Using ROSAT seven isolated neutron stars have been discovered characterised by blackbody spectra at temperatures of 400-800 thousand K and the absence of radio and high energy emissions. Observations with Keck, HST and VLT show faint optical counterparts (m $\sim $ 24–29) with Rayleigh-Jeans-type spectra ($\sim\nu ^{2}$) and large proper motions. These objects are believed to be cooling neutron stars. They are of great interest from the point of view of neutron star astrophysics and nuclear physics. In particular, they allow us to measure neutron star radii and thus to constrain the equation of state at very high densities. We discuss the possibility of discovering larger samples of these objects with future sensitive X-ray sky surveys and follow-up optical observations with extremely large telescopes.

The EGRET experiment detected pulsed emission from several pulsars in the HE energy range 20 MeV < E < 10 GeV. However, no pulsed emission has ever been detected above 300 GeV, which points to a cut-off in pulsed emission somewhere between ∼10 GeV and ∼300 GeV. Software has been developed at UCD which is capable of examining gamma-ray events in the energy range $E>130$ GeV and detecting the signature periodicity of pulsars if it exists. Data recorded on the Crab pulsar with the Whipple Imaging Atmospheric Cerenkov Telescope has been analysed with this software and upper limits on pulsed emission have been obtained.

We have studied the metallicity of 17 high column density forests at $N_{{\rm H}{\sc I}}=10^{15-17}$ cm$^{-2}$ and $2<z<3.5$ toward 7 high-$z$ QSOs taken with the VLT/UVES, in order to study the metallicity of absorption line systems as a function of H I column density and $z$. This relation provides an important constraint on metal enrichment mechanisms of the intergalactic medium as well as early star formation in galaxies. We used higher order Lyman series to measure a reliable H I column density for the saturated Ly$\alpha$ lines, and applied an ionisation correction assuming the Haardt-Madau UV background including both galaxies and QSOs. We have found 3, 6, and 8 systems with no metals, C IV-only, and additional ions other than C IV respectively. A photoionisation model with the Haardt-Madau background generally reproduces the observed metal line ratios. The median [C/H] is $-3.03$ and $-1.96$ for the 6 C IV-only systems and the 8 additional-ion systems respectively. The inferred H I number density is $n_{{\rm H}{\sc I}} \sim 10^{-3.5}$ cm$^{-3}$ and $\sim 10^{-2.5}$ cm$^{-3}$ for the C IV-only systems and the additional-ion systems respectively. When other ions are present, [C/H] of the high-$N_{{\rm H}{\sc I}}$ forest is similar to that of sub-damped Ly$\alpha$ systems.

Conventionally, CMD analyses of nearby star clusters are based on observations in 2 passbands. They are plagued by considerable degeneracies between age, metallicity, distance (and extinction) that can largely be resolved by including additional passbands with $U$ being most appropriate for young star clusters and I or a NIR band for old globular clusters. For star clusters that cannot be resolved, integrated photometry in suitably selected passbands was shown to be as accurate as spectroscopy in independently revealing ages, metallicities, internal extinction, and photometric masses and their respective 1$\sigma$ uncertainties, when analysed with a dedicated analysis tool for their Spectral Energy Distributions (=SEDs) (cf. Anders et al. 2004a, b, de Grijs et al. 2003b). For external galaxies, rich star cluster populations can thus be efficiently analysed using deep exposures in 4 suitable filters. Again, the inclusion of the $U$-band significantly reduces the uncertainties in the cluster parameters. The age and metallicity distributions of star cluster systems yield valuable information about the formation history of their parent galaxies (Fritze – v. Alvensleben 2004). Here, we present our GALEV evolutionary synthesis models for star clusters of various metallicities (Anders & Fritze - v. Alvensleben 2003), recently extended to include the time evolution of CMDs, the dedicated SED Analysis Tool AnalySED we developed, show results on the basis of HST data, and first results from our SALT PVP project on young star clusters in starburst and interacting galaxies.

