An Abundance Spread in the Bootes I Dwarf Spheroidal Galaxy? John E. Norris The Australian National University Gerard Gilmore University of Cambridge R.F.G. Wyse Johns Hopkins University The (together with M. Wilkinson, D. Zucker, V. Belokurov, N. Evans & D. Quinn)

Belokurov et al ApJ, 647, L111; 2007 ApJ, 654, 897 M71  Cen M v = -5.8 r h = 230 pc (13 arcmin) V rad = 100 km/sec Distance = 60 kpc [Fe/H] = -2.5 (Munos 2006, Martin et al 2007)

Mass enclosed within stellar extent ~ 4 x 10 7 M   Globular star clusters, no DM  Gilmore et al 2007 ApJ, 663, 948

Bootes I with AAT/AAOMEGA Blue spectra R=5000 Red spectra R=14000

Bootes I : Radial velocity vs Radial distance Membership criterion: 90 < V r < 115 km/sec (~+/- 2  )

Bootes I : C4150 > 200 cnts/pix, Radial vel. vs Radial dist. rhrh

Spectra of 15 radial velocity members of Bootes I g 0 /(g-r) 0 /[Fe/H] W(CaIIK), B-V Beers et al 1999 calibration [Fe/H] Internal error:  ([Fe/H])= 0.35

Bootes I compared with M15 Bootes IM15 (B-V) 0 /[Fe/H]

Boo-1137 versus extremely metal-poor stars Is Boo-1137 (with r = 24 arcmin) a member? This appears to be very likely, given the rareness of objects with [Fe/H] < From the HK survey for metal-poor stars and for [Fe/H] < -3.0, Beers et al (1992) find 5 stars with V 0.7 over 2300 sq.deg. For the HES, Christlieb (2008, priv. comm.) finds 9 stars with B < 14.5, B-V < 0.7 over 7000 sq.deg. From this, we estimate one should expect only ~0.02 field halo giants having [Fe/H] < -3.0 within the central 30 arcmin of Bootes.

Bootes I: Ca II Triplet vs Ca II K

Helmi et al 2006 ApJ, 651, L121

We have obtained spectra of 16 putative radial velocity RGB members of the low-luminosity Bootes I dSph galaxy (90 < V r < 115 km/s) with sufficient S/N for [Fe/H] determination In this sample there is an abundance range of  [Fe/H] ~ 1.7 dex, with one star having [Fe/H = -3.4 The abundance dispersion is  ([Fe/H]) = 0.4 +/- 0.1, which is of the same order as those of the Galaxy’s more luminous dSph systems, and  Centauri This suggests that the large mass (> 10 7 M o ) normally assumed to foster self-enrichment and the production of abundance spreads of the  - and iron-peak elements was provided by the non-baryonic material in Bootes I. CONCLUSIONS