Dwarf galaxies

Key words Infrared 10 pm - Interstellar medium dust - Star formation - Galaxies dwarf, individual He 2-10... 

B.E.J. Pagel The G-Dwarf Problem and Radio-Active Cosmochronology . In Evolutionary Phenomena in Galaxies, Summer School at Puerto de la Cruz, Spain, July i 15, 1988, ed. by J.E. Beckman, B.E.J. Pagel (Cambridge University Press, Cambridge, New York 1989), pp. 201-223... 

Abstract. In an effort to determine accurate stellar parameters and abundances for a large sample of nearby stars, we have performed the detailed analysis of 350 high-resolution spectra of FGK dwarfs and giants. This sample will be used to investigate behavior of chemical elements and kinematics in the thick and thin disks, in order to better constrain models of chemical and dynamical evolution of the Galaxy. 

Abundances as Tracers of the Formation and Evolution of (Dwarf) Galaxies... 

Abstract. This aims to be an overview of what detailed observations of individual stars in nearby dwarf galaxies may teach us about galaxy evolution. This includes some early results from the DART (Dwarf Abundances and Radial velocity Team) Large Programme at ESO. This project has used 2.2m/WFI and VLT/FLAMES to obtain spectra of large samples of individual stars in nearby dwarf spheroidal galaxies and determine accurate abundances and kinematics. These results can be used to trace the formation and evolution of nearby galaxies from the earliest times to the present. 

The DART large programme at ESO made v ei and [Fe/H] measurements from FLAMES spectroscopy of 401 red giant branch (RGB) stars in the Sculptor (Scl) dSph [6]. The relatively high signal/noise, S/N ( 10-20 per pixel) resulted in both accurate metallicities ( 0.1 dex from internal errors) and radial velocities ( 2 km/s). This is the first time that a large sample of accurate velocities and metallicities have been measured in a dwarf galaxy. 

The most metal-rich stars in dwarf spheroidals (dSph) have been shown to have significantly lower even-Z abundance ratios than stars of similar metallicity in the Milky Way (MW). In addition, the most metal-rich dSph stars are dominated by an s-process abundance pattern in comparison to stars of similar metallicity in the MW. This has been interpreted as excessive contamination by Type la super-novae (SN) and asymptotic giant branch (AGB) stars ( Bonifacio et al. 2000, Shetrone et al. 2001, Smecker-Hane McWilliam 2002). By comparing these results to MW chemical evolution, Lanfranchi Matteucci (2003) conclude that the dSph galaxies have had a slower star formation rate than the MW (Lanfranchi Matteucci 2003). This slow star formation, when combined with an efficient galactic wind, allows the contribution of Type la SN and AGB stars to be incorporated into the ISM before the Type II SN can bring the metallicity up to MW thick disk metallicities. 

The Composition of the Sagittarius Dwarf Spheroidal Galaxy and Implications for Nucleosynthesis and Chemical Evolution... 

The Metallicity-Luminosity Relation for Local Group Dwarf Galaxies... 

Abstract. We present metallicities for 487 red giants in the Carina dwarf spheroidal (dSph) galaxy that were obtained from FLAMES low-resolution Ca triplet (CaT) spectroscopy. We find a mean [Fe/H] of —1.91dex with an intrinsic dispersion of 0.25 dex, whereas the full spread in metallicities is at least one dex. The analysis of the radial distribution of metallicities reveals that an excess of metal poor stars resides in a region of larger axis distances. These results can constrain evolutionary models and are discussed in the context of chemical evolution in the Carina dSph. 

Detailed elemental abundances are now available for several individual stars in the Galaxy s dwarf satellites (Shetrone et a1. 2001, 2003 Geisler et al. 2005 also see the reviews in this proceedings). A comparison of these abundance ratios to those of stars in the Galaxy can be used to address several questions related to galaxy formation and evolution, as well as stellar nucleosynthesis. 

Dwarf Spheroidal galaxies are the smallest and faintest galaxies known. They are typically dominated by old stellar populations (e.g. Sculptor and Sextans), but some of them (e.g. Fornax) exhibit more recent star formation episodes (2-8 Gyr ago). Analysis of the horizontal branch morphology shows that Red HB stars are more centrally concentrated than Blue HB stars which could be interpreted either as an age or a metallicity gradient or both ([1]). Only spectroscopic observations can unambiguously separate metallicity gradients and make a link with the kinematics. 

E.Tolstoy Abundances as Tracers of the Formation and Evolution of (Dwarf) Galaxies . In Chemical Abundances and Mixing in Stars, 13-17 Sep. 2004, Castiglione della Pescaia, Italy, L. Pasquini, S. Randich (eds.)... 

Abstract. We have performed the chemical analysis of extragalactic carbon stars from VLT/UVES spectra. The derived individual abundances of metals and s-elements as well as the well known distance of the selected stars in the Small Magellanic Cloud and the Sagittarius dwarf galaxies permit us to test current models of stellar evolution and nucleosynthesis during the Asymptotic Giant Branch phase in low metallicity environments. 

In order to test the current evolution and nucleosynthesis models predicting the formation and the yields of such carbon stars, we have collected high-resolution spectra of stars located in the SMC and the Sagittarius dwarf galaxy, extragalactic systems with low average metallicity and well known distances. 

Chemical Abundances of RGB-Tip Stars in the Sagittarius Dwarf Spheroidal Galaxy... 

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