General effects of metallicity on the evolution of stars

The metallicity affects the evolution of stars mainly through its impact on the radiative opacities, the equation of state, the nuclear-reaction rates, and the stellar mass-loss rates (Maeder 2002). Metallicity also affects the way in which the various instabilities induced by rotation occur in stars. Recent calculations ordered by increasing metallicity are briefly presented in Table 36.1. The first column gives the reference the second to fourth columns indicate respectively the range of...

Models and yields

The formal definition of the 'yield', often denoted p, is the mass of metals produced per mass of material locked up in long-lived stars or remnants (e.g. Pagel 1997 Edmunds 1990). In a closed-box (or 'simple') model this gives the elementary relation that the gas abundance Z p ln(1 f), where f is the 'gas fraction' - the mass of gas left in the system relative to the mass of stars plus gas. The mean metallicity in the stellar population, often denoted (Z), tends to the value p as the gas is...

Conclusion

Overmetallicity is a frequent phenomenon in stars of our Galaxy. The case of exoplanet-host stars is especially interesting in that respect, because most of these stars are observed to be overmetallic relative to the Sun, with an average value of 0.2 dex. This observed feature is certainly related not only to the planet formation but also to the reason why giant planets migrate towards the central star in some cases. The stars for which no planets have been detected may very well host giant...

Light elements in the Galactic bulge

Zoccali2 & B. Barbuy3 1Observatoire de Paris-Meudon, GEPI and CNRS UMR 8111, 92125 Meudon Cedex, France 2Popular Universidad Cat lica de Chile, Departamento de Astronom a y Astrof sica, Casilla 306, 3 Universidade de Sao Paulo, IAG, Rua do Matao 1226, Sao Paulo 05508-900, Brazil 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...

Effects of high metallicity

The primary effect of metallicity on molecular-cloud formation and the triggering of star formation is on the rate of H2 formation. Since this occurs on dust grains, a higher metal content then corresponds to more dust grains and a faster H2-production rate. Thus in high-metallicity regions molecular clouds should form more rapidly and more efficiently such that the molecular content, and potentially the star-formation rate, should increase. One numerical simulation of H2 formation in turbulent...

Diffuse interstellar bands

Diffuse interstellar bands (DIBs) are common in the spectra of reddened stars in the Milky Way. Although they are numerous (there are now over 100 different known bands), the identification of the DIB carriers is one of the oldest outstanding mysteries in astronomical spectroscopy. Amongst the potential candidates are polycyclic aromatic hydrocarbons and long carbon chains. The DIBs have been detected in only a handful of extra-Galactic sight-lines, including the LMC and SMC (Snow 2001), and in...

Difficulties at high metallicity

Obtaining a direct measurement of chemical abundances in H11 regions requires that we have a good idea of the value of the electron temperature, Te. The strengths of the forbidden emission lines (collisionally excited) from various metal ions commonly detected in nebular spectra are strongly sensitive to Te, besides being sensitive to the abundance of the originating ionic species, N(X+i) since the line emissivity has essentially an exponential dependence on Te eA a (T)Te-0'5e-x (kTe). (17.2)...

Conclusions

Chemical-evolution models of the Solar vicinity for metal-rich stars are in the early stages of development. Nevertheless, I present the following conclusions. Models that assume hierarchical mergers and fragmentation explain most of the chemical and kinematic properties of thick and thin disks for Fe H < 0. Models that assume different SFHs and infalls for the thin and thick disks explain their chemical properties only for Fe H < 0. There is no published chemical-evolution model of the...

A recent merger

It cannot be excluded that the stars of the Hercules stream could have originated from a recent merger event between the Milky Way and another system. This system must then have had properties very similar to the present properties of the Galactic thin and thick disks. Thus, such a hypothetical merging galaxy would have chemical characteristics that depart considerably from those of local dwarf galaxies (e.g. Venn et al. 2004) and would presumably be more similar to a major spiral galaxy.

