8~10m级光学／红外望远镜的高分辨率光谱仪

介绍并比较了KeckSubaruVLTHET及Gemini中的5架8～10m天文望远镜的高分辨率光谱仪,分析这些仪器与2～4m级望远镜的阶梯光栅光谱仪或Coude光谱仪相比所采用的新设计思想和新技术.     

Monte Carlo Simulations of Comet Capture from the Oort Cloud

There is a very large number of small bodies in the Solar System and their orbits are varied and complicated. Some types of orbits and events are so rare that they occur in numerical simulations only when millions or billions of orbits have been calculated. In order to study these orbits or events an efficient Monte Carlo simulation is useful. Here we describe a new Monte Carlo simulation method and test it against some existing simulations of orbits of small bodies which have been obtained by different methods. We find good agreement with many earlier calculations, and study briefly the possibility of the Oort Cloud capture origin of short period comets. This revised version was published online in July 2006 with corrections to the Cover Date.     

Orbital evolution of Jupiter’s new outer satellites

Data on recently discovered outer satellites of Jupiter are used to analyze their long-period orbital evolution. We determine the extreme eccentricities and inclinations, as well as the circulation periods of the pericenter arguments and of the longitudes of the ascending nodes. The satellite orbital elements are plotted against time. The methods of analysis are identical to those that we used to analyze the orbital evolution of Uranus’s and Saturn’s new outer satellites.     

Behaviour of a new type of Runge–Kutta methods when integrating satellite orbits

Recently, González, Martín and Farto have developed new numerical methods (RKGM methods) of Runge–Kutta type and fixed step size for the numerical integration of perturbed oscillators. Moreover, it seems natural to study the behaviour of these new methods for the accurate integration of orbital problems after the application of linearizing transformation, such us KS or BF due to the fact that in these variables, the structure of the problem is of the form of perturbed oscillators, for which the methods constructed are indicated. In this paper, we check the efficiency of these new methods when integrating the satellite problem. The RKGM methods show a very good behaviour when they compete with other, classical and special, methods. This revised version was published online in July 2006 with corrections to the Cover Date.     

An archetype hydrogen atmosphere problem

Populations for the first three bound states and the continuum of hydrogen are determined for an isothermal, hydrostatic atmosphere at 20 000 K. The atmosphere is treated as being optically thin in the Balmer and Paschen continua and illuminated by continuum radiation at these wavelengths with prescribed radiation temperatures. The atmosphere is optically thick in the 2-1, 3-1, 3-2 and c-1 transitions. Three stages of approximation are treated:

1. radiative detailed balance in the 2-1, 3-1 and 3-2 transitions,
2. radiative detailed balance in the 3-1 and 3-2 transitions, and
3. all transitions out of detailed balance.

The solution of this problem is non-trivial, and presents sufficient difficulty to have caused failure of at least one rather standard technique. The problem is thus a good archetype against which new methods, or new implementations of old methods may be tested.     

SIMULATION OF SEEING INFLUENCES ON THE PHOTOMETRIC DETERMINATION OF SUNSPOT AREAS

Various methods for measuring areas of sunspots and umbrae are compared to test their robustness against changing seeing conditions. The influence of the seeing is simulated by artificially degrading high-resolution sunspot images. A new procedure – the so-called inflexion point method – for area determinations is described. It is based on the calculation of the inflexion point contours of the two-dimensional sunspot intensity distribution. The areas derived with this method are much more stable against seeing influences than those obtained by the other procedures tested. The effect of the seeing on the measurements of the bolometric sunspot contrast and irradiance deficit produced by a sunspot is also studied.     

New methods and selection methods

As the topics of study of Lyα emitters evolve, new selection methods are being developed to find these high redshift galaxies. In this proceedings, three new methods are presented, based on large integral field unit spectrographs, ultradeep slit spectroscopy and serendipitous discoveries.     

