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.

We present the results of our search for optical counterparts to High Mass X-Ray transient sources. The observations were carried out from the 1.3m telescope of the Skinakas Observatory. We obtained CCD images of the X-ray fields through BVR and Ha filters to identify early-type stars in the R-Ha versus B-V colour-colour diagram. We confirm their nature from their position in near-IR Q vs K diagram constructed using data available from the 2MASS Point Source Catalog. We also obtained medium-resolution spectroscopy of the candidates in order to confirm the presence of Ha emission and perform spectral classification.

In this paper we present the results of the analysis of the B-light curve for the flares of the red dwarf YZ CMin , which were observed on September 2002, with the help of the 30-inch Cassegrain telescope of the Stephanion Observatory. The combined use of Fractal analysis, DFT-analysis and Wavelet analysis enable us to estimate the proper random noise and detect possible weak transient optical oscillations. Our results indicate that: (1) Transient high frequency oscillations occur during the flare event and during the quiet-star phase as well. (2) The Observed frequencies range between 0.0083Hz (period 2min) and 0.3 Hz (period 3s) not rigorously bounded. The phenomenon is most pronounced during the flare state. (3) During the flare state:(a) Oscillations with period 2 to 1.5min, 11s, 7.5s and 4s appear during the pre-flare state and persist during the whole flare state, (b) From the flare maximum phase on, a progressive increase of oscillations with periods 20s up to 4.0s is markedly indicated and (c) At the end of the flare only the oscillation of the pre-flare state do remain. This result is in favour of (or does not contradict) the suggested explanation, i.e. the evolution of a fast mode magneto-acoustic wave generated at the impulsive phase of the flare and travelling through the magnetic loop. This procedure may occur many times during the development of a large flare. Finally, the transient optical oscillation, which occurs during the quiet-star state, are not necessary connected with any flare and may be a general characteristic of the active stars atmospheres.

About 2100 photometric observations of the δ Scuti star NT Hya were acquired with the 30 inch SAAO telescope in February 2006 in V filter. The data show at least four pulsation frequencies of the star. Two of them form a close doublet separated by 0.64 c/d (Δf/f = 9%) with similar amplitudes. The period listed in the Hipparcos Catalogue is between the doublet frequencies.

Thirty years since its discovery AM Herculis, the magnetic Cataclysmic Variable prototype, continues to surprise us with the richness of phenomena present. We hereby present a multi-epoch spectroscopic study of the system covering more than a decade of its extraordinary behavior. Doppler maps during the regular accretion state (high state), illustrate the H\alpha and HeI emission components which trace the accretion stream and the irradiated inner hemisphere of the lower-mass main sequence donor star. During the low state, radial velocity curves of the various H\alpha components reveal large loop prominences on the magneticaly active secondary. The serendipitous spectroscopic detection of a rare optical low state "event", likely due to coronal mass ejection-induced accretion onto the magnetic white dwarf, is also presented. For the first time, our study offers a comprehensive picture of a Cataclysmic Variable at all times of optical behavior.

Complete CCD light curves of the Algol-type eclipsing binary IU Persei have been obtained in the B, V, R and I filters during 7 nights in 2006 with the 40-cm telescope of the Gerostathopoulion Observatory of the University of Athens. The light curves are analyzed with the W-D program in order to determine the geometrical and photometric elements of the system. Moreover, the outside eclipses light variations have been used for searching of pulsating component(s) in the system.

The new PNe discovered in the Galactic bulge region by Boumis et. al. (2003, 2006), were studied in detail, using the photo—ionization model CLOUDY. Applying the imaging and spectroscopic results to the CLOUDY model, we determined the physical parameters and abundances of these PNe (like Te, ne, Tc, Lc etc). Their distance was also determined using statistical methods.

The first complete CCD light curves of the near contact eclipsing binary DF Puppis with an A7 primary have been obtained in the B, V, R and I filters during 5 nights in 2006 with the 1-m telescope at the South African Astronomical Observatory Sutherland Station. The light curves are analyzed with the W-D program in order to determine the geometrical and photometric elements of the system. These elements are used to compute the physical parameters of DF Pup and study its evolutionary status.

