The present situation with the absolute methods of observations in fundamental astrometry

Conclusions The present situation with absolute methods is the accumulated result of continuous deviations from the classical basic principles during the current century, and this has led to the obfuscation of the general clear concepts.While the available catalogues which contain hybrid coordinates of stars are useful for many purposes, they are of limited use for improving the theories of the solar system bodies or verifying the laws of dynamics. For these tasks, one must compare calculated coordinates with theory independent ones, i.e. such, wich are either related to absolute coordinates of stars or related to extragalactic radio objects. If international cooperation in the field of absolute observations with astrolabes and other BIH instruments should be organized, the coming years will show which of the alternatives is more effective.     

Objectives of ground-based astrometry after HIPPARCOS

After a short summary of the results expected from the HIPPARCOS mission, the author gives several examples illustrating the needs that will arise afterwards in order to maintain the level of precision achieved and to extend it to many more objects. Three domains are particularly dealt with in this paper:

1. The maintenance of the HIPPARCOS reference system that will degrade at the rate of 2 mas per year. The instruments intended to contribute to this task should concentrate on observing a few stars as accurately as possible. The best candidates are astrolabes and optical interferometers.
2. The extension of the HIPPARCOS catalogue to more stars using astrographs, Schmidt telescopes, and photoelectric meridian circles. A particularly important objective would be to reduce the GSE catalogue to this system and determine its proper motions with second epoch plates.
3. The determination of new parallaxes and double star parameters in particular with CCD astrometry, astrometric photometry and various interferometric techniques.

     

The contact transformation groups of the Extended Hamiltonian System

The 1-parameter transformation groups (otherwise known as infinitesimal transformations) admitted by a system of differential equations are fundamental to the study of its properties. In this paper we first of all consider 1-parameter groups of contact transformations. Then, by generalizing Noether's theorem, we show how they are fundamental to what I call the Extended Hamiltonian System. Finally, this is illustrated by the extendedN-Body problem.

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Resume Les groupes de transformations à 1 paramètre (appelés aussi transformations infinitésimales) admis par un systeme d'équations différentielles sont fondamentaux dans l'étude de ses propriétés. Dans cet article, nous considérons d'abord les groupes à 1 paramètre de transformations de contact. Ensuite, par la généralisation du théorème de Noether, nous montrons qu'ils sont fondamentaux dans l'étude de ce que j'appelle le Système Hamiltonien Etendu. Enfin ceci est illustré par le problème étendu desN-Corps.

     

Determination of stellar positions with a cross-correlation procedure

A technique of cross-correlation for the determination of stellar positions is proposed. It is a technique suitable for the recording of stellar positions on transit instruments, photoelectric astrolabes, and also on the meridian circles with reversed observing method. An advantage of this process is that there is no hypothesis required for the modelling image profile, and for the noise. It is closer to unbiased estimation. Results by this new method on a transit instrument are presented. For the brighter stars, there is no great difference in accuracy between the median position and the cross-correlation value according to the results.     

Friedrich Wilhelm Bessel (1784–1846)

May I first express my warmest thanks to the organizers of the Conference for having invited me to present a brief bibliographic report on the great astronomer F. W. Bessel. You have given me a welcome opportunity to express an appreciation of Bessel's work which has marked the beginning of research on the motion of stars and which was pioneer work on astrometric binaries and on the determination of stellar distances. Bessel has established the first celestial coordinate system which approximates an inertial system, and my colleagues and I at Heidelberg in establishing an improved fundamental reference system, the FK5, have had to review again some of Bessel's pioneer contributions to this field, and such contributions shall be mentioned later. My talk shall be divided into the following parts: (1) Bessel's course of life and family; (2) Education in astronomy in Bremen; (3) Fundamenta Astronomiae; (4) Fundamental observations at the Königsberg Observatory (or according to S. Newcomb (1906): the German School of Astrometry); (5) 61 Cygni; (6) Bibliography of Bessel's original works.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

