While theoretical understanding remains to be clarified regarding the mechanisms that may or may not limit stellar masses, it is possible to empirically evaluate the existence of an upper-mass limit. ZAMS masses of the most massive stars have been estimated for a range of environments in our local Milky Way neighborhood and the Magellanic Clouds. Various statistical techniques demonstrate the existence of an upper-mass limit in this stellar sample.

The aim of the present study, based on literature data, is to find signatures of the giant radio continuum structure Loop III on the nearby interstellar medium, and search for molecular cloud and star formation, possibly triggered by its expansion. The preliminary results are as follows: (1) The 3D map of the Local Bubble, published by Lallement et al. (2003) suggests that Loop III is probably more distant than the early models had indicated. (2) The molecular clouds at high galactic latitudes in the 2nd Galactic quadrant are probably associated with the neutral/molecular wall of Loop III. (3) Star formation in Lynds 1333 and Lynds 1082 (GF 9) might have been triggered by the expansion of Loop III. (4) The supernova(e), whose explosion produced Loop III, might have been located in the SU Cas association.

We introduce an extended 3D numerical simulation study of Reynolds stress models of stellar convection and probe fluxes as well as mean temperature gradient profiles.

After discovering microquasars – active stellar systems with relativistic outflows (Mirabel et al. 1992) – many papers bringing the observational arguments on similar nature of accreting systems with different BH masses (from stellar to galactic nuclei) have appeared. It became clear that a level of activity in such systems could depend on few parameters: BH mass and angular momentum; accretion rate and magnetization parameter of accretion disk (AD); relative orientation of BH and AD angular momentum. The bolometric luminosity and characteristic variation time in such systems is proportional to BH masses, which span an interval in 5–8 decades.

A new mass model for M31 is presented. The best possible baryonic mass profile for M31 is derived from the 2MASS Ks-band image and M/L ratios from Bell et al. (2003). The best fitting rotation curve is then found within the context of ΛCDM disk galaxy formation. We find that M31 is well-described by a model that includes an adiabatically contracted halo, with an initial NFW concentration, c = 20. Models without adiabatic contraction fail to reproduce the observed rotation curve at r>15 kpc. The derived halo virial mass is Mvir = (9.4 ± 0.8) × 1011M⊙, consistent with masses derived from other observational methods.

Propagating fluctuation models can reproduce fundamental properties of the variability observed in the X-ray light curves of accreting black hole systems. We explore this type of model and show how extended emitting regions introduce at the same time energy dependent power spectral densities (PSD) and time lags between different energy bands.

The estimation of the distribution of the total (luminous and dark) mass in early type systems is hard! Even for the lucky few systems for which kinematic information is available, its implementation is mired in problems, given uncertainties about the assumptions that enter the calculations; the most critical of such assumptions involve considerations of the system geometry and the shape of its velocity ellipsoid. This work offers an independent means of getting to the mass distributions of early type galaxies, without relying directly on the phase space distribution function. The methodology is based upon the well established idea that in elliptical galaxies, the largest variations in normalised velocity dispersion profiles occur typically at R < 0.5Re (Re≡ half-light radius) and at R ≥ 2Re.

We analyze possible differences in the global environments of very metal-poor BCGs with that of typical metallicity BCGs, basing on the parameter DNN – distance to the nearest “luminous” galaxy. We find very significant difference suggesting that a higher fraction of unevolved dwarfs reside in ‘voids’.

Many galactic nuclei contain disks of gas and possibly stars surrounding a supermassive black hole. These disks may play a key role in the evolution of galactic centers. Here we address the problem of finding stable warped equilibrium configurations for such disks, considering the attraction by the black hole and the disk self-gravity as the only acting forces. We model these disks as a collection of concentric, circular rings.

We find the equilibria of such systems of rings, and determine how they scale with the ring parameters and the mass of the central black hole. We show that in some cases these disk equilibria may be highly warped. We then analyze the stability of these disks, using both direct time integration and linear stability analysis. This shows that the warped disks are stable for a range of disk-to-black hole mass ratios, when the rings extend over a limited range of radii.

The latest observational results on the formation and evolution of early-type galaxies are reviewed by focusing on the issues of mass assembly and downsizing scenario.

Recent observations show that spiral galaxies are surrounded by massive and extended haloes of both neutral and ionized gas. These gaseous haloes have peculiar kinematics with respect to their discs: they rotate more slowly and they show an overall inflow motion. Theoretical models of the formation of these gaseous haloes show that they cannot originate solely from a galactic fountain (supernova outflows from the disk); substantial accretion of material from the Intergalactic Medium should play an important role.

