Based on 3D hydrodynamical model atmospheres computed with the CO5BOLD code and 3D non-LTE (NLTE) line formation calculations, we study the effect of the convection-induced line asymmetry on the derived 6Li abundance for a range in effective temperature, gravity, and metallicity covering the stars of the Asplund et al. (2006) sample. When the asymmetry effect is taken into account for this sample of stars, the resulting 6Li/7Li ratios are reduced by about 1.5% on average with respect to the isotopic ratios determined by Asplund et al. (2006). This purely theoretical correction diminishes the number of significant 6Li detections from 9 to 4 (2σ criterion), or from 5 to 2 (3σ criterion). In view of this result the existence of a 6Li plateau appears questionable. A careful reanalysis of individual objects by fitting the observed lithium 6707 Å doublet both with 3D NLTE and 1D LTE synthetic line profiles confirms that the inferred 6Li abundance is systematically lower when using 3D NLTE instead of 1D LTE line fitting. Nevertheless, halo stars with unquestionable 6Li detection do exist even if analyzed in 3D-NLTE, the most prominent example being HD 84937.

We studied the fast kink modes of a cylindrical model of coronal loops, in coronal conditions, stratified density and low-β plasma. The mode frequencies and profiles are calculated.

Thanks to the high multiplex and efficiency of Giraffe at the VLT we have been able for the first time to observe the Li I doublet in the Main Sequence stars of a globular cluster. At the same time we observed Li in a sample of Sub-Giant stars of the same B-V colour.

Our final sample is composed of 84 SG stars and 79 MS stars. In spite of the fact that SG and MS span the same temperature range we find that the equivalent widths of the Li I doublet in SG stars are systematically larger than those in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis carried out making use of 1D hydrostatic plane-parallel models and 3D hydrodynamical simulations of the stellar atmospheres.

We derived the effective temperatures of stars in our the sample from Hα fitting. Theoretical profiles were computed using 3D hydrodynamical simulations and 1D ATLAS models. Therefore, we are able to determined 1D and 3D-based effective temperatures. We then infer Li abundances taking into account non-local thermodynamical equilibrium effects when using both 1D and 3D models.

We find that SG stars have a mean Li abundance higher by 0.1 dex than MS stars. This result is obtained using both 1D and 3D models. We also detect a positive slope of Li abundance with effective temperature, the higher the temperature the higher the Li abundance, both for SG and MS stars, although the slope is slightly steeper for MS stars. These results provide an unambiguous evidence that the Li abundance changes with evolutionary status.

The physical mechanisms responsible for this behaviour are not yet clear, and none of the existing models seems to describe accurately these observations. Based on these conclusions, we believe that the cosmological lithium problem still remains an open question.

Asteroseismology is a powerful tool to derive stellar parameters, including the helium content and internal helium gradients, and the macroscopic motions which can lead to lithium, beryllium, and boron abundance variations. Precise determinations of these parameters need deep analyses for each individual stars. After a general introduction on helio and asteroseismology, I first discuss the solar case, the results which have been obtained in the past two decades, and the crisis induced by the new determination of the abundances of heavy elements. Then I discuss asteroseismology in relation with light element abundances, especially for the case of main sequence stars.

We present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic H ii regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass ΔY/ΔO, and compare them with predictions based on models of galactic chemical evolution.

Recent simulations of forming low-mass galaxies suggests a strategy for obtaining realistic models of galaxies like the Milky-Way.

The reference time scales maintained at the International Bureau of Weights and Measures (BIPM) are constructed with data from industrial clocks and primary frequency standards operated in national metrology laboratories and observatories world-wide distributed. Clocks are compared making use of techniques of time transfer between remote sites. The algorithm of calculation relies on clock weighting and clock frequency prediction. We briefly present hereafter the influence of some clocks on the scales, as well as the possibilities for improvement.

We present results from an ongoing survey of searching Li-rich K giants among low mass giants along the Red Giant Branch (RGB). A sample of 2500 stars with accurate astrometry have been selected from Hipparcos catalogue covering both the RGB luminosity bump and the red clump regions on the HR diagram. Lithium abundances have been determined for half of the sample from low resolution spectra using line depth ratio method. Results confirm the rarity of Li-rich K giants, just under 1%, in the solar neighbourhood. This study increased the total number of known Li-rich K giants by a factor of two. The analysis of high resolution spectra of candidate Li-rich K giants showed that the K giant HD 77361 is highly enriched in lithium (log ϵ(Li) = 3.82) and at the same time has anomalously low carbon isotopic ratio (12C/13C = 4.3). The results put important constraints on the theoretical modelling of the stellar structure and the mixing process, particularly, of the K giants.

Pulsars provide a wealth of information about General Relativity, the equation of state of superdense matter, relativistic particle acceleration in high magnetic fields, the Galaxy's interstellar medium and magnetic field, stellar and binary evolution, celestial mechanics, planetary physics and even cosmology. The wide variety of physical applications currently being investigated through studies of radio pulsars rely on: (i) finding interesting objects to study via large-scale and targeted surveys; (ii) high-precision timing measurements which exploit their remarkable clock-like stability. We review current surveys and the principles of pulsar timing and highlight progress made in the rotating radio transients, intermittent pulsars, tests of relativity, understanding pulsar evolution, measuring neutron star masses and the pulsar timing array

Several lines of evidence suggest that planet formation may be well underway within the circumstellar disk of the enigmatic Herbig Be star HD100546, including a cleared inner cavity, spiral structure, and similar dust mineralogy as seen in our own solar system. To learn more about the processes occurring in this disk we have conducted a multi-frequency observing program with the Australia Telescope Compact Array (ATCA).

