This paper presents physical properties of interplanetary dust determined by in-situ techniques. It is probable that, like millimeter-sized meteoroids (Jacchia, et al. 1967), most interplanetary dust is cometary matter. Although a cometary origin for interplanetary dust is widely accepted (Whipple 1967) (Millman, 1972) there is currently no unambiguous proof of this hypothesis. The results presented here must be interpreted accordingly. It must also be remembered that even if interplanetary particles are cometary, they might possibly be altered in the interplanetary medium by collisions and by thermal effects during close perihelion passages, so the dust particles may not be representative of unaltered cometary material.

Pathways leading to the formation of complex organic molecules are described. Gas-phase processes that may build large carbon-chain species in cold molecular clouds are summarised. Catalytic reactions on grain surfaces can lead to a large variety of organic species, and model calculations of mantle formation by atom additions to multiply-bonded molecules are presented. The subsequent desorption of these mixed molecular ices can initiate a distinctive organic chemistry via ion-molecule pathways. The predictions of this theory are briefly compared with observations to show how possible organic formation pathways in the interstellar medium may be constrained.

The THEMIS telescope will provide high resolution observations of the solar vector magnetic field. We present some capabilities of this instrument, concerning the polarization analysis, the correlation tracker and the two spectrographs. THEMIS is expected to come into operation in 1995–1996.

The God-father of psychoanalysis Professor Sigmund Freud taught us that the behaviour of adults depends on their early childhood experiences. in the same spirit, the problem of cosmological analysis is to derive the observed present day situation and structure of the Universe from certain plausible assumptions about its early behaviour. Perhaps the most important single statement about the large scale structure is that there is no structure at all on the largest scale − 1000 Mpc and more. On this scale the Universe is rather uniform, structureless and isotropically expanding - just according to the simplified pictures of Einstein-Friedmann……. Humason, Hubble…. Robertson, Walker. On the other hand there is a lot of structure on the scale of 100 or 50 Mpc and less. There are clusters and superclusters of galaxies.

The state of the art of optical studies of isolated neutron stars (INSs) and their pulsar wind nebulae (PWNe) is reviewed. In addition, results obtained from recent HST and VLT observations are presented and discussed.

Recent discoveries of MHD wave motions in the solar corona done with EUV imaging telescopes onboard SOHO and TRACE provide an observational basis for the MHD seismology of the corona. Measuring the properties of MHD waves and oscillations (periods, wavelengths, amplitudes, temporal and spatial signatures), combined with theoretical modeling of the wave phenomena, allow us to determine values of the mean parameters of the corona (the magnetic field strength, transport coefficients, etc.). As an example, we consider post-flare decaying oscillations of loops, observed with TRACE (14th July 1998 at 12:55 UT). An analysis of the oscillations shows that they are quasi-harmonic, with a period of about 265 s, and quickly decaying with the decay time of about 14.5 min. The period of oscillations allows us to determine the Alfvén speed in the oscillating loop about 770 km/s. This value can be used for deduction of the value of the magnetic field in the loop (giving 10-30 G). The decay time, in the assumption that the decay is caused by viscous (or resistive) dissipation, gives us the Reynolds number of 105.3-6.1 (or the Lundquist number of 105.0-5.8).

Loose agreement of a radio position of low accuracy with that of some object listed in the NGC is not sufficient to provide the identification of a radio source. Even satisfactory coincidence of a precise position with that of an astronomical object requires supporting evidence. Agreement of the size of the source with that of the visible object, at least in order of magnitude, is an important argument in favour of an identification; exact agreement of sizes can be expected only where radio and optical emission are physically connected. The radio spectrum, the optical spectrum, and the physical characteristics of the visual object also have to be taken into account. Observations of the radio spectrum should be particularly useful to support the identification of sources with H 11 regions which can be recognized from their thermal emission even if they are obscured and optically inaccessible. If all data are available, satisfactory agreement exists between optical and radio observations. The best example of this kind at the moment is perhaps NGC 2237, the Rosette nebula, reported as a source by Ko and Krauss (1955) [1] and also observed by Mills, Little and Sheridan (1956 [11]; see also paper 18).

