Gaia is an all-sky, high precision astrometric and photometric satellite of the European Space Agency (ESA) due for launch in 2010. Its primary mission is to study the composition, formation and evolution of our Galaxy. Over the course of its five-year mission, Gaia will measure parallaxes and proper motions of every object in the sky brighter than visual magnitude 20, amounting to a billion stars, galaxies, quasars and solar system objects. It will achieve an astrometric accuracy of 10 $\mu$as at $V=15$ – corresponding to a distance accuracy of 1% at 1 kpc – and 200 $\mu$as at $V=20$. With Gaia, tens of millions of stars will have their distances measured to a few percent or better. This is an improvement over Hipparcos by several orders of magnitude in the number of objects, accuracy and limiting magnitude. Gaia will also be equipped with a radial velocity spectrograph, thus providing six-dimensional phase space information for sources brighter than $V$$\sim$ 17. To characterize the objects (which are detected in real time, thus dispensing with the need for an input catalogue), each object is observed in 15 medium and broad photometric bands with an onboard CCD camera. With these capabilities, Gaia will make significant advances in a wide range of astrophysical topics. In addition to producing a detailed kinematical map of stellar populations across our Galaxy, Gaia will also study stellar structure and evolution, discover and characterise thousands of exoplanetary systems (extending down to about ten Earth masses for the nearest systems) and make accurate tests of General Relativity on large scales, to mention just some areas. I give an overview of the mission, its operating principles and its expected scientific contributions. For the latter I provide a quick look in five areas on increasing scale size in the universe: the solar system, exosolar planets, stellar clusters and associations, Galactic structure and extragalactic astronomy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present new narrow-band imaging and optical spectroscopy of Wolf-Rayet stars in the Local Group dwarf galaxy IC 10 (Gemini-N- gmos) and Sculptor group spiral galaxy NGC 300 (VLT fors2).

Nonlinear effects determining the amplitudes of unstable modes of oscillations in stellar modes, are reviewed. The two basic processes - saturation of the driving mechanism and resonant mode coupling - are discussed within the framework of the amplitude equation formalism. There are difficult problems in the theory of multiple mode interaction that must be solved to make a prediction of amplitude spectra possible. The observed spectra for δ Scu stars and other multiperiodic variables, exhibit no simple pattern that would suggest a solution of the theoretical problems.

With the advent of imaging in X-ray astronomy, we can, for the first time, study extended sources with the same detailed spatial and spectral resolution employed by radio and optical astronomers. As in other fields of astronomy, the study of the X-ray emission from clusters of galaxies is beginning to feel the tremendous impact of this advance. The accompanying contributions by Murray and by Grindlay show that the division of clusters into classes based solely on X-ray morphology holds clear implications for the origin of the intracluster medium and the evolution of the cluster as a whole. Comparisons with optical and radio data, along with detailed X-ray studies of nearby objects and the extension of cluster observations to redshifts greater than 0.5, will help connect these ideas to a sound theoretical base. In this report on the cluster observations performed by the Columbia Astrophysics Laboratory with the Einstein Observatory, we restrict ourselves to three brief comments concerning the following areas: (1) The correlation of X-ray brightness with cluster morphology, (2) the detection of a spiral-rich cluster at z ˜ 0.4, and (3) detailed observations of Coma, the nearest rich cluster.

Carlyle S. Beals, former Dominion Astronomer of Canada and one of the most distinguished astronomers Canada has produced, died on 2 July, 1979. Carl Beals was not only a great astronomer, known throughout the astronomical world for his studies of Wolf-Rayet stars and many other contributions to astronomy, but he was also a great human person who exercised considerable influence on the development of astronomy in Canada and elsewhere. I should like to dedicate this lecture to the memory of Carl Beals.

We present examples of activity cycle timescales on different types of stars from lowmass dwarfs to more massive giants, with wide-ranging rotation rates, and compare the observed cyclicities to the irradiance based solar cycle and its modulations. Using annual spectral solar irradiance in wavelength bands typical for stellar observations reconstructed by Shapiro et al. (2011), a direct comparison can be made between cycle timescales and amplitudes derived for the Sun and the stars. We show that cycles on multiple timescales, known to be present in solar activity, also show up on stars when the dataset is long enough to allow recognition. The cycle lengths are not fixed, but evolve – gradually during some periods but there are also changes on short timescales. In case the activity is dominated by spots, i.e., by cooler surface features, the star is redder when fainter, whereas other type of activity make the stars bluer when the activity is higher. We found the Sun to be a member of the former group, based on reconstructed spectral irradiance data by Shapiro et al. (2011).

