Several groups of close binary stars are considered in an attempt to explain their present state as a consequence of a large-scale mass transfer or mass loss in the past: Algol-like semidetached binaries, some shell stars (AX Mon), some binary X-ray sources (Cen X-3, Her X-1), the recurrent nova T CrB, helium-rich binaries v Sgr and KS Per, and the symbiotic variables.

Algol-like binaries like U Sge cannot be products of a conservative case A of mass transfer; rather, mass loss from system and/or a temporary contact stage must be invoked. Nova T CrB as well as the symbiotic variables probably contain a mass-losing giant and a helium star, which again may be a product of a previous mass transfer of type B. Similarly, some of the X-ray sources may actually be binaries undergoing a second process of mass transfer. The systems v Sgr and KS Per may contain helium stars expanding to the right of the helium main sequence, while the other component may be a rather inactive main-sequence star. Some shell stars may be products of mass transfer. Mass loss from convective envelopes is also discussed.

Loss of mass and of angular momentum from many binary systems must be anticipated. Behavior of the mass-accreting stars may often be decisive for the appearance and evolution of the system.

To bring out the basic problem of star formation, consider a non-rotating cosmical gas cloud which is free to contract and so to convert most of its gravitational energy into kinetic energy of mass motion. Fluid dynamical systems in general tend to dissipate their kinetic energy, and a diffuse gas cloud easily radiates excess heat. If the cloud did not break up into fragments, then the steady conversion of gravitational energy into radiation would lead ultimately into the formation of a compact massive body - perhaps a quasar - but not of a star cluster, which is maintained at a comparatively low mean density by random stellar kinetic energy. Thus the transition from a gravitationally-bound cloud of gas and dust into a bound star cluster - or a fortiori into an expanding O-B association - requires that gravitational energy released during collapse be conserved as the random macroscopic kinetic energy. It is very likely that star formation is often triggered by processes that are essentially dissipative, such as shocks following passage of the spiral wave, or cloud-cloud collisions; however, it is equally important to emphasise that we require at some stage a cut-off in kinetic energy dissipation. And indeed, once a cloud has been able to fragment into a group of self-gravitating blobs, each of small geometrical cross-section, the chance of inelastic collisions between blobs is sharply reduced.

Since we cannot put stars in a laboratory, astrophysicists had to wait till the invention of computers before becoming laboratory scientists. For half a century now, we have been conducting experiments in our virtual laboratories. However, we ourselves have remained behind the keyboard, with the screen of the monitor separating us from the world we are simulating. Recently, 3D on-line technology, developed first for games but now deployed in virtual worlds like Second Life, is beginning to make it possible for astrophysicists to enter their virtual labs themselves, in virtual form as avatars. This has several advantages, from new possibilities to explore the results of the simulations to a shared presence in a virtual lab with remote collaborators on different continents. I will report my experiences with the use of Qwaq Forums, a virtual world developed by a new company (see http://www.qwaq.com).

The properties of bright extragalactic planetary nebulae are reviewed based upon the results of low and high resolution spectroscopy. It is argued that bright extragalactic planetary nebulae from galaxies (or subsystems) with and without star formation have different distributions of central star temperature and ionization structure. As regards the chemical compositions, oxygen and neon are generally found to be unchanged as a result of the evolution of the stellar progenitors. Nitrogen enrichment may occur as a result of the evolution of the progenitors of bright planetary nebulae in all stellar populations, though this enrichment may be (more) random in old stellar populations. Helium abundances appear to be influenced by the chemical evolution of the host galaxy, with planetary nebulae in dwarf spheroidals having systematically elevated abundances. Neither the age nor the metallicity of the progenitor stellar population has a strong effect upon the kinematics observed for nebular shells. Both the range of expansion velocites, 8-28 km s$^{-1}$, and the typical expansion velocity, $\sim 18\,\mathrm{km\,s}^{-1}$, are found to be relatively constant in all galaxies. On the other hand, bright planetary nebulae in the bulge of M31 have systematically higher expansion velocities than their counterparts in M31's disk. The expansion velocities show no trend with nebular H$\beta$ luminosity, apart from a lack of large expansion velocities at the highest luminosities (the youngest objects), but appear to correlate with the $5007/\mathrm{H}\beta$ ratio, at least until this ratio saturates. These results suggest a link between the evolution of the nebular shells and central stars of bright extragalactic planetary nebulae.

We review the local determination of the Hubble constant, H0, focusing on recent measurements of a distance ladder constructed from geometry, Cepheid variables and Type Ia supernovae (SNe Ia). We explain in some detail the components of the ladder: (1) geometry from Milky Way parallaxes, masers in NGC 4258 and detached eclipsing binaries in the Large Magellanic Cloud; (2) measurements of Cepheids with the Hubble Space Telescope (HST) in these anchors and in the hosts of 42 SNe Ia; and (3) SNe Ia in the Hubble flow. Great attention to negating systematic uncertainties through the use of differential measurements is reviewed. A wide array of tests are discussed. The measurements provide a strong indication of a discrepancy between the local measure of H0 and its value predicted by Λ Cold Dark Matter theory, calibrated by the cosmic microwave background (Planck), a decade-long challenge known as the ‘Hubble Tension’. We present new measurements with the James Webb Space Telescope of >320 Cepheids on both rungs of the distance ladder, in a SN Ia host and the geometric calibrator NGC 4258, showing good agreement with the same as measured with HST. This provides strong evidence that systematic errors in HST Cepheid photometry do not play a significant role in the present Hubble Tension. Future measurements are expected to refine the local determination of the Hubble constant.

