New findings on asteroid spin-vector distributions

The number of known spin vectors of main belt and near-Earth asteroids is regularly growing, including new objects, and updating the estimates concerning known cases, with the aid of new observations and of improved observational techniques. A reliable statistical analysis of the spin vectors is now possible. In general the poles (both for MB bodies and for NEAs) are not isotropically distributed, as some general theoretical considerations may predict. Main belt asteroids show a lack of poles close to the ecliptic plane. There is a marginally significant excess of prograde spinners in the 100-150 km size range, but interestingly there is not a statistically significant excess in the larger size range. Among NEAs, there is an excess of retrograde rotations. The distributions of longitudes of poles of both groups do not show statistically significant deviations from random. We discuss the possible physical implications of the various resulting pole anisotropies in terms of dynamical—mainly non-gravitational—effects, and point out the importance of new observational campaigns, mainly devoted to compute the poles of small bodies and of the members of asteroid dynamical families.     

Cooperation aspects of international observatories

From the user's point of view, it is essential to promote collaborations to make full use of large telescopes, by covering the wide range of the wavelengths. To do that efficiently, it is necessary to work with other facilities, often abroad. Other talks in this symposium are concerned about the spatial resolution or the coverage at one wavelength or one to two octaves in wavelength. Though the above is important, that is not enough to attach the mysteries in the Universe, since a considerable amount of energy is emitted in the infrared, and mass exists in molecular gas form. In this paper, two examples of international, multiwavelength work are shown which turned out to be beneficial for the world-wide community. One is the Japan-U.K. arrangement mainly between the radio and infrared facilities, and the other is the arrangement around James Clerk Maxwell Telescope (JCMT), challenging a new regime of the observational astronomy.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

利用长期资料改进双星轨道解的一种方法

早期的地面观测积累了大量关于双星系统的观测资料.相对于近年来的各种观测数据,这些资料兼有精度低的缺陷和时间跨度长的优势．针对同时具有长期资料和依巴谷观测数据的较长周期的双星系统(如依巴谷星表的双星和多星附表中的G型双星系统),提出一种联合拟合方法,即首先通过拟合依巴谷的观测数据IAD寻求目标函数局部极小的轨道解,然后从中选出长期资料的最优解．结合这种方法的可行性分析,讨论了适用该方法的双星系统的轨道特征．作为应用实例,研究了文献中存在两种轨道解且仅有7次长期资料可以利用的系统73Leo,通过伴星质量的外符合分析,给出了具有较高可信度的轨道解．     

Galactic Archaeology: The dwarfs that survived and perished

From the archaeological point of view, the local dwarf galaxies are unique objects in which the imprint of the conditions that shaped the early structure formation can be studied today at high resolution. Over the last decade, this new window into the high redshift Universe has started to be exploited using deep wide-field imaging, high resolution spectroscopy and cutting edge N-body and hydro-dynamical simulations. We review the recent advances in the observational studies of the Milky Way dwarf galaxies, with the aim to understand the properties of the population as a whole and to assist an objective comparison between the models and the data.     

The Bootstrap Estimation of the Accuracy of Preliminary Orbit Determination

From the point of view of the non-parametric statistics, a general estimation method of the accuracy and con?dence interval of preliminary orbit determination is proposed for the occasion without any other information but observational data. Based on the bootstrap method, the estimation relies only on the observational data and does not require the precise orbit determination as a reference, or the assumption of normal distribution of observational errors. Numerical experiments show that this method is very simple in implementa- tion, and may serve as an easy accuracy evaluation for the preliminary orbit determination and for the follow-up employments.     

GalaxyCount: a java calculator of galaxy counts and variances in multiband wide-field surveys to 28 AB mag

We provide a consistent framework for estimating galaxy counts and variances in wide-field images for a range of photometric bands. The variances include both Poissonian noise and variations due to large-scale structure. We demonstrate that our statistical theory is consistent with the counts in the deepest multiband surveys available. The statistical estimates depend on several observational parameters (e.g. seeing, signal-to-noise ratio), and include a sophisticated treatment of detection completeness. The java calculator is freely available¹ and offers the user the option to adopt our consistent framework or a different scheme. We also provide a summary table of statistical measures in the different bands for a range of different fields of view.
Reliable estimation of the background counts has profound consequences in many areas of observational astronomy. We provide two such examples. One is from a recent study of the Sculptor galaxy NGC 300 where stellar photometry has been used to demonstrate that the outer disc extends to 10 effective radii, far beyond what was thought possible for a normal low-luminosity spiral. We confirm this finding by a re-analysis of the background counts. Secondly, we determine the luminosity function of the galaxy cluster Abell 2734, both through spectroscopically determined cluster membership, and through statistical subtraction of the background galaxies using the calculator and offset fields. We demonstrate very good agreement, suggesting that expensive spectroscopic follow-up, or off-source observations, may often be bypassed via determination of the galaxy background with GalaxyCount .     

