It is important for understanding stellar evolution to constrain observationally how overshoot occurs for stellar conditions. Simplified models of the dynamics (eg. Zahn 1991) indicate that overshoot results in a slightly subadiabatic region beyond the convectively unstable layers, followed by an almost discontinuous transition to radiative stratification. Abrupt changes such as this contribute with a characteristic periodic signal to the frequencies ωn,l, of modes of low degree l (Gough 1990). This signature may therefore be detectable for distant stars. Here we show that the signal is sensitive to the “severity” of the overshoot and, of practical importance for the solar case, how it may be extracted from modes of higher degree. Finally we apply our method to solar data.

To analyze the applicability of the method, we consider four stellar models, Z1 — Z4, with solar mass, radius (R) and luminosity; of these, Z2 and Z4 have overshoot. The bases of the nearly adiabatically stratified region in the models are at radii rd/R = .729, .713, .713 and .700 respectively.

It was shown by Maitzen & Pavlovski (1989) that a majority of λ Bootis stars stand out by negative Δα indices. Using this as detection tool, three candidate stars with λ Bootis characteristics are picked up in open cluster Praesepe.

We present high resolution (HPBW = 5 arcsec) continuum and molecular-line observations of the circumstellar environment of the emission-line star LkHα 234 made with the Owens Valley Millimeter-Wave Interferometer. These 98 GHz observations have revealed an unresolved continuum source coincident with the star and a 10 000 by 17000 A.U. ridge of enhanced CS(2-1) emission which peaks ∼ 4″ east of the star. The resulting spectral dependence for the radio continuum emission of ν1.5 is most easily interpreted as arising from a partially ionized stellar wind. Attempts are made to describe the properties of the CS emission in terms of a rotating molecular disk which would link LkHα 234 with large scale mass loss activity in the cloud. However, it appears most likely that the CS emission is arising from a dense (n(H2) ∼ 106 cm −3) condensation of gas adjacent to, but not dynamically associated with, the star.

Probable dust counterparts of arching structures are looked for in two cases, (a) the Eridanus expanding shell, Heiles (1976) and (b) the extended Sco-Cen feature, Weaver (1977). Apparently the color excess data may be used to derive distance and dimension estimates of these structures.

Sandage (1986) showed what the star formation rate (SFR) of galaxies of different Hubble type might look like. His curves are based on the study of Gallagher et al. (1984), who determined the SFR at three different epochs of galactic evolution. Sandage's figure establishes a connection of SFR and Hubble type but, as was already mentioned by Sandage, it “contains no physics”. In order to explore the background of this connection, however, it is necessary either to improve the observations or to model the evolution of galaxies self-consistently. However, the results of modelling the SFR are not reliable, if simplified models are used, which only describe some structural properties of galaxies. It is necessary to apply self-consistent models which take into consideration all relevant interaction processes between the gaseous and stellar components of a galaxy. Such models can be checked by comparison with observations like density and abundance distributions, star-gas content, velocities, velocity dispersions, mass-luminosity relations and age distributions of stars. A detailed model will show, whether the initial conditions, the feedback mechanisms during the evolution or the environment determine the evolution of a galaxy.

The evolution of close binaries is discussed in connection with problems concerning mass and angular momentum losses. Theoretical and observational evidence for outflow of matter, leaving the system during evolution is given: statistics on total masses and mass ratios, effects of the accretion of the mass gaining component, the presence of streams, disks, rings, circumstellar envelopes, period changes, abundance changes in the atmosphere.

The effects of outflowing matter on the evolution is outlined, and estimates of the fraction of matter expelled by the loser, and leaving the system, are given. The various time scales involved with evolution and observation are compared. Examples of non conservative evolution are discussed.

Problems related to contact phases, on mass and energy losses, in connection with entropy changes are briefly analysed. For advanced stages the disruption probabilities for supernova explosions are examined. A global picture is given for the evolution of massive close binaries, from ZAMS, through WR phases, X-ray phases, leading to runaway pulsars or to a binary pulsar and later to a millisecond pulsar.

