The distribution of Near-Earth Objects, in particular Near-Earth asteroids is examined using maximum likelihood methods. These are analysed with respect magnitudes, taxonomic classes and to their orbital distances. Comparisons are made with the distributions of main-belt asteroids and short-period comets.

Multi-wavelength analyses of an increasing number of post-AGB stars reveal that they constitute a more inhomogeneous population of stars than previously thought. The new data collected in the last few years allow us to study these sources with unprecedented spatial resolution and to extend our spectroscopic knowledge in a systematic way to the infrared for the first time, where crucial information is contained on the chemical composition of the gas and dust in their circumstellar shells. The overall infrared properties derived from ISO and Spitzer data can be used to trace the mass loss history and the chemical evolution of the ejected material. The new results impose severe observational constraints on current nucleosynthesis models and suggest that the evolution is determined not only by the initial mass but also by the metallicity of the progenitor star. Post-AGB samples are likely to grow in the near future with the advent of new data from space facilities like Spitzer or Akari. Studies of post-AGB stars in the galactic halo, the Magellanic Clouds and other galaxies of the Local Group will certainly improve our knowledge on the evolutionary connections between AGB stars and PNe.

We successfully ported the suite of codes developed by R. L. Kurucz for stellar atmosphere modelling, abundance determination and synthetic spectra calculation, to run under GNU-Linux. The ported codes include ATLAS 9 and ATLAS 12 for 1-D plane-parallel atmosphere model calculation, DFSYNTHE, which calculates the Opacity Distribution Functions (ODF) to be used with ATLAS 9, WIDTH to derive chemical abundances from measured line Equivalent Widths (EW) and SYNTHE to calculate synthetic spectra. The codes input and output files remain fully compatible with the VMS versions, while the computation speed has been greatly increased due to the high efficiency of modern PC CPUs. As an example, ATLAS 9 model calculations and the computation of large (e.g. 10 nm) synthetic spectra can be executed in a matter of minutes on any mainstream laptop computer. Arbitrary chemical compositions can be used in calculations (by using ATLAS 12 through opacity sampling or by calculating ad-hoc ODFs for ATLAS 9). The large set of scripting languages existing under Linux (shell, perl, python. . .) and the availability of low-cost multiprocessor Linux architectures (such as Beowulf) makes the port highly effective to build model farms to produce large quantities of atmosphere models or synthetic spectra (e.g. for the production of integrated light synthetic spectra). The port is hosted on a dedicated website including a download section for source codes, precompiled binaries, needed data (opacities, line lists and so on), sample launch scripts and documentation.

We use RHESSI hard X-ray observations to constrain acceleration of solar flare electrons, generally considered to be a primary recipient of the released energy.

One of the main ingredients of current stellar population models is a library of stellar spectra. Both empirical and theoretical libraries are used for this purpose, and the question about which one to use is still being debated in the literature. Empirical and theoretical libraries are improving significantly over the years, and many libraries have become available lately. It is not clear what are the advantages of using each of these new libraries, and how far behind are models compared to observations. Here we compare in detail some of the modern theoretical libraries availabe in the literature against empirical libraries attempting to detect their weaknesses and strengths. The aim is to be able to compute in the short future a new synthetic stellar library that combines the best qualities of the current available ones, while improving considerably their weaknesses.

We present a first attempt to derive the cosmological evolution of the kinetic luminosity function of AGN based on the joint evolution of the flat spectrum radio and hard X-ray selected AGN luminosity functions. An empirical correlation between jet power and radio core luminosity is found, which is consistent with the theoretical assumption that, below a certain Eddington ratio, SMBH accrete in a radiatively inefficient way, while most of the energy output is in the form of kinetic energy.

We show how the redshift evolution of the kinetic power density from such a low-ṁ mode of accretion makes it a good candidate to explain the so-called “radio mode” of AGN feedback as outlined in many galaxy formation schemes.

