Detailed Composition of Starts in Dwarf Spheroidal Galaxies

Our knowledge about the dynamics, the chemical abundances and the evolutionary histories of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, very little is known about the enrichment of the ultra-faint systems recently discovered in large numbers in large sky surveys. Current low-resolution spectroscopy and photometric data indicate that these galaxies are highly dark matter dominated and predominantly metal poor. On the other hand, recent hi...

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...

Our knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced hi...

Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark matter content of these low-surface-brightness systems is of particular interest, as is...

The dwarf spheroidal galaxies (dSphs) in the Local Group are excellent systems on which we can test theories of galaxy formation and evolution. Color-magnitude diagrams (CMDs) containing many thousands of stars from the asymptotic giant branch to well below the oldest main-sequence turnoff are being used to infer their star-formation histories, and surprisingly complex evolutionary histories have been deduced. Spectroscopy of individual red giant stars in the dSphs is being u...

I will review the progress of VLT spectroscopy of large numbers of individual stars in nearby dwarf spheroidal galaxies. This spectroscopy has allowed us to obtain detailed insights into the chemical and dynamical properties of the resolved stellar population in these nearby systems.

Dwarf galaxies are the least massive, most abundant, and most widely distributed type of galaxies. Hence, they are key to testing theories of galaxy and Universe evolution. Dwarf galaxies sufficiently close to have their gas and stellar components studied in detail are of particular interest, because their properties and their evolution can be inferred with accuracy. This Review summarizes what is known of the stellar and chemical properties of star-forming dwarf galaxies clo...

In the first part of this contribution the observed velocity dispersions in Galactic halo dwarf spheroidal (dSph) galaxies are reviewed, and the consequences for dark matter content outlined. The results are suggestive of a dSph dark matter mass of ~2x10^7 solar masses, independent of the luminosity of the dSph. Alternatives to the dark matter interpretation are also briefly discussed. In the second part of the contribution the emphasis is on the stellar populations of Galact...

The Keck I telescope has been used to obtain HIRES spectra for red giants belonging to the Draco, Sextans and Ursa Minor dwarf spheroidal (dSph) galaxies. An analysis of these spectra is presented, along with abundance ratios for more than 20 elements. The resulting database of element abundances for 17 stars is the most extensive yet assembled for stars in dSph environments. Our main findings are summarized as follows: (1) There is unambiguous evidence for a large internal s...

We present an abundance analysis based on high resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor dwarf spheroidal galaxy. We find [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex and establish the trends of the abundance ratios [X/Fe]. In key cases, particularly for the alpha-elements, these resemble those for stars in the outer part of the Galactic halo, especially at the lowest metallicities probed. The n-capture eleme...