Our group studies active early-type (OB) stars, with historical focus on classical Be stars, but extending in recent years to include Slowly Pulsating B-stars (SPB), Beta-Cephei stars, the strongly magnetic Bp stars, Luminous Blue Vairiable (LBV) stars, and B[e] stars. An overall goal is to understand the nature, origin, and consequences of this activity, in terms of both the stellar structure and evolution, as well as the distribution and dynamics of circumstellar material and mass outflows.

Damped Lyman-$\alpha$ (DLA) and sub-DLA quasar absorption lines provide powerful probes of the evolution of metals, gas, and stars in galaxies. One major obstacle in trying to understand the evolution of DLAs and sub-DLAs has been the small number of metallicity measurements at $z<1.5$, an epoch spanning $\sim 70$% of the cosmic history. In recent surveys with the Hubble Space Telescope and Multiple Mirror Telescope, we have doubled the DLA Zn sample at $z<1.5$. Combining our results with those at higher redshifts from the literature, we find that the global mean metallicity of DLAs does not rise to the Solar value at low redshifts. These surprising results appear to contradict the near-Solar mean metallicity observed for nearby ($z \approx 0$) galaxies and the predictions of cosmic chemical evolution models based on the global star formation history. Finally, we discuss direct constraints on the star formation rates (SFRs) in the absorber galaxies from our deep Fabry-Perot Ly-$\alpha$ imaging study and other emission-line studies in the literature. A large fraction of the observed heavy-element quasar absorbers at $0<z<3.4$ appear to have SFRs substantially below the global mean SFR, consistent with the low metallicities observed in the spectroscopic studies.

We discuss populations of X-ray and $\gamma$-ray sources in star-forming regions (SFR). Interacting winds of massive stars and high supernova activity in SFRs can be powerful sources of high energy emission. Models of nonthermal particle acceleration in the vicinity of active SFRs are reviewed. A class of hard emission sources where a fast wind from a massive star collides with a supernova shell is described. Stellar winds of massive stars and core collapsed supernova explosions with great energy release in the form of multiple interacting shock waves inside the superbubbles are argued as favorable sites of nonthermal particle acceleration. Young stellar objects and supernova activity in the dense environment of starforming regions produce an another potentially abundant class of hard faint X-ray sources due to interaction of fast moving knots with the dense ambient medium. The knots could have very different physical nature, e.g. supernova ejecta fragments or Herbig-Haro-like objects. We argue that the sources may have rather steep logN—logS distribution and can contribute substantially to the galactic diffuse emission including the both low-ionized 6.4 keV and He-like Fe lines.

We study dynamical aspects of circumstellar environment around massive first stars. We show that the stellar winds from stationary massive first generation (Population III) stars driven either by the line or continuum transitions are unlikely. Massive first stars are also unable to expel any element or isotope with a possible exception of $_1^1$H. H-He stars with Eddington parameter $\Gamma\gtrsim$0.859 may have pure-hydrogen wind with mass-loss rates of order $10^{-14}\text{M}_\odot\text{year}^{-1}$. Finally, we show that hydrogen and helium lines could be important for shutting off the initial accretion onto first stars and may influence the initial mass function of first stars.

Sub-Arcsec images in the JHK$_s$, H$_2$ and Br$_\gamma$ of three areas (I(N), F and NGC 6334 IV (MM3)) of the giant molecular cloud NGC 6334 are presented. The preliminary results indicate the presence of a deeply embedded young stellar cluster in the northermost part of the cloud (I(N)). We have identified the exciting source of the cometary UCHII NGC 6334 F. This source has an infrared luminosity L$_{\rm IRacute;{=} $3 10$^3$ L$_{\odot}$ and a very steep infrared spectral index. Finally, a new center of massive star formation associated with the millimeter peak MM3 has been found east of the bipolar HII region NGC 6334 a.

We present preliminary results of 3-D hydro simulations of the interstellar medium evolution in dwarf spheroidal galaxies undergoing star formation for the first time. The star formation is assumed to occur in a sequence of instantaneus bursts separated by quiescent periods. Different models are made changing the number and the intensity of the bursts in such a way that the final mass of the formed stars remains the same. We followed the enrichment of the ISM taking into account the contribution of both type Ia and II supernovae. The aim of our models is to find a star formation history compatible with the observed spread of stellar age and metallicity in such galaxies and to reproduce the observed mass-metallicity relation.