Deep optical CCD images of a large unknown area have been obtained in the light of Halpha+[N II], [O III] and [S II]. The resulting mosaic covers an area of 1.4 deg x 1.0 deg where filamentary and diffuse emission was discovered, suggesting the existence of more than one supernova remnants (SNRs) in the area. Deep long slit spectra were also taken at eight different regions. Both the flux calibrated images and the spectra show that the emission of the filamentary structures originates from shock-heated gas, while photo-ionization mechanism is responsible for the diffuse emission. The optical emission is found to be well correlated with the radio at 1420 MHz and 4850 MHz, suggesting their association. The presence of the [O III] 5007 emission line in one of the candidate SNRs suggests shock velocities into the interstellar "clouds" of >100 Km/s, while the absence in the other indicates slower shock velocities. For all candidate remnants the [S II] 6716/6731 ratio indicates electron densities below 270 cm^-3, while the Halpha emission has been measured to be between 0.6 to 41 10^-17 erg s^-1 cm^-2 arcsec^-2. The detected optical emission could be part of a number of supernovae explosions and the possibility that it is within an OB association can not be ruled out.

Principal Component Analysis (PCA) is a well-known technique used to decorrelate a set of vectors. It has been applied to explore the star formation history of galaxies or to determine distances of mass-lossing stars. Here we apply PCA to the optical data of Planetary Nebulae (PNe) with the aim of extracting information about their morphological differences. Preliminary analysis of a sample of 55 PNe with known abundances and morphology shows that the second component (PC2), which results from a relation produced by the parameters log(N/O), initial and final mass of PNe, is depending on the morphology of PNe. It has been found that when log(N/O) < -0.18 the PNe's nitrogen is low independently on the oxygen abundance for either Bipolar (B), Elliptical (E) or Round (R) PNe. An interesting result is that both E and R PNe have log(N/O) < 0 while only B PNe show negative and positive values. Consequently, B PNe are expected to have higher nitrogen values than the E and R PNe. Also, in all PNe morphologies PC2 appears to have a minimum at 0.89 and PNe's initial mass at 2.6 M$_{\odot}$. 3-D diagrams between PCA's components and abundances are also presented. More results will follow while simple models will be applied in order to try to give physical meaning to the components.

To be included.

We present astrometric characteristics of about 1250 wide visual double stars. They are all binaries contained in the data base of the Washington Double Star Catalogue (WDS), which could be found in the 2.400.000 stars of the Bordeaux PM2000 astrometric catalogue. They sum up to 1.2% of all entries of the last version (2006) of WDS. Minimum angular separation of the pairs is 8 arcseconds. The faintest secondary found is a 15th magnitude star. Although they are very wide double stars, about 30% of them are statistically common proper motion pairs and thus, their components are consequently common origin stars.

We comment on the new astrometric results of our monitoring of visual double stars. Our results contain more than 400 visual binaries and they are based on our recent CCD observations. The targets are distributed on both hemispheres. Existing data bases of visual double stars contain optical as well as physical pairs. Statistical studies of relative proper motions of the components of double star are based on a sample of astrometric measurements. Such studies are an accurate tool for the extraction of the astrophysically interesting common origin (physical) pairs. Astrometric monitoring of visual double stars provide data which are necessary for such studies. As a by-product of our work we present an accurate determination of the scale of the 1m telescope of the South African Astronomical Observatory.

New ground-based BVRI CCD observations of the eclipsing binary system BY Peg are presented. New times of minima are given and a new ephemeris is proposed. The light curves are analyzed using the Wilson-Devinney light curve synthesis code and new geometric and photometric elements are derived. Empirical laws, such as M-R and M-L diagrams and those derived from the correlation between physical parameters of contact binaries, are used in order to compare the physical parameters of the system with their theoretical (expected) values. The system BY Peg is found to be an evolved W-type W UMa system, showing total eclipses.

New times of minima of the W UMa-type eclipsing binaries AH Tauri and AH Aurigae, obtained at the Athens University Observatory using a 40-cm Cassegrain-type telescope, have been used together with all reliable timings found in the literature in order to study the period variation and search for the presence of a third body in each system. Their O-C diagrams are presented and apparent period changes are discussed with respect to possible Light-Time Effect (LITE) in the systems. A least square method has been used to compute new light elements (updated ephemeris of binaries and their period change rate) as well as the mass functions, their minimum masses and periods of the possible third bodies in each case.

The problem of non-constant periodicities or multi-periodic phenomena is often encountered in Astrophysics. These phenomena are usually interpreted either with Fourier transforms or with overlapping functions, or even using a combination of them. In this work, we present a new method based on the idea of a variable sine function. We apply it to data analysis of actual binary stars and compare the results. Moreover, with its aid we describe the subsurface field of active binaries exhibiting magnetic activity cycles. The method can also be implemented in various other topics of applied sciences.