GEM-based TPC with CCD imaging for directional dark matter detection

The most mature directional dark matter experiments at present all utilize low-pressure gas Time Projection Chamber (TPC) technologies. We discuss some of the challenges for this technology, for which balancing the goal of achieving the best sensitivity with that of cost effective scale-up requires optimization over a large parameter space. Critical for this are the precision measurements of the fundamental properties of both electron and nuclear recoil tracks down to the lowest detectable energies. Such measurements are necessary to provide a benchmark for background discrimination and directional sensitivity that could be used for future optimization studies for directional dark matter experiments. In this paper we describe a small, high resolution, high signal-to-noise GEM-based TPC with a 2D CCD readout designed for this goal. The performance of the detector was characterized using alpha particles, X-rays, gamma-rays, and neutrons, enabling detailed measurements of electron and nuclear recoil tracks. Stable effective gas gains of greater than 1 × 10⁵ were obtained in 100 Torr of pure CF₄ by a cascade of three standard CERN GEMs each with a 140 µm pitch. The high signal-to-noise and sub-millimeter spatial resolution of the GEM amplification and CCD readout, together with low diffusion, allow for excellent background discrimination between electron and nuclear recoils down below ∼10 keVee (∼23 keVr fluorine recoil). Even lower thresholds, necessary for the detection of low mass WIMPs for example, might be achieved by lowering the pressure and utilizing full 3D track reconstruction. These and other paths for improvements are discussed, as are possible fundamental limitations imposed by the physics of energy loss.     

A New Algorithm in Computations of Binary Stars’ Observational Quantities and Its Application

The determination of the orbital parameters of binaries is an important constituent of fundamental astronomy. It is the only reliable way to determine the stellar mass, which is crucial for the studies of stellar dynamics and evolution. And the orbital parameters can be used to compute the motions of component stars, which could improve the population of reference stars in the bright star catalogue reference frame. However, the previous studies on the determination of binaries’ orbital parameters adopted some approximations in the computation of observational quantities. According to the statistical results of hundreds of binaries with bright component stars, it could be found that the approximations in the variation of the tangent plane and the prospective effect of the reference plane have made the deviations of computed observational quantities become larger than the present observational precision (1 mas). In this paper, a new algorithm based on the two-body model and the rigorous relation of solid geometry for computing observational quantities is presented. This new algorithm has been verified by fitting the simulation and actually-observed data. And the fitting results show that the fitted parameters solved by the new algorithm usually have a higher confidence than that solved by the approximate algorithm. Therefore, the new algorithm has certain improvements in the determination of the orbital parameters of binaries, especially, for the wide binaries nearby the solar system.     

Empirical calibration of the near-infrared Ca ii triplet – II. The stellar atmospheric parameters

We present a homogeneous set of stellar atmospheric parameters ( T _eff, log  g , [Fe/H]) for a sample of about 700 field and cluster stars which constitute a new stellar library in the near-IR developed for stellar population synthesis in this spectral region ( λ 8350–9020) . Having compiled the available atmospheric data in the literature for field stars, we have found systematic deviations between the atmospheric parameters from different bibliographic references. The Soubiran, Katz & Cayrel sample of stars with very well determined fundamental parameters has been taken as our standard reference system, and other papers have been calibrated and bootstrapped against it. The obtained transformations are provided in this paper. Once most of the data sets were on the same system, final parameters were derived by performing error weighted means. Atmospheric parameters for cluster stars have also been revised and updated according to recent metallicity scales and colour–temperature relations.     

Are Non-Magnetic Mechanisms Such As Temporal Solar Diameter Variations Conceivable for an Irradiance Variability?

