Since Pietrowsky's first analytical study of collisional systems of asteroids (1953), through Dohnanyi's comprehensive theory (1969), to the analytical and numerical studies of the last two decades, the collisional evolution of populations of asteroids — and to a less extent, of Trojans and TNOs— has been investigated by many researchers.

The study of such systems is an intrinsically delicate mathematical problem, as their evolution in time is properly described in terms of systems of first–order, non–linear differential equations. Physically, the limited knowledge of some of the collisional properties, rotations and internal structure of bodies, and the complex interplay with dust, non–gravitational effects and dynamical interactions with planets, make the study of the collisional evolution a hard multi–parametric problem. Nevertheless, the task is worth the effort, in fact the understanding of evolutionary processes in the solar system's small body belts provides the main tools to discriminate between the many different theoretical scenarios proposed to explain the formation of the solar system itself.

This review tries to give an updated overall view of the research done in this field, and to show the connections between apparently independent phenomena that may affect the evolution of collisional systems of asteroids and TNOs.

We present preliminary results from a detailed analysis of the X-ray point sources in the XMM-Newton survey of M31 (e.g. Barnard et al. 2005; Pietsch et al. 2005). These sources are expected to be mostly X-ray binaries.

This paper reviews the nature of normal and starburst galaxies in deep X-ray surveys, focusing on the observational issues. Normal and starburst galaxies may be divided from AGN via X-ray/optical flux ratios, optical spectroscopic identification, hardness ratio, and X-ray luminosity. Each of these is discussed, including the possible impact on derived X-ray-Star Formation Rate (X-ray/SFR) correlations. The measured differences in the normal galaxy X-ray Luminosity Functions (XLFs) by SED type at $z\approx0.3$–1.0 are also described.

The redshift frontiers of deep X-ray surveys are discussed, including those for individually detected accreting binary systems (Ultraluminous X-ray Sources at $z\approx0.1$–0.3) and that for the highest-redshift X-ray detection of star formation (stacking analyses of Lyman Break Galaxies to $z\approx4$). The paper closes with a discussion of normal galaxy studies with future X-ray missions such as Constellation-X, XEUS, and Generation-X.

XMM-Newton and Chandra have ushered in a new era for the study of dwarf galaxies in the Local Group. We provide an overview of the opportunities, challenges, and some early results. The large number of background sources relative to galaxy sources is a major theme. Despite this challenge, the identification of counterparts has been possible, providing hints that the same mechanisms producing X-ray sources in larger galaxies are active in dwarf galaxies. A supersoft X-ray source within 2″ of the supermassive black hole in M32 may be a remnant of the tidal disruption of a giant, although other explanations cannot be ruled out.

We have collected from the literature X-ray fluxes of Young Supernovae, measured with various instruments. After converting the data to one energy range, we have compared the X-ray light curves of these objects. The X-ray luminosities of early Supernovae show coherent trends with Supernova type and provide significant, though short-lived contributions to the X-ray luminosity of Starbursts.

In May/June 2005, Chandra observed M81 fifteen times, roughly once every three days, as part of our proposal to explore the days to weeks timescale of variability for extragalactic point sources. Each observation reached a sensitivity of $5\,{\times}\,10^{36}$ erg/s. Because these observations probe the timescale on which X-ray binaries typically evolve, we can now compare extragalactic sources to Galactic X-ray binaries on a more equal level than has been possible in the past. In addition, we can measure and quantify any possible time variability of M81's X-ray luminosity function and investigate alternative methods to characterize a galaxy's dynamic X-ray source population. We present here preliminary results of the observations.

About 20% of the high mass O-type stars in the Galaxy are found outside stellar clusters and associations. In the solar neighbourhood this fraction amounts to 43 O-type stars. In the framework of high-mass star formation, we search for the origins of these stars. We aim at separating the O-type field stars from runaway O-type stars, where the former does not betray any indication of past dynamical interactions resulting in their present field location. We specifically search for the presence of stellar clusters, but also evaluate spatial velocities, distance from Galactic plane, locations in the Galaxy with respect to young stellar clusters. Among our sample of 43, we find that 5 stars are in fact observed in the K-band to be members of previously unnoticed small clusters. On the other hand it is plausible that nearly half the sample (22 objects) could have undergone a dynamical ejection from a young cluster. Based on the current available data, ${\sim }4%$ of the Galactic O-type stars cannot be associated with a stellar cluster. Finally by assuming that stars form in clusters with a power law in membership number with index −1.7 down to “clusters” consisting of single stars, we calculate the expected statistics regarding isolated O stars and O stars in OB-associations. We conclude that the results of the calculations are consistent with the observed statistics of O-type stars.

We discuss the expected properties of the first stellar generations in the Universe. We find that it is possible to discern truly primordial populations from the next generation of stars by measuring the metallicity of high-z star forming objects through the detection and the study of the emission line spectrum from HII regions associated to primordial massive stars. Moreover, the intensity of HeII emission lines can be used as a diagnostic to reveal the presence of massive stars and determine their importance relative to lower mass stars. Thanks to its very low background, the future James Webb Space Telescope (JWST) will be able to image and study first-light sources at very high redshifts. On the other hand, JWST's relatively small collecting area limits its capability in obtaining spectra of z$\,{\sim}\,$10–15 first-light sources to either the bright end of their luminosity function or to strongly lensed sources. With a suitable investment of observing time JWST will be able to detect individual Population III supernovae, thus identifying the very first stars that formed in the Universe.

