It was shown in a previous paper (Ibáñez 2004) that for certain kind of plasmas the coefficient of second (bulk) viscosity can be orders of magnitude larger than the coefficients corresponding to the dynamical viscosity and to the thermometric conductivity. In the present paper, the damping effects of the second viscosity on the hydromagnetic waves propagation are analyzed. In particular, we study the effect of the second viscosity on the magnetoacustic waves propagating in a photoionized gas of arbitrary metallicity Z and mean energy E of the ionizing photons when an initial steady magnetic field H is present.

The current contribution investigates the solar flare of 16th August 2004 with the multi-wavelength observations with high temporal resolution from RHESSI, Large Solar Vacuum Telescope (LSVT), Hiraiso Solar observatory, Nobeyama Radioheliograph (NoRH, 17 and 34 GHz) and Siberian Solar Radio Telescope (SSRT, 5.7 GHz), TRACE. The main flare was preceded by a pre-flare event with a very short energy release time. The observations of the main flare reveal a close temporal correlation between the Hα intensity observed with LSVT and those in hard and soft X-ray emissions observed with RHESSI, and in microwave fluxes observed with NoRH and SSRT. This close temporal correlation can be only associated with high-energy particles. The role of energetic particles in energy transport and non-thermal excitation and ionisation on Hα emission during the pre-flare and pre-flare event is investigated with full non-LTE approach and possible agents and scenarios of energy transport are discussed.

Astronomers have constructed models of globular clusters for over 100 years. These models mainly fall into two categories: (i) static models, such as King's model and its variants, and (ii) evolutionary models. Most attention has been given to static models, which are used to estimate mass-to-light ratios and mass segregation, and to combine data from proper motions and radial velocities. Evolutionary models have been developed for a few objects using the gaseous model, the Fokker-Planck model, Monte Carlo models and N-body models. These models have had a significant role in the search for massive black holes in globular clusters, for example.

In this presentation the problems associated with these various techniques will be summarised, and then we shall describe new work with Giersz's Monte Carlo code, which has been enhanced recently to include the stellar evolution of single and binary stars. We describe in particular recent attempts to model the nearby globular cluster M4, including predictions on the spatial distribution of binary stars and their semi-major axis distribution, to illustrate the effects of about 12 Gyr of dynamical evolution. We also discuss work on an approximate way of predicting the “initial” conditions for such modelling.

Magneto-hydrodynamic wave modes propagating from the solar photosphere into the corona have the potential to be exploited as an observational tool in an analogous way to the use of acoustic waves in helio/terrestrial seismology. In regions of strong magnetic field photospheric p-modes are thought to undergo mode conversion to slow magneto-acoustic waves, and that these slow magnetoacoustic p-modes may be waveguided from the photosphere into the solar corona along the magnetic field. A Bayesian analysis technique is applied to observations which suggests four distinct p-modes may be resolved in the transition region.

Dynamical interactions that occur between objects in dense stellar systems are particularly important for the question of formation of X-ray binaries. We present results of numerical simulations of 70 globular clusters with different dynamical properties and a total stellar mass of 2×107M⊙. We find that in order to retain enough neutron stars to match observations we must assume that NSs can be formed via electron-capture supernovae. Our simulations explain the observed dependence of the number of LMXBs on “collision number” as well as the large scatter observed between different globular clusters. For millisecond pulsars, we obtain good agreement between our models and the numbers and characteristics of observed pulsars in the clusters Terzan 5 and 47 Tuc.

I discuss my stellar evolution code Ev in the context of simulations of large clusters of stars. It has long been able to handle single stars, and also binary stars up to a point. That point is far beyond what other codes are able to do, but well short of what is necessary for believable simulations. A recent version, Ev(Twin), can in principle deal with the contact phase of binary evolution, but it is not yet clear what the physical interaction is that needs to be simulated.

An upgrade, which I hope will be only a few lines, should allow it to follow Kozai cycles with tidal friction, a process that strongly influences the orbital period of close pairs that reside within wide, non-coplanar triples. However, there are many substantial gaps in the physics of even single stars, let alone binaries or triples.

