Breakup of moving clusters in the galactic disk

Numerical simulations are used to analyze the breakup of moving groups in the Galactic disk through the internal velocity dispersion of the group components and the tidal effect of the external regular gravitational Galactic field and giant molecular clouds. The initial locations of the group centroids correspond to well-known moving streams: the Hyades, the Pleiades, the Ursa Major cluster, and the group HR 1614. The mean group breakup times have been found as a function of the adopted limiting group size. The interactions of stream stars with giant molecular clouds reduce significantly the group lifetime.     

Periodic orbits in the general three-body problem

Stability regions are identified in the neighborhood of periodic orbits. Features of motion in these regions are investigated. The structure of stability regions in the neighborhood of the Schubart, Moore, and Broucke orbits, the S-orbit, and the Ducati orbit is studied. The following features of motion are identified near these periodic orbits: libration, precession, symmetrization, centralization, bounce (a transition between types of trajectories), ejections, etc.     

Encounters of the Sun with nearby stars in the past and future

The relative space motions of the Sun and nearby stars are considered. The coordinates and velocities of the stars are taken from the Catalogue of Nearby Stars by Gliese and Jahreiss (1991). The minimum space separation between the Sun and every star as well as the corresponding moment of time are calculated by two ways. Firstly, the straight line motions are considered. Secondly, the effect of the Galaxy potential is taken into account. The Galaxy model proposed by Kutuzov and Ossipkov (1989) is used. Twenty five stars approaching the Sun closer than two parsecs are selected. The effects of the uncertainties in the observational data are studied. The influence of the encounters to the Oort cloud is discussed.     

A study of the internal structure of variety III diamonds by X-ray section topography

The internal structure of variety III diamonds (Orlov 1977) was examined by X-ray section topography. The crystal space was found to be divided into six cubic sectors of a face-form of rhombododecahedroid variety III (Shafranovsky 1961). The defect lines on the topographs are the traces of {110} defect planes. It is concluded that separate 〈111〉 fibres are grouped into {110} layers (lamellae). The internal structure of the crystals is characterized by continuous warping of crystal planes and is directly connected with {110} defect planes which are tilt boundaries. Examples of variants of filling cubic sectors are given and their connection with misorientation shown on topographs demonstrated. The characteristic internal structure of variety III diamonds can account for their morphological features and structure-dependent properties; for examples, the cleavage on {110} and {100}.     

Identifying compact moving groups based on stellar kinematics data

We investigate the possibility of identifying substructures in velocity space in three well-known stellar streams (the Hyades, the Pleiades, and Ursa Major) using a cluster-analysis method (the maximum-density method). Only compact groups in velocity space with radii no greater than 5 km/s and containing at least 10 members were considered. As an example, we analyzed a sample of 5377 stars from the HIPPARCOS catalog with known radial velocities located within 75 pc of the Sun. We identified a total of 24 groups of stars. Monte Carlo simulations show that most (about 80%) of these groups could be the results of Poisson noise and observational errors. Bona fide identification (at a significance level greater than 90%) of compact moving groups based on kinematic data requires higher accuracy of the stellar spatial velocities (with errors no greater than 1–2 km/s in each component).     

Global repeating events in the history of the Earth and the motion of the Sun in the Galaxy

Chronological analyses of correlations between certain global repeating events (mass extinctions of marine organisms, meteorite impacts, and flashes in the frequency of geomagnetic reversals) during the Phanerozoic Eon and the motion of the solar system in the Galaxy are presented for five rotationally symmetrical models for the regular Galactic gravitational field. Thirteen of sixteen mass-extinction events can be described by a repetition interval of 183±3 million years. This is in agreement with the anomalistic period (interval between two subsequent passages of the Sun through the apocenter of its Galactic orbit) in the model of Allen and Martos. The positions of the minima and maxima in Gaussian functions approximating the frequency distribution for geomagnetic reversals also agree with the times of passage of the Sun through the apocenter and pericenter, respectively, of its Galactic orbit in this model. The maximum in the distribution of the deviations of the dates of mass extinctions from the nearest dates of impacts of large, crater-forming bodies is close to zero, providing evidence that many such events are correlated. As a rule, extinctions follow impact events. The impacts of large bodies have occurred most often when the solar system passes through the Galactic plane, while mass extinctions occur more often at some distance from the Galactic plane (about 40 pc). As a rule, intervals of increases in the frequency of geomagnetic reversals coincide with dates of impacts of large bodies. At the same time, these intervals do not show a clear correlation with the dates of mass extinctions. The intensity of mass extinctions, like the energy released by impacts, is consistently higher in periods when the Sun is moving from the apocenter toward the pericenter of its orbit, than when it is moving from the pericenter toward the apocenter. Thus, there is evidence for a variety of relationships between repeating global events in the Phanerozoic and the motion of the Sun in the Galaxy. Long-period variations in the frequency of geomagnetic reversals are correlated with the orbital motion of the Sun, and increases in the frequency of geomagnetic reversals are correlated with impacts. Mass extinctions are correlated with the impacts of large bodies, whose motions may have been perturbed by clouds of interstellar material concentrated toward the Galactic plane and by the shock front associated with the Perseus spiral arm, through which the solar system passes. The velocity of the Sun relative to the spiral pattern is estimated.     

The dynamical evolution of stellar-planetary systems

We have carried out numerical simulations of the dynamical evolution of young stellar-planetary groups using various means to choose the initial conditions, which reflect the various assumptions about the physics of planetary formation: that planets form in circumstellar disks or simultaneously with stars as a result of the fragmentation of molecular clouds. The main classes of stable stellar-planetary systems resulting from the dynamical evolution of groups are identified (the outer planets around binary stars and “star + planet” binary systems), and their main characteristics analyzed. The probabilities of the formation of various types of planetary systems are estimated. A preliminary analysis of the migration of planets under the action of perturbations from stars is performed in the framework of the adopted model. It is shown that this migration can occur both towards and away from the star.