1. 53° CONGRESSO SAIT PISA, 4 - 8 MAGGIO 2009 SN 2008ha and SN 2008S: is there a role for the super-asymptotic giant branch stars? M.L. Pumo INAF - Osservatorio Astronomico di Padova & INAF – Osservatorio Astrofisico di Catania In collaboration with: M. Turatto, S. Benetti, M.T. Botticella, E. Cappellaro, A. Pastorello, S. Valenti, L. Zampieri

2. Classification scheme of SNe (e.g. Hillebrandt & Niemeyer 2000; Hamuy 2003; Turatto 2003; Turatto et al. 2007) Adapted from Turatto, LNP, 2003, 598, 21

3. Uncertainties Theoretical: uncertainties in modelling stellar evolution and explosion mechanism Observational: “sparse” direct detections of progenitor stars and non-fully reliable classification of the SN events (e.g. Woosley et al. 2002; Heger et al. 2003; Turatto et al. 2007; Smartt et al. 2008) Nature of the CC-SNe progenitors (i.e. initial mass; stellar structure and composition at the explosion; kind of collapse: iron-CC or not) having the required properties to reproduce the different observational features

4. SN2008ha & SN2008S  “exotic” scenarios SN2008ha (e.g. Foley et al. 2009): Accretion Induced Collapse SN2008S (e.g. Smith et al. 2009; Berger et al. 2009): LBV eruption of a star of ≲15M ⊙  alternative scenario (Valenti at al. 2009; Botticella et al. 2009) Ejecta velocities: ~ 2,3·10 3 km·s -1 Amount of ejected 56 Ni: ~ 3-5·10 -3 M ⊙ Bol. luminosity: ~ 10 41 erg·s -1 (at peak) Circumstellar material: NO interaction Signatures of hydrogen features: NO PANEL A Ejecta velocities: ~ 3·10 3 km·s -1 Amount of ejected 56 Ni: ~ 1-2·10 -3 M ⊙ Bolometric luminosity: ~ 10 41 erg·s -1 (at peak) Circumstellar material: interaction Progenitor: star of ~10 M ⊙ + “thick” CSM envelope PANEL B electron-capture SN (ec-SN) from super-AGB progenitor

5. SNe triggered by electron-captures (e.g. Miyaji et al. 1980; Nomoto 1984; Kitaura et al. 2006; Wanajo et al. 2009) Stellar structure of super-AGB progenitors having the required properties to reproduce all the observational features SN2008haSN2008S M ⊙ M ONe ~ 1.375 M ⊙ EC reactions (on 24 Mg, 24 Na, 20 Ne, 20 F) Core collapse ⇓ “weak” SN: explosion ener. ~ 10 50 erg ejecta vel. ≲ 3·10 3 kms -1 ejected 56 Ni ~ 2-4 ·10 -3 M ⊙

6. super-AGB stellar models (e.g. Siess & Pumo 2006; Pumo 2006; Siess 2007; Poelarends et al. 2008) AGB super-AGB Adapted and taken from Pumo, 2006, PhD thesis, Catania Univ. The most massive super-AGBs: M ONe → 1.375 M ⊙ ec-SN super-AGB

7. 1.37 M ⊙ Total stellar mass: core mass + envelope mass time Envelope M 1 < M 2 < M 3 M c1 < M c2 < M c3 t 1 > t 2 > t 3 Core Natural diversity in the optical display of the ec-SNe! Different initial mass ⇒ core mass at the end-CB ⇒ time t1t1 t2 t2 t3t3

8. Preliminary results SN2008ha: super-AGB with M ini ~ M N SN2008S: super-AGB with M ini slightly larger (~ 0.6M ⊙ ) SN2008ha: progenitor with M ini = M N SN2008S: progenitor with M ini = M N + 0.6M ⊙

9. Comments Other observations are necessary to confirm our hypothesis! Theoretical: existence of ec-SNe from super-AGBs confirmed in more refined future studies Observational: information deduced from observations not substantially changed by new observational data SN2008S and SN2008ha: ec-SNe from super-AGBs, without resorting to “exotic” scenarios Other transients (NGC300 OT2008-1; M85 OT2006-1) and “faint” SNe (SN2007J; II-P SNe)

10. Thank you

11. Stellar mass & the ZAMS M up M mas M ZAMS (~ 7-9M ⊙ ) (~ 11-13M ⊙ ) AGB: low-mass & intermediate-mass Super-AGB massive M ZAMS < M up : unable to ignite core C-burn. M ZAMS ≥ M mas : able to evolve through all nuclear burning stages

12. After H- & He-burn. → partial degenerate CO core C-burn. (off-centre) → through a flash Super-AGB Stars After flash: development of a flame that reaches the stellar centre, transforming the CO core into a NeO mixture C-burn. proceeds outside the core before extinguishing, just leaving H- & He-burn. shell (e.g. Garcia-Berro & Iben 1994 ApJ; Pumo & Siess 2007, ASPCS )

13.  Structure is similar to the one of AGB stars, except that their cores are: more massive (1-1.37M ⊙ ) made of Ne (15-30%) and O (50-70%)  After completion of C-burn., the core mass increases due to the H-He double burn. shell AGB Super-AGB

14. M ⊙ M f core =M EC ~ 1.37 M ⊙ M EC M f core < M EC collapsing electron captures supernovae Neutron star NeO White Dwarf Final fate (Nomoto, 1984, ApJ)

15. Interplay between mass loss and core growth 1.37 M ⊙ M end,2 M end,1 M end,2 NeO White Dwarf M end,1 Neutron Star mass loss so efficient ↓ envelop is lost before the core has grown above ~ 1.37 M ⊙ The minimum initial mass for the formation of a neutron star is usually referred to as M N (transition NeO WD / EC SN) (e.g. Woosley et al. 2002, ARA&A)

16. The C-burning nucleosynthesis 12 C( 12 C,α) 20 Ne 12 C( 12 C,p) 23 Na 16 O(α,  ) 20 Ne 12 C (> 0.015) potential trigger of explosion! ↓ Complete disruption of the star (Gutierrez et al. 2005 A&A) 20 Ne (~ 0.15-0.35), 16 O (~ 0.5-0.7), 23 Na (~ 0.03-0.05) + p and α available for nucleosynthesis up to 27 Al

17. Nucleosynthesis in the NeO core 22 Ne(α,n) 25 Mg n: 16 O, 20 Ne, 23 Na, 25 Mg → 17 O, 21 Ne, 24 Mg, 26 Mg 22 Ne(α,  ) 26 Mg α particle: protons: 26 Mg(p,  ) 27 Al 23 Na(p,α) 20 Ne 23 Na(p,  ) 24 Mg

18. Second dredge-up features highly depend on M ini Garcia-Berro & co-workers 1994,1996, 1997, 1999 ApJ (Z=0.02) M ini ~ M up (3.46·10 7 yr) (3.50·10 7 yr) M ini ~ M mas (1.67·10 7 yr) (1.77·10 7 yr) (3.35·10 7 yr) (3.36·10 7 yr) M ini < M mas

19. Second dredge-out M ini value depends on Z and mixing treatment M ini = 9.5 – 10.8M ⊙ if Z =10 -5 - 0.02 M ini ~ 7.5M ⊙ with ovsh.

20. Connessione M N – 2DUP

21. Evoluzione finale e massa M N