Observations of the spectrum of solar radio bursts at meter wavelengths have indicated the desirability of measuring positions on the sun's disk not only as a function of time but also as a function of frequency. With this objective in view, we are now using a swept-frequency interferometer to determine the east-west disk coordinate of the transient solar sources at time intervals of ½ second and freqency intervals of about 5 Mc/s within the frequency range 40 to 70 Mc/s. The accuracy to which the centroid of the source is located is about ±1 minute of arc. In its initial form [1], the interferometer contained two aerials separated by a distance of 1 km. As a result of preliminary tests, two major additions have been made: (1) a second interferometer of much smaller spacing (¼ km) has been added to resolve the usual ambiguities associated with two-aerial interferometry, and (2) an automatic system of lobe-switching and phase-calibration has been incorporated to facilitate the reduction of the complex data recorded.

Observations of stable mainly dipolar magnetic fields at the surface of ~7% of single hot stars indicate that these fields are of fossil origin, i.e. they descend from the seed field in the molecular clouds from which the stars were formed. The recent results confirm this theory. First, theoretical work and numerical simulations confirm that the properties of the observed fields correspond to those expected from fossil fields. They also showed that rapid rotation does not modify the surface dipolar magnetic configurations, but hinders the stability of fossil fields. This explains the lack of correlation between the magnetic field properties and stellar properties in massive stars. It may also explain the lack of detections of magnetic fields in Be stars, which rotate close to their break-up velocity. In addition, observations by the BinaMIcS collaboration of hot stars in binary systems show that the fraction of those hosting detectable magnetic fields is much smaller than for single hot stars. This could be related to results obtained in simulations of massive star formation, which show that the stronger the magnetic field in the original molecular cloud, the more difficult it is to fragment massive cores to form several stars. Therefore, more and more arguments support the fossil field theory.

This paper summarizes the general theory and properties for Apodized Pupil Lyot Coronagraphs which consist of a classical hard-edged Lyot coronagraph with an upstream pupil apodization. The ideal apodization function can be determined from an integral eigenvalue problem which solutions are prolate spheroidal functions. Solutions exist for any geometrty, including rectangular, circular, or elliptical. Formal solutions can be extended to the case of arbitrary apertures, using generalized prolate spheroidal functions for centrally obstructed apertures, spiders, or segmented telescopes. The properties of these coronagraphs enable the possibility of multiple stage coronagraphy and achromatization. The new instrument Gemini Planet Imager (GPI) will include such a coronagraph.

As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~3,400 sq.deg., centered on the Galactic anti-center (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3800–9000 low resolution (R ~1,800) spectra for a statistically complete sample of ≳ 3 M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~5,400 sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity (Vr) and stellar parameters (effective temperature (Teff), surface gravity (log g) and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique data set to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties.

The survey was initiated in the fall of 2012 and expected to complete in the spring of 2017. Hitherto, about 0.4 M spectra of S/N(λ7450) ≥ 10 per pixel have been accumulated. In addition, bright nights have been used to target stars brighter than 14 mag and have so far generated over 0.4 M spectra, yielding an excellent sample of local stars to probe the solar neighborhood. LSP3, a set of pipelines tailored to the need of LSS-GAC, for spectral flux-calibration, and radial velocity and stellar parameter determinations, have been developed at Peking University, based on packages developed for the SDSS and those at the National Astronomical Observatories of Chinese Academy of Sciences. Comparisons of multi-epoch observations, with the SDSS results, as well as applying the pipelines to open and globular clusters show that LSP3 has achieved a precision of 5 km s−1, 110 K, 0.15 dex and 0.15 dex for Vr, Teff, log g and [Fe/H], respectively. The data are publicly available, subject to regulations of the LAMOST data policy, and begin to yield scientific results. The potential of LSS-GAC and power of existing data are illustrated with examples of selected problems.

Brown dwarf atmospheres form molecules, then high temperature condensates (corundum, titanates, silicates, and iron compounds), and then low temperature condensates (ices) as they cool down over time. These produce large opacities which govern entirely their spectral energy distribution. Just as it is important to know molecular opacities (TiO, H2O, CH4, etc.) with accuracy, it is imperative to understand the interplay of processes (e.g. condensation, sedimentation, coagulation, convection) that determines the radial and size distribution of grains. Limiting case models have shown that young, hot brown (L) dwarfs form dust mostly in equilibrium, while at much cooler stages (late T dwarfs) all high temperature condensates have sedimented out of their photospheres. But this process is gradual and all intermediate classes of brown dwarfs can partly be understood in terms of partial sedimentation of dust. With new models accounting for these processes, we describe the effects they may have upon brown dwarf spectral properties.

