This paper explores the advantages of using gravity assisted trajectories to perform flyby and rendezvous missions to accessible near-Earth asteroids (NEAs), in terms of the total velocity budget required for the mission. Combining the Opik's formalism of close encounters with the Monte Carlo sampling technique and Lambert trajectories, we give a general picture of the accessibility regions for NEAs in phase space of orbital elements, without considering the phasing requirements between bodies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We show the utility of the Systematic Ranging technique by analyzing the orbit determination of asteroid 2004 FU$_{162}$, which passed approximately 6400 km from the surface of the Earth on March 31, 2004. The limited observations introduce strong nonlinearities that must be accounted for when estimating the actual encounter distance.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The new cutting edge technologies have opened the possibility of using digital spectrometers to probe the sky. With the sampling rate of $\sim$400 Msamples/s and the capability to digitally process data in real-time it is possible to get wideband spectra covering the frequencies in the range 0-200 MHz with the resolution of a few kHz. This presentation will show how such a spectrometer can be applied to the forward-scattering method of meteor detection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent years have seen a revolution in the possibility to understand cometary capture, i.e., the origin of the cometary population that moves in orbits confined to the inner Solar System. This is due to the discovery of the major source populations: the Edgeworth-Kuiper belt, and the scattered disk. We review the current understanding of the links between the distant sources, including the Oort cloud, and the observed, short-period population, and the problems that remain. Some highlights of present research in this field will serve to illustrate recent progress and major issues that are currently arising.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The current version of the IAU Meteor Data Centre catalogue of photographic orbits comprising the orbital and geophysical data of 4581 meteors is applied for a more representative search of the mean orbits of bolide meteor streams among photographic meteors. We have made the search based on a computerized stream search procedure utilizing the Southworth-Hawkins D-criterion. The results are compared with the previous similar analysis made by Porubčan & Gavajdová (1994).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Planetary systems are made up of objects with sizes ranging from gas giant planets down to asteroids and on to micron sized dust. Dust in the zodiacal cloud in the solar system originates in the break-up of asteroids and comets and then migrates in toward the Sun due to P-R drag. The dynamical evolution of the dust is also affected by the gravitational perturbations of the solar system's planets, and the consequence of those perturbations is evident in the asymmetric and clumpy structure of the zodiacal cloud. In the last couple of years features in the cloud have been identified with asteroid collisions which occurred just a few Myr ago implying that steady state models for the zodiacal cloud will have to be reconsidered. Many extrasolar systems also harbor massive dust belts and the structures of those dust belts have been linked to perturbations from unseen planets. This paper reviews the dominant physical processes affecting the evolution of dust grains and describes the techniques which have been developed to model their dynamics and identify the sources of dust structures in both the solar system and extrasolar systems.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A complete study is made of the 5/2 resonant motion of two planets revolving around a star, in the model of the general planar three body problem. Families of 5/2 resonant symmetric periodic orbits are computed numerically, for the masses of the extrasolar system 47 UMa. The phase of the two planets (alignment or antialignment of perihelia and position of each planet at perihelion or aphelion) plays an important role, and the change of the phase, other things being the same, may destabilize the system. Stable motion exists even in the case where the two planetary orbits intersect. A small value of the eccentricities, for the same phase, stabilizes the system. The above results are applied to the study of 47 UMa, which according to some observations is close to the 5/2 resonance.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A novel method for the preliminary identification of asteroids at discovery and a few days thereafter is being developed in Helsinki. Having two different sets of asteroid observations, the goal is to identify all possible pairs of objects between the sets. An arbitrary asteroid can either remain unidentified, or be preliminary linked to one or more asteroids. In the case of ambiguity, the final decision must usually be based on additional observations. We use a multistep approach, during which possible pairs of objects are first selected by comparing ephemerides that have been generated for three common epochs. The method has been successfully tested using both Very Large Telescope observations, and simulated observations of near-Earth and main-belt objects. Identification results of simulated observations indicate that the observing strategy promoted by the Minor Planet Center might not be the best one, at least for the purposes of identification. The ultimate goal is to produce a real-time asteroid identification tool for ESA's astrometric space observatory Gaia, the Lowell Observatory Near-Earth-Object Search, the Near-Earth Space Surveillance mission, and the Nordic Near-Earth Object Network. The tool could also benefit large-scale surveys done with the Large Synoptic Survey Telescope, and the Discovery Channel Telescope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

