We have derived metallicity, masses, and ages for two samples of nearby giant stars, which have been observed with the aim of understanding their nature of the radial-velocity (RV) variability and to search for planetary companions. Our stars have reliable Hipparcos parallaxes, and for several we also have measured angular diameters; the parameters we retrieve from our inversion process are in very good agreement with the observed ones. Among our results, we find that the stars regarded as candidates to host planetary companions are not preferencially metal-rich, which is at odds with what is found for main-sequence stars. We also find that stars younger than ∼1 Gyr can be described by a single metallicity and that an age–metallicity relationship applies to our samples.

Galactic open clusters provide a key tool to address a variety of issues related to the formation and evolution of stars and the Galactic disk. In the last few years a metallicity higher than Solar has been derived/confirmed spectroscopically for a few clusters, the most famous example being the very old NGC 6791, for which a metallicity [Fe/H] ∼ 0.4 has recently been reported. In this paper current knowledge of these supersolarmetallicity clusters is reviewed and their properties and abundance patterns are compared with those of non-metal-rich clusters and other Galactic populations. Possible implications for their origin and for the metallicity gradient in the disk are briefly discussed. A summary of recent surveys for planets in metal-rich clusters is also provided, together with new results on Li abundances for the 3-Gyr-old metal-rich cluster NGC 6253.

The chemical evolution of the Galactic bulge is calculated by adopting a single-zone framework, with accretion of primordial gas on a free-fall timescale, assuming (i) a correspondingly rapid timescale for star formation and (ii) an initial mass function biased towards massive stars. We emphasise here the uncertainties associated with the underlying physics (specifically, stellar nucleosynthesis) and how those uncertainties are manifested in the predicted abundance-ratio patterns in the resulting present-day Galactic-bulge stellar populations.

Does the initial mass function (IMF) vary? Is it significantly different in metal-rich environments versus metal-poor ones? Theoretical work predicts this to be the case, but in order to provide robust empirical evidence for this, the researcher must understand all possible biases affecting the derivation of the stellar mass function. Apart from the very difficult observational challenges, this turns out to be highly non-trivial, relying on an exact understanding of how stars evolve, how stellar populations in galaxies are assembled dynamically and how individual star clusters and associations evolve. N-body modelling is therefore an unavoidable tool in this game: the case can be made that without complete dynamical modelling of star clusters and associations any statements about the variation of the IMF with physical conditions are most probably wrong. The calculations that do exist demonstrate time and again that the IMF is invariant: there exists no statistically meaningful evidence for a variation of the IMF on going from metal-poor to metal-rich populations. This means that currently existing star-formation theory fails to describe the stellar outcome. Indirect evidence, based on chemical-evolution calculations, however, indicates that the extreme starbursts that assembled bulges and elliptical galaxies may have had a top-heavy IMF.

Galactic chemical evolution witnesses the enrichment of the interstellar medium with elements heavier than H, He, and Li that originate from the Big Bang. These heavier elements can be traced via the surface compositions of low-mass stars of various ages, which have remained unaltered since their formation and therefore measure the composition in the interstellar medium at the time of their birth. Thus, the metallicity [Fe/H] is a measure of the enrichment with nucleosynthesis products and indirectly of the ongoing duration of galactic evolution. For very early times, when the interstellar medium was essentially pristine, this interpretation might be wrong and perhaps we see the ejecta of individual supernovae where the amount of H with which these ejecta mix is dependent on the energy of the explosion and the mass of the stellar progenitor. Certain effects are qualitatively well understood, i.e. the early ratios of alpha elements (O, Ne, Mg, Si, S, Ar, Ca, Ti) to Fe, which represent typical values from Type-II supernova explosions that originate from rapidly evolving massive stars. On the other hand, Type-Ia supernovae, which are responsible for the majority of Fe-group elements and are the products of binary evolution of lower-mass stars, later emit their ejecta and reduce the alpha/Fe ratio. In addition to being a measure of time, the metallicity [Fe/H] also enters stellar nucleosynthesis in two other ways. (i) Some nucleosynthesis processes are of secondary nature, e.g. the s-process, requiring initial Fe in stellar He-burning. (ii) Other processes are of primary nature, e.g. the production of Fe-group elements in both types of supernovae.

As well as being the realm of the first stars, the high-redshift regime is a window on some of the most metal-rich components in our Universe, the massive galaxies destined to become today's ellipticals and the black holes at their centres at a time of peak activity. While much has been learnt in recent years about these ‘get-rich-quick’ objects, progress is still hampered by the same limitations as apply to nearby metal-rich stars and H II regions: our methods for exploring the super solar-metallicity regime require considerable improvement before they can be considered to be reliable. I illustrate this conclusion with a few recent case studies of active galactic nuclei, star-forming galaxies and damped Lyman-alpha systems.

The subject of metal-rich stars has been controversial for over 40 years, and I review some of the major developments in the subject area during that period, emphasizing those papers that set the subject on its presentday course. Metals emerge in the Universe at very high redshift, and galaxies with roughly Solar metallicity are documented even at redshift 3. In the local Universe, disks and bulges are often metal-rich, but metal-rich stars can also be found in distant halo populations, likely ejected into those environments by merger events. The Galactic bulge has a mean abundance of slightly subsolar but contains stars as metal-rich as [Fe/H] ∼+0.5; these stars have a complicated enhancement of light elements.

We present abundance results for 53 bulge giant stars using highresolution spectra obtained with FLAMES/UVES at the ESO/VLT for various regions of the Bulge (−12 < b < −4). The trend of the four light elements O, Na, Mg and Al indicates a chemical enrichment of the bulge dominated by massive stars at all metallicities. For [Fe/H] > −0.5, [O/Fe], [Na/Fe], [Mg/Fe] and [Al/Fe] are enhanced relative to both the thin- and the thick-disc trend. This suggests that the bulge formed on a shorter timescale than did the Galactic discs.

Using Mg as a proxy for metallicity (instead of Fe) we further show the following (i) The [O/Mg] ratio for bulge stars follows and extends to higher metallicities the decreasing trend of [O/Mg] found in the galactic discs. (ii) The [Na/Mg] ratio trend with increasing [Mg/H] is found to increase in three distinct sequences in the thin disc, the thick disc, and the bulge. The bulge trend is well represented by the predicted metallicity- dependent yields of massive stars, whereas the galactic discs have Na/Mg ratios that are too high at low metallicities, indicating an additional source of Na from AGB stars. (iii) In contrast to the case with Na, there appears to be no systematic difference in the [Al/Mg] ratio between bulge and disc stars, and the theoretical yields for massive stars agree with the observed ratios, leaving no space for an AGB contribution to Al.

We discuss recent results based on our ongoing work on the study of the chemical abundances in the central part of spiral galaxies. A robust technique has been used to extrapolate the derived radial abundance gradients of oxygen to the center of the respective galaxies, taking into account the recent ff relation of Pilyugin (2005) and the new model-independent correction for electron-temperature structure within the H II regions as well as the contribution of a possible oxygen depletion by dust grains. In this way, a typical value for the expected maximum O/H abundance in spiral galaxies is derived. Implications of this result for the metallicity–luminosity relation and for the chemical abundances derived for high-redshift-galaxy samples are briefly discussed.

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.