The point radio sources comprise one amongst the major contaminants of the Cosmic Microwave Background radiation. Consequently, they possess a significant potential for causing severe distortion of the information imprinted in its anisotropies. They demand therefore some sort of treatment that usually boils down to removing contaminated pixels in any CMB experiment. As a support to the Cosmic Background Imager (CBI) we have carried out intensive observations of a sample of nearly 6000 NVSS sources that happen to be in the targeted fields at two frequencies (4.85 and 10.45 GHz) with the 100-m telescope at Effelsberg. The objective has been the estimation of the flux density that each one of them could contribute at the central frequency of the CBI (31 GHz) on the basis of their three-point radio spectral index and their 1.4-GHz flux density as extracted from the NVSS catalogue. However, the compilation of such an extended data base of multi-frequency measurements gives handle for a series of further studies. First, we exploit the sample in order to compute the source counts at different frequencies. That provides the opportunity for comparison with direct surveys at those wavelengths and more importantly with the theoretical predictions. Practically, this can assist the computation of the confusion limits that set a physical limit to the reachable sensitivity of radio instruments. Further, the computed spectral indices have been used to trace candidates for GHz-Peacked Spectrum sources and their extreme sub-class of High Frequency Peakers that are believed to be the early evolutionary stages of radio activity. Additionally, although the observations have been designed to be time-efficient we manage to carry some polarization studies. The main aspects of those matters will be discussed.

In recent years, an increasing number of proper motions have been measured for Galactic X-ray binaries. When supplemented with accurate determinations of the component masses, orbital period, and donor luminosity and effective temperature, these kinematical constraints harbor a wealth of information on the systems’ past evolution. We developed an analysis that allows us to consider all this available information and reconstruct the full evolutionary history of X-ray binaries back to the time of core collapse and compact object formation. This analysis accounts for four evolutionary phases: mass transfer through the ongoing X-ray phase, tidal circularization before the onset of Roche-lobe overflow, motion through the Galactic potential after the formation of the compact object, and binary orbital dynamics at the time of core collapse. The constraints on compact object progenitors and kicks derived from this are of immense value for understanding compact object formation and exposing common threads and fundamental differences between black hole and neutron star formation. Here, we present the results of such an analysis for the black hole X-ray binary XTE J1118+480. Assuming that the system originated in the Galactic disk and the donor had solar metallicity. We find that a high magnitude asymmetric natal kick is not only plausible but required for the formation of the system. We also investigate a globular cluster origin of XTE J1118+480 which would requires a low metallicity donor star. It turns out that such a scenario involves a lot of fine tuning and seems rather improbable.

We will review recent theories/models on the effect of supersonic turbulence on star formation in clusters. We will also present the results of a recent comparison of the treatment of astrophysical supersonic turbulence by different numerical codes. Finally, we will present the results of recent hydrodynamic calculations of star and planet formation.

Masses, radii and luminosities of distant stars can only be measured accurately in eclipsing binaries. The most massive eclipsing binary currently known is a Wolf-Rayet binary (WR20a), which consists of two ~80 Mo stars in a 3.7 day orbit. Analogs of WR20a are bound to exist both in massive stellar clusters in our Galaxy and in nearby galaxies. The nearest ones are located in the young massive clusters near the Galactic Center: the Center, Arches, and Quintuplet clusters and in Galactic super star clusters, such as Westerlund 1 and NGC 3603. The severe amount of reddening in the Galactic disk makes the study of Galactic clusters challenging. However, with current 8-m class telescopes, the study of massive stars in nearby galaxies is also feasible. The nearest Local Group galaxies (LMC, SMC, M31, M33) provide the perfect laboratory for studying massive stars and determining their properties as a function of metallicity. I will present the first results of a survey of the most massive stars in eclipsing binaries in the Milky Way and in the Local Group. Measurements of their fundamental parameters will constrain untested formation and evolution models, confirm the dependence of evolution on metallicity, probe the upper stellar mass limit and provide insight on the rate and nature of supernovae and gamma-ray bursts.

The planetary system 55Cnc consists of four planets. Two of the planets, the companions b and c, seem to be in a 3:1 mean motion resonance and the corresponding dynamics is of special interest. First we study the stability of the system in the framework of the three body problem. We show that the system is located in the neighborhood of an asymmetric periodic orbit in phase space and the corresponding resonant angle variables librate. The asymmetry, which is obeyed by the motion, is essential for the long-term stability. If the system was in a symmetric configuration then the evolution would be chaotic. Additional numerical simulations are performed in order to show the effect of the rest planets in the stability of the overall planetary system.

We study the behavior of orbits in a galactic dynamical model composed of an harmonic core and a strong bar potential. Numerical calculations suggest that low angular momentun orbits display chaotic motion. The area on the x-px phase plane covered by chaotic orbits increases as the angular velocity of the system increases or the strength of the harmonic term decreases. The S(c) spectrum is introduced and used to detect the island motion and study the evolution of the sticky regions. Comparison with previous work is also made revealing the leading role of the new spectrum.

The acceleration and radiation of solar energetic particles (electrons and ions) interacting with multiple small-scale dissipation regions resulting from the magnetic energy release process, mimicked by a cellular automaton model, is presented. Each burst of magnetic energy release is associated with a reconnecting current sheet (RCS) in which the particles are accelerated by a direct electric field. We calculate the distribution functions of the kinetic energy of the particles and the X-ray spectra and gamma-ray fluxes produced by them. Finally we compare our results with the existing observations.

HELYCON, the HEllenic LYceum Cosmic Observatories Network, is a network of detector stations distributed over greater Patra, and the Chios and Cyprus Islands. HELYCON aims to observe Extensive Air Showers of very energetic cosmic rays. It is also used for the calibration of KM3NeT, the Mediterranean neutrino telescope. We report on the design, construction and performance of this prototype detector array.

It is suggested that we accept that antiparticles move backward in time, as proposed by Feynman. Then, I show that we have to attribute negative mass and energy to antiparticles. Applying this to the presence of virtual particle-antiparticle pairs in the vacuum, we see that the vacuum has to be considered as containing zero mass-energy, instead of a huge amount of it resulting from considering the antiparticles´ mass-energy being positive. The result is that the cosmological constant has to be taken strictly zero, rather than having a huge value, resulting from taking of the mass-energy content of the vacuum as huge. Then the dark-energy based model universe, presupposing a small but finite cosmological constant, has to be abandoned. The problem then is what it has to be replaced with in order for the observasional data to be explained. To this end, I propose for the Universe a new exact cosmological solution of Einstein´s field equations (with no cosmological term), found by the author, which describes an accelerating expansion of the Universe, and a double rotation of it at the same time, which gives the Universe the shape of an (accelerating expanding) hypertorus. This new metric explains, besides the accelerating expansion of the Universe and the correct age of it, the Ryle effect and the observed large-scale anisotropy of the CMB. It also explains the apparent rotation and the spiral structure of galaxies, which latter one was the motivation underlying the work towards the new metric at the first place. (References under Chaliasos in arXiv.org/find)

We show that the Poynting-Robertson drag on electrons in an optically thin accretion flow around active gravitating objects generates strong azimuthal electric currents that give rise to astrophysically significant magnetic fields. The mechanism is most effective in accretion disks around stellar size black holes, where the characteristic time for building-up equipartition magnetic fields is of the order of a few hours. We support our physical picture with numerical MHD simulations showing continuous magnetic field growth in an initially unmagnetized disk model .