Physical parameters of contact binaries are studied through 3-D correlations among them. Using the standard methods, the determination of mass, radius and luminosity requires both photometric and spectroscopic observations. Secondary quantities (e.g. orbital inclination, filling factor, radial velocities, the shape and the depth of the light curve during the eclipses, and the third light) are necessary for an accurate analysis, since their uncertainties strongly influence the determination of the physical parameters. In this study it is shown that orbital period and mass ratio are sufficient to determine the mass, radius and luminosity of contact binaries, taking advantage of the strong correlation between the geometric and physical parameters in the 3-D domain. These correlations are used to derive empirical laws, connecting orbital period and mass ratio of contact binaries with the masses, radii and luminosities of the two components within a 5% error. These laws can also be used as a quality check for the parameters in every given solution of a contact binary, as all their values should always lie on the same 3-D surface. The extracted empirical laws are a prefect tool for a quick estimate of physical parameters for the numerous contact binaries found in global sky surveys.

We present the results of UBV photometric observations of the eclipsing binary RT Andromedae, a representative member of the Chromospherically Active Binary Stars (CABS). The aim of this study is the identification of possible short term variations as well as times of minima determination, based on observations in various periods from 2005 to the present. The latter was accomplished using suitable methods to overcome difficulties imposed by the presence of asymmetries. High resolution photometry indicates a total secondary minimum revealing a mid-eclipse brightening. For each light curve, a photometric solution is derived along with the absolute elements of each component, using the WD code.

We present BVRI observations of two not previously studied eclipsing binary stars. A significant number of times of minima was determined and therefore new more accurate ephemeredes were produced. Neither photometric elements nor spectral types for these two variable stars were known, thus a first approximation of their effective temperature and absolute magnitude was made by means of standard stars absolute photometry and using appropriate Teff, Mv – color index empirical relations.

We study an exact model of radially self-similar magnetohydrodynamic outflows appropriate to describe collimated jets from astrophysical systems with accretion disks spiraling around a central gravitating object. The mathematical problem is reduced to the integration of a set of nonlinear ordinary differential equations. A physically accepted solution needs to cross several critical surfaces whose knowledge is not known a priori but depends on a number of physical parameters. We search for the right combination of those parameters which produces a superAlfvenic solution crossing the modified fast critical surface, satisfying thus causality. We use a numerical algorithm that tests pre-defined combinations of the problem parameters, classifies the derived solutions and tunes one parameter in each combination so that this solution crosses the modified fast critical surface. The results are discussed in the context of the launching and collimation properties of magnetohydrodynamic disk-winds and jets associated with young stellar objects in star formation regions.

We shall present new results from our deep optical spectral mapping of M42 proplyds secured with the VLT FLAMES Argus integral field unit. Proplyds are partially ionized low-mass star forming clouds immersed in the strong radiation field of the Trapezium cluster. They represent a unique nearby environment for the study of low mass embedded young stellar objects (YSOs) in a region dominated by higher mass main sequence stars. Our investigation will allow us to determine the chemical composition of their photoionized surfaces, and to derive plasma temperatures and densities, in fields of view that encompass each whole YSO and its immediate M42 surroundings with 300 spectra per position. The high spatial resolution of 0.3 arcsec per pixel can help us to study the small-scale mixing processes (at milli-parsec scales) of the proplyd photoevaporated outflows with the local ISM.

Detached binary systems are subjected to a variety of physical mechanisms which are able to change their period in a continuous way and in broad band of timescales. Assuming that these changes should be detectable in O-C diagrams in a way specified by the physical theory of the underlying mechanisms, we carry out a preliminary study in a properly selected sample of detached binaries, where mass transfer is expected to lack. We primarily interested to find traces of tidal moments in observed orbital period changes (possibly coupled with stellar wind angular momentum losses). We focus our attempts on a sample of binaries consisted of late-type components where magnetic braking is expected to play a crucial role in the observed period variation rates. Theoretical and observed values are compared and possible deviations are discussed.

New times of minima of the W UMa-type eclipsing binary FZ Orionis, obtained at the Athens University Observatory, have been used together with all reliable timings found in the literature in order to study the period variation and search for the presence of a third body in the system. Its O-C diagram is presented and apparent period changes are discussed with respect to possible Light-Time Effect (LITE) in the system. New improved LITE elements, orbital periods and minimum mass of potential third body are given.