53° CONGRESSO SAIT

PISA, 4 - 8 MAGGIO 2009

SN 2008ha and SN 2008S:SN 2008ha and SN 2008S: is there a role for the is there a role for the

super-asymptotic giant branch super-asymptotic giant branch stars?stars?

M.L. PumoM.L. PumoINAF - 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

Classification scheme Classification scheme of SNeof SNe(e.g. Hillebrandt & Niemeyer 2000; Hamuy 2003; Turatto 2003; Turatto et al.

2007)

Adapted from Turatto, LNP, 2003, 598, 21

UncertaintiesUncertainties

• 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

SN2008ha & SN2008SSN2008ha & 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: ~ 2,3·103 km·s-1

Amount of ejected 56Ni: ~ 3-5·10-3 M⊙

Bol. luminosity: ~ 1041 erg·s-1 (at peak)

Circumstellar material: NO interaction

Signatures of hydrogen features: NO

PANEL A

Ejecta velocities: ~ 3·103 km·s-1

Amount of ejected 56Ni: ~ 1-2·10-3 M⊙

Bolometric luminosity: ~ 1041 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

SNe SNe triggeredtriggered by by electron-captureselectron-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

SN2008ha SN2008S

MONe ~ 1.375 MM⊙⊙EC reactions

(on 24Mg, 24Na, 20Ne,20F)

Core collapse⇓

“weak” SN:explosion ener. ~ 1050

ergejecta vel. ≲ 3·103 kms-1

ejected 56Ni ~ 2-4 ·10-3

M⊙

super-AGB stellar super-AGB stellar modelsmodels(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:

MONe → 1.375 M⊙

ec-SN

su

per

-AG

B

1.37 M⊙

Total stellar mass: core mass + envelope mass

time

En

velo

pe

M1 < M2 < M3

Mc1 < Mc2 < Mc3

t1 > t2 > t3

Core

Natural diversity in the optical display of the ec-SNe!

Different initial mass ⇒ core mass at the end-CB ⇒ time

t1 t2t3

Preliminary resultsPreliminary resultsSN2008ha: super-AGB with Mini ~ MN

SN2008S: super-AGB with Mini slightly larger (~ 0.6M⊙)

SN2008ha: progenitor with Mini = MN

SN2008S:

progenitor with Mini = MN+ 0.6M⊙

CommentsComments

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)

Thank youThank you

Stellar mass & the Stellar mass & the

ZAMSZAMS

Mup Mmas MZAMS (~ 7-9M⊙) (~ 11-13M⊙)

AGB:low-mass &

intermediate-massSuper-AGB massive

MZAMS < Mup: unable to ignite core C-burn.

MZAMS ≥ Mmas: able to evolve through all nuclear burning stages

After H- & He-burn. → partial degenerate CO core

C-burn. (off-centre) → through a flash

Super-AGB StarsSuper-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)

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

Mfcore =MEC ~ 1.37

MM⊙⊙ Mf

core< MMECEC

collapsing electroncaptures supernovae

Neutron star

NeO White Dwarf

Final fateFinal fate(Nomoto, 1984, ApJ)

Interplay between mass loss Interplay between mass loss

and core growthand core growth

1.37 M⊙

Mend,2

Mend,1

Mend,2 NeO White Dwarf

Mend,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 MN (transition NeO WD / EC SN)

(e.g. Woosley et al. 2002, ARA&A)

The C-burning The C-burning nucleosynthesisnucleosynthesis

12C(12C,α)20Ne

12C(12C,p)23Na

16O(α,)20Ne

12C (> 0.015) potential trigger of explosion!

↓

Complete disruption of the star

(Gutierrez et al. 2005 A&A)

20Ne (~ 0.15-0.35),16O (~ 0.5-0.7), 23Na (~ 0.03-0.05)

+

p and α available for nucleosynthesis up to 27Al

Nucleosynthesis in the NeO coreNucleosynthesis in the NeO core

22Ne(α,n)25Mg

n: 16O, 20Ne, 23Na, 25Mg → 17O, 21Ne, 24Mg, 26Mg

22Ne(α,)26Mg

α particle:

protons:

26Mg(p,)27Al

23Na(p,α)20Ne

23Na(p,)24Mg

Second dredge-upSecond dredge-upfeatures highly depend on Mini

Garcia-Berro & co-workers 1994,1996, 1997, 1999 ApJ (Z=0.02)

Mini~ Mup

(3.46·107 yr) (3.50·107yr)

Mini~ Mmas

(1.67·107 yr) (1.77·107yr)

(3.35·107 yr) (3.36·107yr)

Mini < Mmas

Second dredge-outSecond dredge-out

Mini value depends on Z and mixing treatment

Mini = 9.5 – 10.8M⊙ if Z =10-5 - 0.02

Mini ~ 7.5M⊙ with ovsh.

Connessione MN – 2DUP

Evoluzione finale e Evoluzione finale e massa Mmassa MNN