We present the results of time-series photometry for a sample of candidate pre-cataclysmic variables.

The observations were conducted on 2002-09-17 to 22, 2002-10-16 to 22, 2003-04-08 to 11, 2003-05-13 to 16, and 2003-06-18 to 21, at the 90 cm telescope at CTIO, Chile, using a 2kx2k CCD and a Johnson R filter. Additionally, data for the three targets LBQS 1144+0111, LBQS 1232+1335, and LBQS 1327—0242, were obtained in service mode at the 1.3 m CTIO telescope with ANDICAM. The latter observations consisted in a series of ~2 h runs for each object on five consecutive nights, also in R.

The zero-point of the extragalactic distance scale, defined by about two dozens of nearby, late-type galaxies, has remained nearly unchanged for the last decade, in spite of the advent of new techniques and great efforts. The distances are essentially tied to trigonometric parallax stars and hence independent of the Hyades modulus; they are consistent with RR Lyr stars. The mean zero-point is therefore probably secure to better than 10%.

All known secondary distance indicators are still affected by zero-point errors, by problems in the definition of their relation between distance indicator and absolute magnitude (or linear size), and/or by selection bias. The effect of the very important selection bias (Malmquist effect), which causes a seemingly non-linear expansion field, is illustrated by two examples. To test for any true deviations from a linear expansion the Hubble diagram of nearly bias-free first-ranked cluster galaxies and supernovae Ia is shown; this imposes stringent limits on any non-linearity of the Hubble flow within v<5000 km s−1.

After freeing the available distances of field galaxies from selection bias and after reducing them to a common zero-point, one finds HO=55–65. Several distance indicators require a best Virgo cluster modulus of (m-M)=31.60, which implies for the Coma cluster (m-M)=35.38 and, with v(Coma)=7217 km s−1, HO=60. Supernovae Ia and first-ranked cluster galaxies out to large distances give HO (global)=53. Thus the evidence from clusters and field galaxies is best satisfied by HO=55; the assigned mean error of ±7 is to indicate a 3σ range of 35<HO<75.

Purely physical methods to determine extragalactic distances have modest weight yet; they will contribute eventually much to the determination of HO.

If HO were as large as 100, several paradoxa would arise. The Milky Way would have a very high supernova frequency, our Galaxy and M31 would be oversized, the baryon density would fall short to bind clusters, and Friedman universes were excluded.

Because all systematic errors have conspired and probably still conspire to measure HO too high, the true value could well be 40. Until new, decisive evidence becomes available, it is suggested for all practical purposes to use HO=50.

AGB stars, seen as a stellar population, can be used to probe the dynamical state of galaxies. The relevant data are mostly positions and line-of-sight velocities, sometimes together with information on chemical composition and/or age. As of now, dynamical models have been made for OH/IR stars and Planetary Nebulae. Other candidates are C stars, S stars, and Miras. We review the methods used and the results obtained so far, for the Milky Way and for (relatively nearby) extragalactic stellar systems.

Binary stars in a globular cluster (hereafter, GC) may be primordial (i.e. formed along with the cluster), or the result of cluster dynamics. “Dynamical” binaries can result from conservative three-body encounters (e.g. Spitzer, 1987) if a third star can carry away enough kinetic energy to leave two others bound, or from dissipative two-body encounters, if two stars happen to pass within a few stellar radii of one other (Fabian, Pringle, & Rees, 1975). Such non-primordial systems are likely to be found primarily in evolved GC cores, both because conditions are more favorable for making them there, and because of mass segregation. Knowledge of the formation process allows reasonable estimates to be made of their mass and energy distributions. The initial spatial, mass, and energy distributions of primordial binaries, on the other hand, are largely unknown.

The picture emerging from recent studies of RS CVn-type systems indicates the presence of very active stars showing typical solar-like activity phenomena, such as spots and flares, and possibly mutual interactions. The binary nature of RS CVns is certainly important in enforcing high stellar rotation rates, but the actual clue to the understanding of the intrinsic variability of the component stars resides in their internal structure, where the appropriate physical conditions are met for the generation and intensification of strong magnetic fields, as prescribed by the αω-dynamo models. The most significant results have been derived from multi-wavelength, coordinated observations and long-term monitoring programs.

Recent highlights include: a) the mapping of compact atmospheric structures at various temperature regimes by light curve modelling and spectral (Doppler) imaging techniques; b) clear evidence of long-term activity cycles on RS CVn and other types of interacting binaries; c) the detection and measurement of surface magnetic fields, as derived from the differential Zeeman splitting of spectral lines.

These results clearly demonstrate that the study of RS CVn stars can play a very fundamental role in the understanding of basic stellar physics, as well as in interpreting the characteristic variability of interacting binaries.

We describe the observational capabilities of the SOHO EIT and LASCO instruments for prominence research. A detailed comparison of EIT He II λ304 and BBSO Hα images of a quiescent prominence reveals differences in fine scale structure which are attributed to differences in radiation emission and transport mechanisms. Absorption features present in coronal EIT images are attributed to dense prominence features located between the source of the coronal emission and the observer. These features provide the locations of prominence material in coronal image sequences. Observations of a prominence eruption in both EIT He II and LASCO C1 Fe XIV images show the heating of chromospheric material to coronal temperatures during the prominence eruption. In the last phase of the prominence eruption, a coronal mass ejection (CME) is initiated as a dark cavity forms over the prominence material and a bright loop-like structure forms over the dark cavity.

The geometric deformation, as well as the non-uniform surface gravity and temperature distributions induced by the fast rotation, are taken into account to determine the fundamental parameters of 10 Be stars seen nearly equator-on. The stars occur in the first half of the main sequence evolutionary span, which suggests that their fast rotation is related to initial formation conditions, rather than to evolutionary effects.

