We report on the method developed by Zibetti, Charlot & Rix (2009) to construct resolved stellar mass maps of galaxies from optical and NIR imaging. Accurate pixel-by-pixel colour information (specifically g – i and i – H) is converted into stellar mass-to-light ratios with typical accuracy of 30%, based on median likelihoods derived from a Monte Carlo library of 50,000 stellar population synthesis models that include dust and updated TP-AGB phase prescriptions. Hence, surface mass densities are computed. In a pilot study, we analyze 9 galaxies spanning a broad range of morphologies. Among the main results, we find that: i) galaxies appear much smoother in stellar mass maps than at any optical or NIR wavelength; ii) total stellar mass estimates based on unresolved photometry are biased low with respect to the integral of resolved stellar mass maps, by up to 40%, due to dust obscured regions being under-represented in global colours; iii) within a galaxy, on local scales colours correlate with surface stellar mass density; iv) the slope and tightness of this correlation reflect/depend on the morphology of the galaxy.

Two atomic time scales maintained at the International Bureau of Weights and Measures (BIPM) are realizations of terrestrial time: International Atomic Time (TAI) and TT(BIPM). They are calculated from atomic clocks realizing proper time in national laboratories. The algorithm for the calculation of TAI has been designed to optimize the frequency stability and accuracy of the time scale. Plans for the future improvement of the reference time scales are presented.

Quasars are the choicest objects to define a quasi-inertial reference frame. At the same time, they are active galactic nuclei powered by a massive black hole. As the astrometric precision of ground-based optical observations approaches the limit set by the forthcoming GAIA mission, astrometric stability can be investigated. Though the optical emission from the core region usually exceeds the other components by a factor of a hundred, the variability of those components must surely imply some measure of variability of the astrometric baricenter. Whether this is confirmed or not, it puts important constraints on the relationship of the quasar's central engine to the surrounding distribution of matter. To investigate the correlation between long-term optical variability and what is dubbed as the “random walk” of the astrometric center, a program is being pursued at the WFI/ESO 2.2m. The sample was selected from quasars known to undergo large-amplitude and long-term optical variations (Smith et al. 1993; Teerikorpi 2000). The observations are typically made every two months. The treatment is differential, comparing the quasar position and brightness against a sample of selected stars for which the average relative distances and magnitudes remain constant. The provisional results for four objects bring strong support to the hypothesis of a relationship between astrometric and photometric variability. A full account is provided by Andrei et al. (2009).

Almost 80 years have passed since Trumpler's analysis of the Galactic open cluster system laid one of the main foundations for understanding the nature and structure of the Milky Way. Since then, the open cluster system has been recognised as a key source of information for addressing a wide range of questions about the structure and evolution of our Galaxy. Over the last decade, surveys and individual observations from the ground and space have led to an explosion of astrometric, kinematic and multiwavelength photometric and spectroscopic open cluster data. In addition, a growing fraction of these data is often time-resolved. Together with increasing computing power and developments in classification techniques, the open cluster system reveals an increasingly clearer and more complete picture of our Galaxy. In this contribution, I review the observational properties of the Milky Way's open cluster system. I discuss what they can and cannot teach us now and in the near future about several topics such as the Galaxy's spiral structure and dynamics, chemical evolution, large-scale star formation, stellar populations and more.

A journalist's view on science and journalism. The presentation is based on personal experience gained over the past few years as editor of the minute of science broadcasted at Radio Europa FM, Bucharest, Romania, and as editor and writer for the Romanian electronic science newspaper Ziarul stiintelor. Is it possible to have science with or without journalism? Who is waiting for whom, science or journalism? Is astronomy more attractive to the public than other disciplines? Can it be used as a growing factor for the public understanding of science?

We determine the primordial helium mass fraction Yp using 1700 spectra of low-metallicity extragalactic H ii regions. This sample is selected from the Data Release 7 of the Sloan Digital Sky Survey, from European Southern Observatory archival data and from our own observations. We have considered known systematic effects which may affect the 4He abundance determination. They include collisional and fluorescent enhancements of He i recombination lines, underlying He i and hydrogen stellar absorption lines, collisional excitation of hydrogen lines, temperature and ionization structure of the H ii region. Monte Carlo methods are used to solve simultaneously the above systematic effects. We find a primordial helium mass fraction Yp = 0.2512 ± 0.0006(stat.) ± 0.0020 (syst.). This value is higher than the value given by Standard Big Bang Nucleosynthesis (SBBN) theory. If confirmed, it would imply slight deviations from SBBN.