Chaos appears in various problems of Relativity and Cosmology. Here we discuss (a) the Mixmaster Universe model, and (b) the motions around two fixed black holes, (a) The Mixmaster equations have a general solution (i.e. a solution depending on 6 arbitrary constants) of Painlevé type, but there is a second general solution which is not Painlevé. Thus the system does not pass the Painlevé test, and cannot be integrable. The Mixmaster model is not ergodic and does not have any periodic orbits. This is due to the fact that the sum of the three variables of the system (α + β + γ) has only one maximum for τ = τm and decreases continuously for larger and for smaller τ. The various Kasner periods increase exponentially for large τ. Thus the Lyapunov Characteristic Number (LCN) is zero. The “finite time LCN” is positive for finite τ and tends to zero when τ → ∞. Chaos is introduced mainly near the maximum of (α + β + γ). No appreciable chaos is introduced at the successive Kasner periods, or eras. We conclude that in the Belinskii-Khalatnikov time, τ, the Mixmaster model has the basic characteristics of a chaotic scattering problem, (b) In the case of two fixed black holes M1 and M2 the orbits of photons are separated into three types: orbits falling into M1 (type I), or M2 (type II), or escaping to infinity (type III). Chaos appears because between any two orbits of different types there are orbits of the third type. This is a typical chaotic scattering problem. The various types of orbits are separated by orbits asymptotic to 3 simple unstable orbits. In the case of particles of nonzero rest mass we have intervals where some periodic orbits are stable. Near such orbits we have order. The transition from order to chaos is made through an infinite sequence of period doubling bifurcations. The bifurcation ratio is the same as in classical conservative systems.

The 1600–2500Å spectra of many early-type supergiants are dominated by a broad depression of the continuum near 1920Å. This depression, often called the 1920Å feature, was detected in S2/68 (TD-1) spectra of early B stars (Thompson et al. 1974) and was shown to be strongly luminosity dependent. It was also shown that its profile could be matched by the cumulative effects of FeIII absorption lines.

We present results from the most recent Plateau de Bure observation of the 12CO(2-1) line towards the nearby QSO I Zw 1.

This work was performed in the same way as that corresponding to the Small Cloud (Landi Dessy 1959a, 1959b). Two hundred and seventy-seven new variables have been discovered, whose positions are shown by arrows in Figure 1. The pairs of plates used for blinking have from 80m to more than 1000d intervals.

In the wake of the HIPPARCOS success four highly accurate space astrometry missions are now approved for launch within the next ten years. Stellar physics and galactic physics constitute the core science of these missions with deep impact on star formation and evolution, cosmic distance scales and age determination of the oldest stars. Summary data are provided in this paper to compare the goals and capabilities of these missions.

Rather than review β Cepheids, this paper will address the issue that β Cephei variability is only a readily detectable tip of a much larger iceberg of variability among β stars. This variability being widespread, it becomes crucial to differentiate β Cepheids from other variable subgroups by observational criteria if one is ever to make physical inferences concerning the instability mechanism involved. Shobbrook (1978) has raised this point indirectly in discussing the importance of defining the width of the instability strip: if the strip is narrow, the pulsational instability is more likely to arise in the stellar core; if it is wide, it is probably excited in the envelope. Enormous efforts have gone into delineating the evolutionary and HR-D confines of ß Cepheids. In this paper it will be suggested that the situation is more complicated than the traditional outlook holds.

Novae (N) and Dwarf Novae (DN) are considered to belong to the class of the Cataclysmic Variables (CVs). The Novalike stars and recently discovered Polars (the AM Herculis-type stars) seem to have the same nature as CVs and probably are members of this class. It is usually assumed that CVs are close binary systems, each system contains a degenerate dwarf and a nondegenerate second component, their period being usually less than 16h (e.g. see: Robinson 1976). A second star is believed to overfill its Roche lobe and its matter flows onto the degenerated component. Then around the degenerated dwarf there arises an accretion disk. This disk and the hot spot where the interaction between the disk and outflowing stream occurs are the main sources of the blue and ultraviolet continuum and strong H and He emission lines.

