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An Abundance Spread in the Bootes I Dwarf Spheroidal Galaxy?

The. 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. (together with M. Wilkinson, D. Zucker, V. Belokurov, N. Evans & D. Quinn).

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An Abundance Spread in the Bootes I Dwarf Spheroidal Galaxy?

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  1. The 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 (together with M. Wilkinson, D. Zucker, V. Belokurov, N. Evans & D. Quinn)

  2. Belokurov et al. 2006 ApJ, 647, L111; 2007 ApJ, 654, 897  Cen M71 Mv = -5.8 rh = 230 pc (13 arcmin) Vrad = 100 km/sec Distance = 60 kpc [Fe/H] = -2.5(Munos 2006, Martin et al 2007)

  3. Gilmore et al 2007 ApJ, 663, 948 Mass enclosed within stellar extent ~ 4 x 107M Globular star clusters, no DM

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

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

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

  7. Spectra of 15 radial velocity members of Bootes I g0/(g-r)0/[Fe/H] Internal error: ([Fe/H])= 0.35 W(CaIIK), B-V Beers et al 1999 calibration [Fe/H]

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

  9. 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] < -3.0. From the HK survey for metal-poor stars and for [Fe/H] < -3.0, Beers et al (1992) find 5 stars with V < 14, and B-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.

  10. Bootes I: Ca II Triplet vs Ca II K

  11. Helmi et al 2006 ApJ, 651, L121

  12. CONCLUSIONS • We have obtained spectra of 16 putative radial velocity RGB members of the low-luminosity Bootes I dSph galaxy (90 < Vr < 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 (> 107 Mo) 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.

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