First of all it will be necessary to say a few words on terminology. Different names are now in use either for the same group of variables or for different variants of a rather heterogeneous class. Let me list the following:

• RW Aurigae stars,

• RR Tauri stars,

• T Tauri stars,

• Nebular type variables,

• Orion type variables,

• Nova-like variables,

• Main sequence variables.

Low-mass white dwarfs with helium cores (He-WDs) are known to result from mass loss and/or exchange events in binary systems where the donor is a low mass star evolving along the red giant branch (RGB). Therefore, He-WDs are common components in binary systems with either two white dwarfs or with a white dwarf and a millisecond pulsar (MSP). If the cooling behaviour of He-WDs is known from theoretical studies (see Driebe et al. 1998, and references therein) the ages of MSP systems can be calculated independently of the pulsar properties provided the He-WD mass is known from spectroscopy.

I argue that the widely adopted framework of stellar dynamics survived since 1940s, is not fitting the current knowledge on non-linear systems. Borrowed from plasma physics when several fundamental features of perturbed non-linear systems were unknown, that framework ignores the difference in the role of perturbations in two different classes of systems, in plasma with Debye screening and gravitating systems with no screening. Now, when the revolutionary role of chaotic effects is revealed even in planetary dynamics i.e. for nearly integrable systems, one would expect that for stellar systems, i.e. non-integrable systems, their role have to be far more crucial. Indeed, ergodic theory tools already enabled to prove that spherical stellar systems are exponentially instable due to N-body interactions, while the two-body encounters, contrary to existing belief, are not the dominating mechanism of their relaxation. Chaotic effects distinguish morphological and other properties of galaxies. Using the Ricci curvature criterion, one can also show that a central massive object (nucleus) makes the N-body gravitating system more instable (chaotic), while systems with double nuclei are even more instable than those with a single one.

We investigate the influence of blending on the Cepheid distance scale using two Local Group galaxies, M31 and M33. Blending leads to systematically low distances to galaxies observed with the HST, and therefore to systematically high estimates of H0. High-resolution HST images are compared to our ground-based data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in M31 and 102 Cepheids in M33. For a sample of 22 Cepheids in M31, the average (median) flux contribution from luminous companions not resolved on the ground-based images in the V-band, SV, is about 19% (12%) of the flux of the Cepheid. For 102 Cepheids in M33 the average (median) values of SV, SI, SB are 23% (13%), 28% (20%), 28% (15%). For 64 Cepheids in M33 with periods in excess of 10 days the average (median) SV, SI, SB are 16% (7%), 23% (12%), 20% (10%).

The preliminary results of the CCD search for variable stars in the very young open cluster NGC 6823 are presented. About ten new variable stars were discovered. The most interesting finding is that of the two pre-main sequence (PMS) δ Scuti-type variables. Because the evolutionary rate of period change is large at the PMS stage, these stars could be used in the future for testing it observationally.

Collisions have been a major process that shaped the Kuiper Belt that we see today. Collisional grinding likely played a significant role in removing mass from the trans-neptunian region and collisions are a mechanism for injecting fragments into resonances to start their journey to become short period comets. The Kuiper Belt preserves the accretional size distribution in bodies ≳ 100 km while the size distribution of smaller bodies is the result of collisional evolution. Observational confirmation of the transition size between these different regimes will constrain our understanding of the origin and evolution of the Kuiper Belt.

One way to realize the Large radio Telescope with a collecting area approaching one square kilometer, continuously covering a frequency range between 200 MHz and 2 GHz, is to construct a passive spherical reflector array of about 30 individual unit telescopes, each ∼ 300 m diameter(Butcher 1995). Valleys amid the hills of southwest China would be ideal for such LT concept. We refer to this effort as the Kilometer-square Area Radio Synthesis Telescope project. Site surveying and Radio Interference monitoring looks promising. Engineering considerations are summarized.

A systematic search is reported for phenomena associated with circumstellar matter in interacting binary systems of the Algol and W Serpentis type. Ultraviolet emission lines have been detected by the author in 10 Algols and 6 Serpentids. No conspicuous difference exists between systems with disk accretion and those with direct stream impact. Evidence is indicated that the lines are formed predominantly by scattering in an induced stellar wind. Relative intensity of Fe II and Fe III emissions appears to be correlated with the spectral type of the gainer. It is suggested that in the Serpentids we see a thick disk nearly edge–on, but that the emission lines indicate the nature of the gainer inside.

