Estimates of the region of Nekhoroshev stability of Jupiter's Trojan asteroids are obtained by a direct (i.e. without use of the normal form) construction of formal integrals near the Lagrangian elliptic equilibrium points. Formal integrals are constructed in the Hamiltonian model of the planar circular restricted three body problem (PCRTBP), and in a mapping model (Sándor et al. 2002) of the same problem for small orbital eccentricities of the asteroids. The analytical estimates are based on the calculation of the size of the remainder of the formal series by a computer program. An analysis is made of the accumulation of small divisors in the series. The most important divisors introduce competing Fourier terms with sizes growing at similar rates as the order of truncation increases. This makes impossible to improve the estimates by considering nearly resonant forms of the formal integrals for particular near-resonances. Improved estimates were obtained in a mapping model of the PCRTBP. The main source of improvement is the use of better variables (Delaunay). Our best estimate represents a maximum libration amplitude $D_p=10.6^0$. This is a quite realistic value which demonstrates the usefulness of Nekhoroshev theory.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

One of the main characteristics of Mercury is its 3:2 spin-orbit resonance, combined with a 1:1 resonance between the orbital node of its orbit and the angle describing the precession of the rotation axis, both measured on the ecliptic plane. We build an analytical model, using Hamiltonian formalism, that takes into account this phenomenon thanks to the introduction of three resonant variables and conjugated momenta. We calculate the equilibria corresponding to four different configurations, which means four completely different values of the (ecliptic) obliquity; in particular, we focus on the present (stable) situation of Mercury, and thanks to several canonical transformations, we obtain, near the equilibrium, three pairs of angle-action variables, and consequently, three basic frequencies. Let us note that the model is as simple as possible: the gravitational potential is limited to the second degree terms (the only ones for which a value can be presently given), and the orbit of Mercury is Keplerian. The numerical values obtained by our simplified model are validated by the coherence with existing complete numerical models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present observations of a spectacular eruption of a huge quiescent prominence, which was clearly associated with a coronal mass ejection (CME). The CME consisted of a typical three-part structure: a bright loop-like leading edge, a dark cavity and a bright core. The prominence exhibited a very symmetrical loop-like eruption in low corona and matched well with the bright CME core trailing the CME leading edge. By combining the $H_{\alpha}$, 17GHz and EUV observations with white-light coronagraphs observations, the bright CME core was conclusively identified as the erupting cool, dense prominence material.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A solid observational characterization of cluster regions around the virial radius would allow us to improve considerably our understanding of the physics of galaxy clusters as a whole: sadly current and planned experiments will not allow us to study these regions. Unbeknownst to most but not all, the development of an experiment sensitive to cluster outer regions could be achieved with currently available technology, with no need for breakthroughs. Amongst the major factors that will decide whether and when such an experiment will be flown are the awareness of the cluster community of the importance of such a mission and its determination at supporting it.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Mutual event observations started in the early 1970s with the Galilean satellites. These observations were needed because of the Voyager spacecraft future arrival. Since 1979, IMCCE has organized observational campaigns for the Galilean satellites (called PHEMU), and since 1995 for the Saturnian satellites (also called PHESAT). Meanwhile, the reduction techniques have been greatly improved. Mutual event observations are one of the most accurate methods for obtaining positions of natural satellites, useful for detecting tidal effects. Hence mutual events of Jovian and Saturnian natural satellites are regularly observed around the world. This paper aims to describe mutual events and the advantages of this kind of observation besides the classical astrometric ones.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present an overview on the state of the gas in cluster outskirts. We show that the entropy of the gas in the outskirts often exhibit strong deviations from predictions based on the cluster scaling. We identify the cause of these deviations with incomplete shock propagation observed in clusters with ongoing major merging, survival of substructure and incomplete thermalization, and emission from the surrounding large-scale structure seen in projection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Diffusion of elements in a stellar plasma is strongly modified by the presence of magnetic fields for two primary reasons. The first is that the average motions of ions in outer atmospheres are, because of their charge, substantially constrained by the magnetic field. Both its intensity and orientation play a role. The second is the Zeeman desaturation of absorption lines that often produces amplifications of the radiative accelerations. These effects are important and must lead to the building of complex surface abundance structures. I will present how these two effects are generally modeled and what results have, up to now, been obtained. Future developments will also be considered.