We have made detailed comparisons of coronal structure, as photographed at λ5303 Å, with magnetic lines of force, as computed from measurements of the longitudinal component of the underlying photospheric magnetic fields. Coronal fields were computed under the assumption that the space above the active regions is current-free. Out of 36 regions for which there exist both magnetic and coronal data at the Sacramento Peak Observatory, we found only four suitable for analysis. Using a light-pen attachment to a digital computer, we were able to choose lines of force whose footpoints in the photosphere best matched those of the lines of force which were suggested by local intensity variations in the corona. The lines of force thus computed give excellent agreement with the apparent height and shape of coronal fieldlines. In particular the magnetic field in the loop structures of 2 November 1969 and 18–19 November 1968 falls from several hundred gauss at 10000–20000 km above the photosphere to 2–20 G at heights of 100000–150000 km. These computed values are in general agreement with other measurements. Spectra of the loops reveal that the direction of the line-of-sight component of the motion agrees with that anticipated from a comparison of the computed fieldline orientation and the observed motion in the plane of observation. We conclude that coronal magnetic fields above slowly changing active regions are nearly the same as the vacuum potential fields derived from underlying photospheric field sources (principally the larger sunspots in a region) and that calculations of this type may be relied upon to give the magnetic fields for studies of coronal dynamics.

This is a brief historical review of the discovery of binary stars, starting in the 18th and 19th century with the work of W. Herschel, W. Struve, and their famous sons. I describe how Ch. Doppler in 1842 found the Doppler effect in connection with the colours of double stars. I also describe how the observation of the stationary Calcium H and K lines in the spectrum of the spectroscopic binary δ Ori led to the discovery of the interstellar medium by J. Hartmann in 1904 with the Potsdam refractor. Some steps in the discovery of young binary stars are recounted, starting with the paper of Joy and van Biesbroeck in 1944. The history of ideas regarding the origin of binary systems is also briefly reviewed, beginning with J. Michell's statistical argument in 1767 that many close visual pairs of stars must indeed form physical systems, and W. Herschel's definition of a binary star as “a real double star - the union of two stars that are formed together in one system, by the laws of attraction”.

The coronal mass ejection (CME) link to geomagnetic storms stems from the southward component of the interplanetary magnetic field contained in the CME flux ropes and in the sheath between the flux rope and the CME-driven shock. A typical storm-causing CME is characterized by (i) high speed, (ii) large angular width (mostly halos and partial halos), and (iii) solar source location close to the central meridian. For CMEs originating at larger central meridian distances, the storms are mainly caused by the sheath field. Both the magnetic and energy contents of the storm-producing CMEs can be traced to the magnetic structure of active regions and the free energy stored in them.

The role of magnetic fields for the formation of planets is reviewed. Protoplanetary disc turbulence driven by the magnetorotational instability has a huge influence on the early stages of planet formation. Small dust grains are transported both vertically and radially in the disc by turbulent diffusion, counteracting sedimentation to the mid-plane and transporting crystalline material from the hot inner disc to the outer parts. The conclusion from recent efforts to measure the turbulent diffusion coefficient of magnetorotational turbulence is that turbulent diffusion of small particles is much stronger than naively thought. Larger particles – pebbles, rocks and boulders – get trapped in long-lived high pressure regions that arise spontaneously at large scales in the turbulent flow. These gas high pressures, in geostrophic balance with a sub-Keplerian/super-Keplerian zonal flow envelope, are excited by radial fluctuations in the Maxwell stress. The coherence time of the Maxwell stress is only a few orbits, where as the correlation time of the pressure bumps is comparable to the turbulent mixing time-scale, many tens or orbits on scales much greater than one scale height. The particle overdensities contract under the combined gravity of all the particles and condense into gravitationally bound clusters of rocks and boulders. These planetesimals have masses comparable to the dwarf planet Ceres. I conclude with thoughts on future priorities in the field of planet formation in turbulent discs.

Light reflected from planets is polarized. This basic property of planets provides the possibility for detecting and characterizing extra-solar planets using polarimetry. The expected polarization properties of extra-solar planets are discussed that can be inferred from polarimetry of “our” solar system planets. They show a large variety of characteristics depending on the atmospheric and/or surface properties. Best candidates for a polarimetric detection are extra-solar planets with an optically thick Rayleigh scattering layer.

Even the detection of highly polarized extra-solar planets requires a very sophisticated instrument. We present the results from a phase A (feasibility) study for a polarimetric arm in the ESO VLT planet finder instrument. It is shown that giant planets around nearby stars can be searched and investigated with an imaging polarimeter, combined with a powerful AO system and a coronagraph at an 8 m class telescope.

A similar type of polarimeter is also considered for the direct detection of terrestrial planets using an AO system on one of the future Extremely Large Telescopes.

Prof. Wheeler has asked me to say something for the record about some ideas that I once suggested (at the Clifford Memorial meeting in Princeton in 1970) and to which Hawking and Collins have referred (Astrophys. J.180, 317, 1973). This concerns a line of thought which I believe to be potentially fertile, but which I did not write up at the time because I felt (as I still feel) that it needs further development. However, it is not inappropriate that this matter should have cropped up again on the present occasion, since it consists basically of a reaction against exaggerated subservience to the ‘Copernican principle’.

We summarize the status and results of the OWN Survey, a high-resolution monitoring program of Southern Galactic O- and WN-type stars, after twelve years of observing campaign.

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.

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.

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.

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.

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.

In recent times, there has been keen interest in understanding Sun-Earth connection events, such as solar flares, CMEs and concomitant magnetic storms. Magnetic storms are the most dramatic and perhaps important component of space weather effects on Earth. Super-intense magnetic storms (defined here as those with Dst $<$ −500 nT, where Dst stands for the disturbance storm time index that measures the strength of the magnetic storm) although relatively rare, have the largest societal and technological relevance. Such storms can cause life-threatening power outages, satellite damage, communication failures and navigational problems. However, the data for such magnetic storms is rather scarce. For example, only one super-intense magnetic storm has been recorded (Dst=−640 nT, March 13, 1989) during the space-age (since 1958), although such storms may have occurred many times in the last 160 years or so when the regular observatory network came into existence. Thus, research on historical geomagnetic storms can help to create a good data base for intense and super-intense magnetic storms. From the application of knowledge of interplanetary and solar causes of storms gained from the spaceage observations applied to the super-intense storm of September 1-2, 1859, it has been possible to deduce that an exceptionally fast (and intense) magnetic cloud was the interplanetary cause of this geomagnetic storm with a Dst −1760 nT, nearly 3 times as large as that of March 13, 1989 super-intense storm. The talk will focus on super-intense storms of September 1-2, 1859, and also discuss the results in the context of some recent intense storms.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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.

Discovery of strongly-lensed gravitational wave (GW) sources will unveil binary compact objects at higher redshifts and lower intrinsic luminosities than is possible without lensing. Such systems will yield unprecedented constraints on the mass distribution in galaxy clusters, measurements of the polarization of GWs, tests of General Relativity, and constraints on the Hubble parameter. Excited by these prospects, and intrigued by the presence of so-called “heavy black holes” in the early detections by LIGO-Virgo, we commenced a search for strongly-lensed GWs and possible electromagnetic counterparts in the latter stages of the second LIGO observing run (O2). Here, we summarise our calculation of the detection rate of strongly-lensed GWs, describe our review of BBH detections from O1, outline our observing strategy in O2, summarize our follow-up observations of GW170814, and discuss the future prospects of detection.

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.

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.