In this review we present a short introduction to the X-ray Telescope on Hinode. We discuss its capabilities and new features and compare it with Yohkoh SXT. We also discuss some of the first results that include observations of X-ray jets in coronal holes, shear change in flares, sigmoid eruptions and evolution, application of filter ratios and differential emission measure analysis, structure of active regions, fine structure of X-ray bright points, and modeling non-potential fields around filaments. Finally, we describe how XRT works with other ground and space-based instrumentation, in particular with TRACE, EIS, SOT, and SOLIS.

Through the use of detailed light profiles and dynamical measurements of young clusters we investigate claims that the stellar initial mass function within clusters varies greatly. We find a strong age dependence in the clusters which have been claimed to have non-standard stellar IMFs, and suggest that the lack of equilibrium of these clusters is responsible for their ‘strange’ light-to-mass ratios and not IMF variations. The most likely culprit is the rapid removal of residual gas left over from the star-formation process which leaves the clusters severely out of dynamical equilibrium. By comparing the observations to N-body simulations we quantify to what degree a cluster is out of equilibrium and consequently its survival chances. We find that >60% of young clusters will be disrupted, due gas removal, within the first 20–50 Myr of their lives.

Most stars form in dense star clusters deeply embedded in residual gas. These objects must therefore be seen as the fundamental building blocks of galaxies. With this contribution some physical processes that act in the very early and also later dynamical evolution of dense stellar systems in terms of shaping their later appearance and properties, and the impact they have on their host galaxies, are highlighted. Considering dense systems with increasing mass, it turns out that near 106M⊙ their properties change fundamentally: stellar populations become complex, a galaxial mass–radius relation emerges and the median two-body relaxation time becomes longer than a Hubble time. Intriguingly, only systems with a two-body relaxation time longer than a Hubble time show weak evidence for dark matter, whereby dSph galaxies form total outliers.

The globular cluster ω Centauri is one of the largest and most massive members of the Galactic system. Its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this and the fact that it has one of the largest velocity dispersions for star clusters in our galaxy makes it an interesting candidate for harboring an intermediate mass black hole. We measure the surface brightness profile from integrated light on an HST/ACS image, and find a central power-law cusp of logarithmic slope -0.08. We also analyze Gemini GMOS-IFU kinematic data for a 5”x5” field centered on the nucleus of the cluster, as well as for a field 14″ away. We detect a clear rise in the velocity dispersion from 18.6 kms−1 at 14″ to 23 kms−1 in the center. Given the very large core in ω Cen (2.58'), an increase in the dispersion in the central 10″ is difficult to attribute to stellar remnants, since it requires too many dark remnants and the implied configuration would dissolve quickly given the relaxation time in the core. However, the increase could be consistent with the existence of a central black hole. Assuming a constant M/L for the stars within the core, the dispersion profile from these data and data at larger radii implies a black hole mass of 4.0+0.75−1.0×104M⊙. We have also run flattened, orbit-based models and find a similar mass. In addition, the no black hole case for the orbit model requires an extreme amount of radial anisotropy, which is difficult to preserve given the short relaxation time of the cluster.

In the numerical simulations of evolution of star clusters, binary-single star interactions frequently take place. Since the direct integration of them is time consuming, distant interactions between binaries and field stars are often integrated by using some approximations. Traditionally the effect of the error caused by the approximated treatment is regarded as small enough to be ignored. However, if we have a binary-dominated core, the energy drift is large. In this study, we perform numerical experiments to evaluate the effect of neglecting the weak perturbation from distant single particles. We developed an N-body integrator which can manipulate multiple precision floating point numbers.

The theoretical modelling of prominence vibrations has been performed mainly through the analysis of the magnetohydrodynamic normal modes of oscillation of simple equilibrium structures. Research on this topic has concentrated mostly on the oscillatory properties of prominence slabs (i.e. without taking into account the internal thread structure) and prominence fibrils (i.e. introducing some of this inherent internal complexity of prominences, although in a simplified manner). In an attempt to understand the observed strong damping of prominence oscillations, work has also been done on the attenuation of waves in these objects. The achievements in this particular research area are reviewed and some trends for possible future investigations are given.