Observations of young low-mass binaries (t ≲ 107 yr, M ≲ 3 M_⊙) can be used to calibrate pre-Main Sequence (pre-MS) evolutionary tracks. Recent high angular resolution HST/FGS, speckle, and long-baseline interferometry have resolved the astrometric orbits of a few SB2 pre-MS binaries and have provided the individual dynamical masses of their components as well as the system orbital parallaxes. Spectroscopic fits and filter photometry have permitted to determine SpT (temperatures) and a good estimate of the absolute magnitude (bolometric luminosity) of the components, which in turn allows one to place the components on a theoretical HR-diagram. In this way, one can check (a) whether the measured dynamical masses agree with the predicted masses on the tracks and (b) whether both components lie on an isochrone, as they should for a coeval physical pair of stars.

With a sufficiently large sample of different masses and ages of resolved SB2 systems, most of the parameter space of pre-MS tracks can be tested, even for very low stellar masses (M < 0.5 M_⊙) and very young ages (< 2 Myr). This is a prerequisite in order to derive the IMF and star formation history in very young clusters and associations.

Using the ASAS-3 photometry, we find the components of four eclipsing binary systems — V916 Cen, HD 101838, V4386 Sgr and HD 168050 — to be β Cephei-type pulsators. The first two systems are members of the young open cluster Stock 14. The pulsating stars are presumably the primary, more massive components in all these systems. The components are detached and for at least two systems, V916 Cen and HD 168050, we may suspect that they will appear to be double-lined spectroscopic ones. In consequence, these stars become very attractive targets for studying pulsations in β Cephei stars by means of asteroseismology.

We examined observational characteristics of multi-phase turbulent flows in the diffuse interstellar medium (ISM) by calculating atomic and molecular carbon lines. Radiation field maps of C+, C0, and CO line emissions were generated by calculating the non-local thermodynamic equilibrium (nonLTE) level populations and high resolution hydrodynamic simulations of diffuse ISM. By analyzing synthetic line emission, we found a high ratio between the lines of high- and low-excitation energies in the diffuse multi-phase interstellar medium. Our results shows that simultaneous observations of the lines of warm- and cold-gas tracers will be useful in examining the thermal structure, and hence the origin of diffuse interstellar clouds.

Young brown dwarfs have been identified in a significant population in various star forming regions. Some deep surveys have yielded less massive objects with planetary-mass (e.g., Oasa et al. 1999; Lucas & Roche 2000). Nevertheless, it is not yet clear how abundant these very low-mass objects are formed. S106 is one of the nearest massive star-forming regions associated with prominent bipolar nebulae and an HII region. We have conducted near-infrared photometric and spectroscopic observations of very low-mass young stellar objects (YSOs) in the S106 region.

Since 2005, the workflow working group of OV-France gathers astronomers from five french institutes with common objectives: (i) defining use cases of general interest; (ii) identifying the simplest workflow structure allowing portability; and (iii) suggesting solutions for designing and exploiting easily such workflows (cf. Astrogrid developments). Our workflow definition is the following: a sequence of tasks executed within a controlled context by an architecture taking into account VO standards.

Blue compact dwarf (BCD) galaxies are low-metallicity objects undergoing violent star formation (Searle & Sargent 1972). We present our ongoing work on integral field spectroscopy (IFS) of the two prototypical BCD galaxies IIZw70 and IZw18 (Papaderos et al. 2002). Two-dimensional spectroscopy allows us to collect simultaneously the spectra of many different regions of an extended object, combining photometry and spectroscopy in the same data set. The great advantage of using IFS for the investigation of galaxies is that it allows us to obtain data on the galaxies' positions, velocity fields and star-forming properties all in one data cube. The observations were taken with the instruments INTEGRAL/WYFFOS at the WHT (ORM, La Palma) and PMAS installed on the 3.5m telescope at the CAHA, covering a spectral range from λ 3600 to 6800 Å. The data are mainly used to study the ionized gas and stellar clusters. Our main goal is to investigate the presence of spatial variations in ionization structure indicators, physical conditions and gaseous metal abundances, in these galaxies (Vílchez & Iglesias-Páramo 1998). We also study the kinematical properties of the ionized gas, as well as systematic variations of ionization structure and physical-chemical parameters as a function of the surface-brightness in Hα emission. Maps of the relevant emission lines are presented.

VLA A-array snapshots were obtained of a complete sample of steep-spectrum radio sources from the Texas Radio Interferometer survey. Though similar in sensitivity to the FIRST Survey, our A-array snapshots have better resolution, and are complementary to FIRST. All initial A-array maps are made, and we are comparing them to FIRST.

We examine the intensity of scattered near-infrared (NIR) light in the case of interstellar clouds illuminated by the normal interstellar radiation field. We have developed a way to convert the observed surface brightness into estimates of the column density and have estimated the accuracy of the new method. The NIR intensities can be converted into reliable estimates of the column density in regions with AV up to almost 20 magnitudes. The errors can be further reduced with detailed radiative transfer modelling and by using the lower resolution information that is provided by the colour excess data of background stars. Therefore, NIR scattered light is a promising new way to map quiescent interstellar clouds at a high, even sub-arcsecond resolution.