The Abundance Spread in the Boötes I Dwarf Spheroidal Galaxy

We present medium-resolution spectra of 16 radial velocity red-giant members of the low-luminosity Bootes I dwarf spheroidal (dSph) galaxy that have sufficient S/N for abundance determination, based on the strength of the Ca II K line. Assuming [Ca/Fe] ~ 0.3, the abundance range in the sample is Δ[Fe/H] ~ 1.7 dex, with one star having [Fe/H] = –3.4. The dispersion is σ([Fe/H]) = 0.45 ± 0.08—similar to those of the Galaxy's more luminous dSph systems and ω Centauri. This suggests that the large mass (107 M☉) normally assumed to foster self-enrichment and the production of chemical abundance spreads was provided by the nonbaryonic material in Bootes I.

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