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.

Using the 2dF multi-fibre instrument on the Anglo-Australian Telescope, moderate resolution spectra have been obtained for a large sample of stars on the main sequence and at the turnoff in the unusual globular cluster ω Cen. We investigate the behaviour of CH, CN and SrII line strength indices as a function of overall abundance for the main sequence sample. A number of stars do not follow the relations defined by the majority. These anomalous objects can be categorized into (at least) three types. (1) Carbon enhanced stars, which represent about 5% of the sample, and which are found at all metallicities. Spectrum synthesis calculations show that the atmospheres of these stars are typically enhanced in carbon by factors of between 3 and 10. (2) Nitrogen enhanced stars, revealed for [Fe/H] [ges ]–1.3 by strong CN indices, which make up ∼40% of the cluster main sequence population above this metallicity. The stars are enhanced in nitrogen by factors of up to 100. Our data, however, provide no constraints on their relative numbers at lower [Fe/H]. (3) Stars with enhancements of the s-process element Sr by factors of 30 to 60. The possible origins for these abundance anomalies are discussed.

We have recently completed the measurement of the abundances of the elements Zn and Cr in a small, but complete, sample of damped Lyman alpha systems selected irrespectively of their dust content (the CORALS radio sample). We find that at a mean redshift z = 2.4 their metallicity and degree of dust depletion are statistically indistinguishable from those of larger samples of DLAs assembled from optical surveys. Thus we conclude that reasons other than a dust-induced bias must be found to explain the lack of redshift evolution in the metallicity of the galaxies giving rise to DLAs, and their generally low degree of chemical enrichment compared with luminous galaxies observed at the same epoch.

The classical analysis of the s-process is commonly used to predict the s percentage contribution to the solar system abundance of a given isotope, and by default of the r-process residual (calculated as 1. - s). We discuss the advantages and the disadvantages of this first-order prediction, by comparing stellar model calculations at various metallicities in AGB stars and in massive stars exploding as SNII, with spectroscopic observations of different stellar populations. Observations of short-lived r-process isotopes in the early solar system help to characterize at least three different r-process components.

Our understanding on the nitrogen origin has recently greatly changed. New data on nitrogen abundances in very metal-poor stars ($-4<[Fe/H]<-3$) show a quite surprising result: a high N/O ratio suggestive of high levels of production of primary nitrogen in massive stars. Moreover, none of the stars measured so far has N/O ratios as low as the ones observed in Damped Lyman-α systems (DLAs) (currently the systems showing the lowest N/O ratios in the universe). We studied the implications of the above new data set for our understanding on the nitrogen enrichment in the Milky Way. We find that, to explain the new observations, we need to adopt stellar yields computed with stellar models in which rotation is taken into account and assume that stars born at Z <10−5 contribute a lot more N than the most recent calculations available in the literature for Z= 10−5. The implications of our findings for our understanding of the nature of Damped Lyman-α systems (DLAs) are also briefly discussed.

Thanks to the accurate determination of the baryon density of the Universe by the recent cosmic microwave background experiments, updated predictions of the standard model of Big Bang nucleosynthesis yield the initial abundances of the primordial light elements with an unprecedented precision (Bennet et al. 2003; Spergel et al. 2003; Coc et al. 2004; Cyburt 2004). In the case of $^7$Li, the CMB+SBBN value is significantly higher than the generally reported abundances for Pop II stars along the Spite plateau. Here, we report on the very recent results we obtained by revisiting a large sample of literature Li data in halo stars that we assembled following some strict criteria on the quality of the original analyses published from the early 90s onwards.

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.

This paper reviews the chemistry of star-forming regions, with an emphasis on the formation of high-mass stars. We first outline the basic molecular processes in dense clouds, their implementation in chemical models, and techniques to measure molecular abundances. Then, recent observational, theoretical and laboratory developments are reviewed on the subjects of hot molecular cores, cosmic-ray ionization, depletion and deuteration, and oxygen chemistry. The paper concludes with a summary of outstanding problems and future opportunities.