The advent of larger telescopes and powerful instrumentation enables the exploration of new aspects of faint eclipsing binaries that are just now becoming accessible. An example of this are eclipsing binaries in Local Group galaxies such as the LMC, SMC, M31 and M33, whose study yields not only stellar properties of stars formed in different chemical environments (thus providing useful model tests) but also direct distance determinations to the host galaxies. In general this is also applicable to eclipsing binaries belonging to any stellar ensemble. Another example is the observation and study of eclipsing very-low mass stars, brown dwarfs and planets. Besides the need for large telescopes because of their faintness, these also benefit from improved observational capabilities in the infrared spectral windows. Here we discuss the prospects for eclipsing binary research using photometry and spectroscopy from large telescopes.

We explain the generation of the large-scale unipolar magnetic field regions (global magnetic regions) by the same dynamo action as for the generation of the sunspots and the polar faculae butterfly diagrams as given by Callebaut (2006). The previous global magnetic regions through meridional circulation now serve as the main seed fields (flux-transport dynamo for the global field regions), possibly supplemented by leftovers from the sunspots and some weak fields generated at the tachocline.

We have performed numerical simulations which were designed to further our understanding of the turbulent interstellar medium (ISM). Our simulations include a multi-phase thermodynamic model of the ISM, magnetic fields, and sheared rotation, allowing us to study the effects of the magnetorotational instability (MRI) in an environment containing high density cold clouds embedded in a warm, low density, ambient medium. These models have shown that the MRI is indeed a significant source of turbulence, particularly at low mean densities typical of the outer regions of the Milky Way, where star formation rates are low, but high levels of turbulence persist. Here, we summarize past findings, as well as our most recent models which include vertical stratification, allowing us to self-consistently model the vertical distribution of material in the disk.

We use two methods to establish the relationship between galaxies and dark matter halos. One is based the conditional luminosity function model, which links galaxies and dark matter halos by matching the number density and clustering properties of galaxies with those of dark matter halos in the current CDM model. The second is based on galaxy systems identified from large redshift surveys of galaxies. The galaxy – dark halo relationships established by these two methods match well, and can provide important constraints on how galaxies form and evolve in the universe.

We present 1.6-4.7 $\mu$m images of PPNe and young PNe recently obtained with the Keck Adaptive Optics (AO) system. These observations provide higher angular resolution and probe deeper into the dusty envelopes of post-AGB objects than HST images and, therefore, show with unprecedented detail the morphology of these nebulae. Some objects have limb-brightened lobes displaying a remarkable point-like symmetry, which suggests the presence of underlying precessing jets that may be carving out the nebular lobes. Our images also show a very rich structure at the very small scale of $\sim$0.” 1, including jet-like features, arcs, searchlight beams, as well as faint, extended halos in a number of objects.

With relatively low funds, the Departamento de Astronomía de la Universidad de Guanajuato, in Mexico, has successfully carried out the modernization of a rustic astronomical observatory. At this site, once it is fully refurbished, it is planned to hold not only public observations, but also to have an ambitious programme of science popularization devoted to scholars.

I assess the similarities and differences between the star-formation modes in quiescent spiral galaxies versus those in violent starburst regions, including galactic nuclei. As opposed to the quiescent star-formation mode, current empirical evidence on the star-formation processes in the extreme, high-pressure environments induced by galaxy encounters strongly suggests that star cluster formation is an important and perhaps even the dominant mode of star formation in such starburst events. This implies that by using star clusters as unique diagnostic probes, we can trace a galaxy's most violent star formation history very well, at least for the past few Gyr. The sizes, luminosities, and mass estimates of the young massive star clusters are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). Recent evidence lends support to the scenario that GCs, which were once thought to be the oldest building blocks of galaxies, are still forming today.

The astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at z ∼ 6 are poorly understood. In standard ΛCDM hierarchical cosmologies, the earliest massive holes (MBHs) likely formed at redshift z ≳ 15 at the centers of low-mass (M ≳ 5 × 105 M⊙) dark matter “minihalos”, and produced hard radiation by accretion. FUV/X-ray photons from such “miniquasars” may have permeated the universe more uniformly than EUV radiation, reduced gas clumping, and changed the chemistry of primordial gas. The role of accreting seed black holes in determining the thermal and ionization state of the intergalactic medium depends on the amount of cold and dense gas that forms and gets retained in protogalaxies after the formation of the first stars. The highest resolution N-body simulation to date of Galactic substructure shows that subhalos below the atomic cooling mass were very inefficient at forming stars.

