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.

Low mass AGB Stars are the main contributors to the Galactic s-process enrichment. We present new theoretical results obtained by adopting a full network from H to Bi coupled with the physical evolution of the stellar structure. We describe the formation of a 13C pocket as a consequence of H diffusion from the envelope into the He-rich intershell. Such 13C is burnt during the interpulse phase and provides the main neutron source in these stars. We computed two models with the same total mass (that is 2 M[odot ]) but two different initial chemical composition, namely (Y=0.269 – Z=0.015) and (Y=0.245 – Z=0.0001), representative of disk and halo stars respectively. We evaluate the differences in the final s-process surface composition and compare the results with the available observational data.

The rare light elements — Li, Be, and B — have a unique and highly coupled history in the Universe. A coordinated analysis of their abundances in very low metallicity stars can help us understand the inner workings of stars and can constrain models of Galactic chemical evolution. We measure the Be abundances of nine stars and the Li isotopic ratio of ten stars. We find three stars with interesting Be abundances and three stars with detectable $^6$Li.

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 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.

AMS (Alpha Magnetic Spectrometer) is a particle detector designed to operate at the International Space Station. Starting in 2008, its purpose is to perform accurate, high statistics, long duration measurements of energetic (0.1 GeV to $\sim$TeV) charged cosmic ray spectra in space, providing fundamental information about key ingredients in the spallation reactions taking place in the interstellar medium. We present here the characteristics of this experiment and the extense collaboration supporting the project.

We have derived Mn abundances for more than 200 stars in nineteen globular clusters. In addition, Mn abundance determinations have been made for a comparable number of halo field stars possessing an overlapping range of metallicities and stellar parameters. The primary data set was comprised of high resolution spectra previously-acquired at the McDonald, Lick and Keck Observatories. Additional data were obtained from several other investigators. Data were analyzed using synthetic spectra of the 6000 Å Mn I triplet. Hyperfine structure parameters were included in the synthetic spectra computations. Our analysis shows that over the metallicity range $-0.7>[Fe/H]-2.7$ field stars have a mean relative abundance of $<[Mn/Fe]>=-0.36$ identical to that of the nineteen globular clusters $<[Mn/Fe]>=-0.36$. Our Mn abundance results viewed in conjunction with the globular cluster Cu abundances of Simmerer et al. (2003) suggest the following possibilities: one, the production of these elements is highly metallicity-dependent or two, these elements were manufactured in the Galactic halo prior to formation of present-day globular clusters.

Motivated by the WMAP results indicating an early epoch of reionization, we consider alternative cosmic star formation models which are capable of reionizing the early intergalactic medium. We develop models which include an early burst of massive stars (with several possible mass ranges) combined with standard star formation, in the framework of the hierarchical scenario of structure formation. We compute as a function of redshift the stellar ionizing flux of photons, the supernova rates and the chemical evolution, both in the intergalactic medium and in the interstellar medium of forming galaxies. We apply constraints from the cosmic observed star formation rate and the observed abundances in the Lyman $\alpha$ forest and in Damped Lyman $\alpha$ clouds in conjunction with the ability of the models to produce the required degree of reionization.

We determine the carbon isotopic ratios in the atmospheres of some evolved stars in both globular clusters and the disk of our Galaxy. Analysis of 12CO and 13CO bands at 2.3 micron was carried out using fits to observed spectra of red giants and Sakurai's object (V4334 Sgr). The dependence of theoretical spectra on the various input parameters was studied in detail. The computation of model atmospheres and a detailed abundance analysis was performed in a self-consistent fashion. A special procedure for determining the best fits to observed spectra was used. We show, that globular cluster giants with [Fe/H]$\,{<}\,{-}$1.3 have a low 12C/13C = 4 ±1 abundance ratios. In the spectra of Sakurai's object (V4334 Sgr) taken between 1997-98, the 2.3 micron spectral region is veiled by hot dust emission. By fitting UKIRT spectra we determined 12C/13C = 4 ±1 for the July, 1998 spectrum. CO bands in the spectra of ultracool dwarfs are modelled as well.

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…)

We report on results of VLT/FLAMES observations of the very old cluster Cr 261. We compare the results with those of other clusters older than the Hyades.

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.

