“Sculptor-ing” the Galaxy? The Chemical Compositions of Red Giants in the Sculptor Dwarf Spheroidal Galaxy

By D. Geisler, V. Smith, G. Wallersteín, G. González, C. Charbonnel. 2004

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We used high-resolution, high signal-to-noise ratio spectra obtained with the Very Large Telescope and the UV-Visual Echelle Spectrograph to determine abundances of 17 elements in four red giants in the Sculptor (Scl) dwarf spheroidal galaxy. Our [Fe/H]-values range from -2.10 to -0.97, confirming previous findings of a large metallicity spread. We combined our data with similar data for five Scl 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 Scl sample with the 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 Scl compared with Galactic field stars indicate that our halo cannot be made up in bulk of stars similar to those presently seen in dwarf spheroidal galaxies like Scl, 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 indicate that asymptotic giant branch stars must have played an important role in the evolution of the s-process elements in Scl. A very high percentage of such heavy-element stars are now known in dwarf spheroidals compared with the halo, further mitigating against the formation of the halo from such objects.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/eb6ad08f134c8303d9db56828ce2960892610d50

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THE SEGUE STELLAR PARAMETER PIPELINE. V. ESTIMATION OF ALPHA-ELEMENT ABUNDANCE RATIOS FROM LOW-RESOLUTION SDSS/SEGUE STELLAR SPECTRA (2010, background): “Many stars in the dwarf spheroidal galaxies (dSphs) in the vicinity of the Milky Way possess relatively lower [α/Fe] compared to the Galactic halo stars of the same metallicity (Shetrone et al. 2001, 2003; Fulbright 2002; Tolstoy et al. 2003; Geisler et al. 2005), at least for [Fe/H] > −2.5.”
HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES (2009, background): “…decade has provided a wealth of new information about chemical abundances in dSphs in general (e.g., Shetrone et al. 1998, 2001, 2003; Tolstoy et al. 2003; Venn et al. 2004; Geisler et al. 2005), but the ultra-faint dwarf galaxies were discovered too recently to have been included in these studies.”
A Comparison of Elemental Abundance Ratios in Globular Clusters, Field Stars, and Dwarf Spheroidal Galaxies (2005, methodology): “The detailed and recent stellar abundances in the smallest dwarf spheroidal galaxies (dSphs; Shetrone et al. 2001, 2003; Tolstoy et al. 2003; Geisler et al. 2005) have shown that their stars tend to have lower [ /Fe] abundance ratios than similar metallicity Galactic field stars.”
Rotational mixing in low-mass stars: II. Self-consistent models of Pop II RGB stars (2006, background): “Some indications of such a process have also been detected in the brightest RGB stars of external galaxies like the LMC (Smith et al. 2002) and Sculptor (Geisler et al. 2005).”
Thermohaline instability and rotation-induced mixing I. Low- and intermediate-mass solar metallicity stars up to the end of the AGB (2010, background): “…1994; Charbonnel et al. 1998; Charbonnel & Do Nascimento 1998; Gratton et al. 2000; Tautvaišiene et al. 2000; Tautvaišienė et al. 2005; Smith et al. 2002; Shetrone 2003; Pilachowski et al. 2003; Geisler et al. 2005; Spite et al. 2006; Recio-Blanco & de Laverny 2007; Smiljanic et al. 2009).”
THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, background): “If such strong tidal evolution of the MDF is common for Galactic satellites, it may partially explain the observed chemical abundance mismatch between Galactic halo stars and the present-day dSph population (e.g., Geisler et al. 2005; and references therein).”
A REVISED PARALLEL-SEQUENCE MORPHOLOGICAL CLASSIFICATION OF GALAXIES: STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES (2011, background): “The α element abundances in dSph galaxies are not much enhanced with respect to solar, also consistent with prolonged star formation histories (Shetrone et al. 1998, 2001, 2003, 2009; Tolstoy et al. 2003; Venn et al. 2004; Geisler et al. 2005).”
Λ Cold Dark Matter, Stellar Feedback, and the Galactic Halo Abundance Pattern (2005, background): “Additionally, stars in dwarf spheroidal (dSph) galaxies around the Milky Way have intermediateα-element abundances at low-metallicity, [α/Fe]∼ +0.15 (Smecker-Hane & McWilliam 1999; Shetrone et al. 2001; Smecker-Hane & McWilliam 2003; Shetrone et al. 2003; Venn et al. 2004; Geisler et al. 2005).”