Population studies of faint X-ray sources (e.g. galaxies, AGN, $\gamma$-ray bursts and their afterglows) have become more and more common. The problem of obtaining an average spectrum in the rest-frame of the sources is non-trivial. We show that conventional methods for averaging low signal-to-noise X-ray spectra, when applied to sources at different redshifts, result in a mean rest-frame spectrum that can exhibit artificial features. These include the broadening and weakening of emission/absorption lines, a broad dip in the continuum above an emission line, and a spectral hardening at the highest energies. All of these effects have been observed in real data and have been given fairly weighty astrophysical and/or cosmological interpretations. We present a new method of averaging which considerably reduces the severity of the problems.

We present a study of the s–process nucleosynthesis (weak s-process) occurring during convective core He–burning and convective shell Carbon–burning in a massive star of 25 M$_{\odot}$. We use an updated nuclear network for the various neutron sources and for all neutron captures and β-decay rates involved. Large uncertainties affect the final yields due to the present unsatisfactory knowledge of all neutron capture cross sections involved.

Chandra and XMM detect X-rays emitted during accretion onto supermassive black holes, even when they are highly obscured. I review what has been learned about the cosmic evolution of the X-ray luminosity functions and the reconstruction of the accretion history of supermassive black holes from extensive follow-up observations of both deep and wide-area Chandra X-ray surveys.

We have calculated a set of synthetic spectra for AGB-stars using the MARCS-code (Gustafsson et al., 1975) and improved spectral synthesis. Here we investigate the spectral changes as a function of the stellar parameters and we show a comparison of observed high resolution UVES spectra of galactic disk and bulge AGB-stars with calculated synthetic spectra. Using our set of synthetic spectra, we try to determine the stellar parameters using only these and (J – K) data (Schultheis 1998). To achieve this, we use a minimal-distance method and search for spectral features which can be used as indicators that are sensitive either only to a change in $T_{eff}$ or only to a change in metallicity $[M/H]$ (where M are all metals from Li to U). In a later stage of the project, we will focus on selected lines of s-process elements in an attempt to achieve a more accurate abundance determination leading to a better understanding of nucleosynthesis and dredge-up processes in these stars.

With the detection of relativistic broad emission lines in MCG 6-30-15 (Tanaka 1995) X-ray observations have become an important tool to test the direct environment of black holes.

XMM-Newton observations were the basis of remarkable progress in different directions in recent years. On the one side the birth and the growth of black holes could be addressed in detail. On the other side several observations allowed the study of the strong gravitational field in the vicinity of black holes.

The talk provides an overview of XMM-Newton observations of black holes: starting from the creation of stellar-mass black holes, through mass growth via accretion disks and occasional tidal disruption events, up to intermediate and supermassive black holes in the centre of active and non-active galaxies. Special attention will be given to the achieved status in the determination of the measurable quantities of black holes, i.e. mass and spin.

The Galactic halo is unlikely built up from galaxy populations similar to the dwarf spheroidal galaxies (dSph's) in the Local Group, but it is possible that the halo was formed by accreted dwarf galaxies that had much larger mass and higher star formation rates such as the Saggitarius dSph. Cosmological simulations show that dSph galaxies formed via hierarchical clustering of numerous smaller building blocks. Stars formed at the galaxy centre tend to form from metal-rich infall gas, which builds up the metallicity gradients. Infalling gas has larger rotational velocity and smaller velocity dispersion due to the dissipative processes, resulting the two distinct old stellar populations of different chemical and kinematic properties, which are recently discovered in the Sculptor dSph galaxy.

The chemical composition of 91 stars in the Sculptor dwarf spheroidal galaxy is presented as determined from spectra taken with the FLAMES multiobject spectrograph in the Medusa mode. The analysis methods are outlined. The [α/Fe] ratios are shown for Mg, Ca, and Ti, and compared with those of Galactic stars. Heavy element abundance ratios (Y, Ba, and Eu) are also presented. Since the Sculptor dwarf galaxy has had a significantly different star formation history and chemical evolution than the Galaxy, then comparison of Sculptor's metal-poor (old) stars to similar metallicity stars in the Galaxy can be used to discuss galaxy formation scenarios, as well as test some of our fundamental assumptions in stellar nucleosynthesis.

