We have derived [Fe/H] and [α/Fe] abudnances for Cepheids with Galactocentric distances of 11 to 17 kpc. The stars are as metal-poor as much older open clusters at comparable distances. Like the clusters, and despite their youth, the Cepheids also show enhanced [α/Fe] abundances indicating enhanced contributions from SNe II relative to the Solar neighborhood.

We present results from an Eulerian adaptive mesh refinement simulation demonstrating the formation of a primordial star within an HII region produced by an earlier massive star. Despite the higher temperatures of the ionized gas, this second star formed within 23 million years of its neighbor's death. The enhanced electron fraction within the HII region catalyzes rapid molecular hydrogen formation, leading to enhanced cooling in the preprocessed halo. This “second generation” primordial protostar has a much lower accretion rate than its predecessor, due in part to the higher angular momentum of the halo in which it forms. This situation may allow binaries or multiple systems of low-mass stars to form. The result discussed here is described in more detail in O'Shea et al. (2005).

We present the results of a study of some selected spectral regions, including those around the LiI lines at 6708 Å and 6104 Å in the magnetic chemically peculiar star HD 3980 and in a few other Ap stars with different effective temperatures and different strengths of the magnetic field. High resolution spectroscopic observations were carried out with the Coudé echelle spectrograph at the 74-inch telescope of the Mount Stromlo Observatory ($R=88000$) and with the VLT UV-Visual Echelle Spectrograph UVES at UT2 at ESO ($R=110000$). Using spectral synthesis we determined abundances of Li, Ce, Pr, Nd and some other rare earth elements and showed that the spectral feature at 6708 Å in the spectrum of HD 3980 is due to the Li I doublet with only a minor contribution of the Ce II line at 6708.099 Å.

The rapid neutron capture process (r-process) is understood to be responsible for the synthesis of approximately half of all of the isotopes present in Solar System matter in the mass region from approximately zinc through the actinides. While the general features of this process were identified in the classic papers by B2FH (1957) and Cameron (1957), our current understanding of the r-process remains woefully incomplete. We have yet to cleanly identify which of the studied astrophysical sites contribute significantly to the observed abundance pattern. We have yet to reconcile the apparent duplicity of r-process sites with extant models for the operation of the r-process in diverse astronomical environments. While we may still remain theoretically challenged in our attempts to understand the r-process mechanism and to identify its site, significant clues have come from the observational side. Triggered by the first detections of the element europium (formed predominantly by the r-process) in low metallicity stars (Spite & Spite 1978), observations of heavy element abundances in halo stars have since served to provide tremendously important clues to the nature of the r-process mechanism. Identified constraints include: the utter dominance of the r-process contributions (over those of the s-process in extremely metal deficient stars; an extraordinary robustness of the r-process pattern in the mass range A[gsim ]130–140; and the demand for a second r-process site for the production of the A[lsim ]130 r-process nuclei. We will review these observational trends and theoretical models in the context of the Galactic (Cosmic) evolution of r-process abundances.

I review recent observational progress on the search for accretion signatures in massive young stellar objects (MYSOs). In this context, the primary tool will be 1–5 μm high resolution ($\lambda/\Delta\lambda \,{=}\,$50,000) spectroscopy. The observational regime is the phase between massive star formation (collapse, accretion, mergers, etc) and the fully revealed OB star photosphere, the phase for which the term “Massive Star Birth” was originally coined. In this phase, we seek both the signature of the earlier accretion process and the photospheric markers of the truly massive star which is on the main sequence. The sample of objects used in this endeavor are massive young stars located in nascent clusters powering Galactic giant H II regions. Emission in the 2.3 μm 2–0 vibrational–rotational bandhead of CO is observed as are the ionized lines of Hydrogen, Helium, and other abundant elements. High spectral resolution is key in giving geometrical clues to the circumstellar emission sources, both through individual line profiles (i.e. shapes) and positions.

