This article was co-authored by all invited speakers at Joint Discussion 6 on Neutron Stars and Black Holes in Star Clusters, which took place during the IAU General Assembly in Prague, Czech Republic, on August 17 and 18, 2006. Each section presents a short summary of recent developments in a key area of research, incorporating the main ideas expressed during the corresponding panel discussion at the meeting.

Observations give tight constraints on the temporal and spatial scales of particle heating in solar flares, and on the required efficiency. Electrons are accelerated into a quasi-thermal population of a few tens of keV. X- and γ-rays imply tails in electron and ion distributions reaching tens of MeV and above. Simple estimates indicate that all available electrons are accelerated at least once to moderate energies, pointing to an initial process resembling bulk heating rather than acceleration of a small or localized population. In the absence of effective collisions, wave-particle interactions are the prime candidate. Here we address the outstanding questions, (i) what process can heat the entire reconnecting plasma to the above energies, and (ii) what provides the free energy for wave-particle interactions? We propose a process in which initially the ions are heated and provide the free energy for electron heating and tail formation.

We investigate the near-infrared K-band evolution of early-type galaxies in the cluster of galaxies Abell2390 at z = 0.23. Using the Omega-Prime camera at the 3.5-m Calar Alto telescope deep imaging (texp = 53 min) over a 6' × 6' field has been obtained. The measured K-band magnitudes of 28 galaxies are combined with the spectroscopic and morphological data of Fritz et al. (2005) to construct the Faber-Jackson and Fundamental Plane relations in the NIR. By comparing our distant galaxies to a local sample of cluster ellipticals (Pahre 1999), we find on average a mild luminosity evolution for both scaling relations (ΔMK ~ 0.6 − 0.7 mag) compatible with passive evolution of the stellar populations.

Simulating disk galaxies within the current paradigm of galaxy formation has been a long standing problem. In comparison with observations, the simulated disks were too small and too centrally concentrated, due to a large loss of angular momentum during formation. This is known as the angular momentum catastrophe (Navarro & Benz (1991)). Recently, some progress has been made in reducing this effect by changing the cosmology, including various feedback mechanisms, improving numerical resolution and carefully selecting initial conditions with a quiet merging history after z≈2. Unfortunately, it remains unclear which of these effects, or which combination, has resulted in more realistic disk formation. In order to address this problem, we conduct a systematical study using the N-body code GADGET2 (Springel (2005)). We adopt a flat ΛCDM cosmology with Ωm=0.3, ΩΛ=0.7, Ωbar=0.04 and h=0.65. Using a softening of 0.5 kpc we find disks with a very compact unresolved gas clump in the center and a thin, extended disk (R≈10kpc) of very low mass around it.

In this invited contribution I review the justifications for the attempts, currently very popular, to include in semi-analytic models of galaxy formation prescriptions to describe the mutual link between the star formation and nuclear activity in galaxies, which has been for surprisingly long time neglected.

The majority of normal disk galaxies are characterized by non-axisymmetric structures like spirals or bars. These structural elements have been widely discussed in the literature as a result of gravitational instabilities which are connected to growing density waves or global instabilities of disks. A first insight into the properties of galactic discs was provided by linear stability analysis. However, a disadvantage of linear stability analysis remained its restriction to small perturbations, both in amplitude and wavelength. Thus, numerical simulations, especially hydrodynamical and stellar-hydrodynamical simulations became a primary tool for the analysis of galactic evolution.

Motivated by the GALEX discovery of recent star formation in outermost regions of M83 and NGC4625, we have investigated the nature of the XUV disks with follow-up high resolution imaging and spectroscopy, and attempted to detect them at other wavelengths (IR, Hα). We searched for additional XUV-disk galaxies in the local universe, in order to quantify the incidence of the XUV-disk phenomenon, infer the causes of such extended star formation (SF), and place these systems in the context of disk galaxy evolution.

Chandra and XMM, offering between them high angular resolution, substantial collecting area, and spatially-resolved spectroscopy at good spectral resolution, have given us the means to discover hitherto unanticipated phenomena, in groups as in clusters, and to explore a new set of issues that bring us closer to understanding the formation and evolution of groups and their constituent galaxies: the distribution of heavy elements, the presence of X-ray cavities and their relation to radio observations, the nature of cooling cores, and X-ray signatures of recent galaxy interactions. We here show Chandra and XMM data selected to illustrate recent results regarding some of these themes.