Any predictive theory of star formation must explain observed variations (or lack thereof) in the initial mass function. Recent work suggests that we might expect quantitative variations in the IMF as a function of metallicity (Larson 2005) or magnetic field strength (Shu et al. 2004). We summarize results from several on-going studies attempting to constrain the ratio of high to low mass stars, as well as stars to sub- stellar objects, in a variety of different environments, all containing high mass stars.

First, we examine the ratio of stars to sub–stellar objects in the nearby Mon R2 region utilizing NICMOS/HST data. We compare our results to the IMF by Kroupa (2002) and to the observed ratios for IC 348 and Orion. Second, we present preliminary results for the ratio of high to low mass stars in W51, the most luminous HII region in the galaxy. Based on ground–based multi–colour images of the cluster obtained with the MMT adaptive optics system, we derive a lower limit to the ratio of high-mass to low-mass stars and compare it to the ratios for nearby clusters. Finally, we present the derived IMF for the R136 region in the LMC where the metallicity is 1/4 solar using HST/NICMOS data. We find that the IMF is consistent with that characterizing the field (Chabrier 2003), as well as nearby star–forming regions, down to 1.0 M$_\odot$ outside 2 pc. Whereas the results for both Mon R2 and R136 are consistent with the nearby clusters, the ratio of high to low mass stars in W51 tentatively indicates a lack of low–mass objects.

We summarize the properties of Infrared Dark Clouds, massive, dense, and cool aggregations of interstellar gas and dust that are found throughout the Galaxy in projection against the strong mid-infrared background. We describe their distribution and give an overview of their physical properties and chemistry. These objects appear to be the progenitors of high-mass stars and star clusters, but seem to be largely devoid of star formation, which however is taking place in localized spots.

There seems to be no consensus on the [O/Fe] values found in metal-poor stars nor their trend with metallicity: different indicators give different results. We present here [O/Fe] derived from three different oxygen abundance indicators ([OI], OI and OH UV lines) for a sample of thirteen subgiant stars with metallicities in the range $-3\le\mathrm{[Fe/H]\le-1.5$. Oxygen and iron abundances were determined from the analysis of high $S/N$ spectra acquired with the UVES spectrograph at VLT. We found good agreement between [O/Fe] estimates based on OH and the estimates based on [Oi] ($\mathrm{mean\ difference}\sim-0.09\pm0.25(\mathrm{s.d.})$), although the scatter is not insignificant. Unfortunately, good agreement is not reached for the third indicator ($\mathrm{mean\difference}\sim0.19\pm0.22(\mathrm{s.d.})$). Our [OI] and OH-based estimates do not show a well defined linear trend with metallicity. Another interesting result is that the abundances based on molecular lines ($\mathrm{[O/Fe]}\sim0.45$) are in general lower than previous published results for turn-off stars even though a lower solar oxygen abundance ($A(\mathrm{O})=8.74$) was assumed.

Lithium abundance in Turnoff stars of Globular Clusters (GC) provide precious information about primordial nucleosynthesis and Globular Cluster formation. Out of the three GC so far observed in some detail, the metal poor NGC6397 shows a constant Li abundance, at the same level of the Spite' plateau; while the more metal rich NGC6752 and 47 Tuc show a beautiful Li-Na anticorrelation (the first of this kind observed in PoP II stars), suggesting the presence of gas processed by a previous generation of stars. These observations are quite puzzling: while they are qualitatively compatible with the scenario of contamination from intermediate mass AGB stars, no progenitor can quantitatively reproduce the observations. Beryllium has also been detected in NGC6397 Turnoff stars, indicating that the gas which formed the stars was exposed for about 200 Myr to the Galactic Cosmic Rays. The emerging picture seems to require that in the early Galaxy both local (SNae, AGB stars) and global (Galactic Cosmic Rays) enrichment processes were acting simultaneously in the star formation phase of the halo.