A mixture of thin and thick disks

For Fe H > -0.2 there are several stars with thin-disk chemical compositions. The stars that follow the trends outlined by the thick disk are, however, more numerous. At supersolar metallicities ( Fe H > 0) there is really no way to tell whether we are looking at the thin or the thick disk. If the Hercules stream has a dynamical origin, consisting of stars originating at smaller Galactocentric radii, are we tracing the inner thin disk or the inner thick disk Since no detailed abundance data...

The stellar populations of metalrich starburst galaxies the frequency of Wolf Rayet stars

Joao Rodrigo Souza Leao,1 Claus Leitherer,1 Fabio Bresolin2 & Roberto Cid Fernandes3 1Space Telescope Science Institute, Baltimore, MD, USA 2IfA, University ofHawai'i, Honolulu, HI, USA 3 Universidade Federal de Santa Catarina, Florianopolis, SC, Brazil We conducted an optical survey (Keck Telescope, 3,700-7,000 A) of 24 high-metallicity (Z) starburst galaxies to investigate whether high-Z environments favor the formation of Wolf-Rayet (WR) stars. We searched for the presence of the He ii...

Dust metals and diffuse interstellar bands in damped Lymanalpha systems

Department of Physics & Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada Although damped Lyman-alpha (DLA) systems are usually considered metal-poor, it has been suggested that this could be due to observational bias against metal-enriched absorbers. I review recent surveys to quantify the particular issue of dust obscuration bias and demonstrate that there is currently no compelling observational evidence to support the hypothesis of a widespread effect due to...

Solar abundances

The photospheric Solar abundances provide the reference pattern for general abundance determinations in the Universe (for stars, ionized nebulae, galaxies) and the inferred initial Solar abundances correspond to the interstellar medium (ISM) of the Solar neighborhood 4.5 Gyr ago. During the last 20 years the observational estimations of photospheric Solar abundances regarding the most abundant heavy elements, such as C, N, O, and Ne, have decreased. In Table 43.11 show the chemical-abundance...

Tracing metallicities and chemical abundances with JWST

JWST will be a versatile astronomical facility designed to tackle numerous outstanding issues spanning most of the research fields in astronomy. The key scientific goals for JWST have been grouped into four main areas (1) the investigation of planetary systems (including our own) and the potential for life (2) the investigation of the birth of stars, their early evolutionary stages, and their proto-planetary systems (3) the study of the assembly of galaxies, and their evolution in terms of dark...

On the metallicity of the Hyades cluster

As a by-product of our study on Hyades G stars, it would be appropriate to touch briefly upon some topics that are closely related to the subject of metal-rich stars. The metallicity ( Fe H ) of the Hyades cluster is of profound importance, since it is involved with the definition of super-metal-rich (SMR) stars. While its values reported so far have a scatter of between +0.1 and +0.2 (Figure 32.8(a)), our result suggests A(Fe) 7.7 (Figure 32.6(a)) or Fe H +0.2 (the solar Fe abundance is 7.5)....

Metallicity

43 Models of the Solar vicinity the metal-rich stage 415 L. Carigi 44 Chemical-evolution models of ellipticals and bulges 428 F. Matteucci 45 Chemical evolution of the Galactic bulge 441 B. Gibson, A. J. MacDonald, P. Sanchez-Biazquez & L. Carigi 46 How do galaxies become metal-rich An examination of the 47 Abundance patterns thick and thin disks 454 48 Formation and evolution of the Galactic bulge constraints from S. K. Ballero, F. Matteucci & L. Origlia

And thick disks

Lund Observatory, Box 43, SE-221 00 Lund, Sweden Thick disks are common in spiral and SO galaxies and seem to be an inherent part of galaxy formation and evolution. Our own Milky Way is host to an old thick disk. The stars associated with this disk are enhanced in the a-elements relative to similar stars present in the thin disk. The Milky Way thin disk also appears to be younger than the thick disk. Elemental-abundance trends in stellar samples associated with the thin and thick disks in the...