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss two methods for constraining the equation of state of dark energy using strong gravitational lensing by galaxy clusters. In the so called “arc statistics” approach, we compare the cluster efficiency for producing giant arcs in several dark-energy cosmologies and in the “standard” $\Lambda$CDM and OCDM models. We find that the expected abundance of gravitational arcs depends on the equation of state of dark energy and reflects the dependence of halo concentrations on cosmology. In agreement with results in previous works, the lensing cross section is very sensitive to dynamical processes occurring in the lenses. Then we use gravitational arcs for tracing the position of the lens critical curves and we measure their scaling with the source redshift in a variety of cosmological models. We find that there is a degeneracy between several lens properties and the equation of state of dark energy which can be broken only after an extremely precise modeling of the lens. Instead of using this “golden lens” approach, we check whether combining the information from a statistical sample of clusters we can distinguish among the various cosmologies. We test the method on a sample of numerically simulated clusters and we reproduce the results expected from the analytic models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the observational results of the solar bursts on the band of 1-80 GHz (NORH) associated with both a CME and a flare on Oct. 26 2003. This event shows two parts of radio bursts in the time profile. The first part is associated with an X1.2 flare. However, the following part seams related to both the flare and the CME, as the radio emission is enhanced while the ${\rm H}\alpha$ is decreasing. Thus, these two parts of radio bursts may originate from different physical processes, i.e., flare and CME shock. A primary study is performed on the difference between this two parts.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the NLR emission line spectrum of 12 NLS1s to constrain the EUV – soft X-ray continuum SED using accurate photoionization modeling. We find that the NLR emission line ratios, which we measure for several NLS1 galaxies, can be reproduced within ±15% without a strong BBB component in the framework of a two-component model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We model hot collisionless solar corona/slow solar wind (SW) by kinetic Vlasov equation. The equatorial region with an unprescribed magnetic field is under electromagnetic action, and we have formation of a 3D Quasi-Stationary Coronal Structures (QSCS) in the current-carrying (CC) plasma with SW flows. The QSCS are generated via electromagnetic mode development in plasma having anisotropic velocity distribution function (VDF). As a result we get streamers like stratification mode, CMEs like tearing mode and heliospheric sheet like pinch mode in anisotropic plasma. The scales in the QSCS are defined via angle dependent magnetic Debye scale. The scale itself depends on value and sign of plasma anisotropy parameter which is calculated for postulated plasma VDF.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyze the effect of the temporary capture of comet-like orbits in asteroid mean motion resonance by following the dynamical evolution of 2090 Jupiter-family comet-like orbits over ${\sf 10^7}$ yr under the perturbation of the four major planets. The resonant capture may be related to the phenomenon known as “resonant stickiness” consisting in the temporary stabilization of very eccentric orbits near the separatrices of the mean motion resonances. We found that the population of orbits that were captured at least once during the simulation has a median lifetime larger than that of the complete sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Several observational anomalies seem to confirm the presence of abundance gradients as a function of depth in different types of chemically peculiar stars. Results emanating from the construction of model atmospheres that take into account the abundance gradients caused by radiative diffusion will be presented. The atmospheric structure, which is calculated self-consistently along with the abundance gradients, will be compared to models with homogeneous abundances. Recent improvements brought to these models will be discussed, along with the intricacies of these calculations and the remaining uncertainties. Several possible applications of such models will also be presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Events of energetic particles from solar X-ray flares and shock waves have been studied. The data were taken from the National Geophysical data center (NGDC) in Boulder, Colorado, USA, Where the data were taken during the solar cycle 23rd. The 23rd cycle is the present one, that started in April 1996, and its maximum was in May 2001, and it will be decayed during year 2007. Power spectrum methods have been applied for analysis of the