Interstellar extinction toward the ultradeep Galactic field of the Chandra observatory from 2MASS data     

M. G. Revnivtsev  R. A. Burenin  S. Yu. Sazonov 《Astronomy Letters》2009,35(5):305-310

We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l ^II, b ^II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A _V ～ 3.4, near the center of the Chandra field of view and increases to A _V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region.  相似文献   

Analysis of the three-dimensional stellar velocity field using vector spherical functions     

V. V. Vityazev  A. S. Tsvetkov 《Astronomy Letters》2009,35(2):100-113

We apply vector spherical functions to problems of stellar kinematics. Using these functions allows all of the systematic components in the stellar velocity field to be revealed without being attached to a specific physical model. Comparison of the theoretical decomposition coefficients of the equations for a particular kinematical model with observational data can provide precise information about whether the model is compatible with the observations and can reveal systematic components that are not described by this model. The formalism of vector spherical functions is particularly well suited for analyzing the present and future (e.g., GAIA) catalogs containing all three velocity vector components: the propermotions in both coordinates and the radial velocity. We show that there are systematic components in the proper motions of Hipparcos stars that cannot be interpreted in terms of the linear Ogorodnikov-Milne model. The same result is also confirmed by an analysis of the radial velocities for these stars.  相似文献   

射电选和X射线选BL Lacertae天体的射电性质   总被引：1，自引：0，他引：1  

杨富利  李岳黄  杨江河 《天文研究与技术》2008,5(3)

收集了射电选和X射线选BL Lac天体的射电数据(包括核和延展光度), 并计算了它们的核主导系数R.研究显示: 射电选BL Lac(RBLs)天体的总射电光度是X射线选BL Lac(XBLs)天体的2个量级.详细分析得到这种差别主要是来自于核光度的差别因为延展光度差别只有1个量级.研究RBLs和XBLs的核(延展元)光度与核主导系数之间的关系, 发现延展元光度与核主导系数负相关, 而核(总)光度几乎与核主导系数没有相关.  相似文献   

The anisotropy of cosmic ray arrival directions around 10 eV     

N. Hayashida  M. Nagano  D. Nishikawa  H. Ohoka  N. Sakaki  M. Sasaki  M. Takeda  M. Teshima  R. Torii  T. Yamamoto  S. Yoshida  K. Honda  N. Kawasumi  I. Tsushima  N. Inoue  E. Kusano  K. Shinozaki  N. Souma  K. Kadota  F. Kakimoto  K. Kamata  S. Kawaguchi  Y. Kawasaki  H. Kitamura  Y. Matsubara  K. Murakami  Y. Uchihori  H. Yoshii 《Astroparticle Physics》1999,10(4):125-311

Anisotropy in the arrival directions of cosmic rays with energies above 10¹⁷ eV is studied using data from the Akeno 20 km² array and the Akeno Giant Air Shower Array (AGASA), using a total of about 114 000 showers observed over 11 years. In the first harmonic analysis, we have found a strong anisotropy of 4% around 10¹⁸ eV, corresponding to a chance probability of 0.2% after taking the number of independent trials into account. with two-dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region.  相似文献   

Advances in the Research of Impact of Decadal Solar Cycle on Modern Climate     

Xiao Ziniu  Zhong Qi  Yin Zhiqiang  Zhou Limin  Song Yan  Han Yanben  Huang Cong  Pan Jing  Zhao Liang 《地球科学进展》2013,28(12):1335-1348

Role of solar activity on modern climate change, particularly in the decadal scale is an important scientific issue. This paper reviews the recent observation of decadal solar signal in earth’s climate, with focus on the mechanism of solar radiation, ultraviolet radiation and cosmic rays on climate system ,and its validation. The paper points out that the assessment of uncertainty in observations, amplification process of the climate system, as well as possible future impact of solar extreme events are challenges in the present study. Finally, the keys of breakthrough are pointed, to provide a reference for future research.  相似文献   

Solving the G-dwarf problem with a three-component model of the chemical evolution of the Galaxy     

Li Tian-chao  Zhao Gang  Luo Shao-guang   《Chinese Astronomy and Astrophysics》2000,24(4):453-461

