The current status of microturbulent velocity and abundance determinations for A and F dwarfs in open clusters is reviewed. A programme to observe several tens of A and F dwarfs in open clusters of various ages was initiated several years ago. We have performed high resolution high signal-to-noise spectroscopy of stars well distributed in mass along the Main Sequence. Microturbulent velocities and abundances of several chemical elements have been derived iteratively by fitting grids of synthetic spectra calculated in LTE to the observed spectra. Curve of growths were used in a few instances as well. The results obtained are reviewed for Coma Berenices, the Pleiades, Alpha Persei and the Ursa Major moving group.

The microturbulent velocities exhibit a broad maximum in the range A5V to about F0V as indicated in Smalley (2004).

Convection is the main energy transport mechanism in brown dwarf atmospheres. The overshoot of ascending bubbles affects the upper and cooler region where dust formation can occur. In order to understand the observed presence of dust, the formation of grains and their gravitational settling must be balanced by up-mixing of condensible elements via convective overshoot. Otherwise, brown dwarf atmospheres would be completely dust-free (Woitke & Helling 2004).

We present two 3D Large Eddy Simulations (LES) of the convection-radiation transition layer for both the A and the B component of the α Centauri binary system. Theoretical oscillation spectra are then calculated from stellar evolutionary models that include the effects of turbulence based on the LES simulations. By taking both non-seismic and seismic observational constraints into account we discuss the possibility to probe turbulence beyond standard 5mixing-length-theory in a star other than Sun.

Magnetic fields, convective motions and radiative energy transport all strongly influence each other in the solar photosphere. Attempts to understand, at a quantitative level, the diverse phenomona seen in the photosphere have relied on increasingly powerful computers since the 1980's. This approach has been remarkably successful and some recent examples, particularly cases where all three ingredients are important, will be discussed.

We discuss the impact that the space experiment CoRoT, whose launch is scheduled for late 2006, will have on the field of close binary.

Filamentary structures of early type stars are found to be a common feature of the MCs formed ~0.9 − 2 × 108yr ago. As we go to younger ages these large structures appear fragmented and sooner or later form young clusters and associations. In the optical domain we have detected 56 such large structures of young objects, known as stellar complexes in the LMC (Maragoudaki, Kontizas, Kontizas, et al. (1998)) and investigate their properties. IRAS data of the LMC stellar complexes were compared with observations of starburst galaxies (Helou (1986); Lehnert & Heckman (1996)). It has been found that nearly 1/4 of the stellar complexes are extremely active resembling the IR behaviour of starburst galaxies and HII regions. These stellar complexes are called here “starburst regions”. They host an increased number of HII regions, SNRs, stellar associations and nebulae. The main starburst tracers are their IR luminosity F60 and the 8.6-GHz radio emission (8.6-GHz data: Dickel, McIntire, Gruendl, et al. (2005)). In Table 1 the characteristics of the various types of complexes are given. Finally the evolution of all stellar complexes is discussed based on the CO emission (CO data: Fukui, Mizuno, Yamagushi, et al. (1999)). More than 50% of the starburst and starburst candidate regions show enhanced CO emission, indicating ongoing and future evolution.

With the present level of accuracy it may be necessary to use space borne atomic clocks to directly generate TCG, and to start addressing the limitations in the coordinate time transformations.

We discuss models for high-precision spacecraft and planetary and lunar ephemerides.

The astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at z ∼ 6 are poorly understood. In standard ΛCDM hierarchical cosmologies, the earliest massive holes (MBHs) likely formed at redshift z ≳ 15 at the centers of low-mass (M ≳ 5 × 105 M⊙) dark matter “minihalos”, and produced hard radiation by accretion. FUV/X-ray photons from such “miniquasars” may have permeated the universe more uniformly than EUV radiation, reduced gas clumping, and changed the chemistry of primordial gas. The role of accreting seed black holes in determining the thermal and ionization state of the intergalactic medium depends on the amount of cold and dense gas that forms and gets retained in protogalaxies after the formation of the first stars. The highest resolution N-body simulation to date of Galactic substructure shows that subhalos below the atomic cooling mass were very inefficient at forming stars.

Outflow-cloud interaction is an important issue in discussions about star formation in clusters because it could generate turbulence and restrain star formation activities, as well as it causes outflow-triggered star formation.

We present a few results of a low-frequency southern sky survey carried out using the Mauritius Radio Telescope (MRT).

The star-formation history and chemodynamical evolution of Blue Compact Dwarf (BCD) galaxies are central issues in dwarf galaxy research. In spite of being old in their vast majority, BCDs resemble in many aspects unevolved low-mass galaxies in the early universe. They are gas-rich (Hi mass fraction of typically > 30%) and metal-deficient (7.1 12+log(O/H) 8.3) extragalactic systems, undergoing intense star-forming (SF) activity within an underlying low-surface brightness (LSB) host galaxy.

