Determination of the red shifts of selected IVS program objects. I

The spectroscopic red shifts of seven optical objects whose coordinates coincide with those of radio sources in the IVS (International VLBI Service for Geodesy and Astrometry) program list are determined from observations with the 6-m BTA telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences. A comparison of these spectra and red shifts with data in the radio frequency range shows that four of the objects discussed here are correctly identified, while the other three require further study. The distances to the radio sources derived from our measurements yield more accurate estimates of the cosmological model parameters than those based on the proper motions of these objects derived from geodesic VLBI observations.     

Structure and evolutionary history of the solar system,I

1. Introduction and Survey. The method for studying the structure and evolution of the solar system is discussed. It is pointed out that theories that account for the origin of planets alone are basically insufficient. Instead one ought to aim for a general theory for the formation of secondary bodies around a central body, applicable both to planet and satellite formation. A satisfactory theory should not start from assumed properties of the primitive Sun, which is a very speculative subject, but should be based on an analysis of present conditions and a successive reconstruction of the past states.
2. Orbits of Planets and Satellites. As a foundation for the subsequent analysis, the relevant properties of planets and satellites are presented.
3. The Small Bodies. The motion of small bodies is influenced by non-gravitational forces. Collisions (viscosity) are of special importance for the evolution of the orbits. It is pointed out that the focusing property of a gravitational field (which has usually been neglected) leads to the formation of jet streams. The importance of this concept for the understanding of the comet-meteoroid relations and the structure of the asteroidal belt is shown.
4. Resonance Structure. A survey is given of the resonances in the solar system and their possible explanation. It is concluded that in many cases the resonances must already be produced at the times when the bodies formed. It is shown that resonance effects put narrow limits on the post-accretional changes of orbits.
5. Spin and Tides. Tidal effects on planetary spins and satellite orbits are discussed. It is very doubtful if any satellite except the Moon and possibly Triton has had its orbit changed appreciably by tidal effects. The isochronism of planetary and asteroidal spins is discussed, as well as its bearing on the accretional process.
6. Post-accretional Changes in the Solar System. The stability of the solar system and upper limits for changes in orbital and spin data are examined. It is concluded that much of the present dynamic structure has direct relevance to the primordial processes.

     

Stability of co-orbital ring material with applications to the Janus-Epimetheus system

An analytical model that describes the evolution of ring particles that are co-orbital with two larger bodies on near-circular and near-planar orbits has been formulated. This can be used to estimate the lifetime of the particles within the ring. All the examples investigated, such as the Janus-Epimetheus (JE) system, indicate that the particles should be removed from the co-orbital region within half a synodic period (∼4 years for JE). Numerical modelling confirms the predictions of the model. When the masses are on eccentric orbits the particles remain within the co-orbital system for longer. Our results suggest that the ring associated with Janus and Epimetheus must be continually fed with material, probably by meteoroid impacts on the two satellites.     

Convection in a rapidly rotating system: the smallinclination limit and its planetary applications

An asymptotic method based on a continuous superposition of waves is used to studythe linear stability of convection in a rapidly rotating system. The method gives a uniformrepresentation of the solutions which allows us to impose the boundary conditions and then tominimize the Rayleigh number. This study was done for Prandtl numbers between 0.01 and 100.In the spherical case, for a self-gravitating, internally heated fluid in the small inclination limit,six branches are unveiled. In these branches, infinitesimal amplitude convection takes placepreferentially near the surface of a cylinder coaxial with the axis of rotation in a zone ofthickness ∝ T^−1⧸12, T being the Taylor number. The Rayleigh number ofthree of these flows differs at the most by sixty percent; however, in some intervals of the Prandtlnumber the difference is less than ten percent. Since these flows are located at different radialdistances, this method predicts mixed-modes convection in separate zones at slightlysupercritical values of the Rayleigh number for all Prandtl numbers. A solution exhibitingconvection in separate zones at low supercritical Rayleigh numbers is proposed for the first time.Applications to atmospheres and dynamos of the planets and the starts are discussed.     