Irradiance variability has been monitored from space for more than two decades. Even though data come from different sources, it is well established that a temporal variability exists ≈0.1%, in phase with the solar cycle. Today, one of the best explanations for such an irradiance variability is provided by the evolution of the solar surface magnetic fields. But if some 90–95% can be reproduced, what would be the origin of the 10–5% left? Non-magnetic effects are conceivable. In this paper we will consider temporal variations of the diameter of the Sun as a possible contributor for the remaining part. Such an approach imposes strong constraints on the solar radius variability. We will show that over a solar cycle, variations of no more than 20 mas of amplitude can be considered. Such a variability – far from what is reported by observers conducting measurements by means of ground-based solar astrolabes – may explain a little part of the irradiance changes not explained by magnetic features. Further, requirements are needed that may help to reach a conclusion. Dedicated space missions are necessary (for example PICARD, GOLF-NG or SDO, scheduled for a launch around 2008); it is also proposed to reactivate SDS flights for such a purpose.     

New views of the lunar plasma environment

A rich set of new measurements has greatly expanded our understanding of the Moon–plasma interaction over the last sixteen years, and helped demonstrate the fundamentally kinetic nature of many aspects thereof. Photon and charged particle impacts act to charge the lunar surface, forming thin Debye-scale plasma sheaths above both sunlit and shadowed hemispheres. These impacts also produce photoelectrons and secondary electrons from the surface, as well as ions from the surface and exosphere, all of which in turn feed back into the plasma environment. The solar wind interacts with sub-ion-inertial-scale crustal magnetic fields to form what may be the smallest magnetospheres in the solar system. Proton gyro-motion, solar wind pickup of protons scattered from the dayside surface, and plasma expansion into vacuum each affect the dynamics and structure of different portions of the lunar plasma wake. The Moon provides us with a basic plasma physics laboratory for the study of fundamental processes, some of which we cannot easily observe elsewhere. At the same time, the Moon provides us with a test bed for the study of processes that also operate at many other solar system bodies. We have learned much about the Moon–plasma interaction, with implications for other space and planetary environments. However, many fundamental problems remain unsolved, including the details of the coupling between various parts of the plasma environment, as well as between plasma and the surface, neutral exosphere, and dust. In this paper, we describe our current understanding of the lunar plasma environment, including illustrative new results from Lunar Prospector and Kaguya, and outstanding unsolved problems.     

On Solar Radius Variations Observed with Astrolabes

Ground-based results on cyclic variations of the apparent solar radius are so far controversial and inconsistent. This is blamed to atmospheric noise which effects can be so severe that even in cases in which the observations are made with similar instruments, the results show strong disagreements (Li et al.: 2003, Astrophys. J. 591, 1267). Such claim concerns the results of Danjon astrolabes which during the last decades have been used widely at several sites for solar metrology. The long-term series with thousands of radius measurements made with astrolabe at Calern, France, and at Santiago, Chile, is a case in which the results of radius variations in time are strongly discrepant in spite that the observations were made simultaneously, in quite similar conditions and with almost identical instruments (Noël: 2004, Astron. Astrophys. 413, 725). However, we show here that most of astrolabe discrepancies may be due to data analysis biased by theoretical preconceptions, by empirical results which without scientific arguments are considered as canonical references and by over interpretations of casual agreements between visual and CCD astrolabe results.     

计算机互联网上时间传递的一种设计方案

目前,国内外时间传递方式主要有长波授时、短波地、电话授时、双星比对、ＧＰＳ时间信息等。信息产业的不断发展,使得互联网络已成为一种新的信息传递手段和资源共享方式 。通过计算机网络传输标准时间、频率将是授时领域的新课题,也是时间同步的新手段。讨论了计算机互联网上时间传递的一种设计方案,给出利用计算机网络系统实现标准时间的传递的具体方法,并介绍一种计算机互联网时间传递软件的使用方法等。     

Etude d'une solution de la theorie litterale du probleme principal du mouvement de la Lune convergence formelle

