共查询到20条相似文献，搜索用时 15 毫秒
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H.-J. Tucholke 《Astronomische Nachrichten》1994,315(6):419-426
We measured relative proper motions with a typical accuracy of 1.0 milliarcsec/year (mas/a) for 2000 stars in a 1°4 × 1°4 field around the low-latitude globular cluster NGC 6934. Four plates taken with the Bonn double refractor, spanning an epoch difference of 62 years, were digitized completely. Within the tidal radius of the cluster, we find 106 stars with proper motion errors less than 5 mas/a. Membership probalilities are computed taking into account the individual proper motion errors and the radial distances to the cluster centre. We derive the mean relative proper motion of NGC 6934 using stars with high membership probabilities from radial velocities (Smith and Bell 1986) or from their location in the colour-magnitude diagram (Harris and Racine 1973). The relative proper motions of four Hipparcos stars in the field will be used to obtain the absolute proper motion of NGC 6934 once the extragalactically calibrated Hipparcos Output Catalogue is available. 相似文献
3.
Using the model of the Galaxy presented by Eggen, Lynden-Bell and Sandage (1962), plane galactic orbits have been calculated for several southern high-velocity stars which possess parallax, proper motion, and radial velocity data. Extensive lists of both raw and computed data for these stars are included. Published values ofU-B andB-V for some of these stars were used in plots of each of the orbital parameters versusU-B, B-V, or the ultraviolet excess (U-B). Also, a comparison is made between the H-R diagrams for the southern high-velocity star group and that of M3, a globular cluster, and again for M67, an old open cluster. The high-velocity star group is found to resemble an old open cluster more than a globular cluster. 相似文献
4.
《Chinese Astronomy and Astrophysics》2006,30(3):274-283
or stars in the region around the open cluster NGC6530, cluster memberships are calculated based on the maximum likelihood principle using proper motions obtained from photographic plates acquired with the 40 cm refraction telescope at Shanghai Astronomical Observatory. Analyses show that the membership determination is very effective with 250 stars having membership probabilities p ≥ 0.9. The spatial motion of the star cluster is also determined and a simple discussion is carried out. 相似文献
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利用上海天文台的照相底片资料,确定了疏散星团NGC6530天区364颗恒星的自行和成员概率,并对有关自行测定的方法、结果和精度等问题作了较为详细的介绍和讨论。使用的底片历元差为87年,全部恒星自行中误差的均方根值为1．09mas/a。 相似文献
7.
Astrometric CCD observations of stars with large proper motions were carried out during 2008–2014 using telescopes of the Nikolaev Astronomical Observatory. A catalog of positions and proper motion of 1596 fast stars with proper motions exceeding 150 mas/yr has been compiled based on observation results. The catalog covers the declination zone from 0° to 65°. The standard error of derived proper motion is 1…10 mas/yr for both coordinates depending on the observational history of the star. Data from eight different star catalogs and surveys have been used to derive proper motion. The comparison results of proper motion with data from modern catalogs and results of the statistical test for the detection of possible invisible components are given. 相似文献
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N. V. Kharchenko A. E. Piskunov S. Rser E. Schilbach R.‐D. Scholz 《Astronomische Nachrichten》2004,325(9):740-748
We present a catalogue (CSOCA) of stars residing in 520 Galactic open cluster sky areas which is the result of the kinematic (proper motion) and photometric member selection of stars listed in the homogeneous All‐sky Compiled Catalogue of 2.5Million Stars (ASCC‐2.5).We describe the structure and contents of the catalogue, the selection procedure applied, and the proper motion and photometric membership constraints adopted. In every cluster area the CSOCA contains the complete list of the ASCC‐2.5 stars regardless of their membership probability. For every star the CSOCA includes accurate J2000 equatorial coordinates, proper motions in the Hipparcos system, BV photometric data in the Johnson system, proper motion and photometric membership probabilities, as well as angular distances from the cluster centers for about 166 000 ASCC‐2.5 stars. If available, trigonometric parallaxes, spectral types, multiplicity and variability flags from the ASCC‐2.5, and radial velocities with their errors from the Catalogue of Radial Velocities of Galactic Stars with high precision Astrometric Data (CRVAD) are also given. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
《天文和天体物理学研究(英文版)》2021,(5)
The physical nature of a series of 20 new open clusters is confirmed employing existing data on putative star members, mainly from the second Gaia Data Release(DR2). The clusters were discovered as overdensities of stars by visual inspection of either photographic DSS plates or proper motion plots of random source fields. The reported objects are not present in the most comprehensive or recent catalogs of stellar clusters and associations. For all of them, clumps of comoving stars are revealed in the proper motion space. The parallaxes of the clumped stars are compatible with the real existence of open clusters over narrow ranges of distances. Surface density calculations, free of most noise from non-member sources,allow differentiating a cluster core and an extended cluster corona in some instances. Color-magnitude diagrams generally show a definite main sequence that allows confirmation of the physical existence of the clusters and some of their characteristics. Two of the new clusters seem to form a double system with a common origin. Several of the new clusters challenge the claim of near completeness of the known OC population in the distance range from 1.0 to 1.8 kpc from the Sun(Kharchenko et al.). 相似文献
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In this paper we combine information on photometry, radial velocities and proper motions to study the nature of the suspected open cluster Cr 135. For the first time we introduce proper motions of a large number of stars in the region of Cr 135 into the discussion. The proper motions taken from the PPM catalogue favour the hypothesis that Cr 135 is a real open cluster with at least 12 members at a distance of 300 pc having a space motion U, V, W of (−11, −13, −15) km s−1. But still more accurate observations are needed to separate it from the field stars without any doubt. 相似文献
11.