On the giant supercluster binary-like system formed by the Corona Borealis and Abell 2142

The recent hypothesis of a giant supercluster binary-like structure formed by the Corona Borealis and its close companion Abell 2142 (supercluster) belongs to a little known area of investigation as the dynamics of gravitationally interacting galaxy supercluster pairs. From the observational point of view this structure approximates the configuration of a binary-like system in linear orbit interconnected by a huge filamentary structure which, if confirmed, it would be the first case to date observed at z ≥ 0.07. Given the importance to disentangle this issue, a follow-up analysis has been performed on the region constrained by the common envelop of the two superclusters in order to search for new hints to confirm their mutual gravitational interaction. Observational signatures of that interaction have been found mapping the inner peculiar motions where the observed negative peculiar velocities measured within the A2142 (supercluster) region suggest a general matter flow toward the Corona Borealis supercluster. Besides, analyzing the effects on both superclusters due to the mutual impact of the external tidal forces, turns out that their inner dynamics remain unperturbed up to the turnaround radii. Outside, where the binding forces are overlapped by the tidal ones, the outskirts of both superclusters should be unstable and subject to fragmentation. Such a scenario indicates that both superclusters interact with comparable and reciprocal tidal perturbations leaving the whole system in a substantial dynamical equilibrium. The origin of such a dynamical dichotomy would be explained either by a much more massive Corona Borealis supercluster than that estimated in the present work or by a selection effect biasing the small sample of peculiar velocities due to the remoteness of the system worsened by the large uncertainty on their measurements.     

太阳二维光谱观测研究的进展和展望

论述了太阳二维光谱观测和研究的重大意义，综述了二维光谱观测技术和仪器的进展，特别介绍了应用ＣＣＤ的成像光谱仪的最近发展。文中还介绍了近年来二维光谱观测研究所取得的一些新结果，展望了未来观测技术和课题研究的发展前景。     

Structural Properties of Brightest Cluster Galaxies

We present the first modern systematic study of local brightest cluster galaxy (BCG) profiles that extends to radii beyond 200h ^-1kpc. Measuring the surface brightness profiles of BCGs out to large radii is critical for understanding the processes driving their formation. The form of the profiles yields information about the current dynamical state, constrains the accretion history of these galaxies, and places limits on any radially symmetric component of intracluster light. The observational challenges associated with CCD photometry at low surface brightness levels have until now precluded such an analysis for a statistical sample of BCGs. Utilizing drift-scan data and new techniques that we have developed, we extend upon previous work by modelling the profiles for a sample of 31 clusters at z≃ that span a wide range in mass and dynamical state. We find that the BCGs in our sample generally are best fit using two-component models consisting of inner and outer Sersic profiles. In this proceeding we present the preliminary results of our analysis and discuss implications for current models of BCG formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Collision Probability for Earth-Crossing Asteroids Using Orbital Ranging

We introduce new techniques for the computation of the collision probability for Earth-crossing asteroids in the case of short observational arcs and/or small numbers of observations. The techniques rely on the orbital element probability density computed using statistical orbital ranging. We apply the techniques to the Earth-crossing asteroid 1998 OX₄with non-vanishing collision probability in numerous close approaches after the year 2012 (inclusive). We study the invariance of the collision probability in transformations between different orbital element sets, and develop a Spearman rank correlation measure for the validity of the linear approximation. We introduce an optimized, fast version of the statistical ranging method.     

Small-scale magnetic field diagnostics outside sunspots: Comparison of different methods

We analyse different observational data related to the problem of intrinsic magnetic field strength in small-scale fluxtubes outside sunspots. We conclude that the kG range of fluxtube fields follows from not only classical line ratio method, but also from other old and new techniques. For the quiet regions on the Sun, the most probable mode of such fields has a magnetic field strength of 1.2–1.5 kG assuming the rectangular field profile. To best interpret the observations, a weak background field between fluxtubes should be assumed, and its magnetic field strength is expected to increase with the filling factor of fluxtubes. The alternative point of view about subkilogauss fluxtube fields is critically examined, and possible sources of different conclusions are presented.     

Visual double stars in professional spanish astronomy: Past,present and future projects

Summary This poster describes the contribution of professional Spanish astronomy to all aspects of the study of visual double stars (observation, calculation of orbits and development of new methods of calculation), together with projected programmes of visual and interferometer observations.     

Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

From optical R -band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (with an overlap of about 330 d between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short time-scale events (with a duration of months), where the term 'event' refers to a prominent feature that may be a result of microlensing or another source of variability. Only one event lasting two weeks and rising −33 mmag was found . Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial), a smooth function plus a stationary noise process, or a correlated stationary process . Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.     

On the evolution of the Horizontal Branch stars of metal-poor Globular Clusters

The actual knowledge on Horizontal Branch stars of the metal-poor Globular Clusters of our Galaxy suggests that these stars evolve along the Horizontal Branch from the very blue stars towards lower effective temperature.From this behaviour it follows that a substantial mass loss occurs at the He-flash. On the basis of a gravitational thermalization of Horizontal Branch stars any recent observational data concerning NGC 7006 are re-examined. It is pointed out that today it is not necessary to leave the hypothesis of a strong correlation between the metal and helium content for our Galaxy.At present at the Osservatorio Astronomico, Bologna.     