The Kepler Mission is a space-based photometric mission with a differential photometric precision of 14 ppm (at V = 12 for a 6.5 hour transit). It is designed to continuously observe a single field of view (FOV) of greater then 100 square degrees in the Cygnus-Lyra region for four or more years. The primary goal of the mission is to monitor more than one-hundred thousand stars for transits of Earth-size and smaller planets in the habitable zone of solar-like stars. In the process, many eclipsing binaries (EB) will also be detected and light curves produced. To enhance and optimize the mission results, the stellar characteristics for all the stars in the Kepler FOV with V < 16 will have been determined prior to launch. As part of the verification process, stars with transit candidates will have radial-velocity follow-up observations performed to determine the component masses and thereby separate eclipses caused by stellar companions from transits caused by planets. The result will be a rich database on EBs. The community will have access to the archive for further analysis, such as, for EB modeling of the high-precision light curves. A guest observer program is also planned to allow for photometric observations of objects not on the target list but within the FOV.

The critical property of the black hole is the presence of the event horizon. It may be detected only by means of the detailed study of the emission features of its surroundings. The temporal resolution of such observations has to be better than ∼ rg/c, and it lies in the 10−6–10s range depending on the black hole mass. In SAO RAS we have developed the MANIA hardware and software complex based on the panoramic photon counter and use it in observations on 6m telescope for the search and investigation of the optical variability on the time scales of 106–103 s of various astronomical objects. We present the hardware and methods used for these photometrical, spectroscopic and polarimetrical observations, the principles and criteria of the object selection. The list of the latter includes objects with featureless optical spectra (DC white dwarfs, blazars) and long microlensing events.

We present the results of the observations of two objects-candidates – long MACHO event MACHO-1999-BLG-22 and radio-loud x-ray source with featureless optical spectrum J1942+10 – on the 6-m telescope in June-July 2006.

Samples of Extremely Red Galaxies (ERGs) have generally been seen to comprise a mix of actively star-forming galaxies with significant dust reddening and evolved, passive galaxies, at redshifts about z ≈ 1 − 2. Initial results from deep Keck spectroscopy of ERGs (Doherty et al. 2005) revealed dominant old stellar populations in 75% of our spectroscopic sample, but only 28% have spectra with no evidence of recent star formation activity, such as would be expected for a strictly passively-evolving population. This study suggests that the bulk of the ERGs are luminous, spheroidal, evolved galaxies, but undergoing intermittent activity consistent with continued growth.

Through a detailed investigation of individual galaxies in our sample we aim to address various outstanding questions. What fraction of their mass is produced in ongoing star formation? Is there a characteristic mass at which star formation is abruptly truncated? What mechanism provokes a secondary burst of star formation in evolved galaxies?

We fit Bruzual & Charlot (2003; BC03) simple stellar population models to the broad band SEDs over a wide baseline, using a reduced χ2 minimisation, to investigate ages, stellar masses and star formation histories. The fits for the early types agree well with information in the spectra and return ages of 2–3 Gyr and masses in the range 1011–1012M⊙. The objects with recent star formation episodes are more complex. Some are fit well by continuous star formation models, accounting for the effects of dust. We are now in the process of exploring multi-population fits to investigate the effects of episodic bursts.

Previous morphological studies of ERGs have revealed a diverse mix of galaxies – a combination of pure bulges, disks and a small fraction of irregular or interacting systems. We are curious to determine whether a morphological analysis produces results consistent with the spectroscopic properties of our sample. We are investigating a sub-sample of our galaxies which have HST imaging publically available. Initial results from a quantitative analysis using bulge/disk decomposition with GALFIT and GIM2D indicate that most galaxies with Early type spectra are bulge dominated. In contrast, a significant fraction of the galaxies showing spectroscopic signatures of on-going star formation on top of underlying old stellar populations appear to have a well-established classical spiral morphology, wih knots of star formation located in spiral arms around a central bulge. There is tenuous evidence (under further investigation) that at least half of the post-starbursts in our sample are barred spirals, lending support to theories relating post-starbursts to recent mergers.

Our goal is to evaluate the role of triggering effects on the star formation and early stellar evolution by presenting a statistically large sample of cloud and low-mass YSO data. We conducted large area surveys (ranging from 400 square-degree to 10800 square-degree) in optical, NIR and FIR. The distribution of the ISM and low-mass YSOs were surveyed. A relative excess was found statistically in the number of dense and cold core bearing clouds and low mass YSOs in the direction of the FIR loop shells indicating a possible excess in their formation.

Differential rotation not only occurs in astrophysical plasmas like accretion disks, it is also measured in laboratory plasmas as manifested in the toroidal rotation of tokamak plasmas. A re-examination of the Lagrangian of the system shows that the inclusion of the angular momentum's radial variation in the derivation of the equations of motion produces a force term that couples the angular velocity gradient with the angular momentum. This force term is a property of the angular velocity field, so that the results are valid wherever differential rotation is present.