Neill Reid 《Monthly notices of the Royal Astronomical Society》2003,342(3):837-850
We present high-resolution echelle spectroscopy of 20 stars in 16 systems catalogued as members of the TW Hydrae association, and 16 stars identified as possible new members. We have calibrated the range of coronal and chromospheric activity expected for such young stars as a function of spectral type by combining our observations with literature data for field and open cluster stars. We also compute space motions for TWA members and candidate members with proper motion measurements, using two techniques to estimate distances to stars lacking direct trigonometric parallax measurements. The mean space motion of the four TWA members with known parallaxes is ( U , V , W : −10.0, −17.8, −4.6) km s−1 . 14 of the candidates have properties inconsistent with cluster membership; the remaining two are potential new members, although further observations are required to confirm this possibility. 相似文献
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Xin-Hua Gao 《Astrophysics and Space Science》2018,363(11):232
In this paper, we present an investigation of the memberships, distance and proper motion for the old open cluster NGC 188 using a machine-learning-based method. This method combines two widely used algorithms: spectral clustering (SC) and random forest (RF). The former one is used to construct a reliable training set, the membership probabilities are calculated based on the latter one. This method only depends on reliable training set, no prior knowledge about the cluster is needed. This method is based on the basic assumption that most if not all the information about the cluster members and field stars are contained in a reliable training set, this makes it highly suitable for handling high-dimensional data sets. We use this method to investigate the likely memberships of the old open cluster NGC 188 based on the high-precision astrometry and photometry from the \(\textit{Gaia}\) Data Release 2 (\(\textit{Gaia}\) DR2). Based on seven-dimensional features (positions, parallax, proper motions and color-magnitude) of 3780 sample stars in the region of NGC 188, 645 likely members with high membership probabilities (\(\geq 0.75\)) are obtained. Further analysis confirms the effectiveness of our membership determination. Based on these high-probability memberships, the distance and proper motion of the cluster are determined to be \(1866\pm 4\) pc and \((\overline{\mu _{ \alpha }}, \overline{\mu _{\delta }})=(-2.33\pm 0.01,-0.97 \pm 0.01)\) mas/yr, respectively. 相似文献
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耀星是红矮星早期演化的一个必经阶段，这个阶段的持续时间取决于恒星的质量。在年轻和比较年轻的疏散星闭中，都含有大量耀星，它们的光度分布是疏散星闭年龄的标志。在昴生闭中已发现大量耀星，对它们的自行，测光和分光资料进行深入的统计研究，对于解决疏散星闭及矮星起源和演化问题，有着极其重要的价值。 相似文献
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A. A. Volchkov A. V. Kuzmin V. V. Nesterov U. Bastian S. Rser 《Astronomische Nachrichten》1993,314(1):43-46
Proper motions of the stars of the Astrographic Catalogue are being derived, using the Hubble Space Telecope Guide Star Catalogue as second epoch. Results on the San Fernando and Cordoba AC zones are presented. Identification with GSC stars (i.e. determination of proper motion) was successful for 97 percent of all AC stars. Comparison of the proper motions thus derived with those of Preliminary PPM South shows that the accuracy is about 0.8 to 0.9 arcsec per century. Thus we can derive proper motions for about 4 million stars, with an accuracy higher than that of the SAO Catalogue. 相似文献
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The results of a comprehensive study of the Galactic open cluster NGC 2323 (M50) are presented. The positions of stars to
a limiting magnitude {ie74-1} in a {ie74-2} area centered on the cluster were measured on six plates from the Pulkovo normal
astrograph with a maximum epoch difference of 60 yr. The measurements were performed with the Pulkovo “Fantasy” automated
measuring system upgraded in 2010. The corresponding areas from the USNO-A2.0, USNO-B1, and 2MASS catalogues were used as
additional plates. As a result, the relative proper motions of stars were obtained with a root-mean-square error of 5.85 mas
yr−1. A catalogue of UBV and JHK magnitudes for objects in the investigated area was compiled from available published resources. The astrometric selection
of cluster members was made by the maximum likelihood method. A high individual cluster membership probability of a star (P ≥ 80%) served as the first selection criterion. The position of a star on the photometric color-magnitude (V ∝ (B-V), J ∝ (J-K)) diagrams of the cluster was considered as the second criterion. The position of an object on the color-color ((U-B)-(B-V), (J-H)-(J-K)) diagrams served as the third criterion. On the basis of these criteria, it was established that 508 stars are members of
NGC 2323. These data were used to refine the physical parameters of the cluster: the mean reddening {ie74-3}, the true distance
modulus {ie74-4}, and the cluster age of about 140 Myr from the grid of isochrones computed by the Padova group for solar
chemical composition. Two tables contain the catalogues of proper motions and photometry for stars in the area. The luminosity
and mass functions were constructed. The cluster membership of red and blue giants, variable, double, and multiple stars was
considered. The position of the cluster center was improved: {ie74-5}, δ = −08°20′16″(2000.0). 相似文献
16.