This essay attempts to provide a historical perspective on some of the key questions that engaged the attention of participants at the symposium. In particular, the writer offers and comments on a personal list of milestones in the literature published between 1957 and 1982.

A breakthrough in the studies of magnetic fields in clusters of galaxies has been reached in recent years from the analysis of the Rotation Measure of sources seen through the magnetized cluster medium (Govoni & Feretti 2004). The results obtained can be summarized as follows: (i) magnetic fields are present in all clusters; (ii) at the center of clusters undergoing merger activity the field strenght is around 1 μG, whereas at the center of relaxed cooling core clusters the intensity is much higher (~ 10 μG); (iii) a model involving a single magnetic field coherence scale is not suitable to describe the observational data, because of different scales of field ordering and tangling.

When compared to lithium and beryllium, the absence of boron lines in the optical results in a relatively small data set of boron abundances measured in Galactic stars to date. In this paper we discuss boron abundances published in the literature and focus on the evolution of boron in the Galaxy as measured from pristine boron abundances in cool stars as well as early-type stars in the Galactic disk. The trend of B with Fe obtained from cool F-G dwarfs in the disk is found to have a slope of 0.87 ± 0.08 (in a log-log plot). This slope is similar to the slope of B with Fe found for the metal poor halo stars and there seems to be a smooth connection between the halo and disk in the chemical evolution of boron. The disk trend of boron with oxygen has a steeper slope of 1.5. This slope suggests an intermediate behavior between primary and secondary production of boron with respect to oxygen. The slope derived for oxygen is consistent with the slope obtained for Fe provided that [O/Fe] increases as [Fe/H] decreases, as observed in the disk.

The solar “COmosphere” is an enigmatic region of cold gas (temperatures as low as ~3500 K) coexisting in the low chromosphere with plasma much hotter (~7000 K). This zone probably consists of patchy clouds of cool gas, seen readily in off-limb emissions of CO 4667 nm lines, threaded by hot gas entrained in long-lived magnetic filaments as well as transient shock fronts. The COmosphere was not anticipated in classical 1D models of the solar outer atmosphere, but is quite at home in the contemporary 3D highly dynamic view, which one might call the Magnetic Complexity Zone.

The most accepted model for jet production is based on the magneto-centrifugal acceleration out off an accretion disk that surrounds the central source (Blandford & Payne, 1982). This scenario, however, does not explain, e.g., the quasi-periodic ejection phenomena often observed in different astrophysical jet classes. de Gouveia Dal Pino & Lazarian (2005) (hereafter GDPL) have proposed that the large scale superluminal ejections observed in microquasars during radio flare events could be produced by violent magnetic reconnection (MR) episodes. Here, we extend this model to other accretion disk systems, namely: active galactic nuclei (AGNs) and young stellar objects (YSOs), and also discuss its hole on jet heating and particle acceleration.

We develop a new approach to the well-studied anti-correlation between the optical-to-X-ray spectral index, αox, and the monochromatic optical luminosity, lopt. By cross-correlating the SDSS DR5 quasar catalog with the XMM-Newton archive, we create a sample of 327 quasars with both optical and X-ray spectra, allowing αox to be defined at arbitrary frequencies, rather than the standard 2500 Å and 2 keV. We find that while the choice of optical wavelength does not strongly influence the αox−lopt relation, the slope of the relation flattens significantly with X-ray energy. This result suggests a change in the efficiency of X-ray photon production, where the efficiency of low energy X-ray production depends more strongly on the seed (optical/UV) photon supply. We discuss implications for line-driven wind models.

Using Chandra and XMM-Newton X-ray observations of young, post-merger elliptical galaxies, we present X-ray characteristics of age-related observational results, by comparing with typical old elliptical galaxies in terms of X-ray properties of their low-mass X-ray binaries (LMXBs) and hot interstellar matter (ISM).

Lithium abundance measurements in dwarf stars in open clusters are of crucial importance for our understanding of the mixing mechanism and have allowed us to achieve important conclusions on the matter. However, in order to further our understanding of what drives lithium depletion, lithium abundance measurements have to be coupled with accurate temperature determinations, which are best achieved when the analysis of iron lines is employed. Effective temperature estimations from photometry, on the contrary, can be affected by errors as large as several hundred kelvins due to uncertain open cluster reddening, especially when studying old open clusters, which tend to be more distant. We present lithium abundance in 12 dwarfs belonging to 4 open clusters at about 1 or 2 Gyr. The stellar effective temperatures, along with the other parameters, were estimated from the analysis of about 60 Fe I lines and 10 Fe II. Even though the few datapoints call for caution, we notice that stars in the open cluster IC 4651 seem to present a steep decline with temperature below 6000 K.