Since the last presentation of SC-3 on numerical values of fundamental geodetic parameters at the IAU General Assembly at Kyoto in 1997 there were some conceptual as well as fundamental numerical changes. The four basic parameters of geodetic (ellipsoidal) reference systems (GRS) can no longer be considered as constant with time: J2, a, ω, and GM have to be replaced by clearly (±10−8 or better) specified mean values or have to be associated with a specific epoch or, in case of GM, with specific reference frames (a = semi-major axis of Earth ellipsoid, J2 = second degree zonal harmonic of geopotential, ω = spin of Earth rotation). In case of (a, J2 ....) associated tidal reductions must be specifically defined in view of particular applications and significant differences between different tidal reduction types. Or we may replace “a” by a quantity which is independent of tides like the geopotential at the geoid, W0, where, however, also temporal changes are now discussed. The official geodetic reference systems such as GRS 80 and WGS 84 (revised in 97-form) are also no longer truly representing reality; a new system GRS 2000 is desired. We are, meanwhile, able to define and determine tidal and non-tidal (secular, periodic, aperiodic) variatipns of some fundamental geodetic parameters. Others are under investigation. New precession and/or nutation formulas to be adopted by IAU in 2000 or later would imply, again, changes in geodetic parameters such as H = hydrostatic flattening. Those and related other consequences are considered.

We present the imaging potential of a tomographic technique which combines time-resolved spectroscopy and long baseline interferometry, providing information that cannot be obtained otherwise with each of these techniques separately.

The available information on the statistics of high multiplicity (3–6 components) systems is reviewed. The ratio of triple to binary systems is f3 ≍ 0.11, while fn ≍ 0.25 for higher n. Despite selection effects in the multiple star catalogue, the signatures of formation mechanisms are found in the distributions of period ratios and mass ratios. For example, the frequent occurrence of close sub-systems with periods less than 6 days can be explained by tidal dissipation in a 3-body system. In triple stars the angular momentum vectors of inner orbits are inclined to those of outer orbits by an average angle of 50°, hence the orbital spins are neither co-aligned nor completely random. Close binaries have a tendency to be found in higher-multiplicity systems, showing that close and wide binarity is statistically related. Future theoretical and observational studies are outlined.

A review of the main results from the MACHO project for RV Tauri stars and Type II Cepheids in the LMC is presented. In light and colour curve behaviour, the RV Tauri stars appear to be a direct extension of the Type II Cepheids to longer periods. A single period–luminosity–colour relationship is seen to describe both the Type II Cepheids and RV Tauri stars in the LMC.

Follow-up low resolution spectroscopy of the LMC RV Tauri stars has been undertaken. The spectra of the longest period RV Tauri star in the MACHO sample show that this star has strong C2 bands with a pronounced phase dependence, their strength being greater at minimum light. This and other spectral features are similar to those observed in proto-planetary nebulae. This LMC star therefore appears to combine the main spectral anomaly of the proto-planetary nebulae with RV Tauri-like photometric variability. This is an intriguing result which indicates a possible link between RV Tauri stars and proto-planetary nebulae, and strengthens the post-AGB interpretation of the RV Tauri stars.

Using the data from the catalogue of PNe images of Schwarz et al. (1992), we have classified 255 nebulae into 5 morphological groups. The images were taken through a filter centred on the Hα line and included the [NII]6583 line. Most of the observations were made with the 3.5m ESO NTT during commissioning time. The main groups are called: stellar (st), irregular (i), elliptical (e), bipolar (b), and point-symmetric (p). The ellipticals are subdivided into: simple (e), multiple event (em), and inner structure (es) types. The bipolars into: simple (b), and multiple event (bm). The point-symmetric objects into: simple (p), and multiple events (pm).

