the GCRV for 34553 ASCC‐2.5 stars. The CRVAD was used for the construction of a sample of standard stars with accurate astrometric, photometric and radial velocity data for the RAVE project. A second application of the CRVAD , the radial velocity determination for 292 open clusters (including 97 with previously unknown radial velocities), using their newly defined members from proper motions and photometry in the ASCC‐2.5, is briefly described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献