I suggest that stellar coalescence in mid-size protoclusters ($M {\sim} 10^{3.5}$–$10^{4.5} M_{\odot}$) is a possible scenario for the formation of ultraluminous X-ray sources (ULXs). More massive super-star-clusters are not needed, since the most likely ULX mass range is only ${\sim} 30$–$200 M_{\odot}$; in fact, they are very rarely found at or very near ULX positions. Protostellar envelopes and gas accretion favour captures and mergers in dense cores of embedded clusters. Moreover, protoclusters with masses ${\sim} 10^{3.5}$–$10^{4.5} M_{\odot}$ are likely to disperse quickly into loose OB associations, where most ULXs are found. Sufficiently high protostellar density may be achieved when clustered star formation is triggered by galaxy collisions and mergers. Low metallicity may then be necessary to ensure that a large fraction of the stellar mass ends up in a black hole. In this scenario, most ULXs are naturally explained as the extreme end of the high-mass X-ray binary population.

The IAU Symposium 230, Populations of High Energy X-ray Sources in Galaxies has been a wide-spectrum affair, with talks discussing results from the soft X-ray to the Gamma-ray range on virtually the entire universe, from our Galaxy to the high redshift regions when first galaxies emerged. I do not name any presenter in this summary, but concentrate on themes and results that I have found striking.

We have been using VLT – FLAMES facilities to obtain spectra of large samples of stars from the Large Magellanic Cloud in order to infer chemical abundances of some key elements. Target stars have been selected trying to sample as much as possible the hole metallicity range of the population. In the present paper we continue our report on chemical abundances for stars in the Inner Disk of the LMC. In our previous work (Pompéia, Hill & Spite 2004) we have found a peculiar pattern for such stars, with a deficiency of α and Na relative to stars of the Galaxy. For the iron-peak elements we found an offset when compared to stars from the Galaxy which is difficult to explain when taking into account the present nucleosynthetic theories. In the present paper we report abundances derived from line synthesis for Y, Zr, Ba, Cu and Sc. We have found an interesting behavior for the s-process elements: while the heavy-s elements show supersolar values and overlap the galactic samples, the light-s elements are underabundant with many subsolar values. Cu and Sc show deficient patterns compared to MW stars of similar metallicities.

We present the first metallicity distribution (MDF) derived for the bulge of M31. We have used HST WFPC2 V and I images to construct the color-magnitude diagram of a field located at 1.55 kpc from the center of M31. We have translated the RGB star colors into abundances. We describe the M31 bulge MDF properties, compare them to those of the M31 halo. We discuss the analogy with our Galaxy and the implications for the formation of spiral galaxies.

Although carbon is, together with oxygen and nitrogen, one of the most important elements in the study of galactic chemical evolution its production sites are still poorly known and have been much debated (see e.g. Gustafsson et al. 1999; Chiappini et al. 2003). To trace the origin and evolution of carbon we have determined carbon abundances from the forbidden [C I] line at 8727 Å and made comparisons to oxygen abundances from the forbidden [OI] line at 6300 Å in a sample of 51 nearby F and G dwarf stars. These data and the fact that the forbidden [C I] and [O I] lines are very robust abundance indicators (they are essentially insensitive to deviations from LTE and uncertainties in the stellar parameters, see, e.g., Gustafsson et al. 1999; Asplund et al. 2005) enable us to very accurately measure the C/O ratio as well as individual C and O abundances. Our first results indicate that the time-scale for the main source that contribute to the carbon enrichment of the interstellar medium operate on the same time-scale as those that contribute to the iron enrichment (and can possibly be AGB stars…)

Carbon stars found in the Small Magellanic Cloud and the Sagittarius Dwarf Spheroidal galaxy have been chemically analysed. We found that the abundance ratios derived between elements belonging to the first and the second s-process abundance peaks agree remarkably well with the theoretical predictions of low mass metal-poor AGB nucleosynthesis models. Together with their estimated luminosities, their derived abundances and their carbon isotopic ratio we speculate on the evolutionary status of these carbon stars.

