When a celestial body, e.g., an asteroid, has been observed only over a short time, its orbit is not well determined but may be anywhere in a confidence region where the astrometric residuals are acceptable. This region can be sampled by a swarm of Virtual Asteroids (VA) sharing the reality of the asteroid: one of them is real, but we do not know which one. The problem is how to sample the confidence region with a small number of VA, still being able to solve the main problems of asteroid recovery/identification and impact monitoring.

One class of methods uses random sampling of the confidence region to mimic with the VA population the probabilistic distributions of the orbits. This class includes the Monte Carlo and the Statistical Ranging methods. When it is critical to detect a very small probability (e.g., of a catastrophic impact) by computing a small number of VA orbits, and also when a large catalog of asteroids has to be handled, it is more efficient to sample the confidence region with a geometric object, such as a smooth manifold: it can be sampled uniformly, taking into account its dimension. Our group has developed in the last 6-7 years 1-dimensional sampling methods based upon a differentiable curve, the Line Of Variations (LOV), which can represent, in suitable cases, the spine of the confidence region. The LOV is sampled by uniformly spaced VA, thus interpolation between consecutive VA is possible. This is the basis for the current algorithms of Impact Monitoring, used in Pisa and at JPL. The LOV method is also used for recovery of lost asteroids and for identification of independent discoveries of the same object.

When the asteroid has moved on the sky while being observed by $<1^\circ$, the confidence region is wide in two directions and the LOV may be an inappropriate way of sampling it. We have recently developed 2-dimensional sampling methods based upon the concept of Admissible Region, a 2-dimensional manifold parameterized by a compact subset of the range/range-rate plane. This region is then sampled by triangulation, with each node used as a VA. This allows to define methods for asteroid identification/recovery and for impact monitoring starting from very poor data, such as the ones collected during a single night of observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High resolution radio and X-ray observations of a subsample of composite LINER/H II galaxies with arcsec-scale radio cores were obtained. These observations yield a 12% detection rate of low luminosity AGN among the entire composite sample in the Palomar survey. Four of these low luminosity AGN also possess sub-parsec jet-like radio extensions. While canonical advection-dominated accretion flows may be responsible for the radio and X-ray emission in submillijansky cores like NGC 7331, they do not appear consistent with the radio emission in these milliarcsecond-scale radio cores; the latter sources are more likely to have an energetically important contribution from a radio-emitting jet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Analysis of time series of the solar magnetic field energy (SMFE) at various solar latitudes ($\varphi = -75^{\circ}\div +75^{\circ}$) has been done. Higuchi's technique Higuchi(1988) to measure the fractal dimension (FD) of time series has been chosen and the daily values $B(\varphi,t)$ of the solar magnetic field on the source surface for 1960-1999 have been used. These values had been computed in IZMIRAN using method by Obridko et al. (1994) As a matter of fact, Higuchi's measurements of the FD of time series $X_t$ comes to calculation of the length of the curve $l(k)\sim<\mid X_{t+k}-X_t\mid >k^{-2}$ and estimate of the coefficient $D$ in equation $\lg {l(k)}=A-D\lg k$ for considered range of $k$. The dimensions $D(\varphi,K)$ of the time series $B(\varphi,t)^2$ have been computed for various time scales $0<k<K$ $([k]=[t]=1^d)$. It has been found that at $k>10-27$ the time series of SMFE form fractal with $D\approx1.9$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

While there is convincing evidence that the central regions ($r \ll R_e$) of early-type galaxies are dominated by stars and that the outer regions ($r \gg R_e $) are dominated by dark matter, the structure of early-type galaxies in the transition region (a few effective radii $R_e$) between the stars and the dark matter is unclear both locally and in gravitational lenses. Understanding the structure of galaxies in this transition region is a prerequisite for understanding dark matter halos and how they relate to the luminous galaxy. Potentially the best probe of this region is the sample of $\sim 80$ strong gravitational lenses. I review the determination of mass distributions using gravitational lenses using image positions, statistics, stellar dynamics, time delays and microlensing. While the present situation is confusing, there is little doubt that the existing problems can be resolved by further observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We derive here the mean temperature profile for a sample of hot, medium distant clusters recently observed with XMM-Newton, whose profiles are available from the literature, and compare it with the mean temperature profile found from BeppoSAX data. The XMM-Newton and BeppoSAX profiles are in good agreement between 0.05 and 0.25 $r_{180}$. From 0.25 to about 0.5 $r_{180}$ both profiles decline; however the BeppoSAX profile does so much more rapidly than the XMM-Newton profile.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We calculate multicomponent radiatively driven stellar wind models suitable for A stars. We discuss the possible decoupling of individual elements from the stellar wind and its influence on the chemical peculiarity of these stars. We obtain a range of stellar parameters for different types of multicomponent flow.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on a Coronal Mass Ejection (CME) observed on June 27 1999 by the UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on board the SOHO spacecraft. The CME was also observed by LASCO (SOHO). Emission of hot material has been recorded by UVCS propagating in front of an opening system of loops generated by the CME. The evolution of the UVCS structure is highly correlated to the evolution of the opening loop. The data reveal excess broadening of the O VI doublet lines and an enhancement in the intensity of the Si XII$\lambda 520.66$ and $\lambda499.37$ lines due to the motion of the expanding hot gas. The hot gas emission seems to be due to a shock wave propagating in front of a very fast gas bubble traveling along the opening loop system.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

With the substantial improvements in observational techniques we have to deal with very big databases, consisting of a few positions of an object over a short time span; this is often not enough to compute a preliminary orbit with traditional tools. In this paper we first review a classical method by C.F. Gauss to compute a preliminary orbit for asteroids. This method, followed by a least squares fit to improve the orbit, still today gives successful results when we have at least three separate observations. Then we introduce the basics of a very recent orbit determination theory, that has been thought just to be used with modern sets of data. These data allow us in many cases to know the angular position and velocity of an asteroid at a given time, even though the radial distance and velocity $(r,\dot r)$, needed to compute its full orbit, are unknown. The variables $(r,\dot r)$ can be constrained to a compact set, that we call the admissible region(AR), whose definition requires that the body belongs to the Solar System, that it is not a satellite of the Earth, and that it is not a “shooting star” (i.e. very close and very small). We provide a mathematical description of the AR: its topological properties are surprisingly simple, in fact it turns out that the AR cannot have more than two connected components. A sampling of the AR can be performed by means of a Delaunay triangulation; a finite number of six-parameter sets of initial conditions are thus defined, with each node of the triangulation representing a possible orbit (a virtual asteroid).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Spectroscopic optical data (∼4200-6300 Å in the rest-frame) acquired during the monitoring of some QSOs seem to confirm that AGN spectra normally harden at higher luminosities. Focusing only on the global trend (i.e. comparing different objects), the implications in deriving luminosities using optical photometric data (through the K-correction) is briefly outlined here, as well as the result of its parameterization for calculating BH masses through the M$_{BH} \propto$ L$_V^\gamma$ (FWHM Hβ)2 virial relation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Transits of Venus occur in pairs 8 yr apart, the pairs separated by intervals of either 112 or 130 yr, because of the pattern of approximate orbital resonances. Transits of Mercury show a different pattern, partly because of the more eccentric orbit, and also because the structure of the approximate resonances is different. The near-resonance in Venus' axial rotation strongly suggests a tidal link with the Earth.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Despite of the large number of detections of new asteroids, both in the main belt and in the near-Earth space, our observational knowledge of the asteroid populations is not quite complete. Our catalogs are affected by observational biases. Thus, a modeling work is required in order to infer the real distributions of the asteroid populations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In spite of the great progress of solar physics research, complete understanding of the solar activity nature is still lacking. Although everybody can observe the obvious cyclical sunspot variation, recent models of the process can not describe it quite accurately. Thus the official forecast of the 23-rd solar cycle, mainly basing on the dynamical models and precursors, was not proved. Many official predictions considered that the cycle 23 will have an amplitude higher than the previous one. In this case statistical models were neglected as the less reliable but some of those kinematic forecasts are proved to this time. This situation makes evidence that we have to not ignore statistical approaches in the study of the solar behavior at the current stage of the knowledge.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Observations of multiple-image gravitational lens systems suggest that the projected mass distributions of galaxy haloes may contain substantial inhomogeneities. The fraction of the halo mass in dense substructure is still highly uncertain, but could be as large as a few percent. While halo substructure is seen in numerical simulations of CDM haloes, little of this substructure survives in the innermost regions of haloes, and thus the observational claims for substructure at small projected radii are slightly surprising. There is evidence, however, that even the highest-resolution simulations published to-date are still limited by numerical effects that heat and disrupt substructure artificially in high-density regions. By comparing numerical and semi-analytic (SA) models of halo substructure, we show that current simulations probably underestimate the mass fraction in substructure at small projected radii, by a factor of at least 2–3. We discuss the prospects for using lensing observations as a fundamental test of the nature of dark matter.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe the current status of a programme we started a few years ago to observe a large number of A/F and Am/Fm stars in open clusters of various ages. Spectra were obtained with the AURELIE and ELODIE spectrographs at a resolving power of about 40000 and $S/N$ ratios from 100 up to 500. Abundances of 11 chemical elements have been derived by using Takeda's (1995) procedure. A short review on previous abundance determinations of A and F dwarfs in open clusters and a progress report on the current status of this project are presented. New abundance determinations for 24 A and F dwarfs in the Coma Berenices cluster are presented. These abundance determinations serve to set constraints to self-consistent evolutionary models of A and F stars including transport processes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have analized XMM-Newton data of A2199, a nearby ($z\,=\,0.030$), relaxed, rich cluster of galaxies, whose X-ray emission is strongly peaked on the central galaxy, NGC6166, suggesting the existence of a cluster cool core (Peres et al. 1998). The background subtraction is performed using an observation characterized by features similar to those of the A2199 observation. We have selected, in the XMM-Newton archive, a field observation presenting the following properites:

