共查询到20条相似文献,搜索用时 15 毫秒
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依巴谷星表给出了223颗经典造父变星的天体测量和光度观测资料。根据近年来的光谱和光度观测成果,从不同渠道收集了有关视向速度和光度等资料。基于Feast和Catchpole建立的PL关系,给出造父变星的距离估计。 相似文献
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通过主要在短厘米波长的全球VLBI观测,已经发现强射电类星体4C39.25在十秒差距尺度结构中的视超光速运动,其运动学图景表明该源是一个很特殊的视超光速源.近几年已提出了若干模型,试图解释这特殊的运动图景.报道不多的百秒差距尺度的VLBI观测,很可能有助于检验提出的模型.本文介绍用欧洲网及上海25m天线,在18cm波长对4C39.25所作的VLBI 成象观测的初步结果,显示百秒差距尺度复杂结构及可能存在的视超光速运动. 相似文献
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宇宙大尺度结构的形成与星系形成密切相关,前者的研究把星系基本上视为一质点,而星系形成研究涉及到其内部结构,宇宙大尺度结构形成有两种模式,由小到大与由大到小,这两种模式被交替使用(当然不同简单的重复)很重要的一个原因是星系形成研究的推动。 相似文献
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First-ascent red giants with strong and very strong Li lines have just been discovered in globular clusters. Using the stellar internal prompt (7)Li enrichment-mass-loss scenario, we explore the possibility of (7)Li enrichment in the interstellar matter of the globular cluster M3 produced by these Li-rich giants. We found that enrichment as large as 70% or more compared to the initial (7)Li content of M3 can be obtained during the entire life of this cluster. However, because M3 will cross into the Galactic plane several times, the new (7)Li will be very probably removed by ram pressure into the disk. Globular clusters appear then as possible new sources of (7)Li in the Galactic disk. It is also suggested that the known Na/Al variations in stars of globular clusters could be somehow related to the (7)Li variations and that the cool bottom process mixing mechanism acting in the case of (7)Li could also play a role in the case of Na and Al surface enrichments. 相似文献
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D. F. Lupishko 《Solar System Research》2018,52(2):98-114
Six different calibrations of the polarimetric albedo scale of asteroids have been published so far. Each of them contains its particular random and systematic errors and yields its values of geometric albedo. On the one hand, this complicates their analysis and comparison; on the other hand, it becomes more and more difficult to decide which of the proposed calibrations should be used. Moreover, in recent years, new databases on the albedo of asteroids obtained from the radiometric surveys of the sky with the orbital space facilities (the InfraRed Astronomical Satellite (IRAS), the Japanese astronomical satellite AKARI (which means “light”), the Wide-field Infrared Survey Explorer (WISE), and the Near-Earth Object Wide-field Survey Explorer (NEOWISE)) have appeared; and the database on the diameters and albedos of asteroids obtained from their occultations of stars has substantially increased. Here, we critically review the currently available calibrations and propose a new generalized calibration derived from the interrelations between the slope h and the albedo and between Pmin and the albedo. This calibration is based on all of the available series of the asteroid albedos and the most complete data on the polarization parameters of asteroids. The generalized calibration yields the values of the polarimetric albedo of asteroids in the system unified with the radiometric albedos and the albedos obtained from occultations of stars by asteroids. This, in turn, removes the difficulties in their comparison, joint analysis, etc. 相似文献
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通过分析由五个笔形天区的完备红移巡天和九个1/3采样红移巡天得到的样本,研究了星系分布中的大尺度结构。用一种改进过的方法计算了该分布的分维。结果表明星系分布确实具有3—4.5h~(-1)Mpc的典型尺度,这与Shanks等的结果一致。 相似文献
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在对不同光度星系大尺度分布进行空间两点相关函数分析的基础上,仍以CfA红移巡天资料为样本,对不同光度星系分布进行了交叉相关分析。结果表明,不同光度星系间的交叉相关函数仍可近似地以幂函数表示,说明不同光度星系在空间是一起成团的。但在较小尺度上((?)4—6Mpc),光度较高的星系间相关更强,而在更大一些尺度上光度较高的星系间相关减弱更快,甚至变得比与光度较低星系间的相关更弱。结合前面对自相关函数分析的结果可以看到,统计上看来,星系分布形成群和团。群或团中亮的星系形成更致密的分布而较暗的星系则在这些群和团中分布较弥散。此结果表明星系光度和其环境(密度)有关,从而从观测上为Biased星系形成理论提供了一个可能的证据。 相似文献
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J. L. Parish 《Planetary and Space Science》1984,32(12):1531-1532
We discuss the parameter D in the Goertz et al. (1979) magnetic field model as it relates to the scale height of the current sheet. 相似文献
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D. K. Ojha 《Journal of Astrophysics and Astronomy》2000,21(1-2):53-59
This paper presents an analysis of the first 2MASS (The Two Micron All Sky Survey) sampler data as observed at lower Galactic
latitude in our Galaxy. These new near-infrared data provide insight into the structure of the thin disk of our Galaxy, The
interpretation of star counts and color distributions of stars in the near-infrared with the synthetic stellar population
model, gives strong evidence that the Galactic thin disk density scale length,h
R
, is rather short (2.7 ± 0.1 kpc). 相似文献
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自1990年6月北京天文台太阳射电偏振仪投入实测以来,观测到一百多个“Spike”和短时标精细结构微波幅射,其中包括一些新的微波幅射特征。本文给出了主要的四点特征:(1)窄带辐射;(2)快速偏振逆转;(3)快速频率漂移;(4)不同时标的准周期振荡。 相似文献
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R. F. Pizzo 《Journal of Astrophysics and Astronomy》2011,32(4):567-576
Polarized radio emission is detected at various scales in the Universe. In this document, I will briefly review our knowledge
on polarized radio sources in galaxy clusters and at their outskirts, emphasizing the crucial information provided by the
polarized signal on the origin and evolution of such sources. Successively, I will focus on Abell 2255, which is known in
the literature as the first cluster for which filamentary polarized emission associated with the radio halo has been detected.