The NLTE effects affecting oxygen-abundance determinations of solar-type stars are discussed. LTE is safe for the forbidden lines. The permitted triplet at 777 nm is expected to show NLTE effects so that assuming LTE overestimates the abundance, but the magnitude of the effects is dependent on the poorly known cross sections of collisional excitation by collisions with neutral hydrogen atoms. Little is known about the NLTE effects on molecular line formation.

The problem of the solar atmospheric heat and energy balances is here divided into three sections.

1. (i) Basically the problem is an outward temperature gradient involving additional radiation losses whose estimate involves a model atmosphere. Proposed models described are based on optical and radio emissions together with various theoretical considerations such as thermal conductivity. The models are useful in providing estimates of the required flux of mechanical energy from below. However, they are limited by the use of averaging processes, and the failure to take full account of the many structural features which make up the chromosphere.

2. (ii) It has long been accepted that the main energy input is by acoustic waves generated in the ‘small-bubble’ Vitense model convection zone. We review recent observations of chromospheric magnetic and velocity fields and their interpretation which strongly suggest that this model is not valid and that the acoustic theory of heating is without basis. At the same time the new data remove the objections of Osterbrock and others to a theory of heating based on Alfvén and/or slow-mode hydromagnetic waves.

3. (iii) Observations of a variety of individual magnetic-plasma chromospheric structures, together with the adoption of heating by waves which follow the field lines, suggest a new approach to the whole problem of the heat balance. We discuss the heating problem in a number of these magnetic-plasma structures including the emission network, spicules and related disk features, arch filament systems and flares.

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbital solution shows that the binary period, now 12.062 years, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 ± 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions.

Infrared observations have provided considerable information about the structure and energetics of the galactic center. The stellar bulge dominates the mass and luminosity of the nuclear region. The luminosity of the bulge is strongly peaked toward the center, even within the central parsec. Dust in the nuclear disk absorbs the power output of the central portion of the bulge and reemits it in the far infrared. Near the center, molecular clouds move in a plane apparently tilted toward the Sun. Within the central few parsecs, or core, the inclination may be as large as 45°. The total power output of the core is about twice that of the bulge population alone. The source of excess luminosity is uncertain, but evidence points to ongoing star formation associated with the Sgr A molecular complex.

Archival full disk observations of the central depth of Mn 539.467, a photospheric line, have been found to correlate with chromospheric Ca K intensity. In this paper we present spectroheliograms taken in Mn I 539.467 and 542.32 nm lines and other nearby lines to see if the other photospheric lines show chromospheric structures. We see both Mn images and also Si I 542.118 mimic magnetograms the similar way, while strong Fe and Ti lines only faintly reveal magnetic features, and weak Fe lines of comparable strength to Mn show nothing.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A current-free approximation to the coronal magnetic field is calculated from measured photospheric magnetic fields (Mt. Wilson) and traced by computer. The calculated field structure is then compared to a white-light photograph of the November 12, 1966 eclipse.

A model for the origin of giant radio pulses is suggested. Radio emission is generated by the electric discharge taking place due to the magnetic reconnection of field lines connecting the opposite magnetic poles. The reconnection occurs in the region of the light cylinder near the zero line of the magnetic field. The coherent mechanism of radiation is pure maser amplification of Alfvén waves. The radiated frequencies are found.

One-dimensional photochemical models are used to provide an assessment of the chemical composition of the Shoemaker-Levy 9 impact sites soon after the impacts, and over time, as the impact-derived molecular species evolve due to photochemical processes. Photochemical model predictions are compared with the observed temporal variation of the impact-derived molecules in order to place constraints on the initial composition at the impact sites and on the amount of aerosol debris deposited in the stratosphere. The time variation of NH3, HCN, OCS, and H2S in the photochemical models roughly parallels that of the observations. S2 persists too long in the photochemical models, suggesting that some of the estimated chemical rates constants and/or initial conditions (e.g., the assumed altitude distribution or abundance of S2) are incorrect. Models predict that CS and CO persist for months or years in the jovian stratosphere. Observations indicate that the model results with regard to CS are qualitatively correct (although the measured CS abundance demonstrates the need for a larger assumed initial abundance of CS in the models), but that CO appears to be more stable in the models than is indicated by observations. The reason for this discrepancy is unknown. We use model-data comparisons to learn more about the unique photochemical processes occurring after the impacts.

The current dispute over the oxygen abundance in metal-poor stars has been viewed from a distance by this observer who would claim a measure of independence despite an intermittent interest in ox-gen abundance determinations over 3 decades. This summary attempts to persuade all participants whether they advocate a ‘high’ or ‘low’ oxygen abundance or are simply bemused by the dispute that in resolving the present disagreements we shall learn not only about the oxygen abundance of these oldest Galactic stars but shall achieve a deeper understanding of the atmospheres of the stars.

Among the Western Tobas of the province of Formosa, Argentina, the asterism called Dapi'chi (the Pleiades) is highly important. Traditionally, it is related to the start of the annual cycle and it is also a very significant figure in terms of its symbolic meaning. In fact, this celestial representation offers a range of insights connected to winter frosts, a type of air carnation (Tillandsia spp.–Bromeliaceae) and also to the role of the warrior.

I have been invited by the organisers to provide an overall perspective on the subject of this Symposium. Necessarily, this will be a subjective impression of topics in which there has been quite remarkable progress since the last General Assembly of the IAU, and which are of the greatest interest for the whole of science. In preparing a review of such an enormous field, one veers between optimism and pessimism about the successes and problems which have arisen. I hope to steer a realistic course between these extremes. Fortunately, there are many experts participating in this Symposium who will be able to neutralise my personal biases and provide authoritative opinions on all the topics I will cover.