We use data from 58 strong lensing events surveyed by the Sloan Lens ACS Survey to estimate the projected galaxy mass inside their Einstein radii by two independent methods: stellar dynamics and strong gravitational lensing. We perform a joint analysis of both estimates examining the galaxy-lens density profile (that we approximate by a power law), the anisotropy of the velocity distribution (represented by an effective constant parameter), and a possible line-of-sigh (l.o.s.) mass contamination (which is suggested by various independent works in the literature). For each model, a likelihood analysis is performed to find the parameters that produce the best agreement between the dynamical and lensing masses, and the parameter confidence levels. The Bayesian evidence is calculated to allow a comparison among the models. We find a degeneracy among the slope of the density profile, the anisotropy parameter and the l.o.s. mass contamination. For a density profile close to isothermal, a l.o.s. mass contamination of the order of a few percent is possible, being less probable with larger anisotropy.

We present Li abundances for 73 stars in the metallicity range −3.5 < [Fe/H] < −1.0 using improved IRFM temperatures (Casagrande et al. 2009) with precise E(B-V) values obtained mostly from interstellar NaI D lines, and high-quality equivalent widths (σEW ~ 3%). At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance ALi = 2.64 dex (MARCS models) or 2.72 (Kurucz overshooting models), in good agreement with current predictions (ALi = 2.72) from standard BBN.

Perturbations from asteroids and Trans-Neptunian Objects affect significantly on the orbits of planets and should be taken into account when high-accuracy planetary ephemerides are constructed. On the other hand, from an analysis of motion of the major planets by processing of precise measurements of spacecraft a limitation on the total TNO mass may be obtained. To estimate influence of TNO on motion of planets the largest 21 TNO have been included into the process of simultaneous numerical integration, and positions of planets obtained with taking for TNO have been compared with positions of planets of numerical EPM ephemeris of IAA RAS constructed without these objects. The perturbations of other TNO have been modeled by the perturbation from a circular ring having a radius 43 AU and different masses. It has been shown that all the test masses of the TNO ring except the minimum mass (5.26⋅10−8M⊙) are too large and make the data residuals worse. Thus, the upper limit of the total mass of all TNO including Pluto, the 21 largest TNO and the TNO ring (with the 43 AU radius) should not exceed 8.04⋅10−8M⊙.

Analyzing the power spectrum of Total Solar Irradiance (TSI) for the period from 2003 February 25 to 2009 July 6, observed with the Total Irradiance Monitor (TIM) onboard SOlar Radiation and Climate Experiment (SORCE), we found that there are quite a number of periodic variations. The outstanding shortest one is the period of 6.7 days, about one fourth of the period of solar rotation. Checking the solar magnetic field for the same period of time observed with MDI onboard SOHO, we found that there is about 90 degree difference in longitude for the distribution of solar magnetic field. We therefore conclude that both the 90 degree difference in longitude for the distribution of solar magnetic field and the solar rotation are the reason resulting in the periodic variation of 6.7 days for the total solar radiation.

We describe and discuss most interesting archaeological findings related to old astronomy in Ukraine. Among them are the mammoth tusk fragments (Gontsy and Kiev-Kirilivska settlements) and the famous Mezin bracelets (Mezin settlement), where possible calendar patterns based on the lunar cycles are engraved with fine accuracy, as well as a possible stellar map on the mammoth shoulder bone (Chocurcha-2 settlement).

A long-term project, aiming at systematic search for variable stars in Galactic Open Clusters (OCs), was started at the Geneva Observatory in 2002. We have been observing regularly a sample of twenty-seven Galactic Open Clusters in the U, B, V Geneva filters (hereafter U, B, V). The goal is to identify and to study their variable stars, as well as the connection between the variable stars in a cluster and the cluster properties. We present the status of this work in progress, and show preliminary results for one of these clusters, IC 4651.