Rotating massive stars at $Z=10^{-8}$ and $10^{-5}$ lose a great part of their initial mass through stellar winds. The chemical composition of the rotationally enhanced winds of very low $Z$ stars is very peculiar. The winds show large CNO enhancements by factors of $10^3$ to $10^7$, together with large excesses of $^{13}$C and $^{17}$O and moderate amounts of Na and Al. The excesses of primary N are particularly striking. When these ejecta from the rotationally enhanced winds are diluted with the supernova ejecta from the corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very similar to those observed in the C–rich extremely metal poor stars (CEMP). We show that rotating AGB stars and rotating massive stars have about the same effects on the CNO enhancements. Abundances of s-process elements and the $^{12}$C/$^{13}$C ratio could help us to distinguish between contributions from AGB and massive stars. On the whole, we emphasize the dominant effects of rotation for the chemical yields of extremely metal poor stars.

We present results from our ongoing survey of Galactic Giant HII Regions in the near-infrared. The luminosity function indicates that the IMF is uniform, independent of the galactocentric distance and compatible with Salpeter (1955) slope. Distances measured by the spectroscopic parallax method are systematically smaller than kinematic distances derived from radio techniques. As a consequence, the number of ionizing photons and the star formation rate is much lower than that derived from rotation models. Although the luminosities of the giant HII regions obtained from this method are lower than by other methods, the morphological type of the Milky Way is well in line of previous results, close to Sbc or Sc types.

Using the method of spectral synthesis we derived the abundances of Li in the atmospheres of 100 stars in the range of metallicities −3${<}$[Fe/H]${<}$0.2. The investigated spectra are part of the library collected at the Haute Provence Observatory, they were obtained with the 193 cm telescope equipped with ELODIE spectrometer (R=42000). For the metal-poor dwarfs, in the “Spite plateau” region ([Fe/H]${<}$−1.7, $T_{\rm {eff}}{>}$5700 K) we obtain logA(Li)${=}$2.30${\pm}$0.05, which is in a good agreement with the results of other authors. Our values of Li abundances do not indicate any trends either with $T_{\rm {eff}}$ or with [Fe/H]. The “plateau” is also traced in the metallicity range −0.7${<}$[Fe/H]${<}$−0.3. The behavior of the lithium abundance for stars with [Fe/H]${>}$−1.7, $T_{\rm {eff}}{<}$5700 K shows a depleting mechanism in these stars, the growth of its efficiency with an increase of the metallicity. The “lithium plateau” was also found for thick disk dwarfs with $T_{\rm {eff}}{>}$5800 K.

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.

Chemical abundances and upper limits of three dozen elements have been derived for the binary blue metal-poor, extremely lead-rich star CS29497-030. The findings include a large contribution of s-process material (e.g., [Pb/Fe] >3.5) and a large contribution of r-process material (e.g, [Eu/Fe] ∼2), abundances which place it in the class of objects known as r+s stars. The ratio of [Zr/Nb] ∼0, along with its stellar parameters, indicates that it is not an intrinsic AGB star. Modelling the abundance distribution (which includes the first Bi abundance determination for any metal-poor star) with s-process calculations employing FRANEC models, there is excellent agreement with the observations by adopting a 1.3 M[odot ] AGB model with an enhanced 13C-pocket and a pre-enrichment of r-process material. In this scenario, the initial abundances of CS29497-030 and its binary partner arose from a parent cloud with an extreme r-process abundance, in which star formation was triggered by a core-collapse supernova which polluted, snowplowed, and clumped a nearby molecular cloud. Pollution from the former AGB star's dredged-up material subsequently enriched the envelope composition of CS29497-030 (Ivans et al. 2005). Critical tests of this model and scenario include the dependence of abundance ratios on systematics due to non-LTE effects, the choice of stellar parameters and model atmospheres, and the assumed abundance pattern of the protostellar cloud out of which the CS29497-030 binary system formed.

We develop and test a method for the estimation of carbon abundance ratios, [C/Fe], and metallicities, [Fe/H], in metal-deficient stars, based on application of artificial neural networks and synthesis models to medium-resolution (1–2 Å) spectra in the region of the CH G-band feature at $\lambda$ 4300 Å. We calibrate this method by comparison to modern carbon abundance determinations for N $\simeq 125$ stars reported in the recent literature. As a first application, we estimate the abundance of carbon and [Fe/H] for the sample of 56 stars identified as carbon-rich, relative to stars of similar metal abundance, in the sample of “strong G-band” stars discussed by Beers, Preston, & Shectman.

