Small-scale heros: massive-star enrichment in ultrafaint dSphs Andreas Koch D. Adén, S. Feltzing (Lund) F. Matteucci (Trieste) A. McWilliam (Carnegie) “First Stars IV”, Kyoto, May 23, 2012

Smallest scales MvMv Small-scale puzzle pieces of large scale halo(s). Zucker et al. 2006; Belokurov et al. 20NN; Walsh et al. 2007; Irwin et al dSphs: have long been known as low luminosity systems. Since ~2006: ultra-faint dwarfs. Sites of Fe-poor stars ( [Fe/H] > ; Tafelmeyer et al ) 2/10 Kirby et al. (2008) 8 Martin et al. (2008); Koch (2009)

Ultrafaint dSph, discovered within SDSS (Belokurov et al. 2007) ; M v =-6.6; d=140 kpc low-mass, metal-poor, elongated (one of the most elliptical LG dSphs) (Coleman et a. 2007; Martin et al. 2008; de Jong et al. 2008; Kirby et al. 2008) Stellar Stream ? (Martin & Jin 2010) SDSS DR6; 30’x30’ (ca. 4xr h ) The first high-resolution spectra of 2 red giants in Her : AK et al. (2008, ApJL). 6 hours integration R=20,000; Å) Hercules 3/10

New FLAMES spectra (Adèn, AK, et al. 2011) : very large spread in Fe and Ca Hercules - heavy elements 4/10 Models by F. Matteucci ( = , 0.001, 0.01, 0.1 Gyr -1 ) MW disks and halo dSphs Hercules

Models for high-mass SNe II predict noteably high Mg yields w.r.t. Ca - in fact observed in Her. Our high [O, Mg, Si / Ca, Ti] implies M prog ~ M  (Heger & Woosley 2010) Her-2 Her-3 Hercules – a small scale hero? 5/10 dSphs, Halo

Hercules - n-capture elements Her stars are strongly depleted in Ba (Sr, Eu); Mostly upper limits for Ba. So far seen in a few halo stars, Dra 119 and 2 UFDs (Fulbright et al. 2004; Feltzing et al. 2009; Simon et al. 2010) AK et al. 2008, ApJLAK et al. in prep. Hercules – no heavy elements 6/10

Hercules - n-capture elements AK et al. in prep. Hercules – no heavy elements 7/10

M tot = 7 x 10 6 M  and M/L = 330 implies M * ~ M  (Martin et al. 2008) Incomplete sampling of high-mass end of IMF in small-scale SF events (AK et al. 2008) : stochastic SF tests imply that perhaps only 1-3 massive SNe II influenced the Her stars: - [high Mg/Ca] - initial [Ca/Fe] ~ trace amounts of r-process - later SF –> Fe contributions and Fe spreads High-mass? Rather “ordinary massive” (N. Yoshida); Stochastic star formation 8/10

Courtesy Ken Nomoto High-energy SNe, M prog ~ 25 M o, leaves non-rot. BH, most material ( 56 Ni) falls back. Likely related to EMP stars - first stars in ultrafaints ?!...or faint Supernovae? 9/10

Summary We are approaching ever-smaller scales: extragalactic EMP; ultra faint dwarfs; stochastic chemical enrichment; individual supernovae... Any data point, odd or not, is crucial. Chemical evolution of Hercules (and others) was governed by very few, massive (few tens M o ) SNe. Other indicators ( high Co/Cr... ) argue for the signatures of the “First Stars”. 10/10