Starting from 2.5D MHD modelling of solar flares on a global scale we calculate (using the PIC and test-particle simulations) the radio and X-ray emissions generated in solar flare reconnection. Our results – the radio and X-ray spectra and brightness distributions, and their dynamics – are directly comparable with observations providing thus a test of particle acceleration models as well as of the ‘standard’ global flare scenario.

We are calculating stellar spectra for types A through K using Kurucz codes, Castelli models, and Kurucz laboratory lines plus guessed identifications for other lines in the spectra. Weighted coadditions of these spectra are being constructed to match spectra observed in integrated light of old stellar systems such as elliptical galaxies and globular clusters. Grids of theoretical spectra, both stellar and composite, that include an enhancement of light elements and span a wide metallicity range will be calculated over 2200Å–9000Å, and will be archived on MAST at the Hubble Space Telescope website. Here we summarize our results and describe how we automate the fit to our grid of an observed high-resolution stellar or globular-cluster spectrum, to determine the stellar parameters or to break the age-metallicity degeneracy.

We use numerical simulations of granulation in the Sun and a K dwarf to study the effects of coherent structures on higher order moments. The latter need to be calculated in non-local Reynolds stress models of turbulent convection. Models that explicitly account for the asymmetry between up- and downflows as well as hot and cold drafts provide a substantial improvement over traditional ones, such as the quasi-normal approximation, which is only able to provide order of magnitude estimates for this type of flow.

In the last decade, over 7000 eclipsing binaries have been discovered in the Local Group through various variability surveys. Measuring fundamental parameters of these eclipsing binaries has become feasible with 8 meter class telescopes, making it possible to use eclipsing binaries as distance indicators. Distances with eclipsing binaries provide an independent method for calibrating the extragalactic distance scale and thus determining the Hubble constant. This method has been used for determining distances to eclipsing binaries in the Magellanic Clouds and the Andromeda Galaxy and most recently to a detached eclipsing binary in the Triangulum Galaxy by the DIRECT Project. The increasing number of eclipsing binaries found by microlensing and variability surveys also provide a rich database for advancing our understanding of star formation and evolution.

Solar flares are of great fundamental and practical interest. In some events the energy release might exceed 1026J Tsurutani et al. (2003) and accompanying CME courses extremely severe magnetic storm. Because of very rare occurrence of such global flares a laboratory simulation appears to be an alternative that could provide experimental data necessary for physical understanding of this phenomenon and for verifying theoretical models. Flare involves processes on many widely varying spatial and time scales. In laboratory only some parts of the whole evolution could be attempted for simulation. The present work is focused on the last stage of eruption when a magnetic loop filled with heated plasma is ejected away from the Sun, either itself or pushed by an upcoming jet. The geometry of a flare loop suggests that a magnetic dipole and laser-produced plasma could be used to simulate this structure Nikitin & Ponomarenko (1995). In the present work similarity criteria that relate laboratory parameters to the natural phenomena, experimental set up and preliminary results are presented.

Turbulence is believed to be important to star formation both within GMCs (affecting the IMF and the SFE), and on larger scales in the ISM (affecting GMC formation rates and properties). The traditional view of the ISM attributes most of the turbulent driving to stellar sources – in particular, supernovae and HII regions. However, evidence suggests that sources other than star formation must contribute significantly to large-scale turbulent driving in the diffuse ISM, thus also affecting the turbulence that GMCs inherit. I review recent investigations of alternative sources proposed for driving ISM turbulence, including thermal instabilities, the magnetorotational instability, large-scale self-gravitating modes, and instabilities in spiral shocks. I summarize results based on numerical simulations regarding the levels of turbulence that can be driven, and how these amplitudes depend on galactic conditions. This recent work shows that, under certain circumstances, very large-amplitude (trans-sonic with respect to the warm gas) motions and magnetic fields can be driven even without stellar energy inputs. Since turbulence can either trigger or limit star formation, understanding these potentially large non-stellar driving sources is crucial for a developing a theory of star formation regulation in the Milky Way and other disk galaxies.