By using RM synthesis on our multi-wavelength WSRT observations, we studied the 3-dimensional geometry of the cluster, unveiling
the nature of the polarized filaments at the borders of the central radio halo. Our analysis points out that these structures
are relics lying at large distance from the cluster center. 相似文献
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The local expansion field (v
220 <1200 km s-1) and the cosmic expansion field out to 30 000 km s-1 are characterized by H
0 = 58 [km s-1 Mpc-1]. While the random error of this determination is small (± 2 units), it may still be affected by systematic errors as large
as ±10%>. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample of field
galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNe Ia. The main source
of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence
on metallicity. GAIA will essentially eliminate these systematic error sources. Another source of systematic error is due
to the homogenization of SNe Ia as to decline rate Δm
15 and color (B-V). GAIA will discover most of the 1100 SNe Ia within 10 000 km s-1, which will occur during its four-year lifetime. If their photometric parameters can be determined from the ground, they
will fix the dependence of the SNe Ia luminosity on Δ m
15 and (B-V) with high accuracy. At the same time they will yield exquisite distances to an equal number of field galaxies. – GAIA will
also revolutionize the very local distance scale by determining fundamental distances of the companion galaxies of the Milky
Way and even of some spirals in- and possibly outside the Local Group from their rotation curves seen in radial velocities
and proper motions. Moreover, GAIA will obtain trigonometric parallaxes of RR Lyrae stars, of red giants defining the TRGB,
of stars on the ZAMS, of White Dwarf defining their cooling sequence, and of globular clusters, and determine the metallicity
dependence of these distance indicators. It will thus establish a self-controlling network of distance indicators within the
Local Group and beyond.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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E. M. L. Humphreys A. L. Argon L. J. Greenhill M. J. Reid J. M. Moran 《Astrophysics and Space Science》2005,295(1-2):285-289
Water megamasers have been found to trace parsec/sub-parsec, circumnuclear accretion disks in several AGN (e.g., Circinus, NGC 1068 & NGC 4258). High-spatial (0.5 mas) and velocity resolution (0.2 km s–1) VLBA imaging of the disks reveals thin, warped pannekoeken (pancake)-style structures as opposed to thick tori in the inner regions of the central engines (40 000 Rsch). In this contribution, I will describe some current investigations into the dynamical and physical attributes of the water maser disk in NGC 4258, as revealed by VLBA, VLA and Effelsberg monitoring over 8 years. 相似文献
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We have studied the simultaneous and separate solutions of the basic kinematic equations obtained using the stellar velocities calculated on the basis of data from the Gaia TGAS and RAVE5 catalogues. By comparing the values of Ω'0 found by separately analyzing only the line-of-sight velocities of stars and only their proper motions, we have determined the distance scale correction factor p to be close to unity, 0.97 ± 0.04. Based on the proper motions of stars from the Gaia TGAS catalogue with relative trigonometric parallax errors less than 10% (they are at a mean distance of 226 pc), we have found the components of the group velocity vector for the sample stars relative to the Sun (U, V,W)⊙ = (9.28, 20.35, 7.36) ± (0.05, 0.07, 0.05) km s?1, the angular velocity of Galactic rotation Ω0 = 27.24 ± 0.30 km s?1 kpc?1, and its first derivative Ω'0 = ?3.77 ± 0.06 km s?1 kpc?2; here, the circular rotation velocity of the Sun around the Galactic center is V0 = 218 ± 6 km s?1 kpc (for the adopted distance R0 = 8.0 ± 0.2 kpc), while the Oort constants are A = 15.07 ± 0.25 km s?1 kpc?1 and B = ?12.17 ± 0.39 km s?1 kpc?1, p = 0.98 ± 0.08. The kinematics of Gaia TGAS stars with parallax errors more than 10% has been studied by invoking the distances from a paper by Astraatmadja and Bailer-Jones that were corrected for the Lutz–Kelker bias. We show that the second derivative of the angular velocity of Galactic rotation Ω'0 = 0.864 ± 0.021 km s?1 kpc?3 is well determined from stars at a mean distance of 537 pc. On the whole, we have found that the distances of stars from the Gaia TGAS catalogue calculated using their trigonometric parallaxes do not require any additional correction factor. 相似文献
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Corrections are given which transform the Tables of the solar radiation data (Labs and Neckel, 1968) into the International Practical Temperature Scale of 1968. Additionally, for the adjustment of the data of the true continuum and the corresponding line blanketing as well, the veiled line effect mentioned first by Carbon et al. (1968), but studied in more detail by Holweger (1970a), has been considered also.The corresponding corrections of the solar irradiance result in an improved value of the spectrophotometric solar constant: S = 1.947 cal cm-2 min-1 or 0.1358 W cm-2. Two Tables presenting the highest (window-) intensities and the corrected irradiance data have been added. 相似文献
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C. Sivaram 《Astrophysics and Space Science》1993,207(2):317-324
The notion of discrete scale transformations is invoked to suggest strong links between fundamental interactions and cosmology giving rise to a hierarchy of cosmic scales. 相似文献