The calculation of atomic properties is plasma is critically dependent on the form of the ion-electron interaction potential. In the case of weak collisions in a low density ionized gas, the screening of the ion under consideration by surrounding plasma is adequately described by the Debye-Hückel potential (see, e.g., Weisheit, 1983). If the plasma is very dense, the perturbation approximations leading to the Debye form break down and other techniques must be employed to incorporate additional correlative effects. The transition from classical to this strongly coupled plasma occurs when the parameter , where is the mean charge per ion, , and ro is the ion-sphere radius, is greater than about one.

Current knowledge of the chemical nature of WR stars determined from UV, optical and IR spectral analyses, is reviewed. By number, the H/He ratio is low in most WN stars: 10 ≥ H/He ≥ 0.4 for WNL stars; 3.0 ≥ H/He ≥ 0.0 for WNE stars with most having near zero H-abundances. The C/N ratio in WN stars lies in the range 1–6 × 10−2, whilst N/He ∼10−4 − 4 × 10−3. These abundances for WN stars are broadly consistent with equilibrium CNO-burning products. In WC stars H/He=0 whilst C/He ∼ 0.1 − 0.7 with some evidence for increasing values from WC7 → WC4. N is highly deficient in WC stars, with C/N≥ 60, and for HD 165763 O/C ≤ 0.2 is deduced. In γ Velorum (WC8+O9), IR spectra give a value of Ne/He = 1.0×10-3 (about twice solar). Thus WC abundances are broadly consistent with He-burning products, although the Ne abundance appears lower than predicted. WO stars show C/He ∼ 0.2 − 0.7, and O/He ∼ 0.03 − 0.1, revealing both He-burning and α-capture products. Ring nebulae around several WN stars shown enhanced He and N, consistent with mass loss enrichment expectations from their chemically evolved central stars. Enhanced He (and probably N) is also seen in the atmospheres of several LBVs, OBN and Of stars - potential precursors of, at least, some WN subtypes.

We study the oscillatory behaviour of small-scale magnetic flux-tube concentrations and their immediate surroundings by analysing high spatial resolution time series of spectra of four Zeeman sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, Fe I 5250.7) taken simultaneously in left-hand and right-hand circularly polarized light with the Echelle spectrograph at the Vacuum Tower Telescope in Izaña, Tenerife. The velocity field inside the magnetic elements is dominated by the 5-min oscillations which also show up as periodic variations in the relative amplitude asymmetry of the Stokes V profiles. In other parameters as for instance the Stokes V peak separation we cannot detect an oscillatory component. Neither the magnetic line ratio nor the thermal line ratio is affected by the 5-min oscillations, although the latter reveals remarkable spatiotemporal variations.

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

Recent numerical investigations of fully compressible nonlinear magnetoconvection have clarified the nature of convection in sunspot umbrae. In a shallow layer with a strong vertical magnetic field oscillations give way to travelling waves as the Rayleigh number is increased but in a deep stratified layer oscillatory behaviour only appears after secondary bifurcations. This behaviour leads to a model that explains the formation of umbral dots. Penumbral structure is more difficult to explain owing to the apparent presence of adjacent horizontal and inclined fields in dark and bright filaments. The inner penumbra lies above a transition zone where volume currents are needed to maintain an overall static equilibrium; instabilities in this region may be responsible for filamentary structure in the penumbra as well as for fine structure at the umbral-penumbral boundary.

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.

The properties of the different types of QSO absorption systems are briefly summarized. An overview is given of the potential applications of absorption lines in cosmology. Recent work on the cosmological evolution of the different types of absorbers is discussed. The physical properties of the intergalactic medium are discussed in the light of recent work on the “Lyman alpha clouds”. The uses of the lines for studies of the evolution of clustering in the Universe are described. Recent puzzling results on common absorption in pairs of QSOs, particularly Q1037–2704 and Q1038–2712, are summarized.

There are dozen instruments successfully operating aboard the solar satellite CORONAS-F, which was launched in the summer of 2001. Among them are two (Polish-led) Bragg crystal spectrometers – RESIK and Diogeness – recording solar flare and active region spectra. A short description of the CORONAS-F satellite operation is presented together with that of the two Polish spectrometers, stressing their unique characteristics. The average spectra have been derived and shown here, covering the wavelength range between 3 Å and 7 Å. Future steps in the analysis of the large database collected are outlined.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss the “rotation” curves of SB0 galaxies with self-consistent models constructed with Schwarzschild’s method. Their distribution functions are compared with that of N-body simulations.

Du point de vue de la photometrie, on peut distinguer tres schematiquement trois sortes d'etoiles doubles:

• (1) les couples optiques

• (2) les couples physiques sans orbite connue

• (3) les couples orbitaux.