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The Carbon Abundance Spreads in the Bootes I Dwarf Spheroidal Galaxy and the Segue 1 System

The Carbon Abundance Spreads in the Bootes I Dwarf Spheroidal Galaxy and the Segue 1 System. John E. Norris Gerard Gilmore Rosemary F.G. Wyse Australian National Univ. University of Cambridge Johns Hopkins University

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The Carbon Abundance Spreads in the Bootes I Dwarf Spheroidal Galaxy and the Segue 1 System

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  1. The Carbon Abundance Spreads in the Bootes I Dwarf Spheroidal Galaxy and the Segue 1 System John E. Norris Gerard Gilmore Rosemary F.G. Wyse Australian National Univ. University of Cambridge Johns Hopkins University & University of Edinburgh (together with M. Wilkinson, V. Belokurov, N. W. Evans, D. Zucker) Acknowledgement: Niederste-Ostholt et al.

  2. The Carbon Abundance Spreads in the Bootes I Dwarf Spheroidal Galaxy and the Segue 1 System John E. Norris Gerard Gilmore Rosemary F.G. Wyse Australian National Univ. University of Cambridge Johns Hopkins University & University of Edinburgh (together with M. Wilkinson, V. Belokurov, N. W. Evans, D. Zucker) Acknowledgement: Niederste-Ostholt et al.

  3. The Formation of the Galaxy “This paper is dedicated with thanks for many things to Olin J. Eggen - even though he may not necessarily agree with its contents.”

  4. THE CHEMICAL ENRICHMENT OF w CEN & OTHER GLOBULAR CLUSTERS Acknowledgement: David Malin

  5. THE MOST METAL-POOR STARS Martin John Norbert Mike Tim Sean Wako Aoki Anna

  6. What about dwarf spheroidals?

  7. Belokurov et al. 2007 ApJ, 654, 897 / Martin et al. 2008, ApJ, 684, 1075 Cen M71 Segue1 Mv = -1.5 rh = 29 pc (4.4 arcmin) Vrad = 206 km/sec Distance = 23 kpc [Fe/H] = -3.3 (Geha et al. 2008) M = 600-1300 Msun Bootes I Mv = -6.3 rh = 242 pc (13 arcmin) Vrad = 100 km/sec Distance = 66 kpc [Fe/H] = -2.5 (Munos 2006, Martin et al 2007) M = 3-7 104Msun

  8. Kirby et al 2008 ApJ, 685, L43/ Geha et al 2009, ApJ, 692,1464

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

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

  11. Norris et al. 2008, ApJ, 689, L113 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]

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

  13. Boo-1137 versus extremely metal-poor stars Norris et al. 2008, ApJ, 689, L113 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.

  14. Carbon abundances in Bootes I

  15. Boo-33 - a carbon-rich star in Bootes I

  16. Bootes I and the  Cen thing …

  17. Niederste-Ostholt et al. 2009, submitted Segue 1

  18. Geha et al. 2009 ApJ, 692, 1464

  19. AAOmega results for Segue 1

  20. rgal 3.9’ 14.0’ 9.4’ 10.0’ 16.9’ Segue 1 - radial velocity members

  21. Segue 1 - the carbon rich stars!

  22. Segue 1 - carbon abundances

  23. dSph abundance dispersions Fornax, Sculptor, Sextans, Carina, Draco, UMi CVn I & II, Her, UMa I & II, Leo IV, Com (Kirby et al 2008) Cen, Boo I, Seg 1

  24. CONCLUSIONS • Using AAOmega we have obtained spectra of 16 and 5 putative radial velocity RGB members of the low-luminosity Bootes I dSph galaxy and the Segue 1 system, respectively, with sufficient S/N for [Fe/H] and [C/Fe] determinations • In Bootes I there is an abundance range of [Fe/H] ~ 1.7 dex, while in the extremely sparse Segue 1 the range could be as large as [Fe/H] ~ 2.5 dex. These systems appear to have members with [Fe/H] as low as -3.4 amd -4.0 respectively • In both systems, there is a large range in [C/Fe] • The abundance dispersion of the Milky Way’s dwarf spheroidal galaxy population appears to increase as baryonic mass and heavy element abundance decrease • 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 dSph, and that chemical enrichment was a very stochastic process, with the effect becoming more marked at lowest metallicity and baryonic mass

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