To date, more than 130 extrasolar planets around main sequence stars are revealed mainly by the Doppler radial velocity measurements. Due to the observational biases, most of the detected planets are moving in orbits close to the host stars, with some in highly eccentric orbits. Dynamical processes during the late stage of planet formation are important to account for the present orbital properties. These processes include: planet migrations and resonance trappings caused by gravitational interactions between protostellar disk and planets, dynamical scattering due to interactions between planets, etc. In this paper, we review the major effects of these dynamical processes on the orbital characteristics of the planet systems.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we present the new possibilities of classical ground – based observations for the purpose of improving the proper motions of some HIPPARCOS stars. The coordinates of asteroids, comets and other objects are calculated mostly by using the relative method and presented in a relevant reference frame via nearby stars (at the moment of observation) which materialize that reference frame. To improve the proper motions of stars we can use the latitude/universal time variations of ground – based data. Here, the results of improved proper motions in declination of some HIPPARCOS stars are presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

During the final production stages of the above article, the images of Figures 4 and 5 were transposed. The correct layout, with legends are reproduced below.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Results of the photographic observations of 61 Cyg are given. The orbital elements and mass ratio of the components of the pair are calculated. The preliminary orbit of a hypothetical satellite with a period of 6.5 yr is given.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An internacional project “Lithium in magnetic Ap stars” has been run since 1996 with the purpose of creating an observational database allowing systematic studies of the abnormal occurence of lithium on the surface of cool Ap stars. The 2.6 m telescope at the Crimean Astrophysical Observatory, the ESO CAT, ESO 1.52 m telescope with FEROS, the Nordic Optical Telescope, and the 74″ telescope at Mount Stromlo were employed to collect observations at the regions of the lithium resonance lines $\lambda 6103$ and $\lambda 6708 \AA$.

Observations of the roAp-stars HD 83368, HD 60435 and HD 3980 revealed considerable periodical Doppler shifts of the line of lithium $\lambda 6708 \AA$ which can be explained by the presence of lithium spots on their surfaces. Conjunction with structures of the magnetic field is apparent.