Highly relativistic equations of motions will play a crucial role for the detection and analysis of gravitational waves emitted by inspiralling compact binaries in detectors LIGO/VIRGO on ground and LISA in space. Indeed these very relativistic systems (with orbital velocities of the order of half the speed of light in the last orbital rotations) require the application of a high-order post-Newtonian formalism in general relativity for accurate description of their motion and gravitational radiation [1]. In this contribution the current state of the art which has reached the third post-Newtonian approximation for the equations of motion [2–6] and gravitational waveform [7–9] has been described (see [10] for an exhaustive review). We have also emphasized the successful matching of the post-Newtonian templates to numerically generated predictions for the merger and ring-down in the case of black-hole binaries [11].

We serendipitiously found that the iron-rich low-ionization broad absorption-line (FeLoBAL) quasar SDSS J 163255.46+420407.7 showed a dramatic change in its spectrum over 3.4 years in the rest frame of the quasar. A simple photoionization model suggests the increase in the nuclear radiation caused these changes. Given the recombination coefficient of Fe+, the relaxation time of the absorbing gas suggests ne > 104 cm−3.

The long gamma-ray bursts are at high redshifts, and they trace the star-formation rate. Hence, they may well serve as milestones in the early Universe.

The derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.

We present Chandra X-ray observations of 14 quadruply lensed quasars. The X-ray data reveal flux ratio anomalies which are more extreme than those seen at optical wavelengths, confirming the microlensing origin of the anomalies originally seen in the optical data. The reduction of the anomalies in the optical, as compared to X-ray, indicates that the sizes of the optical emitting regions of the quasars must be about 1/3 the size of the projected Einstein radii of the microlensing stars. The X-ray emitting regions are essentially point sources and therefore give a microlensing signal unencumbered by source size considerations. For each lensing galaxy, we determine the most likely ratio of smooth material (dark matter) to clumpy material (stars) to explain the X-ray flux ratios. The ensemble of Chandra-observed quads indicates that the amount of matter projected along the lines of sight to the images (at radial distances of several kpc from the centers of the lensing galaxies) is ~90% smooth dark matter and ~10% stars.

The globular cluster system in M31 is an ideal laboratory for studying the formation and evolution of M31 as well as the globular clusters themselves. There have been numerous surveys and studies of the globular clusters in M31. However, only recently has the entire body of M31 been searched for globular clusters using wide-field CCD images by our group. A new era for the M31 globular cluster system has begun with the advent of wide-field CCD surveys of M31. We have discovered more than 100 new globular clusters in M31. Our catalog currently includes more than 500 globular clusters confirmed either based on spectra or HST images, many more than in the Milky Way. We present the structure, kinematics and chemical abundance of the M31 globular cluster system based on this large sample, and the implications for the formation and evolution of M31.

Efforts to determine the primordial helium abundance via observations of metal poor HII regions have been limited by significant uncertainties. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Spectra from the literature are used to show the effects of new atomic data and to demonstrate the challenges of determining precise He abundances. Several suggestions are made for meeting these challenges.

In this work, we study the impactor flux on Pluto and Charon due to the collisional evolution of Plutinos.To do this, we develop a statistical code that includes catastrophic collisions and cratering events, and takes into account the stability and instability zones of the 3:2 mean motion resonance with Neptune. Our results suggest that if 1 Pluto-sized object is in this resonance, the flux of D = 2 km Plutinos on Pluto is ~4–24 percent of the flux of D = 2 km Kuiper Belt projectiles on Pluto. However, with 5 Pluto-sized objects in the resonance, the contribution of the Plutino population to the impactor flux on Pluto may be comparable to that of the Kuiper Belt. As for Charon, if 1 Pluto-sized object is in the 3:2 resonance, the flux of D = 2 km Plutinos is ~10–63 percent of the flux of D = 2 km impactors coming from the Kuiper Belt. However, with 5 Pluto-sized objects, the Plutino population may be a primary source of the impactor flux on Charon. We conclude that it is necessary to specify the Plutino size distribution and the number of Pluto-sized objects in the 3:2 Neptune resonance in order to determine if the Plutino population is a primary source of impactors on the Pluto-Charon system.