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.

We present theoretical models for populations of low-mass X-ray binaries in two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code (Belczynski et al. 2006). StarTrack is a state of the art population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the shape characteristics and the normalized number of sources of the X-ray luminosity functions (XLF) in these galaxies. For the first time we explore the population XLF down to luminosities of 5x10E36 erg/s, as probed by the most recent observational results (Kim et al. 2006). We explored the parameter space running models with different common envelope efficiencies, stellar wind prescriptions and initial mass functions. We were able to find models that produce an XLF in excellent agreement with the observations both in shape and number of systems at a specific luminosity. We also find that the treatment of the outburst luminosity of transient systems remains a crucial parameter for the determination of the XLF as the modeled populations are transient-dominated.

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 .

In the early hours of July 28 2006 (MJD 53944) the High Energy Stereoscopic System (H.E.S.S.) observed an unprecedented VHE (>100 GeV) flux state of the BL Lac object PKS 2155-304 (z=0.116). The average flux of the source exceeded that of the Crab nebulae (>200 GeV) by a factor of 7. This is by far the highest flux state ever detected from PKS 2155-304 and it is one of the highest among all the BL Lac objects. The high sensitivity of H.E.S.S. (5\sigma detection in ~30 s for a Crab nebulae flux source at 20 degrees zenith angle) enables for the first time VHE-flux variability studies on time scales of tens of seconds. The issues that are going to be discussed are the cross correlation and the cross spectrum analysis between the VHE bands together with some constraints concerning the black hole mass and the Doppler factor.

The energy is among the characteristics of Ultra High Energy Cosmic Rays (E>5 x 10^19 eV) which could be estimated experimentally and by simulations. The following paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, is simulated to derive the muon density as a function of radial distance from the core of the shower. This scenario of simulations could be applied to the Cerenkov surface detector of the P. AUGER Observatory as well. Due to the fact that this density shows minimal fluctuations at a distance larger than 900 m from the core of the showers and that at the same distance the muon density for inclined showers coincide, we select this favorable distance to derive the energy of such high energy protons. The project is co-funded by the European Social Fund and National Resources (EPEAEK II) PYTHAGORAS II.

We are probing the origin of ring-like structures in AGNs. For this reason we are studying the two powerful radio galaxies Hercules A and 3C310 and their clusters. They present many essential and atypical similarities with the striking one being the presence of large-scale rings instead of hotspots. Employing a multiwavelength observational campaign from radio to X-ray wavelengths we are trying to determine the origin of their unusual structure and tenue (compared with the common AGN) and to disentagle the physical mechanisms taking place interior to them and in their clusters. For example: -In the RADIO we probe the pc- and kpc-scale environment. -In the (Near-)INFRARED we try to constrain the nature of the acceleration mechanism in the rings with the corresponding in the usual hotspots, investigate the ISM, shed light in their evolution. -In the X-RAYS, we probe the intracluster medium, identify possible interactions between the X-ray and radio emission, measure cluster magnetic fields.

Compact groups of galaxies are systems of typically four or five galaxies in close proximity to one another. Due to this proximity, galaxies in groups have interacted with each other extensively. As result their morphology as well as the distribution of galaxy type differs substantially from what is observed among populations of galaxies in the field. The Hickson Compact Groups (HCGs) is a sample of 100 groups selected with well defined criteria which have been studied extensively in various wavelengths. Here we present the first analysis of spatially resolved 12micron mid-infrared properties of galaxies in 35 HCGs using archival data obtained with the Infrared Space Observatory. We estimate the star formation rates of the groups, quantify their dust content as a function of galaxy type, and contrast our results with the optical properties and molecular gas content of the systems.

We present the initial results from a multiwavelength study of the Supernova Remnants' (SNRs) population in a sample of six nearby galaxies (NGC2403, NGC4214, NGC4449, NGC4395, NGC5204, NGC3077) based on optical, X-ray (Chandra) and infrared (Spitzer) observations. Preliminary results show the detection of new SNR candidates. The verification of a number of sources with already known SNRs illustrate the accurate eligibility of the discovery method. We discuss the analysis of the data and we show representative deep Halpha and [S II] emission line images of the galaxies with optical SNR candidates. In order to understand the emission from SNRs and to obtain a more complete picture of the overall SNR population, we compare the optical sources with SNR candidates identified in our X-ray observations. Based on these data we investigate how the optical SNR detection rates compare with detection rates in the X-ray band. Furthermore, we investigate the existence of dust around these sources using infrared observations and the influence of dust obscuration in the detection of SNR candidates.

