一种研究空间谱指数变化的新方法

本文介绍了一种用于射电天文学谱指数研究的新方法－双色微分图解法，在进行谱指数分析所使用的多频图中，一般存在有不同的背景分量及大尺度缓变分量，使用本文介绍的新万法得到的结果不受这两种成分的影响，这种新方法还可用于热及非热射电辐射分离，本文还给出了应用实例，首次精确计算了SNRG78．2＋2．1的多频空间谱指数分布。     

晚型星红外谱拟合的线性化方法

本文针对晚型星红外辐射的一些模型，讨论相应的拟合方法。对有拱星壳层的晚型星的双黑体模型，给出了具体的拟合方法──线性化方法。最后我们就拟合结果及拟合程序编制方面讨论了线性化方法的优缺点。     

差分像运动视宁度测量实验

本文首先阐明了Fried参数(大气相干长度)r_0的物理含义及为什么选取r_0作为表征大气视宁度的参数;然后介绍了一种优良的测量r_0的方法—差分像运动(differential image motion)法,总结了该方法的六个特点,最后给出了在云南天文台用该方法两次实测大气视宁度的实验结果及实验参数,并对结果进行了分析。     

A typical example of the application of the `Multi-Cloud Model'method to the asymmetric profiles processing

Multi-Cloud Model(MCM) is an effective method for dealing with asymmetric profiles of spectral line formed by active objects on the sun. A typical example is given for the application of the MCM method in this paper. The H _β spectral data of a large post-flare loop (PFL) system which occurred on the solar western limb are obtained with MW-SSHG at the Yunnan Observatory and analysed based on the MCM method. The line-of-sight velocity fields observed in different times are derived and discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Period search using the DMRT method: The properties of the test function

The test function for the method proposed by DUMONT, MORGULEFF, RUTILY, and TERZAN (1978) is investigated analytically and numerically for some examples with constant and variable periods. The properties of the test function of the DMRT method are discussed in comparison with that of the leastsquare method.     

低信噪比下短波授时信号的去噪方法研究

提出一种基于经验模态分解与改进型谱减法相结合的低信噪比短波时号语音增强方法,解决在复杂噪声环境下短波时号无法用于定时的问题.该方法的核心思想是利用希尔伯特-黄变换(HHT)算法对带噪短波时号进行经验模态分解,通过最大相关度筛选出含有短波时号的固有模态分量进行重构,再对重构之后的信号进行谱减,从而达到降噪的目的.实验表明:该方法的降噪效果优于传统方法.     

Research on the Method of De-noising the Short-wave Time Signal at Low SNR

A voice enhancement algorithm based on the Empirical Mode Decomposition (EMD) and the improved spectral subtraction is proposed for the low-SNR (Signal Noise Ratio) shortwave time signal. This method is proposed to solve the problem that the shortwave time signal cannot be used for timing in complex noisy environments. The core idea of this method is to use the Hilbert-Huang Transform (HHT) algorithm to make the empirical mode decomposition on the noisy shortwave signal, and to select the intrinsic mode functions containing the shortwave signal information for the signal reconstruction by through the maximum correlation. Then, to make the spectral subtraction on the reconstructed signal to achieve the purpose of noise reduction. The experimental result shows that this method has a better noise reduction than the traditional methods.     

On the possibility of the guidance of small asteroids to dangerous celestial bodies using the gravity-assist maneuver

In this paper, the method of changing the trajectories of hazardous asteroids with orbits known for some years to be on a possible collision course with the Earth is considered. The method relies on the use of small asteroids (asteroid-projectiles) directed at hazardous celestial bodies by giving the projectile a sufficiently small velocity impulse ensuring the Earth gravity assist. As a result, the asteroid-projectile vector can be controllably changed over a wide range. Apophis is considered as an example of the target asteroid. The technical feasibility of this method is discussed. It is noted that despite the potential use of this elegant method, its practical implementation requires further research and development.     