The results of a spectrum synthesis analysis of elemental abundances derived from the high-resolution CCD-spectrograms of the SMC red supergiant stars PMMR23 and PMMR39 (stars 23 & 39 in the catalogue Prevot et al. 1983) are presented. The abundances of 35 elements in the atmosphere of PMMR23 have been obtained. Elements with atomic numbers Z<56 are deficient with respect to the solar abundances. The mean underabundance is about –0.7 dex. The abundances of elements heavier than barium are close to the solar value. In the case of PMMR23, the atmosphere is enriched in elements heavier than barium which show abundances close to the solar value. These abundances can be explained as a combination of r- and s-processes. In PMMR39, all the 20 studied elements present abundances deficient with respect to solar values The abundances of 31 elements with Z>30 are determined in the atmosphere of Arcturus.

We follow the evolution of barium and europium in four Local Group Dwarf Spheroidal Galaxies by means of a detailed chemical evolution model. The model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (II, Ia). By assuming that barium is produced in low mass AGB stars by s-process but also in massive stars (in the mass range 10–30 M[odot ]) by r-process and that europium is a pure r-process element synthesized in massive stars in the same range of masses (10–30 M[odot ]), we are able to reproduce the observed [Ba/Fe] and [Eu/Fe] as functions of [Fe/H] in all four galaxies studied. We confirm also the important role played by the very low star formation efficiencies (ν = 0.005–0.5 Gyr−1) and by the intense galactic winds (wi = 6–13) in the evolution of these galaxies.

The Fornax dSph is an interesting case as it contains five old globular clusters and its field stars, although predominantly of intermediate (3-8 Gyr old) age, cover a wide range of age and metallicity. Detailed abundance analysis is crucial to our understanding of the earliest star formation epoches, where classic CMD analysis fails to provide a unique answer. It also allows us to measure the chemical evolution of the stellar population following tracers of different enrichment mechanisms through time, e.g. SN type II (alpha elements); AGB stars (s-process elements) etc. With our large sample of abundance measurements we will obtain a detailed picture of the evolution of Fornax and of the role played by small galaxies in the building up of larger ones.

Using a kinematic criterion reveals stars of extragalactic origin from our sample. We show that the ratios of r- and α-elements in all the accreted stars differ sharply from those in the stars that are genetically associated with the Galaxy. Since the majority of accreted stars of our sample exhibit a significant Eu overabundance relative to Mg, we conclude that the maximum masses of the SN II progenitors outside the Galaxy were much lower than those inside it. We provide evidence that the maximum mass of the SN II progenitors increased in the Galaxy with time simultaneously with the increase in mean metallicity.

We present elemental abundance ratios for bright red giants in the old, distant open clusters Berkeley 20, Berkeley 21, NGC 2141, Berkeley 29, and Berkeley 31 as well as for distant field red giants in the direction of the southern Galactic warp. At Galactocentric distances beyond 10 to 12 kpc, the metallicity gradient disappears. The open cluster and field red giants of the outer disk exhibit an almost constant iron abundance [Fe/H] = −0.5. We also measured the abundances for 15 other elements and found very similar compositions in the field and cluster stars. Specifically, they all show enhancements of the α elements O, Mg, Si, Ca, and Ti as well as the r-process element Eu. These abundance patterns reveal a rapid star formation history for the outer Galactic disk. A possible explanation for the measured compositions is that the outer disk formed as a result of star formation triggered by a series of merger or accretion events.

The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution. Measuring abundances in distant galaxies with current techniques is often a challenge, and the canonical metallicity indicators can often not be applied. I discuss currently available metallicity indicators based on stellar and interstellar absorption and emission lines, and assess their limitations and systematic uncertainties. Recent studies suggest that star-forming galaxies at redshift around 3 have heavy-element abundances already close to solar, in agreement with predictions from cosmological models.

The enrichment of the intergalactic medium (IGM) with heavy elements provides us with a record of past star formation and with an opportunity to study the interactions between galaxies and their environments. We summarize current data analysis methods and observational constraints on abundances in the diffuse, high-redshift (z>2) IGM. This review is targeted at interested outsiders and attempts to answer the following questions: Why should you care? What do we want to measure? How do we do it? What do we know? What are the common misconceptions?