Observational data concerning the long-term history of cyclic solar activity as recorded in sunspot and isotopic data are discussed in the context of solar dynamo theory. In particular, a simple dynamo model based on differential rotation and the mirror asymmetry of convection with random fluctuations of dynamo governing parameters is shown to reproduce some basic features of the solar magnetic activity evolution.

The study of detached eclipsing binaries is one of the most powerful ways to investigate the properties of individual stars and stellar systems. We present preliminary masses, radii and effective temperatures for the eclipsing binary WW Aurigae, which is composed of two metallic-lined A-type stars. We also reanalyse the data on HD 23642, an A-type eclipsing binary member of the Pleiades open cluster with a metallic-lined component, and determine its distance to be $139 \pm 4$ pc. This is in agreement with the traditional Pleiades distance, but in disagreement with distance to the Pleiades, and to HD 23642 itself, derived from Hipparcos trigonometrical parallaxes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The distance from the Local Group to the ‘sphere’ of small galaxies that no longer expand with the Universe determines the time since the Big Bang, t x M1/2, where M is the mass of the Local Group. Adopting Feast's new distance scale, this distance is found to be 1.35 ± 0.1 Mpc. The velocity of approach and the distance to M31 give a different combination of t and M, thus both can be deduced. We find the time since the Big Bang and The importance of accurate distances for such results is stressed. If all distances are revised by a factor λ then both t and M change by that factor.

Using the IRAM instruments (interferometer on Plateau de Bure and 30-m telescope on Pico Veleta) we have made numerous observations of molecular absorption lines in front of extragalactic millimeter wavelength radio sources. Observations of HCO+, CO and OH show that the lines of sight studied in this way sample the outer edges of molecular clouds or the diffuse clouds with highest column densities. Collisional excitation of the rotational levels is not significant in this density range for most molecular species, and accurate column densities may be derived by assuming radiative equilibrium with the cosmic microwave background. Using this technique we have measured column densities of CO, HCO+, H2CO, CN, HCN, HNC, CS, SO, H2S, C2H, and C3H2 in several lines of sight, intersecting about 20 individual clouds with CO column densities in the range 2 1014 to ∼ 1016 cm−2. These results confirm that complex molecules achieve dark-cloud abundances at low extinctions, either by formation in the gas phase or on grains.

We carried out three-dimensional global MHD simulations of jet formation from an accretion disk threaded by large-scale magnetic fields. Numerical results show that bipolar jets with maximum speed υjet ~ υKepler are created. The surface layer of the disk accretes faster than the equatorial part because magnetic braking most effectively affects that layer. Accretion proceeds along spiral channels which correspond to the surface avalanche flow appearing in previous axisymmetric simulations. Spirally shaped low β (= Pgas/Pmag < 1) regions appear in the innermost part of accretion disks where toroidal magnetic fields become dominant.

With the advent of powerful instruments in various spectral domains many scientists became involved in the study of giant HII regions - i.e. regions as important as 30 Doradus in the Large Magellanic Cloud or NGC 604 in Messier 33 - and of HII complexes still more active such as isolated extragalactic HII regions, some galactic central regions, chains in large spirals and clumpy irregular galaxies.

In view of the importance of these investigations for the problems of formation and evolution of stars and of galaxies, we organized a Meeting at thelAU XVIIIth General Assembly on”Giant HII complexes outside our Galaxy”with the following program:

1. a- Observational results and their primary interpretations in the X-ray, UV, visible, IR and radio domains.

2. b- Confrontation with related investigations in our Galaxy and general interpretations.

In this paper we present the results of our new classification of asteroid families, upgraded by using catalog with > 500,000 asteroids. We discuss the outcome of the most recent update of the family list and of their membership. We found enough evidence to perform 9 mergers of the previously independent families. By introducing an improved method of estimation of the expected family growth in the less populous regions (e.g. at high inclination) we were able to reliably decide on rejection of one tiny group as a probable statistical fluke. Thus we reduced our current list to 115 families. We also present newly determined ages for 6 families, including complex 135 and 221, improving also our understanding of the dynamical vs. collisional families relationship. We conclude with some recommendations for the future work and for the family name problem.