基于系列斑点图像的视宁度估算精度方法研究

半高宽法和像运动法是估算大气视宁度的常用方法,两种方法的估算精度都受到望远镜跟踪误差、风或者机械振动等因素的影响,提高视宁度估算精度在高分辨成像、选址、台站视宁度监测等方面有重要意义.对于半高宽法,用二维高斯函数拟合长曝光点源单星星像并选取合适方向的半高宽估算视宁度,可以有效改善跟踪误差、风或者机械振动等因素的影响.对...     

天文成像数值仿真的相位屏模拟方法

通过利用Monte—Carlo方法对湍流相位屏模拟进行验证和分析。给出加入次谐低频补偿相位屏与直接谱反演相位屏的对比结果,并分析了在考虑内外尺度时次谐低频补偿方法的有效性。此外,给出了基于天文观测的多相位屏的湍流分层模型。在此基础上对天文成像进行数值仿真,并给出了仿真结果。     

Hawking radiation from a dielectric black hole

Using the new global embedding approach and analytical continuation method of wave function we discuss Hawking radiation of acoustic black holes. Unruh/Hawking temperature of the dielectric black hole is derived. The corresponding relation among these methods that calculate Hawking radiation of dielectric black hole is established. Our result shows that these methods are equivalent.     

Multistep methods of numerical integration using back-corrections

A new class of linear multistep methods is proposed for the solution of the equations of motion of certain dynamical systems encountered in celestial mechanics and astrodynamics. These methods are distinguished from the classical predictor-corrector methods in that they permit back-corrections of the solution to be made. As the integration advances in time, the numerical solution is corrected or improved at certain points in the past. The enhanced numerical stability of these methods allows the meaningful application of high-order algorithms. Consequently, stepsizes larger than those attainable with the classical methods may be adopted and thus greater over-all efficiency may be realized. The application of these methods to the problem of determining the orbit of an artificial satellite is accomplished and the results are compared with those obtained using classical methods.     

Measurement of the limb darkening coefficient of stars

This paper introduces a new method of describing the limb darkening phenomenon of stellar atmospheres in the 1st and 2nd order approximations. The limb darkening coefficients are given by direct measurements of relevant physical quantities or measurements of flux and a supplementary quantity, namely, the star's surface temperature. The comparison either with solar observations or with the method of numerical simulation of the atmosphere shows that the new method can very accurately describe the star's limb darkening and determine its relevant coefficients. The accuracy of the new direct method is assessed using 176 observational data points of the Sun, and the mean fractional differences is found to be 0.38% for the 1st-, and 0.26% for the 2nd-order approximations. The mean differences of the indirect method are close to, and slightly larger than these values. When compared with numerical models of the atmosphere, the differences are in the range from under 1% to under 3%.     

Stability of a finite disc under the influence of a spherical halo

We have studied the stability of finite gaseous discs, against large-scale perturbations, under the influence of spherical, massive haloes. A surface-density distribution consistent with the observed spiral-tracer profiles in disc galaxies is considered for the disc. We find that growing eigenmodes with both ‘trailing’ and ‘leading’ spirals exist in ‘cold’ discs for a wide range of values of the halo mass and its radius. The amplification rates of the unstable modes reduce as the ratio of the mass of the halo to the mass of the disc is increased. A uniform halo is not very effective towards stabilizing the disc against these modes. The results from the present study are consideredvis-a-vis previous studies on the global modes of self-gravitating discs.     

Modified multirevolution integration methods for satellite orbit computation

Multirevolution methods allow for the computation of satellite orbits in steps spanning many revolutions. The methods previously discussed in the literature are based on polynomial approximations, and as a result they will integrate exactly (excluding round-off errors) polynomial functions of a discrete independent variable. Modified methods are derived that will integrate exactly products of linear and periodic functions. Numerical examples are given that show that these new methods provide better accuracy for certain satellite problems. It is also shown that information obtained from an approximate analytical solution of the satellite equations of motion, may be used to increase the accuracy and/or efficiency of the multirevolution integration.     