We simulate the reactive-hydrodynamic flow for a variety of convective shell burning epochs in supernova progenitor models. The neutrino-cooled stages of carbon, neon, oxygen, and silicon burning are simulated in two and three dimensions. Even in the absence of rotation significant symmetry breaking occurs (10% in rms variation in thermodynamic variables such as temperature and density). These distortions are caused by turbulent convection interacting with stably stratified boundaries. Strong interactions of multiple active shells is seen; it is mediated by waves generated by convection. Some implications for supernova progenitors are presented.

We have demonstrated the first near-infrared multi-object spectrograph, CIRPASS, on the 4.2-m William Herschel Telescope (WHT) and the 3.9-m Anglo-Australian Telescope. We have conducted an Hα survey of 38 0.77 < z < 1 galaxies over ~100 arcmin2 of the Hubble Deep Field North and Flanking Fields, to determine star formation rates (SFRs) using CIRPASS on the WHT. This represents the first successful application of this technique to observing high redshift galaxies (Doherty et al. 2004). Stacking the spectra in the rest-frame, we find a lower limit (uncorrected for dust reddening) on the star formation rate density at redshift z = 1 of 0.04 M⊙ yr−1 Mpc−3 (Doherty et al. 2006). This implies rapid evolution in the star formation rate density from z = 0 to z = 1 which is proportional to (1 + z)3.1. We intend to extend our work with FMOS on Subaru as the evolSMURF project (the Evolution of Star-formation and Metallicity in the Universe at high Redshift with FMOS). This will represent nearly two orders-of-magnitude improvement on previous work, and for the first time will provide a sample of sufficient size to measure accurately the Hα luminosity function, and so determine the global star formation rate using the same indicator as used in local surveys. Using [O II]3727 Å, Hβ, [O III] 5007 Å and Hα redshifted into the z, J & H bands, we can chart the star formation history over 70% of the age of the Universe, affording complete coverage up to z = 1.6 with the same well-understood diagnostics. The line ratios will also allow the extinction and metallicity to be measured at z>1. This will resolve one of the long-standing puzzles in extragalactic astrophysics – the true evolution of the Madau-Lilly diagram of star formation density.

The seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory (SOHO). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology.

Long-baseline optical interferometry (LBI) can nearly close the gap in selection space between astrometric and spectroscopic detection of binary star systems, bringing the complementary powers of astrometry and spectroscopy to bear on a complete dynamical understanding of such systems, particularly including the determination of the masses of the individual stellar components. In the case of double-lined spectroscopic systems, their resolution by long-baseline interferometry also yields the orbital parallax and hence the luminosities of the individual stars. In some of these cases, the angular diameters of one or more components are accessible, and so a complete specification of a star in terms of its mass, radius and luminosity is made.

The northern hemisphere is now equipped with several interferometers of unprecedented capability in terms of their baseline sizes, numbers of telescopes and telescope apertures. These instruments, most notably the Palomar Testbed Interferometer at Mt. Palomar Observatory, have produced very significant results of a number of interesting systems fulfilling interferometry's promise to produce fundamental astrophysical data at levels of accuracy that challenge or confirm astrophysical theory.

This paper presents basic principles of long-baseline interferometric study of binary stars and summarizes results from northern interferometers with specific examples of their broad impact on binary star astronomy.

I will discuss in this article the emerging concept of virtual observatories, the efforts being made in various countries to set up these structures, and the relevance of the concept to astronomy in developing countries.

The warm neutral medium, warm ionized medium, and cool neutral medium all show strong evidence for turbulence as a process dominating their structure and motions on a wide range of scales. The spatial power spectra of density fluctuations in all three phases are consistent with a Kolmogorov slope. Turbulence in the magnetic field in the diffuse medium can also be measured through the structure function of the Faraday rotation measure. With new surveys, new analysis techniques, and new telescopes, in the next few years it will be possible to measure the structure function of the magnetic field over a similarly wide range of scales. This will give a complete picture of the turbulence as a magneto-acoustic process.

This study is based on the definition of the admissible region introduced by Milani et al.(2004); in the search for potential Earth impactors, this theory allows to take into account the partial data of the TSA (Too Short Arcs) from which it is impossible to deduce a full orbit. Only a set of 4 variables (two angles and their instantaneous time derivatives), called an attributable, is known; a few suitable boundary conditions allow to restrict the motions to a specific bounded 2-dimensional region. In this work, a new inner boundary of this region is introduced, based on the geocentric hyperbolic motion of the immediate impactors; the nodal distances (crossings of the virtual asteroidal orbits with the Earth's orbit) are drawn for two different test attributables, associated with a determination of circular and linear orbits. This could reduce the search for impactors (by propagation of the orbits) to a one-dimensional set. A few comments about elongations and complementary curves complete this paper.