In dense interstellar clouds that are shielded from high-energy radiation (e.g., UV photons or cosmic rays), H-atom addition and abstraction reactions that take place on grain surfaces play principal roles in the synthesis or decomposition of complex organic molecules (COMs). These reactions are extensively investigated with laboratory experiments by bombarding astrophysical analogue ices with a beam of low-temperature H atoms. Here we demonstrate that, although 2-4 K solid para-H2 does not represent a typical environment of the surface of interstellar grains, para-H2 matrix isolation combined with IR spectroscopy is a complementary tool to sensitively detect astrochemical hydrogenation and dehydrogenation processes.

This note describes some of the initial results derived from observations of radar echoes from the moon obtained at 10-cm wavelength at the Royal Radar Establishment, Malvern. The radar, which has been described elsewhere [1], has a transmitter of 2 megawatts peak power with a pulse length of 5 microseconds and a pulse recurrence frequency of 260 per second. The receiver is of conventional design and has a bandwidth of 500 kc/s and a noise factor of 7.5. The aerial used is the 45-foot diameter radio telescope shown in Fig. 1. The telescope is controlled from a mechanical computer that converts the lunar coordinates into azimuth and elevation, which are then fed into a servo drive.

A review of observational data supports the proposal that there are two distinct phases of particle acceleration in solar flares. ‘Phase 1’ is associated with the flash phase and is here interpreted as acceleration during field-line reconnection. ‘Phase 2’ is associated with type II and type IV radio bursts, and is ascribed to stochastic acceleration in the turbulent plasma behind a magnetohydrodynamic shock formed ahead of an ejected plasmoid.

A vacuum evaporation technique has been used to produce thin, optical quality films of samples of Type II kerogen and of insoluble organic residue from the Murchison meteorite. Using these films, optical constants have been measured from 0.15 to 40 μm for kerogen, and from 2.5 to 40 μm for the Murchison residue. The infrared absorption properties of these materials show many similarities, although Murchison residue is more opaque throughout the infrared than is kerogen, and shows no distinct aliphatic absorptions.

For the interpretation of the physical events occurring at the beginning of a flare it seems to be significant not only to observe the spectra of the short-wavelength X-ray radiation but also its polarization. Solar X-ray spectra below 10 Å during flares observed by Bowen et al. (1964) show in the region of long wavelength a slow fall in their intensity and below 5 Å approximately a rapid fall (Figure 1). This spectral variation cannot be understood on the basis of thermal radiation only. However, it is possible to explain the observed spectra by assuming a superposition of a thermal radiation as well as a non-thermal one. Indeed, one should assume that the fast electrons, during their acceleration, obtain a preferred direction and that only afterwards their velocity distribution becomes a Maxwellian one. The assumption of the existence of a non-Maxwellian distribution of electrons in the beginning of a flare is also supported by the fact that the rise in intensity by more than one order of magnitude takes place in a few minutes. This point has already been emphasised by Bowen et al.

At a time when so much of the prestigious astronomical research is devoted to new and highly speculative phenomena, it has been rewarding to see and hear the cautions and accurate approach to the measuring and interpreting of stellar quantities. It has been shown by many speakers, perhaps clearest of all by our participant of honor Professor Popper, how insufficient attention to calibration problems can lead to erroneous results.

Future extremely large telescopes will be the engines of major progress in the fields of star and planet formation, brown dwarfs, and extrasolar planets. Their throughput will enable spectroscopic studies of the structure of brown dwarf atmospheres; reveal the composition and kinematics of protoplanetary disks; extend radial velocity searches for extrasolar planets to fainter stars and lower masses; and characterize the surfaces of the most distant Kuiper Belt objects. Their resolution will allow us to resolve and track the orbits of close binary young stars and brown dwarfs, establishing their dynamical masses and calibrating their evolutionary tracks; probe the inner region of young stellar object disks, resolving the jet collimation region in accreting systems and disk inner holes in more evolved ones; and move the horizon for stellar companion searches inward to 40 mas, enabling the direct detection of hot young planets orbiting 10 AU from young T Tauri stars. The high contrast imaging capability of future ELTs is uncertain, and depends on future developments in extreme adaptive optics. Wavefront control considerations suggest a fundamental atmospheric contrast limit of 10$^{-8}$ for companion searches to nearby solar-type stars, below which detections are unlikely to be possible. To reach this performance level, continuing investments will be needed in extreme adaptive optics work, in addition to careful attention to the specialized requirements of ultra-high contrast imaging in ELT design. Above the 10$^{-8}$ contrast limit, a 30m telescope has the potential to directly image about a dozen of the currently known radial velocity planets.

The stellar associations are defined as loose unbound concentrations of young stars with a bright OB stellar component, mainly located at the most recent star forming regions, representing the smallest units in the hierarchy of stellar systems in galaxies. The definition of the associations is discussed and the main properties of their stellar content are summarized. Using plates taken with the 1.2m UK Schmidt Telescope a method is developed to detect all stellar associations in the LMC and to find their spatial distribution relative to the LMC's recent star formation history. In 40% of the LMC region, the number of “single peak” associations has increased considerably (~ 3x). A very interesting result is that the faint limit, where the identified associations are revealed, varies by about 3 mag. This indicates not only extinction differences but also the presence of pre-main sequence stars at a wide range of masses.