The characteristics of the large-scale distribution of the solar magnetic fields on the basis of a series of solar magnetic synoptic charts covering more than 15 years of observations are given. The major part of our information concerns the morphology and only some results deal with the kinematics of the field distribution. Results of averaged solar magnetic field fluxes and polarity reversal studies as well as of preliminary investigation of the very-low angular resolution magnetic measurements are given. The regular zonal and sectoral distribution of photospheric background fields, the different role or visibility of structures in both polarities is discussed. The reflection of both main types of the longitudinal distribution of large-scale solar background magnetic fields (the 27-day, the 28–29-day successions, the ‘supergiant’ structures) in the interplanetary magnetic field distribution is also considered.

A compilation is given of transition probabilities of forbidden lines which occur in the spectra of gaseous nebulae.

Recent progress in modeling core-collapse supernovae is summarized and set in perspective. Two-dimensional simulations with state-of-the-art treatment of neutrino transport still fail to produce powerful explosions, but evidence is presented that they are very close to a success.

I report recent results of numerical simulations designed to study the inner structure of Cold Dark Matter (CDM) halos. This work confirms the proposal of Navarro, Frenk & White (NFW) that the shape of ACDM halo mass profiles differs strongly from a power law and is approximately independent of mass. the logarithmic slope of the spherically-averaged density profile, as measured by β = –d ln ρ/d ln r, decreases monotonically towards the center, becoming shallower than isothermal (β < 2) inside a characteristic radius, r–2, and shows no evidence for convergence to a well-defined asymptotic value (β0) at the center. the dark mass contained within the innermost radius resolved by the simulations places strong constraints on β0; cusps as steep as r–1.5 are clearly ruled out in our highest resolution simulations. A profile where the radial dependence of the slope is a simple power law, β(r) ∝ rα, approximates the structure of halos better than the NFW profile and so may minimize errors when extrapolating our results inward to radii not yet reliably probed by numerical simulations. We compare the spherically-averaged circular velocity (Vc) profiles to the rotation curves of low surface brightness (LSB) galaxies in the samples of de Blok et al. and Swaters et al. the Vc profiles of simulated CDM halos are generally consistent with the rotation curves of LSB galaxies, but there are also some clearly discrepant cases. This disagreement has been interpreted as excluding the presence of cusps, but it may also just reflect the difference between circular velocity and rotation speed likely to arise in gaseous disks embedded within realistic triaxial halos.

It is now more than eleven years since the discovery of the first accreting millisecond X-ray pulsar. Since then, eleven additional systems have been found, two of them during the last year. Here I briefly discuss the most recent developments with respect to these systems.

Observational evidence of transient flares which produce conspicuous changes in the total brightness and in the spectra of dwarf stars is limited, at present, to a small number of faint late-type stars. The outbursts take place with extraordinary rapidity and the duration is usually only a few minutes or hours. Accompanying spectral changes such as veiled and fuzzy absorption lines, greatly increased intensity of the bright lines of hydrogen and helium, and the appearance of an emission continuum shortward of λ 3750, have been reported.

Over the last decade, we have made great strides in better understanding dust composition and evolution in dense clouds and the diffuse interstellar medium (ISM). Thanks to improvements in IR detector sensitivity on ground-based telescopes and the Spitzer Space Telescope mission, we are no longer limited to a handful of bright background stars in order to study dust composition in quiescent dense clouds and the diffuse ISM. More thorough sampling of lines of sight in these regions has highlighted the dichotomy of the nature and composition of dust in these environments. In addition, successes in recreating interstellar processes and dust-analogs in the laboratory have helped us to understand the differences in dust absorption features we observe in the ISM. In this article, we focus on the organic components of interstellar dust, reviewing past work and highlighting the most recent observations and laboratory experiments.

Results from Chandra-HST-VLA observations of 13 hybrid sources are presented. Data from ten sources in the literature are analysed along with new data from three hybrid blazars belonging to the MOJAVE sample. Studies of such hybrid sources displaying both FRI and FRII jet characteristics could provide the key to resolving the long-standing Fanaroff-Riley dichotomy issue. A majority of the 13 hybrid sources show FRII-like total radio powers, i.e., they are “hybrid” in radio morphology but not in total radio power. VLBI observations of ten of the 13 sources show that the X-ray jet is on the same side as the one-sided VLBI jet. X-rays are therefore emitted from relativistically-boosted approaching jets. This is consistent with the X-ray emission being IC/CMB in origin in the majority of sources. It is not completely clear from our study that asymmetries in the surrounding medium can create hybrid sources. Hybrid radio morphologies could also be indicative of intrinsically asymmetric jets.

