The scientific objectives of the Gaia mission cover areas of galactic structure and evolution, stellar astrophysics, exoplanets, solar system physics, and fundamental physics. Astrometrically, its main contribution will be the determination of millions of absolute stellar parallaxes and the establishment of a very accurate, dense and faint non-rotating optical reference frame. With a planned launch in spring 2012, the project is in its advanced implementation phase. In parallel, preparations for the scientific data processing are well under way within the Gaia Data Processing and Analysis Consortium. Final mission results are expected around 2021, but early releases of preliminary data are expected. This review summarizes the main science goals and overall organisation of the project, the measurement principle and core astrometric solution, and provide an updated overview of the expected astrometric performance.

High-mass star formation is not well understood chiefly because examples are deeply embedded, relatively distant, and crowded with sources of emission. Using VLA and VLBA observations of H2O and SiO maser emission, we have mapped in detail the structure and proper motion of material 20-500 AU from the closest high-mass YSO, radio source I in the Orion KL region. We observe streams of material driven in a rotating, wide angle, bipolar wind from the the surface of an edge-on accretion disk. The example of source I provides strong evidence that high-mass star formation proceeds via accretion.

We review current understanding of the underlying, as opposed to the observed, pulsar population. The observed sample is heavily biased by selection effects, so that surveys see less than 10% of all potentially observable pulsars. We compare various techniques used to correct the sample for these biases. By far the most significant recent development has been the discovery of over 700 pulsars in the Parkes Multibeam (PM) survey. This new sample is far less affected by selection effects and we use it to make a preliminary analysis of the Galactic pulsar distribution, finding further evidence for a deficit of pulsars in the inner Galaxy.

We report on a re-analysis of the Galactic O-type star sample presented by Puls et al. (1996) by means of non-LTE model atmospheres including line-blocking and line-blanketing. In particular, we concentrate on the question concerning the dependence of the wind-momentum luminosity relation (WLR) on luminosity class. Owing to the line-blanketing, the derived effective temperatures become significantly lower when compared to previous results, whereas the so-called ‘modified wind-momentum rates’ remain roughly at their former values. Therefore, we obtain a new WLR for O-type stars. By comparing these ‘observational’ results with new theoretical predictions and simulations, we conclude that the Hα forming region for objects with Hα in emission might be considerably clumped and thus a larger mass-loss rate than actually present is mimicked. We suggest that the previously found dependence of the WLR on luminosity class is an artefact.

The unidentified emission feature at 21 μm is now observed in 12 sources, all being objects in transition between the asymptotic giant branch and planetary nebulae phases. The relations between the 21 μm and other emission features, such as the PAH features and the broad 30 μm feature, and the possible origins of the 21 μm feature are discussed.

We collected radial velocities of more than 50.000 individual stars in 156 Galactic globular clusters (GGC) and matched them with HST photometry and Gaia DR2 proper motions. This allowed us to derive the GGC’s mean proper motions and space velocities. By fitting a large set of N-body simulations to their velocity dispersion and surface density profiles, combined with new measurements of their internal radially dependent mass functions, we have determined their present-day masses and structural parameters, and for 144 GGCs their internal kinematics. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass-loss and dynamical friction. The new fundamental parameters of GGCs are publicly available via an online database, which will regularly be updated.