Motion in a double nucleus galactic dynamical model

We construct a 2D-dynamical model in order to study the motion in a galaxy with a double nucleus. Numerical calculations show that the majority of high energy stars, near the double nuclear region, are on chaotic orbits. On the contrary, low energy stars are on chaotic orbits only near massive nuclei while, for less massive nuclei, the motion is regular. Using a semi-numerical approach we explain the chaotic scattering of orbits near each nucleus. The high values of the velocities near the dense nuclei are also explained. Computation of the LCEs indicates a very high degree of chaos. The results derived from our double nucleus dynamical model are compared with models with single ones. Our outcomes are in satisfactory agreement with observational data for the double nucleus system $\mathit{NGC}6240$.     

A survey of third components in spectroscopic and eclipsing systems

Summary Multiplicities recorded in catalogues as well as in the current literature are considered. The basis of the statistical treatment is about one half of the material collected in theSeventh Catalogue of spectroscopic binaries by A. Batten and his collaborators, subjected also to a magnitude limit atV=6.8, altogether 310 systems. It is hoped that this sample of brighter stars represents close and also wider systems with a reasonable degree of completeness. Incidence of higher multiple systems, in particular of ab-c-type triple stars, turns out rather high: the ratio of double to multiple systems is about 2:1, in terms of the directly observed data. Allowing for some more obvious observational bias, this ratio approaches 1:1. The number of individual components in multiple systems is almost certainly superior to that of double star components. An investigation in progress, concerning multiplicities in the specific classes of W UMa-systems and cataclysmic variables, is briefly described.     

Time evolution of orbital uncertainties for the impactor candidate 2004 AS1

We evaluate the asteroid impact risk from the discovery night onwards using six-dimensional statistical orbit computation techniques to examine the a posteriori probability density of the orbital elements. Close to the discovery moment the observational data of an object are typically exiguous: the number of observations is very small and/or the covered orbital arc is very short. For such data, the covariance matrices computed in the linear approximation (e.g., with the least-squares technique) are known to fail to describe the uncertainties in the orbital parameters. The technique of statistical ranging gives us rigorous means to assess the orbital uncertainties already on the discovery night. To examine the time evolution of orbital uncertainties, we make use of a new nonlinear Monte Carlo technique of phase-space sampling using volumes of variation, which complements the ranging technique for exiguous data and the least-squares technique for extensive observational data. We apply the statistical techniques to the near-Earth Asteroid 2004 AS₁, which grabbed the attention of asteroid scientists because, for one day, it posed the highest and most immediate impact risk so far recorded. We take this extreme case to illustrate the ambiguities in the impact risk assessment for short arcs. We confirm that the weighted fraction of the collision orbits at discovery was large but conclude that this was mostly due to the discordance of the discovery-night observations. This case study highlights the need to introduce a regularization in terms of an a priori probability density to secure the invariance of the probabilistic analysis especially in the nonlinear orbital inversion for short arcs. We remark that a predominant role of the a priori can give indications of the feasibility of the probabilistic interpretation, that is, how reliable the results derived from the a posteriori probability density are. Nevertheless, the strict mathematical definition of, e.g., the collision probability remains valid, and our nonlinear statistical techniques give us the means to always deduce, at the very least, order-of-magnitude-estimates for the collision probability.     

Observing Magnetic Fields in Star-Forming Regions

Magnetic field strengths and directions can be estimated using many different observational techniques that span a wide range of wavelengths. Each observational method favours different regimes of scale size, density and other physical conditions. The available techniques and their ranges of applicability are briefly described and the current status of observations is reviewed, with particular emphasis on high-resolution observations of star-forming regions.     

Evolution of double layers in magnetised plasmas contaminated with dust charge fluctuations

Coherent structures entailing the existence of double layers have been studied in magnetised plasma contaminated with dust charging fluctuations. It has been shown that the dust charging in magnetic plasma leads to complexity in the derivation of the Sagdeev wave equation, but under way new procedure enable one to study the nature of double layers showing the effective role of the constituents of the plasma. A parametric analysis is a subject of interest in laboratory and space plasmas, and it has been explained with the input of various typical plasma numerics. The proposed mathematical mechanism has shown the success to yield plasma acoustic modes in a dusty plasma which, in turn, has been solved convincingly for double layers. Observations have been evaluated in an appropriate model with a view to agree with the observations in astrophysical problems dealing with present new findings.     

Unstable objects in the galaxy and the star-formation process

Using observational data, we consider the problem of instability of astronomical objects and systems of objects and its close connection with the star-formation process. We show that it is only due to the discovery and study of stellar associations that the enormous role of stellar instability in the formation of stars in the Galaxy (and in other galaxies) has been definitively explained. Many kinematic properties of stellar associations are inexplicable from the old point of view. This gives grounds for doubting the correctness of the classical hypothesis that stars form from diffuse matter.Translated fromAstrofizika, Vol. 38, No. 3, 1995.