Three major modes of interaction in binary systems are identified, corresponding to (I) physical contact, (II) tidal mass loss from a star with a radiative envelope, and (III) tidal mass loss from a star with a convectlve envelope. The qualitative evolution of binary systems in each of these cases is outlined, leading to the formation of single white dwarfs, long-period remnants of quasi-conservative mass transfer, or short-period cataclysmic binaries. The origin of short-period double white dwarfs in a second phase of mass transfer is outlined. Implications for the frequency of different systems of these types, and of planetary nebulae with close binary nuclei, are discussed.

The progress over the last years in modelling the atmospheres and winds of PN central stars is reviewed. We discuss the effect of the inclusion of the blanketing by millions of metal lines in NLTE on the diagnostics of photospheric and stellar wind lines, which can be used to determine stellar parameters such as effective temperature, gravity, radius, mass loss rate and distance. We also refer to recent work on the winds of massive O-type stars, which indicates that their winds are possibly inhomogeneous and clumped. We investigate implications from this work on the spectral diagnostics of PN central stars and introduce a method to determine wind clumping factors from the relative strengths of H$_{\alpha}$ and He II 4686. Based on new results we discuss the wind properties of CSPN.

We show that only two adjustments are necessary to harmonize the Group Sunspot Number with the Zürich Sunspot Number. The latter has been increased from the 1940s on to the present by 20% due to weighting of sunspot counts according to size of the spots and can be corrected by increasing the earlier values as well. The Group Sunspot Number before ~1885 is too low by ~50%. With these adjustments a single sunspot number series results. Of note is that there is no longer a distinct Modern Grand Maximum.

The scope of this contribution is to review and discuss recent findings concerning the molecular environment of high-mass star forming regions. Special attention is devoted to “hot molecular cores” and their role in the formation of massive stars. After analysing the relationship between such cores and the surrounding molecular clumps, we discuss the results of interferometric observations of these objects and propose an evolutionary sequence proceeding from cold, pre-stellar cores to ultracompact HII regions.

Optical studies of ultraluminous X-ray sources (ULX) in nearby galaxies have turned out to be instrumental in discriminating between various models including the much advertised intermediate mass black hole hypothesis and various beaming scenarios. Here we report on ESO VLT and SUBARU observations of ULX that have revealed the parent stellar clusters with ages of some 60 million years in two cases. Thus we are able to derive upper limits of about 8 M$_{\odot}$ for the mass donors in these systems. The optical counterparts are dominated by X-ray heated accretion disks, and the discovery of the He II $\gamma$4686 emission line now allows to derive dynamical masses in these systems. Apparent radial velocity variations of 300 km/s have been detected in NGC 1313 X-2 which, if confirmed by further observations, would exclude the presence of IMBH in these systems.

New developments in understanding the stellar populations of elliptical nuclei are discussed. Variations in iron-peak spectral features have recently been detected, which are much smaller than changes in CN, Mg, and Na. A study is presently in progress to determine whether this pattern is consistent with lockstep enhancements in all heavy elements. Present evidence on the ultraviolet spectra of ellipticals now suggests that the source of the excess UV light is not young OB stars. A new correlation is also pointed out between UV excess and mean line strength. If real, this trend is further evidence against significant numbers of young OB stars in elliptical galaxies.

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 ratio R of the corotation radius to the bar radius ranges from 1 to 1.8 in theoretical models that fit the observed dynamics of gas or stars in the bar and spiral regions of galaxies. Most models cluster around a ratio R = 1.2 for early type galaxies. This ratio confirms the bar-aligned orbit theory long held by Contopoulos and others, which requires that R < 1, but it also suggests that bars do not end exactly at corotation, as is often assumed, but significantly inside. The difference between R = 1 in the old interpretation and R = 1.2 or 1.4 in the fitted models is critical for our interpretation of bar-spiral morphologies. It appears that the bar-to-spiral transition in early Hubble types occurs between the inner 4:1 resonance and corotation, in the range corresponding to R = 1.55 to 1 for a flat rotation curve, because of orbit stochasticity where the 2m: 1 orbits in the x1 family cluster together in space. Corotation then occurs relatively far out in the arms, at an angle from the bar end that may exceed 60° for tightly wrapped spirals. This position sometimes corresponds to the crossing of a dust lane from inside the arms to outside (NGC 1300, NGC 1365) or to a spiral arm bifurcation as in non-barred galaxies. The relatively high value of R is also consistent with the identification of inner rings with the inner 4:1 resonance, outer rings with the outer Lindblad resonance, and offset bar dust lanes and nuclear rings with the inner Lindblad resonance. In contrast to this clear interpretation for early type galaxies, there is little consensus on the location of corotation in late type galaxies, which usually lack an inner Lindblad resonance interior to the bar. It is also not known whether late type spirals corotate with their bars, although this appears to be the case for early type galaxies based on the ubiquity and location of outer spirals and rings.

