2 00 4 ‘ Sculptor ’ - ing the Galaxy ? The Chemical Compositions of Red Giants in the Sculptor Dwarf

We have used high-resolution, high signal-to-noise spectra obtained with the VLT and UVES to determine abundances of 17 elements in 4 red giants in the Sculptor dwarf spheroidal galaxy. Our [Fe/H] values range from –2.10 to –0.97, confirming previous findings of a large metallicity spread. We have combined our data with similar data for five Sculptor giants studied recently by Shetrone et al. to form one of the largest samples of high resolution abundances yet obtained for a dwarf spheroidal galaxy, covering essentially the full known metallicity range in this galaxy. These properties allow us to establish trends of [X/Fe] with [Fe/H] for many elements, X. The trends are significantly different from the trends seen in galactic halo and globular cluster stars. This conclusion is evident for most of the elements from oxygen to manganese. We compare our Sculptor sample to their most similar Galactic counterparts and find substantial differences remain even with these stars. The many discrepancies in the relationships between [X/Fe] as seen in Sculptor compared with Galactic field stars indicates that our halo cannot be made up in bulk of stars similar to those presently seen in dwarf spheroidal galaxies like Sculptor, corroborating similar conclusions reached by Shetrone et al., Fulbright and Tolstoy et al. These results have serious implications for the Searle-Zinn and hierarchical galaxy formation scenarios. We also find that the most metal-rich star in our sample is a heavy element-rich star. This star and the [Ba/Eu] trend we see indicates that AGB stars must have played an important role in the evolution of the s-process elements in Sculptor. A very high percentage of such heavy element stars are now known in dwarf spheroidals compared to the halo, further mitigating against the formation of the halo from such objects. Subject headings: galaxies: dwarf; galaxies: individual (Sculptor); galaxies: