We investigate the development of Kelvin-Helmholtz instabilities in magnetized jets by means of high-resolution spatial simulations. Our main finding is the existence of a stabilizing mechanism driven by the initial disruption of the jet. This mechanism gives rise to a local amplification of the magnetic field, which in turn leads to an enhanced stability of the jet configuration.

In his book Plurality of Worlds, Steven J. Dick (1984) has chronicled the millennia of discourse about other inhabited worlds, based upon deeply held religious or philosophical belief systems. The popularity of the idea of extraterrestrial life has waxed and waned and, at its nadir, put proponents at mortal risk. The several generations of scientists now attending this General Assembly of the International Astronomical Union at the beginning of the 21st century have a marvelous opportunity to shed light on this old question of habitable worlds through observation, experimentation, and interpretation, without recourse to belief systems and without risking their lives (though some may experience rather bumpy career paths). The newly-named and funded, multi-disciplinary field of astrobiology is extremely broad in its scope and is encouraging IAU members to learn and speak the languages of previously disparate disciplines in an attempt to answer the big picture questions: ‘Where did we come from?’, ‘Where are we going?’, and ‘Are we alone?’ These are questions that the general public understand and support, and these are questions that are attracting students of all ages to science and engineering programs. These questions also push the limits of modern instrumentation to explore the cosmos remotely across space and time, as well as to examine samples of interplanetary space returned to the laboratory and samples of distant time teased out of our own Earth.

Within my personal event horizon, the other planetary systems long-predicted by theorists have been uncovered, along with many whose structures were not predicted. The ‘just-so’ conditions requisite for the comfort of astronomers have been understood to be only a very narrow subset of the conditions that nurture extremophilic, microbial life. Thus the potentially habitable real estate beyond Earth has been greatly expanded and within the next few decades it may be possible to detect the biosignatures or technosignatures of inhabitants on distant worlds, should there be any.

The Tully-Fisher Relation (TFR) links two fundamental properties of disk galaxies: their luminosity and their rotation velocity (mass). The pioneering work of Vogt et al. in the 1990's showed that it is possible to study the TFR for spiral galaxies at considerable look-back-times, and use it as a powerful probe of their evolution. In recent years, several groups have studied the TFR for galaxies in different environments reaching redshifts beyond one. In this brief review I summarise the main results of some of these studies and their consequences for our understanding of the formation and evolution of disk galaxies. Particular emphasis is placed on the possible environment-driven differences in the behaviour of the TFR for field and cluster galaxies.

We carried out relativistic force free simulations and Particle In Cell (PIC) simulations of twist injection into the magnetic arcades emerging on the surface of a magnetar. As the magnetic energy is accumulated in the arcades, they expand self-similarly. In the arcades, a current sheet is formed and magnetic reconnection takes place. We also carried out 2-dimensional PIC simulations for the study of particle acceleration through magnetic reconnection. As a result, the energy spectrum of particles can be fitted by a power-law.

In this work we estimated the statistical age of a set of HII galaxies obtained from the Sloan Digital Sky Survey Data Release Three (SDSS DR3). Applying an inversion method to the observed distribution of an age sensitive parameter such as the equivalent width of (Hα), we estimate the age of the galaxies. We find strong dependence of the age with stellar luminosity, mass and metallicity with the youngest HII galaxies being those with the lowest mass and metallicity. These dependences found among HII galaxies indicate that “downsizing” extends to the low end of the mass distribution of galaxies.

The star forming region S235A-B has been studied at high resolution with radio (IRAM Interferometer and VLA) and infrared (JCMT and Spitzer) observations. The region was mapped in HCO+, C34S, H2CS, SO2 and CH3CN as well as in the 1.2 and 3.3 continuum, in the cm continuum at 6, 3.6, 1.3 and 0.7 cm and in the 22 GHz water maser line, in the far infrared at 450 and 850 μm and in the mid infrared from 3.6 to 8 μm. Finally, use was made of the Medicina water maser patrol, from 1987 to 2005, to study the maser variability.

Turbulent convection carries most of the solar luminosity from the stable radiative interior to the visible surface over a substantial fraction of the solar radius. The turbulent motions are highly nonlinear displaying activity on several spatial and temporal scales. The effects of these motions are to redistribute angular momentum, mix light elements, excite gravity waves and power magnetic activity. In this talk, I shall review some of the recent efforts, mostly based on numerical simulations, to model turbulent convection spanning multiple scale heights. I will discuss what we have learnt about the nature of convective transport, and what the relevant timescales are on which convection operates.

A remarkable and intriguing fact is that few DB white dwarfs, i.e., objects with a helium-rich atmosphere, are found in the effective temperature range between 45000-30000 K, and this exclusion zone is known as the DB gap. Since the temperatures of the blue and the red edges of the DB gap coincide with the effective temperatures where HeII/III and HeI/II convection zones show up respectively, convective mixing is suspected to be the cause of the appearance of DBs outside the DB gap. Chemical separation due to gravitational settling in the convectively stable atmosphere is then suspected to be the cause of the presence of the DB gap. The white dwarfs which turn back to DBs after the DB gap phase are expected to have a semiconvective layer, which is superadiabatic but convectively stable, when they are located near the red edge of the DB gap. Such white dwarfs are expected to be pulsationally unstable. Discovery of pulsation in them will open up a new class of pulsating white dwarfs to asteroseismic study.