A robust determination of halo environment in the cosmic field

A number of methods for studying the large-scale cosmic matter distribution exist in the literature. One particularly common method employed to define the cosmic web is to examine the density, velocity or potential field. Such methods are advantageous since a Hessian matrix can be constructed whose eigenvectors (and eigenvalues) indicate the principal directions (and strength) of local collapse or expansion. Technically this is achieved by diagonalizing the Hessian matrix using a fixed finite grid. The resultant large-scale structure quantification is thus inherently limited by the grid’s finite resolution. Here, we overcome the obstacle of finite grid resolution by introducing a new method to determine halo environment using an adaptive interpolation which is more robust to resolution than the typical “Nearest Grid Point” (NGP) method. Essentially instead of computing and diagonalizing the Hessian matrix once for the entire grid, we suggest doing so once for each halo or galaxy in question. We examine how the eigenvalues and eigenvector direction’s computed using our algorithm and the NGP method converge for different grid resolutions, finding that our new method is convergent faster. Namely changes of resolution have a much smaller effect than in the NGP method. We therefore suggest this method for future use by the community.     

Determination of the parabolic orbit for a body moving in the plane of the ecliptic,by the Laplace method

A modification of the Laplace method for the determination of a preliminary orbit of a body moving in the plane of the ecliptic is presented. It is shown that on the basis of three close positions on the celestial sphere, the parabolic orbit can be determined in cases, when the classical Laplace method is not suitable. The numerical estimation of the number of possible solutions is carried out, and their spatial distribution depending on initial conditions is shown. An example of the determination of an orbit for the comet C/2007 N3 (Lulin) is given.     

Improved Determination of the Location of the Temperature Maximum in the Corona

The most used method to calculate the coronal electron temperature [\(T_{\mathrm{e}} (r)\)] from a coronal density distribution [\(n_{\mathrm{e}} (r)\)] is the scale-height method (SHM). We introduce a novel method that is a generalization of a method introduced by Alfvén (Ark. Mat. Astron. Fys. 27, 1, 1941) to calculate \(T_{\mathrm{e}}(r)\) for a corona in hydrostatic equilibrium: the “HST” method. All of the methods discussed here require given electron-density distributions [\(n_{\mathrm{e}} (r)\)] which can be derived from white-light (WL) eclipse observations. The new “DYN” method determines the unique solution of \(T_{\mathrm{e}}(r)\) for which \(T_{\mathrm{e}}(r \rightarrow \infty) \rightarrow 0\) when the solar corona expands radially as realized in hydrodynamical solar-wind models. The applications of the SHM method and DYN method give comparable distributions for \(T_{\mathrm{e}}(r)\). Both have a maximum [\(T_{\max}\)] whose value ranges between 1?–?3 MK. However, the peak of temperature is located at a different altitude in both cases. Close to the Sun where the expansion velocity is subsonic (\(r < 1.3\,\mathrm{R}_{\odot}\)) the DYN method gives the same results as the HST method. The effects of the other free parameters on the DYN temperature distribution are presented in the last part of this study. Our DYN method is a new tool to evaluate the range of altitudes where the heating rate is maximum in the solar corona when the electron-density distribution is obtained from WL coronal observations.     

An improved algorithm due to laguerre for the solution of Kepler's equation

A root-finding method due to Laguerre (1834–1886) is applied to the solution of the Kepler problem. The speed of convergence of this method is compared with that of Newton's method and several higher-order Newton methods for the problem formulated in both conventional and universal variables and for both elliptic and hyperbolic orbits. In many thousands of trials the Laguerre method never failed to converge to the correct solution, even from exceptionally poor starting approximations. The non-local robustness and speed of convergence of the Laguerre method should make it the preferred method for the solution of Kepler's equation.     

A Test of the Active-Day Fraction Method of Sunspot Group Number Calibration: Dependence on the Level of Solar Activity

The method of active-day fraction (ADF) was proposed recently to calibrate different solar observers to standard observational conditions. The result of the calibration may depend on the overall level of solar activity during the observational period. This dependency is studied quantitatively using data of the Royal Greenwich Observatory by formally calibrating synthetic pseudo-observers to the full reference dataset. It is shown that the sunspot group number is precisely estimated by the ADF method for periods of moderate activity, may be slightly underestimated by 0.5?–?1.5 groups (\({\leq}\,10\%\)) for strong and very strong activity, and is strongly overestimated by up to 2.5 groups (\({\leq}\,30\%\)) for weak-to-moderate activity. The ADF method becomes inapplicable for the periods of grand minima of activity. In general, the ADF method tends to overestimate the overall level of activity and to reduce the long-term trends.     

New technique to compute the geometrical elements of the eclipsing of W UMa-type

The aim of this paper is to present a general method for computation of the geometrical elements of totally eclipsing W UMa (close, or in actual contact) binary systems in the frequency-domain.This method has been done using a new technique (two minima with the improved values of the photometric perturbation effects). The results are compared with the results calculated by different methods, that have used the same observation references.The improved photometric perturbation terms have been discussed and its effects are computed for both (primary and secondary) minima.     