Résumé Dans l'exposé qui va suivre, nous rappelons d'abord le système d'équations et le mode d'intégration que nous avons utilisés pour construire une théorie littérale du problème principal du mouvement de la Lune. En particulier, puisque, du fait de la présence des petits diviseurs, nous avons à effectuer plusieurs itérations à un ordre donné, pour obtenir tous les termes correspondant à cet ordre, nous allons étudier un système d'équations réduit qui se substitue au système complet, après la première intégration à un ordre donné. Ce système permet d'alléger au maximum les calculs.Nous étudions alors la convergence formelle de la solution littérale obtenue. Cette démonstration est faite par récurrence. Au cours de celle-ci, nous avons utilisé les propriétés du système d'équations réduit (C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, et C12), système dont nous donnons dans les tableaux I à IV, les coefficients et les arguments. L'étude de l'ordre des termes engendrés par ce système nous permet de conclure que, si l'on connaît tous les termes d'ordren–1 alors on peut déterminer tous les termes d'ordren.Enfin, nous indiquons les résultats que nous avons actuellement obtenus par cette méthode.

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In this paper, we first recall the set of equations and the method of integration for a literal solution of the main problem of the lunar theory. As, owing to small divisors, we have to make many iterations at a given order to obtain all the corresponding terms, we study a restricted set of equations which replaces the complete system after the first integration at a given order. This set helps to make the calculations less bulky.Then we study the formal convergence of the literal solution thus obtained. The demonstration uses a recurrent process in which we made use of the properties of the restricted system of equations (C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11 and C12), the coefficients and arguments of which are given in Tables I to IV.The study of the order of magnitude of the terms formed by this system leads to the conclusion that if then–1 order terms are known, all then-order terms may be determined.In the end, we show the results obtained so far with this method.

     

An Analysis of Gsc0008.324, Newly Discovered Binary Star

A separate solution of the R *light curves was carried out using the 1998version of the Wilson's synthetic light curve code. In this paper we considered observations of Robb et al. (1999) for analysis. The photometry showed that star exhibits variable and asymmetric light curve. The asymmetric in the light curve is fitted with a spot on the surface of the hotter component. The fundamental orbital and physical parameters of this system have determined. The mass ratio is defined to be always q ≤ 1. The results indicate that the system is a late-type detached binary so that the components seem to be a very close pair of dwarfs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sur la recherche des mouvements stationnaires dans les systèmes ayant des variables cycliques

Résumé Ayant défini la notion de système lié associé à un système mécanique comportant des variables cycliques, on montre que l'ensemble des mouvements stationnaires du système coïncide avec l'ensemble des mouvements stationnaires du système lié. L'étude de la stabilité de ces mouvements montre que si le système lié est stable, il en est de même pour le système initial. La recherche des mouvements stationnaires des gyrostats fournit une application de cette étude.

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A constrained system is associated with a mechanical system having cyclic coordinates. We prove that the set of steady motions of this mechanical system and the set of steady motions of the constrained system are the same. Investigating the stability of these motions, we prove that, if the constrained system is stable, then the mechanical system is also stable. As an example, we consider the problem of the relative equilibrium of gyrostat satellites.

     

恒星大气物理参量的非参数估计方法

恒星大气物理参量（有效温度、表面重力、化学丰度）是导致恒星光谱差异的主要因素．恒星大气物理参量的自动测量是LAMOST等大规模巡天望远镜所产生的海量天体光谱数据自动处理中一个重要研究内容．针对测量大样本的恒星光谱数据估计每个恒星的大气物理参量，提出了一种基于变窗宽核函数的估计算法：变窗宽算法是对固定窗宽算法的改进，分为3个步骤：（1）将历史恒星光谱数据进行PCA处理，得到光谱的低维特征数据；（2）利用特征数据与其物理参数的对应关系，建立一种变窗宽的非参数估计模型；（3）利用该估计模型，直接计算待测恒星光谱的3个物理参量（有效温度、表面重力、金属丰度）．实验结果表明：该方法与固定窗宽估计模型以及在其他文献中报道的方法相比，具有较高的估计精度和鲁棒性．     