For 236 of 650 Galactic open clusters identified in the ASCC-2.5 catalogue, we determine tidal radii from a three-parameter fit of King's profiles to the observed integrated density distribution of cluster members. The results are used to calibrate the observed sizes of the remaining clusters to a uniform scale of tidal radii of open clusters in the Solar neighbourhood. The tidal masses are computed from tidal radii. Within a distance of 850 pc where our sample is complete, the observed distributions of cluster masses can be explained by a general mass loss in open clusters with increasing age.

Stellar mass compact object binaries are promising sources of gravitational radiation for the current generation of ground-based detectors, VIRGO and LIGO. Accurate templates for gravitational waveforms are needed in order to extract an event from the VIRGO/LIGO data stream. In the case of relativistic, compact object binaries accurate orbital parameters are necessary in order to produce such templates. Binary systems are affected by their stellar environment and thus the parameters of the binary population of a dense star cluster will be different from those of the field population. We propose to investigate the parameters of relativistic binary populations in dense star clusters using direct N-body simulations with a Post-Newtonian treatment of general relativity for the close binaries.

Although the overall dynamics of globular clusters involves many complexities, much of their dynamics can be understood on the basis of some simple and straightforward physical arguments. Those arguments are presented here, in an effort to lead the reader through the basic stages of cluster dynamics in a quick and easy way.

High frequency acoustic waves have been suggested as a source of mechanical heating in the quiet solar chromosphere. To investigate this, we have observed intensity oscillations of several lines in the frequency interval 1.64-70mHz using data from the VTT Tenerife and the Dunn Solar Telescope at the National Solar Observatory. Our analysis of Fe i 543.45 nm, Fe i 543.29 nm and the G-band, indicate that the majority of oscillations are connected with the magnetic fields and do not provide sufficient mechanical flux for the heating of the chromosphere. This correlation is also observed in quiet Sun areas.

The motion of a black hole about the centre of gravity of its host galaxy induces a strong response from the surrounding stellar population. We consider the case of a harmonic potential and show that half of the stars on circular orbits in that potential shift to an orbit of lower energy, while the other half receive a positive boost. The black hole itself remains on an orbit of fixed amplitude and merely acts as a catalyst for the evolution of the stellar energy distribution function f(E). We then consider orbits in the logarithmic potential and identify the response of stars near resonant energies. The kinematic signature of black hole motion imprints the stellar line-of-sight mean velocity to a magnitude ≃ 13% the local root mean-square velocity dispersion σ. The high velocity dispersion at the 5:2 resonance hints to an observable effect at a distance ≃ 3 times the hole's influence radius.

We propose an explanation for the origin of hyperfast neutron stars (e.g. PSR B1508+55, PSR B2224+65, RX J0822–4300) based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star (or its helium core) which attained its peculiar velocity (similar to that of the neutron star) in the course of a strong three- or four-body dynamical encounter in the core of a young massive star cluster. This hypothesis implies that the dense cores of star clusters (located either in the Galactic disk or near the Galactic centre) could also produce the so-called hypervelocity stars – ordinary stars moving with a speed of ~ 1 000 km s−1.

We present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

We present a Gemini/GMOS program to measure spectroscopic metallicities and ages of globular clusters (GCs) and nuclei in dwarf elliptical galaxies in the Virgo and Fornax Clusters. Preliminary results indicate that the globular clusters are old and metal-poor, very similar to the GCs in the Milky Way halo. The nuclei tend to be more metal-rich than the globular clusters but more metal-poor and older, on average, than the stars in the bodies of the galaxies. The [α/Fe] ratio appears to be solar for the GCs, nuclei, and dEs, but the uncertainties do not exclude some globular clusters from being enhanced in alpha elements.