Studying star formation in spiral arms tells us not only about the evolution of star formation, and molecular clouds, but can also tell us about the nature of spiral structure in galaxies. I will address both these topics using the results of recent simulations and observations. Galactic scale simulations are beginning to examine in detail the evolution of Giant Molecular Clouds (GMC) as they form in spiral arms, and then disperse by stellar feedback or shear. The overall timescale for this process appears comparable to the crossing time of the GMCs, a few Myrs for 105 M⊙ clouds, 20 Myr or so for more massive GMCs. Both simulations and observations show that the massive clouds are found in the spiral arms, likely as a result of cloud-cloud collisions. Simulations including stars should also tell us about the stellar age distribution in GMCs, and across spiral arms. More generally, recent work on spiral galaxies suggests that the dynamics of gas flows in spiral arms are different in longlived and transient spiral arms, resulting in different age patterns in the stars. Such results could be used to help establish the main driver of spiral structure in the Milky Way (Toomre instabilities, the bar, or nearby companion galaxies) in conjunction with future surveys.

Radiation environment of near-Earth space is one of the most important factors of space weather. Space Monitoring Data Center of Moscow State University provides operational monitor and forecast of radiation conditions both at Geostationary Orbits (GEO) and at Low Earths Orbits (LEO) of the near-Earth space using data of recent space missions (Vernov, CORONAS series) and current (Lomonosov, Meteor-M, Electro-L) ones. Internet portal of Space Monitoring Data Center of Skobeltsyn Institute of Nuclear Physics of Lomonosov Moscow State University (SINP MSU - [swx.sinp.msu.ru]) provides possibilities to monitor and analyze the space radiation conditions in the real time mode together with the geomagnetic and solar activity including hard X-ray and gamma-emission of solar flares.

It has been suggested that coronal mass ejections (CMEs) remove the magnetic helicity of their coronal source region from the Sun. Such removal is often regarded to be necessary due to the hemispheric sign preference of the helicity, which inhibits a simple annihilation by reconnection between volumes of opposite chirality. Here we monitor the relative magnetic helicity contained in the coronal volume of a simulated flux rope CME, as well as the upward flux of relative helicity through horizontal planes in the simulation box. The unstable and erupting flux rope carries away only a minor part of the initial relative helicity; the major part remains in the volume. This is a consequence of the requirement that the current through an expanding loop must decrease if the magnetic energy of the configuration is to decrease as the loop rises, to provide the kinetic energy of the CME.

An automated rapid classification of the transient events detected in modern synoptic sky surveys is essential for their scientific utility and effective follow-up when resources are scarce. This problem will grow by orders of magnitude with the next generation of surveys. We are exploring a variety of novel automated classification techniques, mostly Bayesian, to respond to those challenges, using the ongoing CRTS sky survey as a testbed. We describe briefly some of the methods used.

The seasonal changes in the sporadic radiant distribution are investigated on the basis of the complete data for different classes of echo duration from the Ottawa 32·7 MHz radar taken over the years 1958–62, using a more accurate response function for the Ottawa radar equipment recently determined by McIntosh (1966). A model of the radiant distribution with four point sources (i.e. apex, helion, antihelion, and toroidal) and a uniform background is assumed. The strengths of the sources have been calculated by a least-squares fit to the observed mean hourly rates in 5-day intervals. The seasonal variations have different trends for meteors with different echo duration, showing stronger shower properties for long-duration echoes (4–8 sec). Meteors with short duration echoes (≤ 1 sec) show the same properties in radiant distribution, as was found in a previous paper based on preliminary Ottawa radar records. The toroidal source is without significant activity from August till November and shows a maximum in January. The diurnal variation calculated from this model is compared with the observed hourly rates. Some recent calculations have been made by Veverka and McIntosh (unpublished) using a continuous source model, elliptical in ecliptic longitude and exponential in latitude. The agreement of their results with observed diurnal rates is not as good. This suggests that the seasonal changes in the sporadic radiant distribution have a significant influence on the diurnal and annual variations of the hourly meteor rates.

At the Sydney IAU General Assembly (GA) the statutes were modified to remove the votes by individual members. Few noticed this at the time but the subsequent reaction by disenfranchised members led us to revise this position in Prague. The need to have a members’ vote on the status of Pluto was complicated by these changes and the drama behind the scene at the Prague GA where the planet definition was resolved is not well known despite the huge public impact of this GA. I will describe some of the activities of the executive and its working groups during this very exciting GA. The IAU structures served us well during this process but of course there were also many lessons learned.