[bull ] duration of about 90 ksec;

[bull ] performed with the same filter as the A2199 observation;

[bull ] characterized by a galactic HI column density and a soft X-ray background, the latter being calculated from the ROSAT All-Sky survey diffuse background maps, which differ from those of the A2199 observation ($N_H\,=\,8.7 \times 10^{19}\,\,{\rm cm}^{-2}, R_{45}\,=\,208.2 \times 10^{-6}\,\,{\rm cts/arcmin}^2$) by 3% and 30% respectively.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We selected 133 solar microwave bursts (SMBs) recorded by SGD and 133 CMEs observed by SOHO/LASCO from November 1999 through September 2003. These SMBs are associated with CMEs and flares. We analyzed the characteristics of the SMBs, including duration, flux peak, burst type, and spectral index. Correlated events were distinguished by time and the location of flare associated with the SMB. We find that (1)The duration of SMBs associated with narrow(0°<width<20°)/normal CMEs(20°<width<120°) or slow CMEs is below 40 minutes. (2)The duration of SMBs associated with Halo-like CMEs(120°<width<360°) or fast CMEs is from several minutes to 200 minutes. (3)The flux peak of SMBs associated with narrow CMEs/normal CMEs or slow CMEs is below 400sfu. (4)The flux peak of SMBs associated with Halo-like CMEs or fast CMEs is from several sfu to several thousands sfu. (5)the majority of SMBs,which are associated with Full Halo CMEs, are Complex/GB bursts. The majority of SMBs, which are associated with narrow CMEs/normal CMEs, are simple bursts. (6)U-shape spectra are observed. The spectra of SMB associated with CME is very flat when f>fmax. A statistical result suggest that CME/flares and SMBs is probably a different manifestation of the same physical process. CME/flare and SMB have intrinsically a physical relationship.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of over 20 years of optical spectroscopic monitoring of the prototypical double-peaked emitter, Arp 102B. Its distinct double-peaked, extremely broad (FWHM ≈15,000 km s−1) low-ionization lines (Hα, Hβ, and Mg II) are well-modeled by emission from photoionized gas in a relativistic Keplerian accretion disk around a central black hole (Chen & Halpern 1989; Halpern et al. 1996). A ubiquitous property of double-peaked emitters is long-term variability in the shape of their line profiles on the timescale of months to years, which is consistent with the dynamical timescale of an accretion disk. This variability can be attributed to inhomogeneities in the line-emitting disk, i.e., hot spots, spiral arms, eccentricity, and warps. We characterize the profile variability of Arp 102B in detail, and use it to constrain physical models for the structure and dynamics of its line-emitting accretion disk.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use $\Lambda$CDM numerical simulations to model the density profiles and substructure populations in a set of sixteen dark matter halos with resolutions of up to seven million particles within the virial radius. These simulations allow us to follow robustly the formation and evolution of the central cusp over a large mass range of 10$^{11}$ to 10$^{14}$$\msun$ down to approximately 0.5% of the virial radius, and from redshift 5 to the present. The cusp of the density profile is set at redshifts of two or greater and remains remarkably stable to the present time, when considered in non-comoving coordinates.

We fit our halos to a 2 parameter profile where the steepness of the asymptotic cusp is given by $\gamma$, and its radial extent is described by the concentration, $c_{\gamma}$. In our simulations, we find $\gamma$ = 1.4 - 0.08Log($M/M_*$) for halos of 0.01$M_*$ to 1000$M_*$, with a large scatter of $\Delta\gamma \sim \pm 0.3$; and $c_{\gamma} = 8(M/M_*)^{-0.15}$ with a large $M/M_*$ dependent scatter roughly equal to $\pm c_{\gamma}$. Our redshift zero halos have inner slope parameters ranging approximately from r$^{-1}$ to r$^{-1.5}$, with a median of roughly r$^{-1.3}$. This two parameter profile fit works well for all halo types present in our simulations, whether or not they show evidence of a steep asymptotic cusp.

The substructure population is independent of host halo mass and redshift with halo to halo scatter in the substructure velocity distribution function of a factor of roughly two to four. The radial distribution of substructure halos (subhalos) is consistent with the mass profile over the radial range where the possibility of artificial numerical disruption of subhalos can be most reliably excluded, r$\simgt$0.3 r$_{vir}$, although a weakly shallower subhalo profile is favored by the data. We discuss the implications that our results have on gravitational lensing studies of halo structure.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

Abundance determinations obtained from spectroscopic observations of Am stars provide information concerning the transport processes present in these stars. In this paper we have used models of Am stars which include gravitational settling, thermal diffusion, and radiative accelerations for 24 elements. We used a specific model of rotation induced mixing which has reproduced anomalies in other types of stars. For this preliminary study, models of $1.7 M_{\odot}$ and $1.9 M_{\odot}$ have been computed. A comparison of the predicted abundances to the observed ones for the Praesepe star HD 73045 sets constraints on rotational mixing.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html