A three-component chemical evolution model of the Galaxy is presented, which we believe will cast a new light on the G-dwarf problem. The model is based on a scenario of the Galaxy consisting of three major evolutionary phases: halo, thick disk and thin disk, separated by two short interludes of rapid collapse. The evolution of different stellar populations are treated separately, the combination of which yields an overall metallicity distribution function for the solar neighbourhood. We tested three different models using the same set of basic equations: the “prompt initial enrichment” (PIE) model, the “proportional yield” (PPY) model and the “collapse” (CLP) model. Best-fit parameters are derived. The results show that the different populations have remarkably different IMFs, while mass exchange has only minimally affected the chemical evolution in the solar vicinity, so that the solar vicinity can be regarded as a closed system, at least in the late stage of the Galactic evolution.  相似文献   

逆康普顿散射对中等银纬区银河弥漫γ射线的贡献     

张力 《中国天文和天体物理学报》1995,(4)

使用最近期的ＧＲＯ库中ＥＧＲＥＴ的γ射线数据，研究了逆康普顿散射对中等银纬区银河弥漫γ射线的贡献。采用了两种分析方法：其一为本文的新分析方法，其中银河宇宙与星际气体相互作用的γ射线的发射率ｑ／４π由γ射线数据本身确定；其二为通常的分析方法，即ｑ／４π由使用了局部银河宇宙线强度的观测值的理论估计给出。通过分析，我们获得了两种方法中逆康普顿散射的贡献与能量的依赖关系。结果表明，逆康普顿散射的贡献是大的。  相似文献   

Rotation velocity and neutral hydrogen distribution dependency on magnetic field strength in spiral galaxies     

Charles M. Snell  Anthony L. Peratt 《Astrophysics and Space Science》1995,227(1-2):167-173

The rotation velocity of a simulated plasma galaxy is compared to the rotation curves of Sc type spiral galaxies. Both show flat rotation curves with velocities of the order of several hundred kilometers per second, modified by E × B instabilities. Maps of the strength and distribution of galactic magnetic fields and neutral hydrogen regions, as-well-as as predictions by particle-in-cell simulations run in the late 1970s, are compared to Effelsberg observations.Agreement between simulation and observation is best when the simulation galaxy masses are identical to the observational masses of spiral galaxies. No dark matter is needed.  相似文献   

Magnetic field structure in differentially rotating discs     

K. J. Donner  A. Brandenburg 《地球物理与天体物理流体动力学》2013,107(1-3):121-129

Abstract

In order to gain a better understanding of the processes that may give rise to non-axisymmetric magnetic fields in galaxies, we have calculated field decay rates for models with a realistic galactic rotation curve and including the effects of a locally enhanced turbulent magnetic diffusivity within the disc. In all cases we have studied, the differential rotation increases the decay rate of non-axisymmetric modes, whereas axisymmetric ones are unaffected. A stronger magnetic diffusivity inside the disc does not lead to a significant preference for non-axisymmetric modes. Although Elsasser's antidynamo theorem has not yet been proved for the present case of a non-spherical distribution of the magnetic diffusivity, we do not find any evidence for the theorem not to be valid in general.  相似文献   

Mass Human Migration and the Urban Heat Island during the Chinese New Year Holiday: A Case Study in Harbin City,Northeast China          下载免费PDF全文

WU Ling-Yun  ZHANG Jing-Yong  SHI Chun-Xiang 《大气和海洋科学快报》2015,8(2)

Many Chinese people leave big cities for family reunions during the Chinese New Year(CNY), which is the most important public holiday in China. However, how modern mass human migration during the CNY holiday affects the urban heat island(UHI) is still unknown. Here, the authors investigate the role of modern human migration for the UHI effects during the CNY holiday for the period of 1992–2006 in Harbin City, Northeast China. The results show that during the CNY week, the UHI effects expressed as daily mean, maximum, and minimum temperature differences between urban and rural stations averaged over the period of 1992–2006 are 0.65°C(43%), 0.31°C(48%), and 1.14°C(71%) lower than during the background period(four weeks before and four weeks after the CNY week), respectively. Our findings identify previously unknown impacts of modern mass human migration on the UHI effects based on a case study in Harbin City.  相似文献