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].

We present preliminary oxygen abundances in a sample of four red-giants belonging to the bulge population. The abundances were derived from OH molecular transitions in the infra-red high-resolution spectra obtained with the Phoenix spectrograph on Gemini South. The target stars were taken from the previous study by McWilliam & Rich (1994) and selected in order to span a range in [Fe/H] from $-$1.0 to +0.5. Our oxygen results are found to be enhanced and fall above the Milky Way disk trend; in agreement with the high abundances obtained previously for other $\alpha-elements$. It is important to note, however, that the enhanced OH abundances obtained here are based upon stellar parameters taken directly from McWilliam & Rich (1994). Significant revisions to these published values are found more recently in McWilliam & Rich (2003) Such revisions would result in derived oxygen abundances that are systematically lower and perhaps in better agreement with the Milky Way trend. The conclusion is that further efforts are needed in order to better define the stellar parameters for the target stars, as they are crucial in order to decide the important issue of whether the oxygen abundances are enhanced in the bulge K-giants, as we find here. Or, on the other hand, if they follow the trend defined for the Milky Way disk.

It is shown that there is no underlying basic theory which will lead to the idea that the lightest isotopes were produced in an early universe. Everything depends on the choice of the initial ratio of the energy density of photons to baryons that is chosen (originally by Gamow and his colleagues). There is a clear alternative for the origin of the light isotopes. This is that they were generated by hydrogen burning in stars which produces the helium directly while $^{2}D$ and $^{7}Li$ are produced by flare activity in stellar atmospheres. All of this activity takes place in the centers of active galaxies where matter is being created in a cyclic (quasi-steady) state universe.

The study of C-enhanced metal poor stars with s-process elements overabundances offers a chance of testing the AGB models at low metallicity and constrain the nucleosynthesis codes. We analyzed a total of 13 C-enhanced metal poor stars, of which 12 turned out to be s-process enriched. The combination of our results with the analyses already published in the literature allows to highlight the discrepancies present between the current state of the art AGB low metallicity models, suggesting that they are still lacking some ingredient.

We present a new analysis of the abundances observed in extremely metal poor stars based on both a new generation of theoretical presupernova models and explosions of zero metallicity massive stars and a new abundance analysis of an homogeneous sample of stars having $\rm [Fe/H]\leq -2.5$ (Cayrel et al. 2004).

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.