The Skewness of a Solar Cycle as a Precursor of the Amplitude of the Next

As a precursor for predicting the maximum amplitude of the coming solar cycle, the skewness of the previous cycle proposed by Ramaswamy (1977) is revisited. The reliability of the prediction method is improved by separating odd and even cycles. A first method is proposed on the basis of calculated skewness. In that case, the prediction is available at the end of the previous cycle. A possibility to anticipate the availability of the skewness by about one year is pointed out. A second method, adding prediction of the skewness itself is studied. The statistical reliability is lower than in the first case, but the prediction of a cycle maximum is available at the maximum of the previous cycle.     

星周尘埃壳层的消光值

本文首次提出了从观测得到的具有星周尘埃壳层的恒星的能谱分布求取星周尘埃云的消光,并由此可通过改正星周消光改正后的星际消光法求得恒星距离的方法。     

Smoothing supernova data to reconstruct the expansion history of the Universe and its age

We propose a non-parametric method of smoothing supernova data over redshift using a Gaussian kernel in order to reconstruct important cosmological quantities including   H ( z )  and   w ( z )  in a model-independent manner. This method is shown to be successful in discriminating between different models of dark energy when the quality of data is commensurate with that expected from the future Supernova Acceleration Probe ( SNAP ). We find that the Hubble parameter is especially well determined and useful for this purpose. The look-back time of the Universe may also be determined to a very high degree of accuracy (≲0.2 per cent) using this method. By refining the method, it is also possible to obtain reasonable bounds on the equation of state of dark energy. We explore a new diagnostic of dark energy – the ' w -probe'– which can be calculated from the first derivative of the data. We find that this diagnostic is reconstructed extremely accurately for different reconstruction methods even if Ω_{0 m} is marginalized over. The w -probe can be used to successfully distinguish between Λ cold dark matter and other models of dark energy to a high degree of accuracy.     

平场数据采集间隔对莱曼阿尔法太阳望远镜平场精度的影响分析

莱曼阿尔法太阳望远镜(LST)是先进天基太阳天文台(ASO-S)卫星的载荷之一,它包括白光太阳望远镜(WST),全日面太阳成像仪(SDI)和日冕仪(SCI)等仪器. 1991年Kuhn, Lin和Loranz提出的方法(简称KLL方法)是WST和SDI在轨平场定标的方法之一.为了研究WST和SDI的平场定标精度对KLL方法的相邻位置时间间隔的敏感性,使用太阳动力学观测卫星(SDO)的日震和磁成像仪(HMI)及太阳大气成像仪(AIA)的全日面成像观测数据测试和分析在使用KLL方法时相邻位置时间间隔对所得平场精度的影响.结果显示在LST使用KLL方法进行平场定标时,相邻位置时间间隔越短越好.具体分析表明,WST平场精度对相邻位置采样时间间隔不敏感,而SDI时间间隔需要在240 s范围内.分析结果对卫星姿态调整到稳定所需的时间给出了一定限制.     

Determination of the linear mass power spectrum from the mass function of galaxy clusters

We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation  σ( M )  using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum  Δ²( k )  from  σ( M )  namely the   k _eff  approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the τCDM and ΛCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k . This estimate is comparable to, or even better behaved than, the FKP solution.
The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution.     

Investigation of flare stars in the pleiades by the method of stellar tracks. I

Observations of the Pleiades cluster by the method of stellar tracks, carried out on the 40-inch Schmidt telescope of Byurakan Astrophysical Observatory, have resulted in the detection of 49 flares from 38 stars, 17 of which were not previously known to be flare stars. It is shown that for bright stars (U ≤ 16.0) the detection of flares in observations by the method of stellar tracks is at least three times more efficient than for observations by the method of stellar chains. Another advantage of the first method is that one can detect brief flares that last less than 6 min. The visual stellar magnitude at the minimum for the brightest of the flare stars that we found is 11.92. This raised the upper luminosity limit of known flare stars in the Pleiades by 0.21 magnitude. A comparison of the expected number of bright flare stars in the Pleiades with the number of all bright members of the cluster (falling in the range from V ≈ 12.0 toV ≈16.0) suggested that all these stars evidently must be flare stars. Translated from Astrofizika, Vol. 42, No. 3, pp. 351–358, July–September, 1999.