Among the Solar-type stars observed in the Galaxy, many appear to be metal-rich relative to the Sun. The case of exoplanet-host stars is particularly interesting in that respect since they present, on average, an overmetallicity of 0.2 dex. This metallicity is probably original, from the protostellar nebula, but it could also have been increased by accretion of hydrogen-poor material during the early stage of planetary formation. Asteroseismic studies provide an excellent way to determine the internal structure and chemical composition of these stars. Such studies may also establish constraints on the external parameters (gravity, effective temperature, metallicity) that are more precise than the constraints obtained from spectroscopy. After a general discussion on this subject, I present the special cases of three stars: µ-Arae, which was observed with the HARPS spectrograph in June 2004; ι-Horologii, which has been modeled in detail and will be observed with HARPS in November 2006; and finally HD 52265, one of the main targets of the COROT mission, an exoplanet-host star that will be observed with the COROT satellite for five consecutive months.

Observed properties of Wolf–Rayet (WR) stars at high metallicity are reviewed. Wolf–Rayet stars are more common at higher metallicity, as a result of stronger mass-loss during earlier evolutionary phases with late-WC-subtypes signatures of Solar metallicity or higher. Similar numbers of early (WC4–7) and late (WC8–9) stars are observed in the Solar neighbourhood, whilst late subtypes dominate at higher metallicities, such as Westerlund 1 in the inner Milky Way and in M83. The observed trend to later WC subtype within metal-rich environments is intimately linked to a metallicity dependence of WR stars, in the sense that strong winds preferentially favour late subtypes. This has relevance to (a) the upper mass limit in metal-rich galaxies such as NGC 3049, due to softer ionizing fluxes from WR stars at high metallicity; and (b) the fact that evolutionary models including a WR metallicity dependence provide a better match to the observed N(WC)/N(WN) ratio. The latter conclusion partially rests upon the assumption of constant line luminosities for WR stars, yet observations and theoretical atmospheric models reveal higher line fluxes at high metallicity.

The James Webb Space Telescope is a 6.6-m-aperture, passively cooled space observatory optimized for near-IR observations. It will be one of the most important observing facilities in the next decade, and it is designed to address numerous outstanding issues in astronomy. In this article we focus specifically on its capabilities to investigate the chemical abundances of various classes of astronomical objects and their metallicity evolution through the cosmic epochs.

We discuss results of an exploratory NLTE analysis of two metal-rich A-type supergiants in M31. Using comprehensive model atoms we derive accurate atmospheric parameters from multiple indicators and show that NLTE effects on the abundance determination can be substantial (altering results by a factor of 2–3). The NLTE analysis removes systematic trends apparent in the LTE approach and reduces statistical uncertainties. Characteristic abundance patterns of the light elements provide empirical constraints on the evolution of metal-rich massive stars.

We present new atmosphere models for Wolf–Rayet (WR) stars that include a self-consistent solution of the wind hydrodynamics. We demonstrate that the formation of optically thick WR winds can be explained by radiative driving on Fe-line opacities, implying a strong dependence on metallicity (Z). Our Z-dependent model calculations for late-type WN stars show that these objects are very massive stars close to the Eddington limit, and that their formation is strongly favored for high-metallicity environments.

Thanks to the impressive evolution of IR detectors and the new generation of line-blanketed models for the extended atmospheres of hot stars we are able to derive accurately the physical properties and metallicity estimates of massive stars. Here, we review quantitative spectroscopic studies of massive stars in the three Galactic Center clusters: the Quintuplet, Arches, and Central clusters. Our analysis of the LBVs for the Quintuplet cluster provides a direct estimate of chemical abundances of α-elements and Fe in these objects. For the Arches cluster, we introduce a method based on the N abundance of WNL stars and the theory of evolution of massive stars. For the Central cluster, new observations reveal IRS8 to be an outsider with respect to the rest of the massive stars in the cluster in terms of both age and location. Using the derived properties of IRS8, we present a new method by which to derive metallicity from the O iii feature at 2.115 µm. Our results indicate that the three clusters have Solar metallicity.