The strategies for image reconstruction from optical synthetic-aperture data can be divided into two camps according to their historical legacies: those coming from the field of more conventional optical image processing, where the data are relatively complete in terms of Fourier coverage, have concentrated on trying to recover images using “brute force” methods. They make use of the massive size of the typical datasets to try and derive an image without having to use any a-priori constraints. The size of the datasets to some extent restricts the algorithms used towards being as simple and hence fast as possible. Radio-astronomical imaging strategies, on the other hand, have always been designed to cope with sparse and missing data, and many sophisticated algorithms have been designed to make maximum use of a-priori constraints with iterative global fitting techniques.

Synthetic aperture telescopes are more and more considered as a promising scheme for the next generation of Very Large Telescopes : the basic idea is to combine the beams of two or more independent telescopes. The question immediately raising when considering such a technique is the pathlength stability and the amount of pathlength difference that can be tolerated, assuming a reasonable bandwidth, to preserve coherent addition of the wavefronts and hence, high spatial frequencies observations.

To that respect the I2T (two telescopes interferometer) in operation at CERGA constitutes a remarkable test-bench for studies of mechanical, optical and atmospheric constraints that are to be faced when dealing with amplitude interferometry between several telescopes.

By assuming that RR Lyrae stars have fairly strong dipole magnetic fields with symmetry axis oblique to the rotation axis of the star, I show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, whose symmetry axis coincides with the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent amplitude variation is interpreted as the Blazhko effect in RR Lyrae stars. It is shown that, in the case of off-axis magnetic field, phase modulation is expected. I list up some theoretical predictions based on this model, which would observationally examine this hypothesis.

Understanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly before the CME.

In this review we discuss the occurrence and statistical properties of Grand minima based on the available data covering the last millennia. In particular, we consider the historical record of sunspot numbers covering the last 400 years as well as records of cosmogenic isotopes in natural terrestrial archives, used to reconstruct solar activity for up to the last 11.5 millennia, i.e. throughout the Holocene. Using a reconstruction of solar activity from cosmogenic isotope data, we analyze statistics of the occurrence of Grand minima. We find that: the Sun spends about most of the time at moderate activity, 1/6 in a Grand minimum and some time also in a Grand maximum state; Occurrence of Grand minima is not a result of long-term cyclic variations but is defined by stochastic/chaotic processes; There is a tendency for Grand minima to cluster with the recurrence rate of roughly 2000-3000 years, with a weak ≈210-yr periodicity existing within the clusters. Grand minima occur of two different types: shorter than 100 years (Maunder-type) and long ≈150 years (Spörer-type). It is also discussed that solar cycles (most possibly not sunspots cycle) could exist during the Grand minima, perhaps with stretched length and asymmetric sunspot latitudinal distribution.

These results set new observational constraints on long-term solar and stellar dynamo models.

On the basis of the most recent compilation of narrow-band photometry and absolute visual magnitudes of Wolf-Rayet stars, and adopting a normal interstellar extinction law in all directions, the galactic distribution of 132 of the 159 known galactic WR stars is presented and discussed.

The spiral structure is found to be more clearly pronounced than in earlier studies. Furthermore we find an indication of two spiral arms at r=4 and 6 kpc. There appears to be an asymmetry of the z-distribution of single stars with respect to galactic longitude.

The location of the WC8.5 and WC9 stars between 4.5 and 9 kpc from the galactic center is discussed in the context of Maeder's red supergiant to WR star scenario.

We report on the first successful coordinated observations of stellar flares carried out on March 28, 1984 simultaneously over a wide range of wavelengths, from UV to microwaves, using the IUE satellite, three ESO telescopes at La Silla (Chile) and the VLA at Socorro (NM, USA).

Series of simultaneous spectra in different spectral regions, representing all ‘visible’ layers of the solar atmosphere, of high spatial and temporal resolution are used to compute power spectra and diagnostic diagrams of intensity and velocity fluctuations in order to study the dynamic response of the chromosphere to disturbances from below.