The new gamma-ray satellite GLAST foreseen for October/November 2007 provides a tremendous opportunity for future blazar studies. In order to fully benefit from the offered capabilities of this instrument and to interpret the high energy emission, it is of great importance to conduct dedicated multi-frequency campaigns that will produce comprehensive observations prior to and after the GLAST launch. GAMMA-project (GLAST AGN Multi-wavelength Monitoring Analysis) comprises a series of dedicated flux-density campaigns with the several facilities attempting an unprecedented frequency coverage. The 100-m Effelsberg, 30-m IRAM and OVRO radio telescopes will cover the radio and millimeter wavelengths. The REM telescope in Chile as well as the AIT in Italy and the 1.2-m telescope in Kryoneri take over the optical band. mm VLBI campaigns as well as sub-mm campaigns are also underway.

We use a 3D Radiative transfer model to perform diagnostic studies of the morphology of the stellar bars in spiral galaxies. The model galaxy is described by three axisymmetric components (a stellar disk, a dust disk and a stellar bulge) and one non-axisymmetric (a stellar bar). Using the unsharp masking technique, we reveal the morphological signatures of the bar component when changing various parameters (such as the inclination angle and the PA of the galaxy and the size of the bar). These signatures are then compared with real galaxy observations as well as orbital profiles of the disc galaxies.

We identify the intergalactic medium as a major sink for galactic dust. We discover a systematic shift in the colour of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-gas mass ratio is high (1/20) compared to that of the solar neighborhood (1/120) suggesting that the dust originates from the centre of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.

Blue Compact Dwarfs (BCD), is a subclass of dwarf galaxies which are dominated by a recent burst of star formation, responsible for their blue optical colors. Many of the BCDs are low metallicity systems, suggesting that they are genuinely young systems forming their first generation of stars and have been identified via the objective prism surveys such as the SBS. Thus they may provide an ideal local laboratory to understand the galaxy formation process in the early Universe. Using the unprecedented sensitivity of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope we have observed for the first time a sample of 30 of these BCDs. Using low and high resolution mid-IR spectroscopy we examine the presence of organic molecules such as PAH and calculate their ionization field and elemental abundances. We compare our findings with similar analyses performed in normal and starbursting galaxies.

We present a BVRI CCD surface photometry analysis of the interacting compact galaxy group NGC 4410. Along with our photometric study we show residual images (after subtracting isophotal models) and unsharp masked images in order to uncover any hidden structures in this system of galaxies. We have calculated BVRI surface brightnesses and colours within regions such as galaxy centers, bridges, tails and optical knots in this system, generating B-V color maps and color profiles. The information obtained was used to discover the predominant stellar populations. Most of the galaxies have the colours of K0-K5 giant stars, with ages at least 10 Gyr assuming solar metallicity. These results lead us to the conclusion of a moderate star formation rate and a tranquil evolving state of the system, apart from NGC 4410D which has a blue nucleus, bulge, bar and ring and may be interacting with a H I cold gas cloud. An optical knot E coincident with a radio knot may be optical synchrotron emission or an H II region. Some observed structures in NGC 4410A are coincident with previously studied H II regions, a tidal arm and an optical/radio knot found in this galaxy.

Results of ideal-magnetohydrodynamic (MHD) numerical simulations of relativistic jets are presented. It is found that initially Poynting flux-dominated jets can be effectively accelerated to high bulk Lorentz factors with an efficiency (defined as the ratio of the final kinetic energy flux to the total energy flux) of the order of 50%. The connection between the collimation of the flow, which is manifested in the curved streamlines, and the acceleration process is analyzed. In validating the basic features of previous semi-analytic (radially self-similar) solutions for steady-state flows, these numerical results go a long way toward establishing an "MHD acceleration and collimation paradigm" for relativistic astrophysical jets.

We investigate the large-scale distribution of the HII regions in a sample of 6 nearby spiral galaxies for which we have obtained deep Ha images. By performing azimuthally averaged radial profiles we find that for all the galaxies the radial distribution of the HII regions is well approximated by an exponential law. We also examine the HII region size distribution and we derive that the average size is ~100 pc while the largest ones may be as much as ~1 kpc.

We study the dynamical behaviour of LMC star clusters with emphasis given in those being either members of binary star cluster systems or elliptical in shape, located in star forming regions of this galaxy. In particular, we aim to study their dynamical history via mass segregation phenomena and the imprints of dynamical interactions between the binary cluster members, analysing their spatial distribution and their density profiles, as a way to understand formation and evolution of these peculiar star clusters in the parent galaxy environment. In order to conduct our study we use archival data from HST/WFPC2 obtained through MAST and reduce them with the photometry package HSTphot.

We present new general relativistic simulations of stellar core collapse to a proto-neutron star, using various microphysical equations of state as well as a description of deleptonization. We show that for a wide variety of rotation rates and profiles the gravitational wave burst signals from the core bounce are of a generic type, known as Type I in the literature. We identify and individually quantify the micro- and macrophysical mechanisms leading to this result. Such a generic type of signal templates will likely facilitate a more efficient search in current and future gravitational wave detectors of both interferometric and resonant type.