With the COLLISA foil experiment onboard the Mir space station we have collected samples of interstellar helium, which have been returned to the Earth and investigated by mass spectrometric analysis. Recently, we have been able to reduce the experimental uncertainties as given earlier (Salerno et al. 2003). Our improved estimate of the helium isotopic ratio in the local interstellar medium is now ($^3$He/$^4$He)$_{LISM}$=(1.62 $\pm$ 0.29)$\,{\times}\,$10$^{-4}$ (Busemann et al. 2005).

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.

Theoretical estimates of nucleosynthesis yields are widely used to infer the meaning of abundance trends, and to predict behavior of abundances in the first stars. We show that the standard prescriptions are incomplete, and illustrate some simple improvements. We consider the effects of internal gravity waves (induced in radiative regions by convective zones) on the evolution of slowly rotating (nonrotating) stars. We demonstrate that such modifications to the standard evolutionary algorithms give better agreement with observation. They imply new phenomena: interations between carbon and oxygen burning shells, detached flames in convective layers, and intermittency, for example. We argue that such hydrodynamic behavior must be part of realistic stellar evolution. Some preliminary results for the Sun and Sirius are discussed.

Oxygen abundances for a large sample of dwarf and giant stars kinematically selected to be part of the Galactic thin and thick disks have been determined from a non-LTE analysis of the O I triplet lines at 777 nm. The abundance analysis was performed using the infrared flux method temperature scale, trigonometric surface gravities, and accurate atomic data. Within this framework, the ionization balance of iron lines could not be satisfied and so we adopted the iron abundances from Fe II lines only given that they are relatively less sensitive to changes in the atmospheric parameters. We show the resulting [O/Fe] vs. [Fe/H] relationship and briefly discuss its implications.

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.

As part of a study of the detailed abundance patterns in extremely metal-poor stars, we have compared our samples of giants and dwarfs with two samples of dwarfs measured by different teams. For most elements the abundances are in good agreement, but for C, Na, and Al we show that the atmospheric abundances are different in dwarfs and in giants. For C the difference could be explained by “atmospheric effects” or by the influence of the first dredge-up, but for Na and Al deep mixing inside the stars must be invoked. Until now, such deep mixing has not been observed in metal-poor field stars. An excess scatter in [Mg/Fe] in giants remains unexplained.

We assume that Damped Lyman-α absorbers are gas rich galaxies on early stages of their evolution, and check this idea on the basis of a spectrophotometric, chemical and dust evolution model. Influence of the dust on the chemical pattern of galaxies is calculated self-consistently according Dwek's (1998) model, where up-to-date dust yields from supernovae, intermediate and low mass stars on their AGB phase are taken into account. We conclude that gas rich galaxies are good candidates on the role of DLA systems.

We show that rotation plays a major role for very low metallicity stars, even if the distribution of angular velocities $\Omega$ with respect to critical values is the same as at solar $Z$. The internal gradients of $\Omega$ are much larger at lower metallicity $Z$, which enhance internal mixing and give rise to N-enrichments. Low $Z$ stars easily reach break–up during MS evolution and lose mass. They also lose mass as red giants or supergiants due to their surface enrichments in heavy elements. The winds of low $Z$ stars make peculiar contributions to the chemical yields. We suggest that the helium rich blue Main Sequence (bMS) of $\omega$ Centauri bears the signature of such enrichments by the stellar winds of rotating stars in the first stellar generations.

The first generation of stars to form in the universe may have been very massive, and, due to the absence of initial metals, they could have retained most of their mass until their death and thus explode as pair instability supernovae. These supernovae encounter the late burning phases beyond carbon burning in an implosive/explosive way, leading to very powerful thermonuclear-powered explosions, up to a hundred times more powerful than ordinary supernovae. For primordial stars, these explosions also produce a peculiar abundance pattern, showing a strong odd-even pattern in the elemental abundances, a sharp drop-off of nucleosynthetic production beyond the iron group, and no r-process contribution. These results are greatly altered if only a small mass of 14N is dredged down into the helium burning core before the star becomes unstable. Such mixing could be a consequence of differential rotation or convective overshooting.