We present the results from optical high-resolution spectroscopic surveys of the Milky Way bulge. The bulge is observed to have stars with [Fe/H] values up to at least +0.5 and [Mg/H] values up to at least +0.8. Age information from color–magnitude diagrams suggests these stars formed at nearly the same time as old metal-rich globular clusters, and the abundance ratios imply that the chemical evolution of the bulge was dominated by Type-ii supernovae, including progenitors at least as metal-rich as those seen in the local disk today.

In this contribution, we use chemo-dynamical models to investigate the influence of the initial mass function (IMF) on the evolution of disc galaxies, in particular of their metallicities and colours. We find that ‘bottom-light’ IMFs (IMFs with a high high-to-low-mass-stars ratio) lead to higher metallicities both in the stellar content and in the interstellar gas than do ‘top-light’ IMFs, and also to a higher star-formation rate (SFR) beginning ∼ 5 Gyr after the galaxy's birth.

Unfortunately, in terms of integrated colours and magnitudes, these two effects work in the opposite sense, the higher SFR turning the galaxy brighter and bluer, but the higher gas metallicity increasing the extinction and turning it fainter and redder, which complicates making statements about the IMF from these observables. The most likely wavelength region in which to detect IMF effects is the infrared (i.e. JHK), where the absorption overcompensates for SFR effects.

Several topics of interest involved with precise determination of surface abundances and stellar parameters in the metal-rich regime are reviewed. The main emphasis is placed upon Solar-type F–G dwarfs, though K giants are also mentioned briefly. In particular, in connection with the problem of the validity of the hypothesis of LTE, recent spectroscopic studies of Hyades-cluster stars are discussed together with our own results. Some further discussion concerns age determination using evolutionary tracks, in connection with the existence of old metal-rich stars and the high metallicity of planet-host stars.

Topics figuring in this conference include limits to high metallicity, metallicity characteristics of stellar populations, [M/Fe] in bulges and discs, effects of metallicity on star formation and the initial mass function, its relation to planet formation, effects of high metallicity on stellar evolution, yields and galactic chemical evolution, metal-rich H ii regions and metallicities at high redshift.

I review the properties of starburst galaxies, compare the properties of the local ones with those of more distant starburts and examine their role in the metal enrichment of the interstellar medium and the intergalactic–intracluster medium. Metallicity is not an arrow of time and, contrary to current belief, metal-rich galaxies can also be found at high redshift.

We discuss the metallicity of massive stars in the Solar neighbourhood, comparing new results with those for the Sun. We find that, despite there being small systematic differences between various NLTE determinations of [O/H] in hot stars, there is reasonable agreement among results from various studies of nearby stars, with a value of 8.60±0.1 dex being implied. This is in good agreement with the latest Solar estimate based on three-dimensional models, and is in good agreement with recent estimates of the nebular oxygen abundance in Orion. We review the evidence for metal-rich massive stars in our own galaxy and in M31, concluding that there is little convincing evidence for supersolar [O/H] in massive stars in the Milky Way, while there is only limited evidence for mildly metal-rich regions in M31 with [O/H] relative to Solar of only +0.2. Discrepancies between stellar and nebular abundances at high metallicity can be traced to problems in calibrating the R23 index for H II regions in the metal-rich regime.

Elliptical galaxies probably host the most metal-rich stellar populations in the Universe. The processes leading to both the formation and the evolution of such stars are discussed in terms of a new multi-zone photochemical-evolution model, taking into account detailed nucleosynthetic yields, feedback from supernovae, Population-III stars and an initial infall episode. Moreover, the radial variations in the metallicity distributions of these stars are investigated using G-dwarf-like diagrams.

By comparing model predictions with observations, we derive a picture of galaxy formation in which the higher the mass of the galaxy, the shorter are the infall and the star-formation timescales. Therefore, the stellar component of the most massive and luminous galaxies might attain a metallicity Z ≥ Z⊙ in only 0.5 Gyr.