Astrometric CCD observations of 1123 stars with large proper motions (μ > 300 mas yr−1) from the LSPM (I/298) catalog in the declination zone +30°–+70° have been carried out with the Pulkovo normal astrograph
since 2006. The observational program includes mostly stars that previously have not entered into high-accuracy projects to
determine the proper motions. Our studies are aimed at determining new proper motions of fast stars in the HCRF/UCAC3 system
and searching for stars with invisible companions in the immediate Galactic neighborhoods of the Sun. Having analyzed about
10 000 CCD frames, we have obtained the equatorial coordinates of 414 program stars in the HCRF/UCAC3 system at an accuracy
level of 10–50 mas and determined their new proper motions. To derive the proper motions, we have used the data from several
star catalogs and surveys (M2000, CMC14, 2MASS, SDSS) as early epochs. The epoch differences range from 5 to 13 years (on
average, about 10 years); the mean accuracy of the derived proper motions is 4–5 mas yr−1. For 70 stars, we have revealed significant differences between the derived proper motions and those from the LSPM and I/306A
catalogs (these proper motions characterize the mean motion of the photocenter in 50 years or more). Apart from systematic
errors, these differences can result from the existence of invisible components of the program stars. 相似文献
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利用绝对自行资料,确定了年轻疏散星团NGC 2244天区恒星的运动学成员概率,并对星团成员概率以及自行矢量的分布、不同成员概率恒星的位置分布情况、径向数密度轮廓等进行了讨论并给出了星团的特征尺度;进一步结合已知的星团距离和视向速度资料,计算了NGC 2244的三维空间运动速度,结果表明NGC 2244是一个典型的薄盘族星团。 相似文献
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对著名老年疏散星团M67的成员星进行了两点相关函数分析,讨论了团星的空间分布情况及质量分层现象.结果表明:M67成员星的两点相关函数能很好地用幂律形式来描述,其成员星在空间分布上具有显著的成团性和自相似性.对M67不同光度成员星两点自相关函数的分析表明,亮星相比暗星具有更强的相关强度和更大的相关指数,说明在星团内部出现了明显的空间质量分层现象,亮星比暗星具有更强的成团性和更大的中心聚度.不同光度成员星间两点交叉相关函数的分析进一步表明,不同光度成员星之间并没有表现出绝对的空间质量分层现象,亮星和暗星在空间分布上相互交织、相互渗透. 相似文献
19.
The proper motions and stellar magnitudes for more than 20 000 stars distributed in areas around eight open clusters in the directions of the Sagittarius-Carina and Perseus spiral arms were used to determine the cluster membership. Both spatial-kinematical and statistical criteria were used for member seletion. The luminosity functions of cluster members were constructed and used for the further data improvement. The safest portions of the luminosity function free both from evolved stars and faint field star contamination were used for mass function construction. The composite mass function was derived from the data on five young clusters with log t < 8.2. A dependence of the mass function slope on the adopted input parameters (mass-luminosity relation and distance scale) and on member selection procedure was tested. The slope was found to vary in a range from 1.36 to 1.80 for lg M/M⊙ between 0.3 and 1.2. A possible relation between the individual MF slopes and cluster ages was indicated. The results are in good agreement with published data. 相似文献
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We discuss the determination of membership of 42 open clusters. Our analysis shows that Vasilevskis' mathematical model can be reasonably applied to this case. Our improved version of Sanders' method and our definition of cluster member based on the principles of discriminatory analysis effectively exclude stars of low probabilities. It is important in the study of open cluster to use only those with high probabilities. The effectiveness of the statistical method is closely related to the velocity distributions of the member and field stars. For fields where the error rate is high, it is better to combine other data than proper motion in determining membership. 相似文献