Magnetic fields may be observed via the Zeeman effect, linear polarization of dust emission, and linear polarization of spectral-line emission. Useful parameters that can be inferred from observations are the mass-to-flux ratio $M/\Phi$ and the scaling of field strength with density. The former tells us whether magnetic fields exert sufficient pressure to provide support against gravitational contraction; the latter tells whether or not magnetic fields are sufficiently strong to determine the nature (spherical or disk geometry) of the contraction. Examples of massive star formation regions for which detailed observations have been made of magnetic field strengths and morphologies include DR21OH, OMC1, and S106; observational results for these regions and relevant results for the diffuse ISM and masers will be reviewed. Results are that the strength of interstellar magnetic fields remains invariant at $B {\sim} 6\mu$G between 0.1 cm$^{-3} < n(H) < 10^3$ cm$^{-3}$, but increases as $B \propto \rho^{0.4-0.5}$ for $10^3$ cm$^{-3} < n(H_2) < 10^{8}$ cm$^{-3}$. Moreover, $M/\Phi$ is significantly subcritical (strong $B$ with respect to gravity) in diffuse H I clouds that are not self-gravitating, but becomes approximately critical in high-density molecular cloud cores. This suggests that GMCs form primarily by accumulation of matter along magnetic field lines, a process that will increase density but not magnetic field strength. How clumps in GMCs evolve will then depend critically on the $M/\Phi$ ratio in each clump.

Core collapse supernovae are responsible for at least half of the galactic inventory of Fe-group elements and probably for most of the Fe-group abundances seen in metal poor stars. Recent simulations show the emergence of a proton-rich ($Y_e>0.5$) region in the innermost ejected mass zones due to the neutrino interaction with matter. We explore the nucleosynthesis implications of these findings that result in enhanced abundances of 45Sc, 49Ti, and 64Zn, which is consistent with chemical evolution studies and observations of low metallicity stars.

Observed large scatters in abundances of neutron-capture elements in metal-poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. Comparing predictions by an inhomogeneous chemical evolution model and new observational results with Subaru HDS, we attempt to constrain the origins of r-process elements.

We present new carbon-enhanced stars identified from the third public release of the Sloan Digital Sky Survey, SDSS-DR3. We have generated synthetic spectra with varying carbon abundances, and compare them with the SDSS spectra. We have also performed a preliminary analysis of s-process enhancement in several SDSS carbon-enhanced stars. Spectral features that are sensitve to stellar luminosity and temperature have also been explored. These methods will be applied to the large set of public SDSS data, as well as to the forthcoming data from SEGUE, the Sloan Extension for Galactic Understanding and Evolution, in order to study carbon enhancement at different metallicities, the fraction of s-process enhancement that occurs in carbon-enhanced stars, and possibly isotopic carbon abundances and nitrogen abundances.

A new class of carbon-rich stars was revealed by large surveys of very metal-poor objects, the carbon-enhanced metal-poor stars (CEMPs). This carbon enhancement is reminiscent of that found in classical CH stars, which despite being halo stars, are not as metal-poor as CEMPs. Although a mass-transfer scenario similar to that formerly at work in CH stars could account for the abundance pattern of CEMPs, differences arise for some key heavy elements. Moreover, statistical studies find 14%; of metal-poor C-rich stars among very metal-poor stars. Thus, this important population of stars represents a precious testimony for nucleosynthesis and chemical evolution at early stages of the Galaxy. We have started a detailed analysis of a large sample of both CH and metal-poor C-rich stars. Here we present results concerning the chemical composition obtained via high resolution and high signal-to-noise VLT-UVES spectra, with special emphasis on the challenges encountered during the abundance analysis. The discussion also includes preliminary results of our ongoing radial velocity monitoring programme which aims at evaluating the relevance of the binary scenario.

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.

Recent years have seen accumulating evidence for infall and rotation around disk like structures toward young stars of spectral types of early B and possibly late O. Observations indicate that the disks or tori are massive in comparison with the mass of the central stars and geometrically thick. Both properties distinguish them from the disks around low mass stars, in particular T-Tauri type stars.

I review observational techniques used in studying disks around massive young stars and summarize properties of disks derived from observations. I will discuss implications of these findings for the formation of massive stars.

We present the results of analysis of “snapshot” spectra (i.e., R=20,000 and S/N=50 per pixel) of 253 metal-poor halo stars $-3.8<$[Fe/H]$<-1.5$ obtained in the HERES survey. The spectra are analysed using an automated line profile analysis method based on the Spectroscopy Made Easy (SME) codes of Valenti & Piskunov (1996). Elemental abundances of moderate precision (absolute r.m.s. errors of order 0.25 dex) have been obtained for 22 elements, C, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, where detectable. The results are presented and discussed, particularly trends and scatter in the abundance distributions.