We review the characteristics of nucleosynthesis in ‘hypernovae’, i.e., core-collapse supernovae with very large explosion energies (≳ 1052 ergs). The hypernova yields show the following characteristics: (i) the mass ratio between the complete and incomplete Si burning regions is larger in hypernovae than normal supernovae. As a result, higher energy explosions tend to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which could explain the trend observed in very metal-poor stars; (ii) because of enhanced α-rich freeze-out, 44Ca, 48Ti, and 64Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars strongly suggest a significant contribution of hypernovae; and (iii) oxygen burning takes place in more extended regions in hypernovae to synthesize a larger amount of Si, S, Ar, and Ca (‘Si’), which makes the ‘Si’/O ratio larger. The abundance pattern of the starburst galaxy M 82 may be attributed to hypernova explosions. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution.

We present the current performances of the AMBER / VLTI instrument in terms of differential observables (differential phase and differential visibility) and show that we are already able to reach a sufficient precision for very low mass companions spectroscopy and mass characterization. We perform some extrapolations with the knowledge of the current limitations of the instrument facility.

We show that with the current setup of the AMBER instrument, we can already reach $3\sigma = 10^{-3}$ radians and have the potential to some low mass companions characterization (Brown dwarves or hypothetical very hot Extra Solar Giant Planets). With some upgrades of the VLTI infrastructure, improvements of the instrument calibration and improvements of the observing strategy, we will be able to reach $3\sigma = 10^{-4}$ radians and will have the potential to perform Extra Solar Giant Planets spectroscopy and mass characterization.

On board the space probes Giotto and VEGAs and 2, which were sent through the coma of comet Halley, were the mass spectrometers PIA and PUMAs 1 and 2 for the in situ analysis of cometary dust. This paper summarizes the results obtained up to now, about four years after the flybys. It is sought to make the reader aware of the significance, but also of the limitations, of these unprecedented data gathered within a few hundred seconds with an innovative instrument about 1.5 x 108 km away from Earth. The first part of this paper shows how the bulk properties of the dust are derived—the main constituents CHON and silicates, the core-mantle structure, the molecular composition of the organic component, the average composition of the dust and of the whole comet, and the gas/dust ratio. The second part reviews what can safely be said about the properties of the individual grains—their similarity to a certain class of interplanetary dust particles and their distinction from others, and their density and masses. The final part of this paper shows that some cometary grains contain isotopically ultra-light carbon (12C/13C up to 5000), a finding that is significantly substantiated by reports of similar carbon isotopic composition in meteoritic graphite.

Due to their extremely small luminosity compared to the stars they orbit, planets outside our own Solar System are extraordinarily difficult to detect directly in optical light. Careful photometric monitoring of distant stars, however, can reveal the presence of exoplanets via the microlensing or eclipsing effects they induce. The international PLANET collaboration is performing such monitoring using a cadre of semi-dedicated telescopes around the world. Their results constrain the number of gas giants orbiting 1–7 AU from the most typical stars in the Galaxy. Upgrades in the program are opening regions of “exoplanet discovery space” – toward smaller masses and larger orbital radii – that are inaccessible to the Doppler velocity technique.

Accurate measurement of the frequencies of low-degree acoustic oscillations of sun-like stars is imminent. We report on our first calculations with proxy data, aimed at assessing the kind of physical information that is likely to be acquired from seismic analysis and the precision with which the frequencies must be measured in order to obtain that information. The results will have an important bearing on future observing strategies, for the duration of observation should be determined primarily by the precision required of the frequency measurements. Our inversions are of eigenfrequencies of modes of an evolved main-sequence star of mass 1.1M⊙. The modes are of degree 0, 1 and 2, with frequencies in the range 1-3 mHz. Thus, by analogy with solar oscillations, they are modes that one should expect to observe in stars similar to the sun. Figure Ia depicts an idealized spectrum of stellar acoustic oscillations as one might expect from intensity variations such as those that could be measured from the proposed ESA spacecraft PRISMA. We report on the extent to which we have found it possible to determine the mass and radius of the stars, and on the seismic evidence for evolution having taken place in the core.

Stellar winds may be important for angular momentum transport from accreting T Tauri stars, but the nature of these winds is still not well-constrained. We present some simulation results for hypothetical, hot (∼ 106 K) coronal winds from T Tauri stars, and we calculate the expected emission properties. For the high mass loss rates required to solve the angular momentum problem, we find that the radiative losses will be much greater than can be powered by the accretion process. We place an upper limit to the mass loss rate from accretion-powered coronal winds of ∼ 10−11M yr−1. We conclude that accretion powered stellar winds are still a promising scenario for solving the stellar angular momentum problem, but the winds must be cool (e.g., 104 K) and thus are not driven by thermal pressure.

This review deals with the local instabilities arising when the effects of rotation are taken into account in the evolution of a non-magnetic star.

The Rayleigh and shear instabilities will be examined under the conditions prevailing in radiative zones where the effect of density stratification, thermal diffusion, viscosity and varying chemical composition must be taken into account. The possible consequences on the evolution of a star are finally outlined.