On the origin of the solar system,I

The principal dynamical properties of the planetary and satellite systems listed in Section 2 require these bodies to have condensed in highly-flattened nebulae which provided the dissipation forces that produced the common directions of orbital motion, and the lowe andi values. Minimum masses of these nebulae can be estimated on the assumption that the initial solar abundances apply, starting from the empirical data on present planetary and satellite compositions and masses. The asteroids and comets are assumed to be direct condensations and accretion products in their respective zones (2–4 AU and 20–50 AU), without the benefit of gravitational instability in the solar nebula, owing to the comparatively low density there; with gravitational instability accelerating and ultimately dominating the accretion of the planets and major satellites, in zones approaching and exceeding the local Roche density. Only in the case of Jupiter, gravitational instability appears to have dominated from the outset; the other planets are regarded as hybrid structures, having started from limited accretions. In Section 3 the empirical information on protostars is reviewed. ‘Globules’ are described, found to have the typical range of stellar masses and with gaseous compositions now well known thanks largely to radio astronomy. They contain also particulate matter identified as silicates, ice, and probably graphite and other carbon compounds. The measured internal velocities would predict a spread of total angular momenta compatible with the known distribution of semi-major axes in double stars. The planetary system is regarded as an ‘unsuccessful’ binary star, in which the secondary mass formed a nebula instead of a single stellar companion, with 1–2% of the solar mass. This mass fraction gives a basis for an estimate of thefrequency of planetary systems. The later phases of the globules are not well known empirically for the smaller masses of solar type; while available theoretical predictions are mostly made for non-rotating pre-stellar masses. Section 5 reviews current knowledge of the degree of stability of the planetary orbits over the past 4.5×10⁹ yr, preparatory to estimates of their original locations and modes of origin. The results of the Brouwer and Van Woerkom theory and of recent numerical integrations by Cohenet al. indicate no drastic changes in Δa/a over the entire post-formation history of the planets. Unpublished numerical integrations by Dr P. E. Nacozy show the remarkable stability of the Jupiter-Saturn system as long as the planetary masses are well below 29 times their actual values. Numerical values of Δa/a are collected for all planets. The near resonances found for both pairs of planets and of satellites are briefly reviewed. Section 6 cites the statistics on the frequency and masses of asteroids and information on the Kirkwood gaps, both empirical and theoretical. An analogous discussion is made for the Rings of Saturn, including its extension observed in 1966 to the fourth Saturn satellite, Dione. The reality, or lack of it, of the divisions in the Rings are considered. The numbers of Trojan asteroids are reviewed, as is the curious, yet unexplained, bimodal distribution of their orbital inclinations. Important information comes from the periods of rotation of the asteroids and the orientation of their rotational axes. The major Hirayama families are considered as remnants of original asteroid clusterings whose membership has suffered decreases through planetary perturbations. Other families with fewer large members may be due to collisions. The three main classes of meteorites, irons, stones, and carbonaceous chondrites all appear to be of asteroidal origin and they yield the most direct evidence on the early thermal history of the solar system. While opinion on this subject is still divided, the author sees in the evidence definite confirmation of thecold origin of the planetary system, followed by ahot phase due to the evolving sun that caused the dissolution of the solar nebula. This massive outward ejection, that included the smaller planetesimals, appears to have caused the surface melting of the asteroids by intense impact, with the splashing responsible for the formation of the chondrules. The deep interiors of the asteroids are presumably similar to the C1 meteorites which have recently been found to be more numerous in space by two orders of magnitude than previously supposed.     

Computer studies of the evolution of planetary and satellite systems I. Description of the program: Preliminary tests

In this paper we describe a CDC-Cyber 74 program for computer simulation of the evolution of a system consisting of a large number of objects in orbit around a central body or primary. Some preliminary tests done with the program will also be described.     

