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Small-scale heros: massive-star enrichment in ultrafaint dSphs

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. dSphs: have long been known as low luminosity systems.

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Small-scale heros: massive-star enrichment in ultrafaint dSphs

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  1. 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

  2. Smallest scales • dSphs: have long been known as low luminosity systems. • Since ~2006: ultra-faint dwarfs. • Sites of Fe-poor stars ( [Fe/H] > - 3.96; Tafelmeyer et al. 2010) Zucker et al. 2006; Belokurov et al. 20NN; Walsh et al. 2007; Irwin et al. 2007 ... 8 Mv Small-scale puzzle pieces of large scale halo(s). Kirby et al. (2008) Martin et al. (2008); Koch (2009)

  3. Hercules • Ultrafaint dSph, discovered within SDSS (Belokurov et al. 2007); Mv=-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) The first high-resolution spectra of 2 red giants in Her: AK et al. (2008, ApJL). (MIKE@Magellan; 6 hours integration R=20,000; 4000-9000 Å) SDSS DR6; 30’x30’ (ca. 4xrh)

  4. Hercules - heavy elements New FLAMES spectra (Adèn, AK, et al. 2011): very large spread in Fe and Ca MW disks and halo dSphs Hercules Models by F. Matteucci (n = 0.0001, 0.001, 0.01, 0.1 Gyr -1)

  5. Hercules – a small scale hero? 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 Mprog ~ 35-50 M Her-2 Her-3 dSphs, Halo (Heger & Woosley 2010)

  6. Hercules – no heavy elements 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, ApJL AK et al. in prep.

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

  8. Stochastic star formation • Mtot = 7 x 106 M and M/L = 330 implies M* ~ 40000 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] ~ 0.4 - trace amounts of r-process - later SF –> Fe contributions and Fe spreads • High-mass? Rather “ordinary massive” (N. Yoshida);

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

  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 Mo) SNe. Other indicators ( high Co/Cr ... ) argue for the signatures of the “First Stars”.

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