An Abundance Spread in the Bootes I Dwarf Spheroidal Galaxy?

John E. NorrisThe Australian National University

Gerard GilmoreUniversity of Cambridge

R.F.G. WyseJohns Hopkins University

The

Belokurov et al. 2006 ApJ, 647, L111; 2007 ApJ, 654, 897

M71

Cen

Mv = -5.8rh = 230 pc (13 arcmin)Distance = 60 kpc[Fe/H] = -2.5

Mass enclosed within stellar extent ~ 4 x 107M

Globular star clusters, no DM

Gilmore et al 2007 ApJ, 663, 948

CORRESPONDENCE WITH THE SOC Achim wrote: > your talk is scheduled to follow right after that by Inese Ivans. Do > you have any idea how identical your two talks could be? Are > you coworkers? Could you and Inese make sure that the overlap > is reduced? John replied: > While Inese and I have worked together in the past, there has > been no correspondence or conversation between us on > Bootes I. Indeed we are apparently competitors in an active and > fast moving field. Achim again: > thank you for the clarifying words. As these are two completely > independent projects, I see no problem in leaving both talks as > they are, and wait for surprises. I hope the two of you arrive at > completely different conclusions! John: > Thanks. And yes, there's nothing like a good bun fight!

Bootes I with AAT/AAOMEGA

Bootes I : Radial velocity vs Radial distance

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

Spectra of 15 radial velocity members of Bootes I

g0/(g-r)0/[Fe/H]

Bootes I compared with M15

Bootes I M15

(B-V)0/[Fe/H]

Boo-1137 versus extremely metal-poor stars

Bootes I: Ca II Triplet vs Ca II K

Helmi et al 2006 ApJ, 651, L121

• We have isolated a sample of 16 putative radial velocity RGB members of the low-luminosity Bootes I dSph galaxy (90 < Vr < 115 km/s)

• In this sample there is an abundance range of [Fe/H] ~ 2 dex, with one star having [Fe/H = -3.5

• 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 the production of abundance spreads of the - and iron-peak elements was provided by the non-baryonic material in Bootes I.

SUMMARY