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.

We constrain energy spectra of supernova neutrinos using the $\nu$-process light element synthesis in supernovae and the $^{11}$B abundance during Galactic chemical evolution. We calculate supernova nucleosynthesis due to the $\nu$-process assuming that neutrino energy spectra are Fermi-Dirac distributions with zero chemical potential. We investigate the dependence of the $^{11}$B yield on the total neutrino energy and the temperature of $\nu_{\mu,\tau}$ and $\bar{\nu}_{\mu,\tau}$. From the obtained yields and the contribution to the $^{11}$B yield from supernovae constrained by observed abundances and Galactic chemical evolution models, we find an acceptable range of the temperature of $\nu_{\mu,\tau}$ and $\bar{\nu}_{\mu,\tau}$ of 4.8 MeV to 6.6 MeV.

Massive stars are known to be formed in clusters. To understand their birth process it is essential to know the physical conditions of the parental cloud which is thought to play a critical role in determining the formation mechanism. In this contribution I summarize recent results from observations of dust, molecular and ionized gas emission we have made toward several massive star forming regions in the southern hemisphere. These observations are providing key evidence concerning the initial conditions for the formation of cluster of massive stars, allowing to characterize the physical properties of massive and dense cores and permitting to identify them in different stages of their early evolution.

Abundances of α-, iron peak, s- and r-elements were determined for a sample of Barium stars and the [α,iron peak/s], [α,iron peak/r], [s/r] ratios were derived.

We present the even-to-odd Ba isotope ratios in 16 thick disk and 3 halo stars as determined from hyperfine structure (HFS) seen in the Ba II resonance line λ 4554. We find in our stars a higher fraction of the odd Ba isotopes compared with the solar one 18% (Cameron 1982): 35% in the halo stars and between 25% and 53% in the thick disk stars. There is a hint of increasing this value with the Eu/Fe abundance ratio growth. Based on the r-process even-to-odd Ba isotope ratio 54 : 46 (Arlandini, Käppeler, Wisshak, et al. 1999) we deduce the ratio of the s/r-process contribution to barium in the thick disk stars as 30 : 70 (±24%).

The HST Treasury Program on the Orion Nebula Cluster has been recently completed (May 2005). Using 104 orbits of HST time we have imaged a field ${\sim }1/6$ of a square degree nearly centered on the Trapezium stars. The survey, made with ACS, WFPC2 and NICMOS-Camera 3 in parallel, has imaged this cornerstone region with unprecedented sensitivity (23-24 mag), dynamic range (${\sim}12$ mag), spatial resolution (50mas), and wide spectral coverage (9 filters from U to H). We have assembled the richest, most accurate and unbiased dataset of stellar photometry for pre-main-sequence objects ever obtained, an essential tool for understanding of the star formation process in regions dominated by massive OB stars.

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.

The pioneering observations of Spite & Spite showed lithium abundances in halo dwarfs to be almost uniform, irrespective of metallicity and mass over a range of effective temperatures from $\sim$5600 K up to the main-sequence turnoff. They inferred that the observed abundance was “hardly altered” from that produced in the hot Big Bang. Subsequent efforts have endeavoured to determine how small or large “hardly” could be. Simplistic arguments based on the uniformity of the Spite plateau suggest there should only be a small difference between the Big Bang lithium abundance and the observationally inferred plateau value, whereas more physical lines of reasoning suggest the difference could be more substantial. This review paper discusses observational and theoretical developments.

Stars in globular clusters exhibit abundance patterns such as the well-known O-Na and Mg-Al anticorrelations which have no counterpart among halo stars. Whereas winds from AGB stars have been proposed as the primordial sources for these anomalies, the impact of rotation in these stars has not been studied in the GC context. To address this issue we present a model of a rotating AGB star with an initial mass of 7 M[odot ] and a metallicity Z = 10−5. We discuss the effect of rotation on the evolutionary features, and focus on the surface abundances which can be modified by rotation, dredge-up events and hot bottom burning.

The preliminary results of abundance analysis are presented for extremely metal-poor carbon star HD 112869 = TT CVn = CGCS 3319. The radial velocity was found to be −137.7 km s−1. Our LTE abundance analysis supports an extremely low metallicity for TT CVn, [Fe/H] = −3.2, and a significant overabundance of carbon and neutron-capture elements. The 12C/13C ratio in the atmosphere of HD 112869 is high.

Since the discovery of the “Spite plateau” in 1982, lithium observations in halo stars have been used to deduce the primordial $^{7}Li$ abundance. Compared with the results of Big Bang nucleosynthesis (BBN) it provided an estimate of the baryonic density of the Universe, together with the other cosmological isotopes. However, recently, the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, by the WMAP satellite, has provided a determination of this baryonic density ($\Omega_bh^2$) with an unprecedented precision. There is a very good agreement with deuterium observed in cosmological clouds, but we note a discrepancy between the deduced $^{7}Li$ abundance and the one observed in halo stars. The origin of this discrepancy, observational, stellar, nuclear or more fundamental remains to be clarified. A recent nuclear physics experiment provided new results on the $^{7}{\rm Be}({\rm d,p})2\alpha$, an up to now neglected reaction in BBN. Unfortunately, this cannot solve the $^{7}Li$ discrepancy.

In order to study the effects of fast rotation on primordial stars, we present the evolution and the chemical yields of zero metallicity models with masses between 15 to 200 M[odot ].