The main investigations of the local magnetic field are reviewed and are found to contain some conflict in interpretation. At radio wavelengths, studies have been made using both the Faraday rotation of the polarized radiation from extragalactic sources and pulsars, and the polarization of the galactic background radiation. With the former type of observation, although more data are available for extragalactic sources, any interpretation may be complicated by the influence of distant field structure. The results are consistent with a large-scale field parallel to the galactic plane, with a field strength of about 2 µG, and which is directed towards l=90°. This field contains irregularities in direction and strength on a scale of about 100–200 pc. The polarization of galactic background radiation may yield the most detailed information about the local field structure – the results to date show loops of magnetic fields extending along the radio spurs.

The interpretation in terms of small-scale irregularities embedded in a large-scale field parallel to the galactic plane differs from that proposed to explain the optical polarization of starlight, in which a helical field configuration near the Sun was preferred to a more disordered pattern.

This report is organized according to twelve subjects of interest in modern celestial mechanics. Emphasis is placed on the results of an exhaustive literature search in which assistance was received from several members of Commission 7. The impetus on celestial mechanics by space projects, by new observational techniques and by the use of high speed electronic computers continued to be of considerable importance. The fact that celestial mechanics became an experimental science is still too recent to be fully evaluated. The high accuracy of radar and laser observations, the new analytical and numerical techniques, the recent sophisticated statistical orbit determination methods and many other results achieved during the past three years suggest that celestial mechanics is an exploding field of science in which new and exciting results emerge. Celestial mechanics is influencing other fields of scientific endeavor and is intimately connected and embedded in almost all areas of modern astronomy and space research.

Moffett (1972) pointed out the existence of short-time outbursts in flare stars as long ago as 1972. Gershberg & Petrov (1986) had registered a flare in EV Lac with a duration of 28.4 and an amplitude of 38.4 in 1984 with ASTRON. In recent years, a few reports appeared about observations of short-time outbursts in EV Lac with a duration in the range from 08.1 to several seconds. These results were summarized briefly by Zhilyaev (1993). Our observations confirm the existence of short-time flare activity on EV Lac.

The observations reported here were obtained at the 60 cm telescope at the Peak Terskol high-altitude Observatory (3 100 m above sea level) with a highspeed two-channel photometer (Zhilyaev et al. 1992) in B as well as simultaneously in both, U and V bands, with a time resolution down to 08.1. A new prefiltering technique (Zhilyaev 1995) has been used for the detection of smallscale activity of the flare star EV Lac.

Research in radio astronomy at the Ohio State University covers a wide range of astronomical and engineering phases. In this paper the principal topics currently under investigation are briefly discussed. Reference is made to more detailed papers or reports published within recent months or now in the press.

The study of the context of LBV stars, that is close neighbourhood (companions) and spatial relationship to young objects such as cepheids. stellar associations, red supergiants. enriched OB supergiants. Hll regions. WR stars can provide useful clues on their true luminosity, their age thus eventually initial mass and evolutionary status.

Fully ten percent of the Wolf-Rayet stars known in our galaxy are central stars of planetary nebulae. These stars are highly-evolved stars of approximately one solar mass. The existence of WR characteristics in the spectra of central stars as well as in massive, younger stars proves conclusively that WR spectra are a phenomenon that occurs in hot stars of widely different masses and evolutionary histories. Just what this phenomenon is — the nature of the instability that drives the wind — is not known, but the phenomenon is associated with a prior event in the star's evolutionary history. The common event that links Wolf-Rayet stars is loss of most, if not all of the outer, hydrogen-rich envelope just prior to the onset of WR characteristics. As Tutakov (this volume) and others have emphasized, there are many ways for a star to lose its H-rich envelope. These ways include mixing, ejection via a wind, or, in the case of a close binary, ejection via Roche-lobe overflow. The existence of WR-type central stars implies simply that we should include one more path leading to the Wolf-Rayet phenomenon, and that is, ejection to form a planetary nebulae.