The influence of the surroundings on the morphology of galaxies

The characteristics of galaxies within galaxy groups are investigated as a function of the surroundings. It is shown that the relative number of the galaxies with different morphological type is correlated with the number of members within the group, but the fraction of E+S0 galaxies does not depend on the mean-pairwise distance between the galaxies, the density of the luminous matter as well as the velocity dispersion in the group.     

射电脉冲星观测资料及其启示

在本文中先简要介绍了８０年代以来射电脉冲星方面的观测进展，然后详细介绍了射电脉冲星的第一手观测资料，包括空间分布，传播特性，时间特性，脉冲轮廓与偏振以及频谱特性等，并详细综述观测资料对我们提供的信息及给我们的启示，为理论模型的建立和检验提供了基础。     

The time-scale for core collapse in spherical star clusters

The collapse time for a cluster of equal-mass stars is usually stated to be either 330 central relaxation times (t_rc) or 12-19 half-mass relaxation times (t_rh). But the first of these times applies only to the late stage of core collapse, and the second only to low-concentration clusters. To clarify how the time depends on the density profile, the Fokker-Planck equation is solved for the evolution of a variety of isotropic cluster models, including King models, models with power-law density cusps of ρ ∼ r^−γ, and models with nuclei. The collapse times for King models vary considerably with the cluster concentration when expressed in units of t_rc or t_rh, but vary much less when expressed in units of t_rc divided by a dimensionless measure of the temperature gradient in the core. Models with cusps have larger temperature gradients and evolve faster than King models, but not all of them collapse: those with 0 < γ < 2 expand because they start with a temperature inversion. Models with nuclei collapse or expand as the nuclei would in isolation if their central relaxation times are short; otherwise their evolution is more complicated. Suggestions are made for how the results can be applied to globular clusters, galaxies, and clusters of dark objects in the centers of galaxies.Scott D. Tremaine     

关于"太阳线性无力场评注和快速傅氏分析法的应用"的评论

“太阳线性无力场评注和快速傅氏分析法的应用”一文对太阳线性无力场的工作做了一些评注,在此基础上对快速傅立叶方法的应用提出了改进的计算方法．该文的某些观点值得商榷,有必要对其中存在的问题予以澄清．另外,对该文关于快速傅氏分析法的工作从理论的角度提出看法．     

On the Period Variation of the W UMa-type Contact Binary V502 Ophiuchi

The variation in the orbital period of the W UMa type contact binary V502 Oph is analyzed. The orbital period exhibits a wavelike variation with a periodicity of 23.0 years and an amplitude of △P = 1.24×10~(-6) days superimposed on secular decrease of dP/dt = 1.68×10-7 day per year. The long-term decrease may be accompanied by the contraction of the secondary at a rate of 83 m per year and a mass transfer rate from the primary to the secondary of 4.28×10~8 M per year. The short-term oscillation may be explained by the presence of a third component. Orbital elements of the third body and its possible mass are presented.     

Comparison between Windowed FFT and Hilbert-Huang Transform for Analyzing Time Series with Poissonian Fluctuations: A Case Study

Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated light curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which are typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.     

Tail Emission from a Ring-like Jet: Its Application to Shallow Decays of Early Afterglows and GRB 050709

Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the processing magnetic axis. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with a temporal index of -1/2 if the Lorentz factor of the ejecta is not very high, which is consistent with the shallow decay phase of some early X-ray afterglow detected by Swift. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation for the re-brightening and sharp decay of the X-ray afterglow of GRB 050709.     

Automatic Normalization and Equivalent-Width Measurement of High-Resolution Stellar Spectra

It is well known that normalization, radial velocity correction and equivalent-width measurement of high-resolution stellar spectra are time-consuming work. In order to improve the efficiency we present an automatic method for these routines. The continuum is determined by fitting the 'high points' in the spectrum. After continuum normalization, the program automatically searches for the position of the Ha line and obtains a rough radial velocity, then computes an accurate radial velocity by cross-correlation between the given spectrum and the solar spectrum. In this method, the equivalent-width is automatically measured using Gaussian fitting. A comparison between our results and those from traditional analysis shows that the typical error for equivalent width is around 3.8% in our method. Developing such automatic routines does not mean to replace the interactive reduction method: it is just for a quick extraction of information from the spectra, especially those obtained in large sky surveys.     

修正的Neupert效应

Neupert效应的定性描述是耀斑中脉冲分量(硬X射线、微波暴)与渐变分量(软X射线发射)之间存在的因果关系,即耀斑最初的能量是以加速粒子的形式释放,加速的电子在大气传输过程中产生非热硬X射线轫致辐射,并加热大气,耀斑软X射线发射是高能粒子注入大气的响应.根据经典Neupert效应的定量描述,硬X射线发射(表征非热电子注入)结束时软X射线应该立刻达到极大,但以往的观测发现一些耀斑软X射线峰值时间(t2)明显晚于硬X射线结束时间(t1)(τ=t2–t1,τ 0),热与非热辐射之间存在明显的偏离经典Neupert效应的情况.为了研究偏离经典Neupert效应的事件,在2002—2015年间的RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager)和GOES (Geostationary Operational Environmental Satellites)耀斑列表中,按照在25–50 keV范围内光变较简单、软X射线有对应发射峰等判据,共选择276个耀斑样本,统计了这些耀斑的τ分布、环长d (用双足点源之间的距离来表征)与τ的关系.结果显示:(1)有227个耀斑τ 0,即有约82%的耀斑偏离经典Neupert效应;(2)τ与d之间存在一定的线性相关,即环越长,软X射线极大的时间越延后;(3)似乎存在一个临界距离,当环长小于临界距离时,经典Neupert效应成立.这些结果印证了修正Neupert效应的必要性,并对其物理意义进行了讨论.