The Salpeter and Kroupa models

The two IMFs differ in the sense that, when two populations have the same total mass, the one with the Kroupa IMF has more high-mass stars than does the one with the Salpeter IMF. Therefore, it is brighter and bluer, produces more stellar wind and also has more metals. As a consequence, the model galaxy with the Kroupa IMF implemented, henceforth called the Kroupa model, has a lower star-formation rate (SFR) in the beginning, when stellar winds keep the gas from collapsing. After 5 Gyr,...

An abundance survey of the Galactic thick disk

Lambert2 & Carlos Allende Prieto2 1Indian Institute of Astrophysics, Bangalore, India 2 McDonald Observatory and Department of Astronomy, University of Texas, Austin, TX, USA We present the results of our recent abundance survey of the Galactic thick disk. We selected from the Hipparcos catalog 176 sample stars satisfying the following criteria they are nearby (d < 150 pc) subgiants and dwarfs, of spectral types F and G, and with thick-disk kinematics (VLSR <...

Stellarpopulation models

Here I give a short overview of the method, which involves applying stellar populations to strengths of absorption lines tuned to decouple age and metallicity (and abundance ratios) in the spectra. A more complete description can be found in Trager (2004) for details the reader is referred to Trager et al. (2000a), with updates in Trager et al. (2008). An unfortunate drawback of this method at present is its inability to determine MDFs only mean quantities (weighted in a peculiar way described...

The explosive alphaelements silicon calcium and titanium

The elements silicon, calcium, and titanium are all believed to be created in the explosive nucleosynthesis phase of Type-II supernovae (Woosley & Weaver 1995). Owing to our belief in their common origin, we have averaged the three X Fe ratios of these elements to reduce the effects of random observational scatter. We define aEx Fe (Si + Ca + Ti) Fe ( Si Fe + Ca Fe + Ti Fe ) 3. We plot the results for this combination in Figure 12.3. As we have seen in Figures 12.1 and 12.2, the bulge field...

Galaxies at intermediate redshift

With JWST it will be possible to extend the near- and mid-IR metallicity diagnostics used for nearby galaxies to objects at z 1-2, with important implications for our understading of the evolution of the stellar and interstellar-medium (ISM) metallicity in the Universe. The near-IR spectroscopic diagnostics discussed in the previous section are clearly detected in the spectra of nearby galaxies (e.g. Boisson et al. 2004 Dasyra et al. 2006), and have been widely used to determine stellar...

Abundances from colourmagnitude diagrams

Currently, CMDs have been determined for at least seven (non-dwarf) elliptical and S0 galaxies M32 (Grillmair et al. 1996), NGC 5128 (Rejkuba et al. 2005 and references therein), NGC 3379 (Gregg et al. 2004), NGC 3115, NGC 5102, NGC 404 (Schulte-Ladbeck etal. 2003), and Maffei 1 (Davidge & van den Bergh 2001). For all of these galaxies, CMDs have required HST imaging in the optical or near-infrared (NIR), except for Maffei 1, which was observed in the NIR with the CFHT adaptive-optics...

Contributors

Karin Ammon, Astronomical Institute, Department of Physics and Astronomy, Universit t Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland S. Arribas, CSIC - Departamento de Astrof sica Molecular e Infrarroja, Madrid, Spain Silvia K. Ballero, Dipartimento di Astronomia, Universita di Trieste, Via G. B. Tiepolo 11, I-34124 Trieste, Italy B. Barbuy, Universidade de Sao Paulo, IAG, Rua do Matao 1226, Sao Paulo 05508900, Brazil T. Bensby, European Southern Observatory, Alonso de Cordova 3107,...

S C Trager

Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, Postbus 800, NL-9700 AV Groningen, the Netherlands 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...