data given, to find the short and intermediate periodicities. The periodicity around 14 days has appeared in this analysis. This has important implications for understanding and predicting the effects of solar activity on the Earth and on the earth's atmosphere. If a Coronal Mass Ejections (CMEs) hit the Earth, it can excite a geomagnetic storm. Large geomagnetic storms, among other things, can cause electrical power which can damage satellite communications. In space CME typically drive shock waves that produce energetic particles that can damage both electronic equipment and astronauts that are outside the protection of the Earth's magnetic field. So, the prediction of the high energetic particle events is of vital importance for space navigation and airline disasters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using the observations of the EUV Imaging Telescope(EIT) and the Large Angle Spectrometric Coronagraph(LASCO) on the Solar and Heliospheric observatory(SOHO) and solar soft X-ray flux and radio bursts data, we study the low coronal signatures of a solar limb coronal mass ejection(CME) on November 4, 2003. The two prominent dimmings in EIT difference images were closely related to two large loops in this event. The onset time and height of the CME and the lower limit of the masses loss from dimming regions are estimated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The orbital distribution of asteroids and Kuiper-belt objects (KBOs) provides important information for the dynamical evolution of the solar system. Recent advances in modelling the dynamics of asteroids and KBOs have increased our understanding of the mechanisms responsible for the main features observed in the small-body belts. There are, however, several pieces left to complete the puzzle of the dynamical history of the solar system. In particular, we now understand that the solar system probably looked very different during the first $500-1000$ Myr than today, mainly because of two processes that took place during those times: (i) planetary formation and (ii) planetary migration. I will discuss observational and dynamical constraints that any model, attempting to reconstruct this early period, should obey. I will then present a new model for planetary migration, which successfully reproduces the observed orbital distribution of the trans-Neptunian objects. I will then discuss the implications of this model on the early evolution of the inner solar system, in particular the distribution of main-belt asteroids and the bombardment of the terrestrial planets by small bodies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss how strong lensing by galaxy clusters may be used to study the properties of dark matter halos and the expansion history of the universe. First, we show how the characteristics of $\Lambda$CDM clusters determine their lensing properties, and show how these properties are manifested in some of the new giant arcs discovered behind SDSS clusters. Next, we compare the statistics of strong lensing by clusters expected in the $\Lambda$CDM model to the observed statistics of giant arcs and wide-separation quasars. Finally, we discuss the cosmographic uses of clusters with multiple arcs, pointing out several sources of noise which can produce $\gtrsim100$ % errors in derived cosmological parameters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on our theoretical and numerical results concerning the transport mechanisms in the asteroid belt. We first derive a simple kinetic model of chaotic diffusion and show how it gives rise to some simple correlations (but not laws) between the removal time (the time for an asteroid to experience a qualitative change of dynamical behavior and enter a wide chaotic zone) and the Lyapunov time. The correlations are shown to arise in two different regimes, characterized by exponential and power-law scalings. We also show how is the so-called “stable chaos” (exponential regime) related to anomalous diffusion. Finally, we check our results numerically and discuss their possible applications in analyzing the motion of particular asteroids.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Brightness variations across the entire electromagnetic spectrum, occurring at several time scales, are known properties of blazars. The variability of the continuum emission may be related to the formation and propagation of shock waves in the relativistic jet. In this case we may expect variations also in the degree of polarization and its position angle. In order to effectively constrain such models, we begun in 2003 a program to monitor the optical polarimetry of a sample of blazars, of which we present here the first results.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present spatially resolved X-ray spectra taken with the EPIC cameras of XMM-Newton of a sample of 17 cooling clusters and three non-cooling clusters for comparison. The deprojected spectra are analyzed with a single-temperature model. All cooling clusters show a central decrement of the average temperature, most of them of a factor of $\sim$2. Three clusters show a weak temperature decrement, while two others have a very strong temperature decrement. We investigate the role of heat conduction by electrons and find that the theoretically predicted conductivity rates are not high enough to balance radiation losses.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html