Download - 53° CONGRESSO SAIT PISA, 4 - 8 MAGGIO 2009
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