E3D,the Euro3D visualization tool I: Description of the program and its capabilities

We present the first version of E3D, the Euro3D visualization tool for data from integral field spectroscopy. We describe its major characteristics, based on the proposed requirements, the current state of the project, and some planned future upgrades. We show examples of its use and capabilities. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The OPD photometric survey of open clusters I. Techniques,program details and first results of robust determination of the fundamental parameters

Open clusters are considered valuable objects for the investigation of galactic structure and dynamics since their distances, ages and velocities can be determined with good precision. According to the New Catalog of Optically Visible Open Clusters and Candidates (Dias et al., 2002) about 10% of the optically revealed open clusters remain unstudied. However, previous analysis (Moitinho, 2010) has indicated that not considering this unstudied population introduces significant biases in the study of the structure and evolution of the Milky Way. In addition, a systematic revision of the data contained in the catalog, collected from the literature, is needed, due to its inhomogeneity.In this first paper of a series, we present the observational strategy, data reduction and analysis procedures of a UBRVI photometric survey of southern open star clusters carried out at Pico dos Dias Observatory (Brazil). The aim of the program is to contribute to an unbiased, homogenous collection of cluster fundamental parameters. We show that the implementation of a sequence of systematic procedures considerably improves the quality of the results.To illustrate the methods we present the first results based on one night of observations. The parameters, reddening, distance, age and metallicity, were obtained by fitting theoretical isochrones to cluster color–color and multidimensional color–magnitude diagrams, applying a cross-entropy optimization algorithm developed by our group, which takes into account UBVRI photometric data weighted using a membership-likelihood estimation.     

Satellite laser ranging and its applications

Satellite laser ranging (SLR) provides an important capability for precise orbit determination and for geophysical parameter estimation to support a number of contemporary geodynamic and oceanographic investigations. The precision of the SLR measurement has improved from the early meter-level systems to the current capabilities of a few centimeters for the best systems. The accuracy of the orbits and geophysical parameter recovery have shown an associated improvement. Polar motion with accuracies of 2 mas, station coordinates better than 10 cm, and interstation baseline rates indicative of tectonic motion are determined routinely with the current set of global SLR data. This discussion reviews the SLR measurement, analysis approach, and some of the recent results derived from the current SLR data set.     

A perturbation method and some applications

For differential equations with one fast variable, a perturbation method is introduced that transforms a solution valid over only a short time interval to a new solution composed of averaged variables plus a periodic function of the averaged variables. The averaged variables are governed by a set of differential equations where the fast variable has been removed and thus can be numerically integrated quickly or solved directly. This method is applied to a perturbed harmonic oscillator with a cubic perturbation, van der Pol's equation, coorbital motion in the restricted three-body problem, and to nearly circular motion of a particle near one of the primaries in the restricted three-body problem.     

The Soviet CETI program

In March 1974 the Board of the Scientific Council on the Radio Astronomy Problem Area, Academy of Sciences of the USSR, considered and approved a Research Program on the Problem of Communication with Extraterrestrial Civilizations. The Program was developed by the Search for Cosmic Signals of Artificial Origin section of the Council on Radio Astronomy, on the basis of recommendations made at the Soviet National Conference on the Problem of Comunication with Extraterrestrial Civilizations held at the Byurakan Astrophysical Observatory in Armenia in May 1964, and the Soviet-American CETI conference held at Byurakan in September 1971. The projected program was reported to the 7th Soviet National Conference on Radio Astronomy, which convened at Gor'kii in 1972.     

Experimental determination of partitioning in the Fe‐Ni system for applications to modeling meteoritic metals

Experimental trace element partitioning values are often used to model the chemical evolution of metallic phases in meteorites, but limited experimental data were previously available to constrain the partitioning behavior in the basic Fe‐Ni system. In this study, we conducted experiments that produced equilibrium solid metal and liquid metal phases in the Fe‐Ni system and measured the partition coefficients of 25 elements. The results are in good agreement with values modeled from IVB iron meteorites and with the limited previous experimental data. Additional experiments with low levels of S and P were also conducted to help constrain the partitioning behaviors of elements as a function of these light elements. The new experimental results were used to derive a set of parameterization values for element solid metal–liquid metal partitioning behavior in the Fe‐Ni‐S, Fe‐Ni‐P, and Fe‐Ni‐C ternary systems at 0.1 MPa. The new parameterizations require that the partitioning behaviors in the light‐element–free Fe‐Ni system are those determined experimentally by this study, in contrast to previous parameterizations that allowed this value to be determined as a best‐fit parameter. These new parameterizations, with self‐consistent values for partitioning in the endmember Fe‐Ni system, provide a valuable resource for future studies that model the chemical evolution of metallic phases in meteorites.