Studying the structure of the SMC and particularly population distributions, led us to multiwavelength analysis of data obtained from different surveys such as 2MASS, DENIS and radio data. We have found that an exponential disk is formed from the older population of the SMC and calculated the scale heights for all the cases.

We study particle acceleration and radiation in the jets of active galactic nuclei (AGN). Although the jet outflow is relativistic, we make the assumption that electrons are accelerated in a shock-front that is moving non-relativistically in the jet frame. Acceleration and energy losses are treated self-consistently through a kinetic equation which also includes particle injection and escape. As a first step we consider only losses from inverse Compton scattering (ICS) of the high energy electrons on the disc photons. The disc model we adopt is of a standard, multi-temperature Shakura-Sunyaev type. The particle distribution function resulting from the solution of the kinetic equation, is convolved with the single particle emissivity for ICS using the full Klein-Nishina cross-section and the emitted spectrum at each height of the jet is obtained. The total spectrum is calculated by integrating the contribution from all heights and then it is compared to high-energy AGN observations.

Radio imaging of |Ultra Luminous InfraRed galaxies (ULIRGs) is ideal to explore the connection between the starburst and the AGN phenomenon since it is unaffected by dust obscuration, and provides the required high angular resolution to distinguish between an AGN and starburst emission. We will present radio continuum, EVN and MERLIN observations of ULIRGs that have the parsec and deci-parsec scale resolution necessary to distinguish between an AGN and supernovae remnants at the centres of these galaxies, and assess the contribution of each to the total energy distribution.

Many objects studied in the context of stellar and extragalactic astronomy fall into the category of accretion ejection systems, such as young stars and radio loud active galactic nuclei. Since these systems are far from transient in their timescales, the issue of temporal stability can be efficiently addressed through high resolution MHD numerical simulations of resistive magnetized accretion disks launching a supersonic jet, in a self-consistent way. To this perspective, we present a series of simulations performed using the PLUTO code that aim to study the parameters of such systems and discuss how these affect their properties (eg. ejection efficiency, transfer of energy and angular momentum, magnetic field topology and collimation) and their capability to reach a quasi-stationary final state.

We shall present an overview of our VLT studies of such diverse objects as galactic planetary nebulae and blue compact galaxies. Using the FLAMES Argus integral field spectrograph (IFS) we have mapped the sub-parsec, high metallicity regions embedded in typical planetary nebulae and investigated in detail the occurence of the long-standing 'abundance discrepancy problem' in these objects. This study highlights the type of science obtained with a proper synergy of deep emission line spectroscopy with an 8-m telescope and a new recombination line theory for heavy ions. Using the VIMOS IFS we have also studied a class of low metallicity blue dwarf galaxies that exhibit peculiar chemical composition at <100 pc scales: deep spectral mapping allowed us to investigate the variation of the star formation rate across the targets and the homogeneity of their ionized gas in terms of the helium, oxygen and nitrogen abundance. These two examples demonstrate the superb capabilities of VLT IFS for the study of chemically inhomogeneous nebulae at small and large scales.

Recent observations of jets in young stellar objects suggest that both disk- and stellar-winds are present, with the dominant component being dictated by the intrinsic physical conditions of the YSO system. In this context, we construct and evolve in time, using the PLUTO code, several numerical models by properly setting as an initial condition different contributions of a magneto-centrifugal driven disk wind and a thermally accelerated stellar jet. Such outflows are obtained from a radially and a meridionally self-similar exact solutions of the steady-state MHD equations, respectively. We find that all models reach a steady-state, in a few cases asymptotically. The final outcome of the simulations is found close enough to the initial configurations, thus retaining the validity of the analytical studies. Moreover, the magneto-centrifugally driven disk wind remains almost unmodified, while it effectively collimates the inner thermally driven stellar outflow. Proper choice of the parameters can explain the different cases of the two-component jets observed, i.e. from the one extreme of stellar dominated ones, up to the other, with the disk-wind being the only contributor.

We present a new, versatile numerical code PLUTO, suitable for the solution of high-mach number flow in 1, 2 and 3 spatial dimensions and different systems of coordinates. The code provides a multiphysics (newtonian or relativistic HD or MHD), multialgorithm modular environment particularly oriented toward the treatment of astrophysical flows in th presence of discontinuities. The modular structure exploits a general framework for integrating a system of conservation laws, built on modern Godunov-type shock-capturing schemes. Recently implemented features include Adaptive Mesh Refinement, radiative cooling, resistivity and heat conduction.

We present the first results from our HST-ACS survey of the nearby galaxy M81. These data provide the deepest and most detailed picture of the stellar populations in this prototypical spiral galaxy, allowing to study in detail its spatially resolved star-formation history. In combination with deep Chandra observations allow us to classify the X-ray sources and study their link with the star-formation history of the galaxy. In this presentation we will discuss the analysis of the HST data, the derivation of the colour-magnitude and colour-colour diagrams and we will present preliminary results on the stellar populations of different regions of M81.