星系的恒星速度弥散度的归算方法

星系的恒星视向速度分布是星系动力学模型的重要观测约束,其特征参数包括速度弥散度、分布轮廓以及红移。这些参数对研究星系的动力学、结构和演化以及中央黑洞的质量等都具有重要的价值。该文全面总结了从星系光谱归算星系的恒星视向速度分布及其弥散度的各种方法,以及对观测和处理的一些要求。这些方法都假设星系谱线可看作是模板星光谱经多普勒位移并加宽后的线性叠加。提取尽可能多的星系内部恒星运动信息、减少模板星失配的影响、简化误差分析,是这些方法追求的目标。     

Anelastic convection-driven dynamo benchmarks

Benchmark solutions for fully nonlinear anelastic compressible convection and dynamo action in a rotating spherical shell are proposed. Three benchmarks are specified. The first is a purely hydrodynamic case, which is steady in a uniformly drifting frame. The second is a self-excited saturated dynamo solution, also steady in a drifting frame. The third is again a self-excited dynamo but is unsteady in time, and it has a higher Rayleigh number than the steady dynamo benchmark. Four independent codes have been tested against these benchmarks, and very satisfactory agreement has been found. This provides an accurate reference standard against which new anelastic codes can be tested.     

New Numerical/Analytical Methods for Solving Equations of Orbital Motion

New methods are proposed for solving equations of motion of celestial bodies. The methods are based on the use of superosculating orbits with second- and third-order tangency to the trajectory of the real motion of a body. The construction of these orbits is related to the concept of a fictitious attracting center, whose mass varies in accordance with the first Meshchersky law. In the original reference methods, the perturbed trajectory is represented by a sequence of small arcs of superosculating orbits. The order of accuracy of the reference methods coincides with the order of tangency of the superosculating orbit used in calculations. Using Runge's rule and Richardson's extrapolation scheme leads to the methods of higher order. The efficiency of the new methods in comparison with the numerical integration of equations of motion based on the well-known fourth- and seventh-order Runge–Kutta–Fehlberg methods is illustrated by examples of the calculation of perturbed orbits of some asteroids.     

低纬子午环的研制过程

叙述了低纬子午环研制的全过程，从低纬度地区子午绝对测定方法的提出和验证，仪器几种主要误差测定方法的提出，到设计、加工和安装，最后叙述了在调试中遇到的几个主要问题和解决办法。文中还以与传统子午环比较的方式，论述了在对加工精度未提出苛刻要求的情况下如何能达到高精度测量的原因。     

Accuracy of meteoroid speeds determined using a Fresnel transform procedure

New methods of determining meteor speeds using radar are giving results with an accuracy of better that 1%. It is anticipated that this degree of precision will allow determinations of pre-atmospheric speeds of shower meteors as well as estimates of the density of the meteoroids. The next step is to determine under what conditions these new measurements are reliable.Errors in meteoroid speeds determined using a Fresnel transform procedure applied to radar meteor data are investigated. The procedure determines the reflectivity of a meteor trail as a function of position, by application of the Fresnel transform to the time series of a radar reflection from the trail observed at a single detection station. It has previously been shown that this procedure can be used to determine the speed of the meteoroid, by finding the assumed speed that gives a reflectivity image that best meets physical expectations. It has also been shown that speeds determined by this method agree with those from the well established “pre-t_o phase” method when applied to reflections with a high signal to noise ratio. However, there is a discrepancy between the two methods for weaker reflections. A method to investigate the discrepancy is described and applied, with the finding that the speed determined by using the Fresnel transform procedure is more accurate for weaker reflections than that given by the “pre-t_o phase” method.     

Error bounds for perturbation methods

There are many papers dealing with the problem of error bounds for perturbation methods (development with respect to a small parameter, method of averaging, stroposcopic method etc.). The majority of these bounds, however, is very pessimistic and does not really reflect the qualities of the underlying perturbation method. In this paper a new attempt is made to overcome this problem. By using a new comparison theorem and the higher order approximations we are led not only to upper bounds, but to lower bounds as well.