We build a sample of O VI absorption systems in the redshift range 2.0 $\lesssim z \lesssim$ 2.6 using high spectral resolution data of ten quasars from the VLT-UVES Large Programme. We investigate the existence of a metal-rich O VI population and define observational criteria for this class of absorbers under the assumption of photoionisation. The low temperatures of nearly half of all O VI absorbers, implied by their line widths, are too low for collisional ionisation to be a dominant process. We estimate the oxygen abundance under the assumption of photoionisation; a striking result is the bimodal distribution of [O/H] with median values close to 0.01 and 0.5 Solar for the metal-poor and metal-rich populations, respectively. Using the line widths to fix the temperature or assuming a constant, low gas density does not drastically change the metallicities of the metal-rich population. We present the first estimate of the O VI column density distribution. Assuming a single power-law distribution, $f$(N) $\propto$ N$^{-\alpha}$, yields $\alpha \sim 1.7$ and a normalisation of $f$(N) $=2.3\times 10^{-13}$ at log N(O VI) $\sim$ 13.5, both with a $\sim$30% uncertainty. The value of $\alpha$ is similar to that found for C IV surveys, whereas the normalisation factor is about ten times higher. We use $f$(N) to derive the number density per unit $z$ and cosmic density $\Omega_{\rm b}$(O VI), selecting a limited column density range not strongly affected by incompleteness or sample variance. Comparing our results with those obtained at $z\sim0.1$ for a similar range of column densities implies some decline of $dn/dz$ with $z$. The cosmic O VI density derived from $f$(N), $\Omega_{\rm b}$(O VI)$\approx (3.5\pm ^{3.2}_{0.9}) \times 10^{-7}$, is 2.3 times higher than the value estimated using the observed O VI sample (of which the metal-rich population contributes $\sim$35%), easing the problem of missing metals at high $z$ ($\sim$ 1/4 of the produced metals) but not solving it. We find that the majority of the metal-rich absorbers are located within $\sim$ 450 km s$^{-1}$ of strong Ly-$\alpha$ lines and show that, contrary to the metal-poor absorbers, this population cannot be in hydrostatic equilibrium. All of the O VI absorber properties imply that there are two distinct populations: metal-poor absorbers tracing the intergalactic medium and metal-rich absorbers associated with active sites of star formation and most probably linked to galactic winds.

We are presently undertaking, at the Stellar Data Center, a large effort to produce the Catalogue of Stellar Groups, which is a catalogue listing all the kinds of stars with spectral peculiarities existing up to now. The work is in progress and presently about fifty groups (Ap, Am, Be, WR, H and K emission line stars, etc.) are defined, gathering more than 25000 stars. The catalogue was started with the aim to set up lists defined by homogeneous criteria, because up to now the available information is scattered through the literature. We hope that the catalogue will be useful for formulating observing programs and for further detailed research on each of the groups.

The aim of this paper is to introduce the software and astronomical web-services developed in frame of the Ukraine Virtual Observatory (UkrVO) and VIrtual Roentgen and Gamma Observatory (VIRGO) to the broad astronomical community. We report briefly on such web-services as the public databases “Sky Maps” of X-ray observations by XMM-Newton, the Earth Orbital Parameters for International Earth Rotation System, and the UkrVO Joint Digitized Archive of astroplates. We refer to such software as the “Multi-Column View”, “Variable Stars Calculator”, “FrameSmooth” for variable star’s research and “Collection Light Technology” (CoLiTec) software for search and discovery of new Solar System bodies.

We report on a technique to construct a flux rope (FR) from eruption data at the Sun. The technique involves line-of-sight magnetic fields, post-eruption arcades in the corona, and white-light coronal mass ejections (CMEs) so that the FR geometric and magnetic properties can be fully defined in addition to the kinematic properties. We refer to this FR as FRED (Flux Rope from Eruption Data). We illustrate the FRED construction using the 2012 July 12 eruption and compare the coronal and interplanetary properties of the FR. The results indicate that the FRED input should help make realistic predictions of the components of the FR magnetic field in the heliosphere.

This paper reviews various hydrodynamical models proposed for explaining bipolar molecular outflows from young stars. The different possibilities discussed are : wind-driven molecular shells, steady state filled flows, and jet-driven bow shocks. Particular emphasis is placed on comparisons between model predictions and observations of molecular flows. While it appears that jet-driven bow shocks are at the present time the most popular mechanism for explaining molecular outflows, other models have interesting characteristics that might be relevant for at least some objects.

Dynamical, vibrational, and thermal instabilities of massive blue stars are discussed as possible mechanisms for the observed brightness variations of such objects. Relaxation oscillations (on local thermal time scales) due to dynamical instabilities of the stellar wind flows appear to be the most likely mechanism, at least for the S Dor variables. Very massive main-sequence stars with M > 103 M⊙ should be violently vibrationally unstable and therefore should differ significantly from stable main-sequence stars of lower mass.