On the formation of TW Crv optical radiation

We present the analysis of the optical radiation of the young pre-cataclysmic variable TW Crv. Spectroscopic and photometric observations were obtained at the SAO RAS 6-m BTA telescope and at the Russian-Turkish RTT-150 telescope. The light curves of the system posses nearly sinusoidal shapes with the amplitudes of Δ_m > 0.^m7, what is typical for young pre-cataclysmic variables with sdO-subdwarfs and orbit inclinations of less than 45?. The optical spectrum contains dominant radiation of the hot subdwarf with the HI and He II absorption lines and strong emission lines, which are formed in the atmosphere of the secondary owing to the reflection effects. Radial velocities of the cool star were measured by analyzing the λλ 4630–4650 Å Bowen blend, which for the first time allowed to determine the component masses. A numerical simulation of the light curves and spectra of TW Crv, obtaining a complete set of systems fundamental parameters was carried out. The hot star parameters prompt its belonging to the sdOsubdwarf class at the stage of transition to the cooling white dwarf sequence. The absence of its observable planetary nebula is caused by a long-lasting evolution of the system after the common envelope state. The secondary component has a luminosity excess, which is typical for other young sdO-subdwarf precataclysmic variables. Its position on the “age??luminosity excess” diagram points at the accuracy of the obtained set of TW Crv fundamental parameters and at the similarity of its evolutionary and physical conditions with that of other BE UMa-type objects.     

The Performance of MEFOS, the ESO Multi-Object Fibre Spectrograph

We are describing a new multi-fibre positioner, MEFOS, that was in generaluse at the La Silla Observatory, and implemented at the prime focus of theESO 3.6 m telescope. It is an arm positioner using 29 arms in a one degreefield. Each arm is equipped with an individual viewing system for accuratesetting and carries two spectroscopic fibres, one for the astronomical objectand the other one for the sky recording needed for sky subtraction. Thespectral fibres intercept 2.5 arcsec on the sky and run from the prime focusto the Cassegrain, where the B&C spectrograph is located. Afterdescribing the observational procedure, we present the first scientificresults.     

A method for the simultaneous estimation of the fundamental atmospheric parameters using the photometric indices in the BVRI and JHK color systems

This is the second paper in a series reporting a new method developed to estimate the fundamental atmospheric parameters of effective temperature, surface gravity, and metallicity simultaneously. In the first paper three parameters were estimated using only photometric indices in the uvby color system. Whereas, in this paper, we use BVRI and JHK color systems. Using the model atmosphere grids, all three parameter values were estimated with respect to both [(B–V):(V–R)] and [(B–V):(R–I)], as well as [(V–K):(H–K)] and [(J–K):(H–K)] pair indices. It was confirmed that (B–V) and (V–K) indices are good temperature indicators, but all color indices for the BVRI and JHK systems are very poor indicators of metallicity and surface gravity. This new method was applied to a number of field dwarfs and giants, and the results were compared with those from the uvby color system. We found that the JHK color system can compete with the uvby system only in the estimation of temperature.     

利用地基GPS技术反演武汉地区大气可降水分

利用武汉地区的探空资料和GPS实测数据，对对流层干分量延迟、对流层加权平均温度进行了检验分析．结果表明，对于武汉地区而言，常用的大气干分量延迟模型(SAAS Hopfield and Black)存在着1-2cm的系统误差，这在利用GPS资料估算大气可降水分(PWV)时会引入2-3mm的误差；对流层加权平均温度与常用的Bevis公式也存在着一定的差异，但这种差异对PWV结果影响很小．为此，提出了校正对流层干分量延迟的方法，并利用实测数据对该方法进行了检验．实践证明，这种校正方法基本上可以消除常用干分量模型的系统误差。