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Evolution of metal poor massive stars towards GRBs

Evolution of metal poor massive stars towards GRBs. Sung-Chul Yoon (Amsterdam) In collaboration with Norbert Langer (Utrecht). Tartu, Aug. 15, 2005. Outline. GRB progenitors Single star models & problems Binary models & problems

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Evolution of metal poor massive stars towards GRBs

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  1. Evolution of metal poor massive stars towards GRBs Sung-Chul Yoon (Amsterdam) In collaboration with Norbert Langer (Utrecht) Tartu, Aug. 15, 2005

  2. Outline • GRB progenitors • Single star models & problems • Binary models & problems • New evolutionary models of rapidly rotating metal poor single stars • Discussion

  3. GRB progenitors • Some clues • Association with star-forming regions in galaxies • GRB 980425  SN 1998bw (Galama et al. 1998) • GRB 030329  SN 2003dh (eg. Hjorth et al. 2003) • At least, some GRBs are deaths of massive stars! -- especially from massive He stars (or WR stars) • Association with Type Ibc supernovae • Crossing time of jet ~ 10 secs: compact progenitors • GRBs are a subset of SN Ibc? (RGRB/RSNIbc ~ 0.01—0.001)

  4. Necessary Conditions for GRB formation • Formation of relativistic Jets => central engines are rapid rotators • Collapsar scenario (Woosley) – formation of a Keplerian disk around a black hole: j > 1016 cm2/s • Difficult to achieve (Maeder & Meynet 03; Heger et al. 05) • Removal of H envelope • Difficult at very low/zero Z • He core massive enough to form BH

  5. Angular momentum redistribution inside stars • Core contraction/chemical gradient between the core and the envelope • Angular momentum transport by Eddington Sweet circulations, Shear instability, magnetic torques, etc. • Stellar wind mass loss

  6. Angular momentum redistribution Using a hydrodynamic stellar evolution code (e.g. Heger et al. 00; Petrovic et al. 05). Effect of magnetic torques is considered according to Spruit (2002)

  7. Role of magnetic fields in J-transport Models with B-fields are more consistent with observations!!

  8. Binary Evolution Mass accretion will spin up the secondary star.

  9. Mass and J accretion in close binaries Petrovic, Langer, Yoon & Heger (2005) • Spin-up by accretion leads to strong stellar winds. • J-transport during He core contraction is very rapid. • the core becomes slow again – as slow as in single stars. • Spin-up during MS does not help. M1 = 56, Pinit =6 days

  10. Spin-up in WR stages? • Tidal locking of a massive helium star in a very close binary (Izzard et al.03; Podsiadlowski et al.04)? • Orbit should be very short: P < 5 hr • Massive He stars in X-ray binaries? – eg. Cyg X-3 (P ~ 4.8 hr; van Kerkwijk et al. 1992) • He star merger (Fryer & Heger 2005) • BUT: Any evolutionary scenario related to common envelope phase may not work at very low Z

  11. Homogeneous evolution of single stars • Found by Maeder(1987)

  12. Homogeneous Evolution Rapidly rotating helium stars can be made even without removing hydrogen envelope => particularly important at low Z

  13. Homogeneous Evolution Yoon & Langer (2005); see also Woosley & Heger (2005)

  14. Uncertainties in WR winds • Maximun Z for such evolution to GRBs sensitively depends on the WR wind mass loss rate. • With current estimate of WR winds by Vink & de Koter (05): Zmax ~0.001

  15. Observational evidence for homogeneous evolution GRB progenitor? NGC346 in SMC; Bouret et al. (2003)

  16. Z dependence of GRB progenitor evolution

  17. Future Work • Understand better GRB formation channel and its rate as a function of metallicity.

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