We show how the expansion of classical Galactic Hii regions can trigger massive-star formation via the collect & collapse process. We give examples of this process at work. We suggest that it also works in a turbulent medium.

We discuss implications of a strong flare event observed in the Seyfert galaxy MCG–6-30-15 assuming that the emission is due to localized magnetic reconnection. We conduct detailed radiative transfer modeling of the reprocessed radiation for a primary source that is elevated above the disk. The model includes relativistic effects and Keplerian motion around the black hole. We show that for such a model setup the observed time-modulation must be intrinsic to the primary source. Using a simple analytical model we then investigate time delays between hard and soft X-rays during the flare. The model considers an intrinsic delay between primary and reprocessed radiation, which measures the geometrical distance of the flare source to the reprocessing sites. The observed time delays are well reproduced if one assumes that the reprocessing happens in magnetically confined, cold clouds.

γ Per looks like an unexceptional composite–spectrum binary, and has habitually been classified as G8 III+A3 V. Nevertheless, previous studies have produced conflicting results, of component masses that are uncomfortably high, or luminosities that are too large, or (most recently) showing that there is nothing abnormal about the components after all. However, new high-precision CCD spectroscopy and isolation of the secondary spectrum finds that mass of the giant is 3.9 M⊙, which is indeed greater than would be expected from its published spectral type, and that both components have somewhat enhanced luminosities, thus re-opening the question of the origin and evolution of this somewhat unusual system.

I review the potential for observing cosmic re-ionization using the HI 21 cm line.

We analyzed a new photometry of this well-known Algol-like eclipsing binary together with old photoelectric measurements with the aim of better understanding of its orbital period changes and short-time light variations modulating the mean light curve. The analysis has been done by the new method based on the combination of the principal component analysis and robust regression. New spectroscopic observations and radial-velocity curve are also presented.

Galaxies in groups and clusters often experience strong tidal forces from its neighbors, expelling a significant amount of matter (stars and gas) to the surrounding environment, giving rise to ‘tidal debris’ features. We present the first experiments in a program of identification of substructures of extragalactic tidal debris elements in images from the HST archive, using wavelet-based multiresolution analysis. Tidal structures in two compact groups of galaxies, HCG 79 (Seyfert's Sextet) and HCG 92 (Stephan's Quintet) have been analyzed so far.

Fe K emission line is a powerful probe of the inner part of an accretion disk. We analyze X-ray spectra of 43 Palomar-Green (PG) quasars taken from Boroson & Green (1992) observed with XMM-Newton and make an averaged Fe K line profile. We study the Eddington ratio dependence of the Fe K line profile. The width of the Fe line becomes broader (σ=0.1 to 0.7 keV) and its peak energy becomes higher (6.4 to 6.8 keV) as the Eddington ratio gets larger.

These results indicate that the physical state of the accretion disk, such as the geometrical structure and/or ionization state, changes with the Eddington ratio.

Major mergers of gas-rich galaxies, each comparable in mass to the Milky Way, are rare at the present epoch. These events were readily identifed, however, two decades ago in far-infrared sky surveys (Soifer et al. 1986, 1987). Removal of the dust enshrouding these starbursts was almost immediately proposed as an evolutionary path to quasar formation (Sanders 1988). Recent measurements of the stellar velocity dispersion, rotation speed, and stellar surface brightness profile of these mergers suggest ULIRGs are indeed progenitors of field elliptical galaxies (Genzel et al. 2001; Tacconi et al. 2002).

We attempt to provide new insights into the kinematics of narrow-line regions (NLR) in Seyfert galaxies and quasars, the understanding of which, as well as of their intrinsic 3D morphology, is still rather limited. Motivated by the rise of the integral-field spectroscopy, capable of mapping full 2D velocity fields, and by our observational projects on NLRs (see e.g. Stoklasová et al., this volume) we have developed a computer code producing 2D kinematical maps resulting from projections of various gas geometries and velocity fields.

The standard mixing length model of convection is ill behaved at the centre of a star since the pressure scale height Hp=P/(ρg)→∞ as r→0, and the convective flux remains non zero at r=0. We propose a modifcation of this model of convection that has the correct behaviour in the central regions of a star and smoothly changes to the standard MLT away from the centre.

The formation of special binaries in a globular cluster is regulated by the total encounter rate γ in the cluster, but their life expectancy by the number of encounters γ that one system experiences. The orbital periods indicate whether a neutron star or white dwarf entered a binary via direct collision, via tidal capture, or via exchange encounter. The numbers of X-ray binaries with a neutron star scales with γ. Magnetically active binaries (including blue stragglers) are formed via evolution of primordial binaries, and their numbers scale with the cluster mass. Cataclysmic variables are formed by stellar encounters or via evolution of a primordial binary in clusters with high and low central density, respectively.

It is great privilege for me to welcome so many of you to Prague, or Praha as we call our capital in Czech.

We have been witnessing a very rapid development of observational techniques over the past few decades, leading to many exciting discoveries, quite often in the field of extragalactic research. I sometimes sense the tendency to consider the studies of binaries and stars in general as exhausted topics. However, we all know that the better our real and deep understanding of the principal sources of radiative energy in the Universe becomes, the safer will be the ground for studies of all higher hierarchical systems.