Theoretical as well as observational aspects of the s-process nucleosynthesis are reviewed. The classical site-independent s-process model as well as the s-process in massive stars are shortly described. A special attention is paid to the nucleosynthesis taking place in AGB stars and the extra-mixing invoked to explain the production of neutrons in the C-rich layers during the interpulse. We also discuss the nucleosynthesis found in hot AGB stars for which the s-process during the interpulse phase is inhibited, but the one resulting from the large temperatures in the thermal pulse is boosted. We comment on the uncertainties affecting our understanding of the physical mechanisms responsible for a successful s-process. Finally, various types of spectroscopic observations of s-process elements are discussed.

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.

In da Silva et al. (2005) is presented the detailed spectroscopic analysis of 60 evolved stars, which were previously studied for accurate radial velocity variations (Setiawan et al. 2003). The observations were made with FEROS and the 1.52m ESO telescope of La Silla, partially in the ESO-Observatório Nacional (Brazil) agreement. The main goal of this study is to determine precise atmospheric fundamental data (Teff, log g, [Fe/H] and micro-turbulence velocity) to derive ages and masses of the stars, trying to link them to the detected radial velocity variabilities. Here, due the short space at our disposal, we discuss only the effective temperature determination, comparing the values obtained from the excitation equilibrium of FeI and from (V-K) index with those from (B-V).

We present Very Long Baseline Array (VLBA) proper motion observations of water masers toward two young stellar objects (YSOs) of the W75N(B) high-mass star forming region. These observations (Torrelles et al. 2003) show two objects having a similar spectral type (early-B stars), separated in the sky by 0$0^''$7 (corresponding to 1400 AU at the source distance), sharing the same molecular gas environment, but presenting a strikingly different outflow ejection geometry. One of these YSOs, W75N(B)-VLA 1, has a jet-like outflow at 2000 AU scale, with the water masers moving at velocities of ${\simeq}$20 km s$^{-1}$ along the major axis of the thermal radio continuum jet, while the other YSO has a water maser shell outflow of 160 AU radius expanding at ${\simeq}$30 km s$^{-1}$ in multiple directions with respect to the central compact radio continuum source W75N(B)-VLA 2. Given the small dynamical time obtained for the water maser shell (${\simeq}$13 yr), we propose that in the very early stages of the star-formation process there may exist short lived, possibly repetitive, events associated with very poorly collimated outflows. All these results suggest that outflow collimation is not only a consequence of ambient conditions, but something intrinsic to the evolution of the individual stars, opening the important question of how and when these non-collimated wind ejection events occur in the evolution of YSOs. Although we argue in this paper that W75N(B)-VLA 2 could be in an earlier stage of evolution than W75N(B)-VLA 1, we think that observations at (sub)millimeter wavelengths with angular resolutions of ${\simeq}0^''1$ can provide the key for determining the relative stage of evolution of these two remarkable YSOs.

For refining cosmochemical studies, we are investigating the statistical equilibrium (non-LTE) of neutral and singly-ionized calcium (CaI/II) in the atmospheres of solar-type stars. The envisioned applications are a) detailed abundance studies beyond classical models, b) using CaI/II as a gravity indicator for ultra-metal-poor (UMP) stars and c) detailed modelling of the CaII IR triplet lines for the astrophysical parametrization of the Gaia mission. We present first results for some well-studied reference cases, both at solar and low metallicity.

In the context of a large observational project on old open clusters, we employed FLAMES + UVES on VLT UT2 to collect new high resolution spectra for giant stars in 7 clusters with the aim of investigating the radial abundance distributions in the Galactic disk. The gradients of Fe, α and Fe-peak elements and their evolution with Galactic age are indeed one of the most critical constraints to the star formation history in the Galactic disk and to Galactic chemical evolution models. We present here our preliminary results on the metallicity and abundance ratios for red clump stars in the ∼1 Gyr old cluster NGC 3960, located at a Galactocentric distance $R_{gc}\sim8$ kpc.

We present the main results of our study of photometric solar-analog stars.

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.