Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21743002k&link_type=abstract
American Astronomical Society, AAS Meeting #217, #430.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
The dwarf spheroidal (dSph) satellite galaxies of the Milky Way make good subjects for testing chemical evolution models because they contain many stars bright enough for medium-resolution spectroscopy and because they span a wide range of velocity dispersion and luminosity. A Keck/DEIMOS spectroscopic campaign of eight Milky Way dSphs has produced a catalog of nearly 3000 stars with spectral synthesis-based abundance measurements of Fe and the alpha elements Mg, Si, Ca, and Ti. Maximum likelihood fits of analytic chemical evolution models to the eight metallicity distributions show that the histories of the less luminous dSphs were marked by massive amounts of gas loss. The average [α/Fe] ratios for all dSphs follow roughly the same path with increasing metallicity. There is little evidence of the predicted knees in the [α/Fe] vs. [Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae begin to explode. Instead, Type Ia supernova ejecta contribute to the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. Finally, a new numerical chemical evolution model tracks elemental abundance patterns, star formation rate, Types II and Ia supernova explosions, and supernova feedback. Similar to the analytic models, the numerical models reveal that the star formation history of a dSph is a strong function of its present-day luminosity, but not velocity dispersion, half-light radius, or Galactocentric distance.
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