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a spacecraft-borne imaging and nulling interferometer for the near to mid-infrared spectral region. FKSI is a scientific and technological pathfinder to the Darwin and Terrestrial Planet Finder (TPF) missions and will be a high angular resolution system complementary to the James Webb Space Telescope (JWST). There are four key scientific issues the FKSI mission is designed to address. These are: 1.) characterization of the atmospheres of the known extra-solar giant planets, 2.) assay of the morphology of debris disks to look for resonant structures characteristic of the presence of extrasolar planets, 3.) study of circumstellar material around a variety of stellar types to better understand their evolutionary state, and in the case of young stellar systems, their planet forming potential, and 4.) measurement of detailed structures inside active galactic nuclei. We report results of simulation studies of the imaging capabilities of the FKSI, current progress on our nulling testbed, results from control system and residual jitter analysis, and selection of hollow waveguide fibers for wavefront cleanup.

Molecular hydrogen is the most abundant molecule in the Universe and dominates the mass budget of the gas, particularly in regions of star formation. H2 is also an important chemical intermediate in the formation of larger species and can be an important gas coolant when the medium lacks metals. Because of the inefficiency of gas-phase reactions to form H2, this molecule is generally thought to form on grain surfaces. Observations of H2 in a wide variety of objects showed that this molecule could form efficiently over a wide range of physical conditions. To understand the mechanism responsible for such an efficient formation, we developed a model for molecular hydrogen formation on grain surfaces. This model considers the interaction between atom and surface as beeing either weak (Van der Waals interaction—physisorption) or strong (covalent bound—chemisorption), as well as the mobility of the atom on a surface due to

quantum mechanical diffusion and thermal hopping. This model solves the time-dependent kinetic rate equation for the formation of molecular hydrogen and its deuterated forms. Our results have been benchmarked with laboratory experiments on silicates, carbonaceous and graphitic surfaces. This comparison allowed us to derive some characteristics of the considered surfaces. An extension of our model to astrophysical conditions gives an estimate of H2 formation efficiency for a wide range of physical conditions. One of our main results is the efficient formation of molecular hydrogen for gas and grain temperatures up to several hundreds of kelvins. We also compared our predictions to observations in astrophysical objects such as photodissociation regions (PDRs). The addition of deuterium in our model for the formation of HD and D2 molecules is also discussed.

We present new experimental data and review previous experimental results on molecular hydrogen formation from atomic recombination on porous amorphous solid water (ASW) surfaces at temperatures from 10 K to 30 K, i.e. under conditions of relevance to cold dense interstellar clouds. We show that the desorption of molecular hydrogen formed on porous ASW surfaces is well described by a model, in which the molecules are assumed to be completely thermalized to the surface temperature and to be evenly distributed throughout the porous network of the ASW films. These results emphasize that, not only the chemical properties, but also the physical morphology of dust grain surfaces must be considered to obtain a full understanding of molecular hydrogen formation on interstellar dust grain surfaces.

A meeting of the IAU Working Group on Chemically Peculiar and Related Stars was held in Sydney on July 16th, 2003. The focus of the business session was on possible effects on our WG due to plans for restructuring the IAU. Working Groups are to be evaluated every 3 years and in general, will be limited to a period of 3 or 6 years.

Molecular absorption lines in the line of sight to distant quasars are an extremely powerful tool to probe the dense interstellar medium and its chemical composition in intervening galaxies from low to high redshifts. The absorption line measurements of different isotopomers even allow us to study isotopic ratios, which can be interpreted as the signature of past nucleosynthesis activity, and put some constraints on the chemical evolution models.

In this paper, we present the study of molecular absorption lines in front of the quasar PKS 1830-211. The absorption is due to an intervening galaxy at $z=0.89$ which is identified as a nearly face-on spiral galaxy. We have carried out a survey of absorption lines of various HCO$^+$, HCN, HNC, and CS isotopomers with the Plateau de Bure Interferometer and derived for the first time the C, N, O, and S isotopic ratios in such a distant object.

