The upper main sequence magnetic chemically peculiar (Ap) stars exhibit a non-uniform distribution of chemical elements across their surfaces and with height in their atmospheres. These inhomogeneities, responsible for the conspicuous photometric and spectroscopic variation of Ap stars, are believed to be produced by atomic diffusion operating in the stellar atmospheres stabilized by multi-kG magnetic fields. Here I present an overview of the current state-of-the-art in understanding Ap-star spots and their relation to magnetic fields. In particular, I highlight recent 3-D chemical spot structure studies and summarize magnetic field mapping results based on the inversion of the full Stokes vector spectropolarimetric observations. I also discuss a puzzling new type of spotted stars, HgMn stars, in which the formation and evolution of heavy element spots is driven by a poorly understood mechanism, apparently unrelated to magnetic fields.

I describe two recent projects to test star formation theory using Zeeman observations. First, using Bayesian analysis, the probability distribution function of the magnitude of the total magnetic field strength Bt and its dependence on volume density n(H) were inferred from Zeeman observations of the line-of-sight strengths Bz. The result was that from one molecular cloud to another Bt ranges uniformly between values close to zero and a maximum B0, and that B0 scales as n2/3. Second, observations of the ratio of the mass/flux (M/Φ) between the core and envelope regions of four dark clouds yielded values < 1. All of these results disagree with predictions of the strong magnetic field, ambipolar diffusion driven theory of star formation.

Multi-wavelength imaging of the solar corona is a powerful observational method to study CME-related dynamics of structures in spectral bands related to the solar corona and transition region. We analyze large-scale eruptive events caused by halo-type CMEs observed at the solar disk with the CORONAS-F/SPIRIT (175, 304, and 284 Å) and SOHO/EIT telescopes on November 4, 2001 and October–November, 2003. For most events, CME-associated dimmings coincide in different bands, but the 304 Å dimming in November 4, 2001 event was delayed by $>1/2$ hours. In October–November events, coronal waves were observed in 195 Å and some in 175 Å channel. In a CME event associated with a filament eruption on November 18, the SPIRIT images display a propagating disturbance seen as a darkening in 304 Å channel only. This phenomenon was not described earlier.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the strong links between music and astronomy over 25 centuries.

The properties of conservative dynamical systems of two or more degrees of freedom are reviewed. The transition from integrable to ergodic systems is described. Nonintegrability is due to the interaction of two, or more, resonances. Then one sees, on a surface of section, infinite types of islands of various orders, while the asymptotic curves from unstable invariant points intersect each other along homoclinic and heteroclinic points producing an apparent ‘dissolution’ of the invariant curves. A threshold energy is defined separating near integrable systems from near ergodic ones. The possibility of real ergodicity for large enough energies is discussed. In the case of many degrees of freedom we also distinguish between integrable, ergodic, and intermediate cases. Among the latter are systems of particles interacting with Lennard-Jones interparticle potential. A threshold energy was derived, which is proportional to the number of particles. Finally some recent results about the general three-body problem are described. One can extend the families of periodic orbits of the restricted problem to the general three-body problem. Many of these orbits are stable. An empirical study of orbits near the stable periodic orbits indicates the existence of 2 integrals of motion besides the energy.

This paper compares the statistical features of the sample of discovered extrasolar planets with those of the secondaries in nearby spectroscopic binaries, in order to enable us to distinguish between the two populations. Based on 32 planet candidates discovered until March 2000, we find that their eccentricity and period distribution are surprisingly similar to those of the binary population, while their mass distribution is remarkably different. The mass distributions definitely support the idea of two distinct populations, suggesting the planet candidates are indeed extrasolar planets. The transition between the two populations probably occurs at 10–30 Jupiter masses. We point out a possible negative correlation between the orbital period of the planets and the metallicity of their parent stars, which holds only for periods less than about 100 days. These short-period systems are characterized by circular or almost circular orbits.

Recent simulations of supernova-driven turbulence within the ISM support the existence of a large-scale dynamo. With a growth time of about two hundred million years, the dynamo is quite fast – in contradiction to many assertions in the literature. We here present details on the scaling of the dynamo effect within the simulations and discuss global mean-field models based on the adopted turbulence coefficients. The results are compared to global simulations of the magneto-rotational instability.

At its 1994 General Assembly, the International Astronomical Union resolved to introduce new arrangements to establish and maintain an accessible and authoritative set of constants, algorithms and procedures that implement standard models used in fundamental astronomy. The initiative was the responsibility of the Working Group on Astronomical Standards (WGAS), part of Division 1 of the IAU, and the set of procedures and constants was named SOFA, for “Standards Of Fundamental Astronomy”. The background to the IAU Resolution is given by Fukushima (1995) and Wallace (1996).