Each galaxy is created outside-in, i.e. the outermost regions accrete gas, form stars and develop a galactic wind very quickly, in contrast to the central core in which star formation can last up to ∼ 1.3 Gyr. This finding will be discussed in the light of recent observations of the galaxy NGC 4697 which clearly exhibits a strong radial gradient in the mean stellar [〈Mg/Fe〉] ratio.

It is currently impossible to determine the abundances of the stellar populations star by star in dense stellar systems more distant than a few megaparsecs. Therefore, methods to analyse the composite light of stellar systems are required. I review recent progress in determining the abundances and abundance ratios of early-type galaxies. I begin with ‘direct’ abundance measurements: colour–magnitude diagrams of stars and planetary nebulae in nearby early-type galaxies. I then give an overview of ‘indirect’ abundance measurements: inferences from stellar-population models, with an emphasis on cross-checks with ‘direct’ methods. I consider the variations of early-type galaxy abundances as a function of mass, age and environment in the local Universe. I conclude with a list of continuing difficulties in the modelling that complicate the interpretation of integrated spectra and I look ahead to new methods and new observations.

After a review of the many effects of metallicity on the evolution of rotating and non-rotating stars, we discuss the consequences of a high metallicity for massive-star populations and stellar nucleosynthesis. The most striking effect of high metallicity is to enhance the amount of mass lost by stellar winds. Typically, at a metallicity of Z = 0.001 only 9% of the total mass returned by non-rotating massive stars is ejected by winds (91% by supernova explosions), whereas at Solar metallicity this fraction may amount to more than 40%. High metallicity favors the formation of Wolf–Rayet stars and Type-Ib supernovae, but militates against the occurrence of Type-Ic supernovae. We estimate empirical yields of carbon on the basis of the observed population of WC stars in the Solar neighborhood, and obtain that WC stars eject 0.2%–0.4% of the mass initially locked into stars in the form of newly synthesized carbon. Models give values well in agreement with these empirical yields. Chemical-evolution models indicate that such carbon yields may have an important impact on the abundance of carbon at high metallicity.

The search for consistency between nebular and massive-star abundances has been a longstanding problem. I briefly review what has been done regarding this topic, also presenting a recent study focused on the Orion nebula: the O and Si stellar abundances resulting from a detailed and fully consistent spectroscopic analysis of the group of B stars associated with the Orion nebula are compared with the most recent nebular gas-phase results.

We present results from comparisons of elemental abundances and dust content between damped Lyman-alpha (DLA) absorbers and gamma-ray-burst (GRB) afterglows, as determined by absorption-line spectroscopy. Our sample of DLA absorbers includes the results from 76 quasar spectra taken with the HIRES spectrograph of the Keck observatory, from which we obtain a sample of 38 DLA absorbers in the redshift range 2 < z < 4. The GRB absorption lines were obtained in collaboration with the Caltech Carnegie NOAO GRB collaboration, in which rapid spectroscopy is obtained from newly discovered GRBs, to obtain high-quality optical spectra. We present results of O, N, C, Si, Zn, Cr, and C II*/C II ratios from a “core sample” of 15 of the best of the DLA absorbers, and detailed analysis of GRB 051111 and GRB 050505, which are at redshifts of z = 1.549 and 4.275, respectively. From our analysis we can see trends in the DLA dust content, and in [C/H], [N/H] and [O/H] values as a function of DLA redshift, as well as evidence for dust formation and highly excited dense gas within the disks of GRB host galaxies.

Recent progress in the study of the various proposed SN Ia-progenitor scenarios is reviewed. We discuss the effects of rotation on the evolution of SN Ia progenitors, in particular the stabilization of helium-shell burning and the increase of the Chandrasekhar limit. The latter may have been confirmed by a recent analysis of an overluminous SN 2003fg. For the evolution of CO white dwarf mergers, we discuss new arguments in favor of obtaining Type-Ia SNe from those systems, in contrast to the previous consensus. We onsensus. We address the issue of SN Ia delay times, and the dependence of average SN Ia properties on the type of host galaxy, in the light of recent observations and progenitor models, and derive implications for SN Ia yields.