This $z=0.89$ absorption system offers an unique opportunity to study the chemical composition in the disk of a spiral galaxy only a few Gyr old. Our results show significantly different isotopic ratios as compared to those measured in the Solar System or in the local ISM, indicating a poorly enhanced abundance of material processed by intermediate and low mass stars.

Since its launch in October 2002, ESA's INTEGRAL observatory has enabled significant advances to be made in the study of Galactic nucleosynthesis. In particular, the imaging Ge spectrometer SPI combines for the first time the diagnostic powers of high resolution gamma-ray line spectroscopy and moderate spatial resolution. This review summarizes the major nucleosynthesis results obtained with INTEGRAL so far. Positron annihilation in our Galaxy is being studied in unprecented detail. SPI observations yield the first sky maps in both the 511 keV annihilation line and the positronium continuum emission, and the most accurate spectrum at 511 keV to date, thereby imposing new constraints on the source(s) of Galactic positrons which still remain(s) unidentified. For the first time, the imprint of Galactic rotation on the centroid and shape of the 1809 keV gamma-ray line due to the decay of $^{26}$Al has been seen, confirming the Galactic origin of this emission. SPI also provided the most accurate determination of the gamma-ray line flux due to the decay of $^{60}$Fe. The combined results for $^{26}$Al and $^{60}$Fe have important implications for nucleosynthesis in massive stars, in particular Wolf-Rayet stars. Both IBIS and SPI are searching the Galactic plane for young supernova remnants emitting the gamma-ray lines associated with radioactive $^{44}$Ti. None have been found so far, which raises important questions concerning the production of $^{44}$Ti in supernovae, the Galactic supernova rate, and the Galaxy's chemical evolution.

We report on the recent developments of our long-term investigation of the near-IR luminosity-metallicity relation for dwarf irregular galaxies in nearby groups. A very well-defined relation is emerging from our observational database, and a preliminary discussion of its implications is given.

The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We present a Chandra tour of several high-mass star-forming regions, highlighting physical processes that characterize the life of a cluster of high-mass stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of stellar sources powering great HII region complexes, suffused by both hard and soft diffuse X-ray structures caused by fast O-star winds thermalized in wind-wind collisions or by termination shocks against the surrounding media. Finally, we examine the effects of the deaths of high-mass stars that remained close to their birthplaces, exploding as supernovae within the superbubbles that these clusters created. We present new X-ray results on W51 IRS2E and 30 Doradus and we introduce new data on Trumpler 14 in Carina and the W3 HII region complexes W3 Main and W3(OH).

We calculate evolution, explosion and nucleosynthesis of 1000$M_{\odot}$ stars. Even such massive stars may explode at the end of their lives if they rotate. We use a 2 dimensional hydrodynamical code to take aspherisity by the effect of rotation into account. Our results show that (1) abundance pattern of ejected matter by explosion is consistent with observational data of intracluster medium gas and M82 hot gas, (2) such massive stars can supply more efficient UV photons to re-ionize HI, HeI and HeII than ordinary massive stars (less than 100 solar-masses) and (3) final black hole mass is 500 solar-mass, which is consistent of the mass scale of intermediate-mass black hole (IHBH) found in M82.

Spectropolarimetry has a broad spectrum of applications, for which there are mostly no substitute observing techniques. They range from the measurement of the strength and structure of magnetic fields via the detection of scattered light from sources obscured by high-density matter or lost in the glare of a nearby bright object to the possibility of individual corrections to the intrinsic luminosities of far-away Type Ia supernovae - and many more. First reconnaissance projects have succeeded with 10m-class telescopes. But the application and extension of the insights gained require substantially larger telescopes. An ELT would in particular enable studies of the formation of structure (AGNs, $\gamma$-ray bursts) in early phases of the universe. At the large distances an ELT will reach, the spatial resolution of point sources, even though only at a very low level, will eventually beat any interferometer. Low cost, the possibility to exploit also not perfectly photometric nights, and the $D^4$ sensitivity of background-limited observations of point sources to telescope diameter are other strong assets.