Imaging of a large number of faint galaxies with the Hubble Space Telescope reveals a significant excess of interacting and peculiar objects among them (Griffiths et al., 1994, Burkey et al., 1994). Being expected in general, this result needs, however, to be expressed quantitatively. To estimate evolutionary changing of the relative number of interacting galaxies, δint(z), from their redshift z, one must determine reliably the local value, δint(0). But due to a subjective manner of definition of interacting galaxy system, the published values of δint(0) differ from one author to another several times. The most appropriate sample to estimate δint(0) would be quite a representative sample of very nearby galaxies, which is restricted by their distance or radial velocity. Below we consider data on such a fair sample, named the Local Volume (=LV), which is the most complete one at the present moment.

The capability of ground-based photometry to detect and monitor low-level stellar variations is discussed in the particular case of amplitudes in the range of few magnitudes to few percent. The technical and atmospherical constraints are briefly recalled. The variability level of the so-called constant stars is discussed as function of the spectral type, the luminosity class and the effective temperature. The photometric aspects of the Hipparcos mission are presented here since this satellite allows a systematic detection of microvariables and the obtention of light curves across the whole HR-diagram with an unprecedented efficiency.

A collisional model for interplanetary debris, formulated earlier by the writer, is applied presently to the problem of asteroids and their debris. Following observational evidence, a population-index type-number density function is assumed. The integro-differential equation describing the evolution of a system of colliding brittle particles derived earlier is satisfied for this special case. The result is a stable steady state solution subject to certain boundary conditions. It is found that catastrophic collisions dominate over the erosion process in the present steady state model.

Using a root mean-squared average collision velocity of 5 km/sec, the population index, α, for asteroids is calculated to be α = 1·837. This value of α is rather insensitive to the physical parameters and is within the margin of error of an empirical least squares fit by the writer α = 1·80 ± ·04 to the distribution of asteroids reported by Kuiper et al. If the largest three asteroids are statistically interpreted, the distribution of asteroids in the asteroidal belt is consistent with the present collisional model. This would imply that most asteroids are fragments from some parent object(s).

The theoretical distribution is normalized to the observed number of asteroids in the survey by Kuiper et al., and using the present theory various statistical properties of the population of asteroids and their debris are calculated. The total mass of objects in the asteroidal belt is almost entirely concentrated in the masses of the three largest objects. The total asteroidal mass, crushed yearly, is of the order of 1012 kg and the rate of mass loss to radiation forces is about 7 × 1010 kg/yr.

The mean lifetime of large asteroids is found to be of the order of 108–109 years. The lifetime of objects is limited by the probability of catastrophic collisions; erosion and radiation damping only have a minor influence on the particle lifetimes.

The erosion rate of the largest objects is of the order of 1m /106 yr, and this rate decreases for smaller objects. Comparison with erosion rates estimated by Whipple indicates that the lifetimes, with respect to erosion, of objects smaller than about 1 kg may be dominated by collisions with cometary particles.

Interferometric imaging of evolved stars has been performed in the near-IR at the Keck Observatory revealing diffraction-limited structure at unprecedented spatial resolution. By studying the hottest regions of the circumstellar dust shells of a number of bright prototypical objects, we have revealed complex and anisotropic structures in the inner regions where dust nucleation occurs. We find that dramatic dust plumes and clumps dominate the morphology of the circumstellar environment at a scale of a few stellar radii for extreme carbon stars such as IRC+10216 and CIT 6. Furthermore our observations have yielded near-IR diameters and images of the stellar photospheres of nearby red giant and supergiant stars. With the additional benefit of multi-epoch observations, we have begun to investigate the time-evolution of our enshrouded objects as dust is created and accelerated away from the nucleation zone. Armed with such a powerful new set of observational constraints, we are able to address contemporary problems such as the origin of structure in PNe, the physics of mass loss, and the dynamical properties of Mira pulsation.

A total of 9 nonthermal sources near the plane of the Galaxy have now been definitely identified with nebulosities. The identifications are well established; positions and sizes of the nebulosities and of the sources are in satisfactory agreement. At least three types of objects can be recognized:

1. Remnants of supernovae of type I.

2. The Cassiopeia A source, a remnant of a supernova of type II.

3. The Cygnus loop and several other large nebulosities which are most likely of similar origin. They also may be remnants of supernovae type II.

The large size and the low surface brightness of these objects render their detailed investigation a difficult and time-consuming task. The true picture may emerge slowly, and conclusions drawn at an early stage of the work may have to be discarded as the investigation progresses.

It is difficult if not impossible to explain the abundances of assorted interstellar molecules in both the gaseous and condensed phases without the use of grain chemistry. Unfortunately, the chemistry occurring on grains is not well understood because of a variety of uncertainties including the nature, size, and shape of dust particles, the binding energies of key species, the dominant mechanism of surface chemistry, and the correct mathematical treatment of surface processes. Still, intrepid astrochemists have used granular chemistry in chemical models of an assortment of sources including cold clouds, protostellar disks, and hot cores. Indeed, the dominant explanation of the saturated gas-phase molecules observed in hot cores involves grain chemistry during an earlier, low temperature phase. Although gas-grain models have elucidated major features of the chemistry, much more work remains to be accomplished before they can be used to help characterize the physical conditions in star-forming regions and their temporal variations.