A detailed study of the blend at $\lambda 6708 \AA$ in HD 101065 confirmed the anomalous overabundance of lithium amounting to 3.1 dex, as well as unusual isotopic ratio $^6{\rm Li}/^7 {\rm Li} \sim 0.3$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of observations made over three weeks using the UCT CCD Photometer on the 0.75-m telescope at the South African Astronomical Observatory. Candidate long period roAp stars were identified from their positions on the H-R diagram and observed for a typical period of 4 hr to test for the existence of pulsations, with particular emphasis on pulsations with periods in excess of 15 min. Although 13 stars were successfully observed, none exhibited significant pulsations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The lines of lithium at $\lambda 6708$ and $\lambda 6103$ are analyzed in high resolution spectra of some sharp-lined and slowly rotating roAp stars. Three spectral synthesis codes, STARSP, ZEEMAN2 and SYNTHM were used. New lines of the Rare Earth Elements from the DREAM database, and lines calculated on the basis of the NIST energy levels were included. Magnetic splitting and other line broadening processes were taken into account. Enhanced abundances of lithium in the atmospheres of the stars studied are obtained for both lithium lines. High estimates of $^6{\rm Li}/^7{\rm Li}$ ratio ($0.2\div0.5$) for the studied stars can be explained by Galactic Cosmic Ray (GCR) production by spallation reactions and the preservation of the original $^6{\rm Li}$ and $^7{\rm Li}$ by the strong magnetic fields.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Putting their chemically peculiarities aside, Ap and Am stars have many common properties. The discriminating property between them could be the rotation of their interiors beneath their slowly rotating surface. In the PV Cas (HD 240208) binary system whose light curve shows Ap-like variation, the agreement between the theoretical and observed apsidal advance rate is satisfied only with differentially rotating models of the component stars in which rapid rotation is extended almost to the surface. Thus, it seems that there is a steep rotation rate gradient near the surface of the Ap stars. The conclusion we reach in the analysis of PV Cas system leads us to introduce the effective mass as a new conceptual tool in stellar astrophysics: $M_{\rm eff}= M_\star (1-\bar{\Lambda})^{1.75}$, where $M_\star$ and $\bar{\Lambda}$ are mass of the star and average of ratio of centrifugal to the gravitational acceleration throughout the model, respectively. We find that the effective mass of PV Cas A whose true mass is $2.82\pm 0.05\,M_\odot$ is $2.6\,M_\odot$ for both solar and metal rich compositions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I present recent observations from two Hubble Space Telescope(HST)/ACS programs that target the most X–ray luminous and thus (presumably) most massive galaxy clusters at $z{=}0.5$ – the highest redshift at which complete, well–defined samples of such rare systems are available. The first program (GO:9836, PI: R.S. Ellis) exploits a huge mosaic of 41 ACS pointings spanning a 10 Mpc region centered on MS0451-03. This is the largest contiguous space–based image of a cluster to date. I describe a preliminary weak–lensing analysis and a new Keck/DEIMOS redshift catalog of 1000 galaxies in this field. The second program (GO:9722, PI: H. Ebeling) studies the core regions of the twelve most luminous clusters at $z{\ge}0.5$ from the MAssive Cluster Survey (MACS; Ebeling et al. 2001). Multi–color ACS observations in combination with recent Keck/LRIS spectroscopy of gravitational arcs constrain the distribution of mass in the cluster cores, thus laying the foundation for detailed multi–diagnostic (lensing, X–ray, near–infrared, SZE) investigation of this sample. For example, it is of particular interest to explore how the structure and state of relaxation of massive clusters evolved between this sample at $z{\ge}0.5$ that measured by Smith et al. (2004, astro–ph/0403588) at $z{=}0.2$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I derived the elemental abundances of metallic-line star 2 UMa, using high-dispersion, high signal-to-noise ratio spectra obtained from Dominion Astrophysical Observatory. This study used Kurucz's ATLAS9 and WIDTH9 programs. The star was selected as 1) it has not been the subject of a detailed elemental abundances analysis, and 2) it is relatively sharp-lined and hot enough so that the continuum can be well placed even in the blue. For even cooler Am stars determining the continium will be a major problem. As a guide for the broad-lined and cooler Am stars, a spectral line atlas of 2 UMa will be prepared.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The kinetic equilibrium of Nd II -Nd III in the atmospheres of A-type stars is investigated for the first time with a model atom containing 1651 levels of Nd II, 607 levels of Nd III, and the ground state of Nd, IV. NLTE leads to an overionization of Nd II resulting in weakening the Nd II lines at mild neodymium overabundances relative to the solar Nd abundance ([Nd/H] $\lt$ 2.5) and produces the opposite effect at the higher [Nd/H] values. NLTE abundance corrections grow with effective temperature and reach $\sim$0.6 dex at $\Teff$ = 9500 K. The Nd III lines are strengthened compared with LTE. NLTE abundance corrections range between -0.3 dex and -0.2 dex for $\Teff$ between 7500 K and 9500 K. Therefore NLTE effects may explain ionization discrepancies up to 0.8 – 0.9 dex, derived with the LTE approach.

NLTE effects are even larger for a stratified Nd abundance distribution compared with a homogeneous one resulting in positive NLTE abundance corrections up to 1.4 dex for the Nd II lines and negative ones as small as to -0.5 dex for the Nd III lines. The influence of uncertainty in the photoionization cross-sections on NLTE results is investigated. NLTE calculations were applied to Nd analyses in the atmospheres of roAp stars $\gamma$ Equ and HD 24712.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We observed the magnetic field of the CP star $\alpha^2$ CVn with the 6-m telescope and the echelle-spectrometer (spectral resolution $R=50000$, spectral range $\lambda\lambda 3400--4100$) using a CCD device and Zeeman analyzer. The longitudinal magnetic field $B_{\rm e}$ measured using lines with wavelengths shorter than the Balmer jump ($\lambda 3646$) are systematically 25% smaller at all rotational phases compared with measurements made in the region $\lambda > 3646$. Because in general lines with $\lambda > 3646$ form at deeper levels than lines with $\lambda < 3646$ we get additional evidence for the increase of $B_{\rm e}$ with depth in the atmosphere of $\alpha^2$ CVn.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html