We show that in a sample of Extremely Metal-Poor (EMP) giants (<[Fe/H]>=−3.1) all the stars with a luminosity higher than logL/L⊙ ≈ 2.6 present the characteristics of a mixing of the surface with the H-burning layer: low abundance of carbon and high abundance of nitrogen. In these “mixed stars” the lithium abundance and the ratio 12C/13C are very low. Some of these stars are also Na or/and Al rich.

We report about the multi-frequency (1–30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during 2005–2006. After a quiescent radio emission we have detected a drop down of the fluxes (∼20 mJy) from Cyg X-3, a sign of the following bright flare, and indeed a 1 Jy flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum was found flat from 2 to 110 GHz, using the quasi-simultaneous observations at 109 GHz with the RT45m telescope and the NMA millimeter array of Nobeyama Radio Observatory in Japan. Several bright radio flaring events (1–15 Jy) followed during the state of highly variable and intense 1–12 keV X-ray emission (∼0.5 Crab), monitored in the RXTE ASM program. We discussed various spectral and temporal characteristics of the detected 180 day light curves from three microquasars in comparison with the Rossi XTE ASM data.

The James Webb Space Telescope (JWST) is the scientific successor to the Hubble and Spitzer missions. Its wavelength range (1 - 28μm) and sensitivity (1 nJy - 1 μJy) complement the submillimeter facilities of the coming decade, Herschel and ALMA. The JWST development is on schedule for a June 2013 launch to L2 on an Ariane 5.

We have used the 20 largest radio continuum catalogues contained in VizieR (CDS) to determine radio continuum spectra between wavelengths of 2cm and 1m. For 67,000 out of the 3.5 million catalogued sources we could extract radio spectra with measurements at at least three independent frequencies (Vollmer et al. 2005, A&A, 431, 1177). These have been validated by comparison with existing spectral indices from the literature. This work allowed us to investigated the compatibility between the 20 radio continuum catalogues (Vollmer et al. 2005, A&A, 436, 757). Our radio spectra data base was searched for Gigahertz peaked source candidates, which we then observed quasi-simultaneously with the Effelsberg 100-m radio telescope at 6cm (4.85GHz), 2.8cm (10.45GHz), and 9mm (32GHz). This represents an efficient procedure to discover new Gigahertz peaked sources, which are believed to be AGNs at the beginning of their radio evolution. In our sample of more than 200 sources we find more than 50% bona fide GPS sources. In addition, we can estimate the percentage of variable sources in our multi-epoch sample of radio sources which show an inverted spectrum. We are generalizing the method by using VO capabilities to: (i) identify pertinent radio catalogues in the VO registry using Uniform Content Descriptions (UCDs); all catalogues containing a user defined set of UCDs (e.g., PHOT_FLUX_RADIO* for a radio flux, POS_EQ_RA and POS_EQ_DEC for the position) are located in the VO registry and listed for further queries; (ii) extract relevant data, the user can easily assign a row of a given catalogue to a row of a previously defined output catalogue; and (iii) normalize these for the determination of radio spectra; units can be converted, aconymes can be created, flags can be created, etc. This procedure allows to homogenize the information retrieved from a heterogenuous set of catalogues. For this purpose software allowing semi-automated information retrieval is being developed at the CDS within the framework of the European VO-TECH project. The potential usage of all available radio catalogues will strongly increase the number of independent radio source cross-correlations and radio spectra. Our aim is to include more than 100 radio catalogues into the radio spectra determination software. The results are progressively being made available to the community through the CDS services.

The distribution of Near-Earth Objects, in particular Near-Earth asteroids is examined using maximum likelihood methods. These are analysed with respect magnitudes, taxonomic classes and to their orbital distances. Comparisons are made with the distributions of main-belt asteroids and short-period comets.

We present a comparative study of three dark globules CB52, CB107, and DC267.4-07.5. By means of an accurate photometry, near-IR two-colour diagrams were derived for the stellar backgrounds and used to determine the colour excesses of the reddened stars (Campeggio et al. 2004). By assuming a normal interstellar reddening law (Rieke & Lebofsky 1985), the visual extinction can be obtained as Av = 15.87 E(H–K).

Using detailed Monte Carlo radiative transfer simulations in realistic models for galactic nuclei, we critically investigate the influence of interstellar dust in ionised gas discs on the rotation curves and the resulting black hole mass measurements. We find that absorption and scattering by interstellar dust leaves the shape of the rotation curves basically unaltered, but slightly decreases the central slope of the rotation curves. As a result, the “observed” black hole masses are systematically underestimated by some 10 to 20% for realistic optical depths.

Some results of Galaxy star clusters and associations observation are presented.