We review the techniques which are applied to study by means of laboratory simulation the chemical and physical processes taking place in ices in interstellar dense clouds. We summarize the current situation with regard to spectroscopy of interstellar ice analogs and with regard to the simulation of chemical processes such as modification of the ices by UV photons and surface reactions between reactive atoms and molecules. It is discussed how such data can be used to explore the potential of the icy mantles both as a record of the various chemical conditions that occur in dense clouds and as an environment for unique interstellar chemical processes.

Variable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems are reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.

During the Skylab Mission, the NRL slitless spectrograph photographed a number of flares in the 170–600 Å region with a spatial resolution approaching 2″. At flare maximum the 2s2S1/2 — — 2p2P1/2, 3/2 transitions of Fe XXIV are present, and show the location of the (approx.) 20 × 106 deg plasma with respect to the surface magnetic field and chromospheric (He iiemissions. Three examples are discussed (two only briefly).

In the small, intense disk flare of 1973, August 9 the high temperature region appears at the foot of a low altitude arch. The estimated electron density is 5 × 1011 cm–3.

In the limb flare of 1974, January 15 the hot X-ray emitting component is at a very low altitude compared to the flare loops.

In the impulsive double ribbon flare of 1973, June 15 the Fe XXIV emission is centered over the neutral line, forming a bridge-like structure between magnetic regions of opposite polarity. The estimated electron density is 5 × 1010 cm–3.

The Fe XXIV emission was visible 8 to 10 min as compared with a calculated cooling time by conduction of only 5 min. The lengthened life of the emission may be associated with the observed ‘turbulence’, which inhibits the heat conduction, or alternatively, with a slower energy release prolonged beyond the end of the burst phase.

We have modeled the mid-infrared emission from the Galactic Center using our array camera images at eight wavelengths. The results suggest that the high infrared luminosity of the region is provided by a cluster of luminous stars. There is no direct indication in the new model results of a very luminous object or “central engine” near Sgr A∗.

Ever since the pioneering work by Morgan and his collaborators (1952, 1953), it has been well known that the distribution of the associations of young stars, HII regions, and young clusters defines the optical spiral features. Although considerable progress has been made in spiral structure studies during these past 25 years, the basic picture of optical spiral structure has not been significantly altered. The three spiral features first described by Morgan are still recognized. Modern work on the various optical spiral features has strengthened and improved the definition of the optical features, especially to larger distances. Most of the improvements and any additions to the basic three-arm pattern have resulted primarily from observations of the spiral tracers in the Southern Milky Way. Specifically, the Sagittarius feature is now generally recognized as the Sagittarius-Carina arm which may indeed be a major arm of the Galaxy. It can now be traced optically to very large distances, up to 6 kpc or more in the direction ℓ = 290°. The Local arm (Cygnus-Orion) probably extends to 4 kpc in the direction of Puppis (ℓ ≅ 240°), and most astronomers would probably agree that our local spiral feature is not a major arm, but an inter-arm feature.

The long period (P = 27.1 yr) eclipsing binary є Aurigae (F0 Ia + disk?) is truly an exotic star. It has a deep eclipse that lasts for nearly two years. This eclipse arises as a huge, cool, flattened disk transits the F-supergiant star. Modeling of the eclipse observations shows that the disk has a radius as large as ∼ 9 AU. Infrared observations indicate that the disk is cool with temperatures between 450 − 1000 K. Yet there is evidence of significant FUV emission also originating from the disk.

At present, our knowledge of the mass and luminosity of the binary is still too uncertain to distinguish between two competing models of the system. The high mass model assumes that the F0 supergiant is a normal Pop. I star with a mass appropriate for its spectral type of M ∽ 15 M⊙. It is accompanied by a flattened disk companion with a slightly smaller mass. In this model the disk object is a young proto-stellar or protoplanetary disk. In the low mass model, the F0I star is assumed to be a bloated, old, solar mass post-AGB star. In this case the secondary object is an accretion disk with a mass of 4-5 M⊙. This disk is a remnant of postmain sequence mass transfer that occurred within the last few thousand years. In both models there are still problems explaining the object (or objects) at the center of the disk. Candidates include a pre-main sequence object, a black hole, or a close binary.

In this paper we review the properties of ϵ Aurigae and discuss the advances in our understanding of this enigmatic star from observations made since its last eclipse in 1982-1984. With new technologies and advanced instrumentation it is possible that the physical properties of this puzzling binary star will be found during the next decade. Once found, then ϵ Aurigae and its eclipses can be used as a laboratory for exploring (and testing) current astrophysical concepts and theories that include rapid stages of stellar evolution, binary star evolution, and the structure and dynamics of large disks.