The cosmic baryon budget is revisited using modern observations that have become available since our first publication. I also present an estimate for the heavy element abundance. An increased accuracy in the accounting of the baryon budget reveals ‘missing baryons’, which amount to ≈ 35% of the total. This would provide an interesting test for models of the cosmic structure formation.

We discuss the observed multiplicity of massive stars and implications on theories of massive star formation. After a short summary of the literature on massive star multiplicity, we focus on the O-and B-type stars in the Orion Nebula Cluster, which constitute a homogenous sample of very young massive stars. 13 of these stars have recently been the targets of a bispectrum speckle interferometry survey for companions. Considering the visual and also the known spectroscopic companions of these stars, the total number of companions is at least 14. Extrapolation with correction for the unresolved systems suggests that there are at least 1.5 and perhaps as much as 4 companions per primary star on average. This number is clearly higher than the mean number of ∼ 0.5 companions per primary star found for the low-mass stars in the general field population and also in the Orion Nebula cluster. This suggests that a different mechanism is at work in the formation of high-mass multiple systems in the dense Orion Nebula cluster than for low-mass stars.

I review the possible formation mechanisms of close binary stars. The formation of close binary systems is problematic in that there is no theory that does not encounter significant difficulties or unknowns. Fission does not appear to occur in stars. Capture is unlikely to form many close binary systems except possibly amongst massive stars. Fragmentation can form close binary systems but these need to accrete the majority of their eventual mass. Furthermore, there appears to be a limited window in initial conditions that may preclude forming sufficient systems in this way. Possible alternatives include the orbital migration of a binary due to its circumbinary disk and the disintegration of a non-hierarchical multiple system.

We describe an ongoing project to migrate the emission-line analysis package nebular from its current environment, IRAF, to a modern programming environment where it can be used from command line, a local GUI, or the web. We are also updating the supporting atomic data where they have been superseded by superior calculations or measurements.

Imaging atmospheric Cherenkov telescopes (IACTs) are sensitive to rare gamma-ray photons, buried in the background of charged cosmic-ray (CR) particles, the flux of which is several orders of magnitude greater. The ability to separate gamma rays from CR particles is important, as it is directly related to the sensitivity of the instrument. This gamma-ray/CR-particle classification problem in IACT data analysis can be treated with the rapidly-advancing machine learning algorithms, which have the potential to outperform the traditional box-cut methods on image parameters. We present preliminary results of a precise classification of a small set of muon events using a convolutional neural networks model with the raw images as input features. We also show the possibility of using the convolutional neural networks model for regression problems, such as the radius and brightness measurement of muon events, which can be used to calibrate the throughput efficiency of IACTs.

We present a new 3D MHD code for the simulation of solar magnetoconvection. The code is designed for use on parallel computers and in the choice of methods emphasis has been laid on efficient parallelization. We give a description of the numerical methods and discuss the non-local and non-grey treatment of the radiative transfer. Test calculations underlining the importance of non-grey effects and first results of the simulation of a solar plage region are shown.

The Square Kilometre Array (SKA) is a global project to design and construct the next-generation international radio telescope operating at metre to cm wavelengths. The SKA will be an interferometric array with a collecting area of up to one million square metres and maximum baseline of at least 3000 km, and is designed to address fundamental questions in cosmology, physics and astronomy. The key science goals range from the epoch of re-ionization, dark energy, the formation and evolution of galaxies and large-scale structure, the origin and evolution of cosmic magnetism, strong-field tests of gravity and detection of gravity waves.

The SKA project is now entering a final design for an SKA Observatory to begin to be built in the latter half of this decade that will include facilities in South Africa and Western Australia. The SKA design relies on advances in several technologies that will be prototyped over the next few years, and demonstrated for astronomical observations on SKA precursor telescopes. Scientific operations of the first 10% scale phase of the SKA is targeted for 2020.