Double detonations in double white dwarf binaries Ken Shen (UC - - PowerPoint PPT Presentation

Carnegie / 05 August 2015

Double detonations in double white dwarf binaries

(Warren+ ’05)

C/O core Helium layer Ken Shen (UC Berkeley) He WD or ! low-mass C/O WD + helium layer

?

Double detonations: Overview

• Taam / Nomoto / Woosley+ / Livne+ in 1980s-1990s!

! ! !

• MPA / Woosley & Kasen / etc. in 2000s-2010s!

! ! !

• Helium shell detonation → inward converging shock

wave → carbon core detonation!

! ! !

• Pure detonations of ~1.0 Msol C/O WDs:!

decent match to SNe Ia (Shigeyama+ ’92, Sim+ ’10, Kromer+ ‘10)

Ken Shen

(Fink+ ’07) He C + O

r [1000 km] r [1000 km] z [1000 km] z [1000 km] ρ [107 g cm−3]

• 6
• 6
• 4
• 4
• 2
• 2

1 1 1 2 2 2 2 2 3 3 3 4 4 4 4 4 5 5 5

t = 0.40 s t = 0.70 s t = 1.00 s t = 1.09 s

Double detonations: Overview

# of papers mentioning “double detonation” and “white dwarf” # of papers mentioning “supernova” and “white dwarf” (Google scholar)

• 1985

1990 1995 2000 2005 2010 0.02 0.04 0.06 0.08

• Ken Shen

He detonations via stable accretion and convection (~106 yr)…

• 1980s-1990s (Nomoto / Woosley / et al.): stable H-burning or He MS donor (sdB/sdO)!
• Late 2000s (Bildsten, Shen, et al.): low-mass He WD donor (low mass ratio, pre-AM CVn)!
• For “large enough” He shell, convective transport is inefficient → strong turbulent fluctuations

Convective He envelope C/O core He-burning layer

Ken Shen

…Or He detonations via dynamical accretion (~100 s)

• 2010s (Guillochon / Dan / Raskin / Pakmor):!

Dynamical processes during He + C/O or C/O + C/O WD merger!

• Especially if all double WD binaries merge (Shen ’15a)

(Guillochon+ ’10)

Helium WD or low-mass C/O WD + helium layer

Ken Shen

rhotspot ρ, T cold fuel hot fuel

• Spontaneous initiation via Zel’dovich gradient mechanism → minimum rhotspot
• Hotspot expectations: T ~ 109 K, ρ = 105 - 106 g/cm3
• Shen & Moore ’14: Small CNO pollution + complete nuclear network

→ Minimum rhotspot < 10-100 km, helium detonation easy to ignite

First detonation: Does the helium ignite? Likely yes

C/O core

Ken Shen

• Helium detonation propagates for Menv > 0.004 Msol!
• 0.7 Msol C/O WD donor has ~0.01 Msol He layer!
• Smallest (first) helium detonations → 28Si + 40Ca + unburnt 4He!
• No IGE!
• High velocity features? Asymmetry (accretion stream, point explosion, etc.)?

(Shen & Moore ’14)

Does the helium detonation propagate? Yes, even for small shells

Menv (M) Xi

MWD = 1.0 M

103 102 101 104 103 102 101 1

28Si 40Ca 44Ti 48Cr 52Fe 56Ni

C/O core Unburnt helium shell Post-shock radial expansion Burnt helium ashes

Ken Shen

(Fink+ ’10)

2 4 6 8 r [1000 km]

• 10
• 5

5 10 z [1000 km]

ρ7

0.0 0.4 0.7 1.1 1.5 1.9 2.2 2.6 1.60 s

• Impossible to resolve ignition in full-star 2D sim

(burning lengthscale ~ 0.1-1 cm ; RWD ~ 108-9 cm)!

! ! !

• Shen & Bildsten ’14: zoom in on the inner 103 − 105 cm

around focal point in 1D spherical symmetry!

• C/O easy to ignite via converging shocks!
• O/Ne very difficult (high primary mass cutoff)!
• Lower densities difficult (low primary mass cutoff)!

! ! !

• Also the possibility of “edge-lit” detonation!
• Not well-studied yet

Second detonation: Does the C/O ignite? Likely yes

Ken Shen

How does a surviving companion influence the remnant?

• If it survives, RLOF companion (non-degenerate or WD) casts shadow

Density Temperature

(Shen ‘15b)

Ken Shen

(Winkler+ ’14)

SN 1006, Hα Tycho, 24 µm

(Williams+ ’13)

SNR forward shock is usually spherical (more or less) LMC 0509, Hα

(Warren & Hughes ’04)

Kepler, Hα RCW 86, Hα

(Blair+ ’91)

• Almost certainly dominated by ISM inhomogeneities, but could mask ejecta asymmetry

(Smith ’97)

Ken Shen

Tycho, Fe Kα

(Warren+ ’05)

Reverse-shocked ejecta less spherical LMC 0509, Fe L Kepler, Fe Kα

(Cassam-Chenaï+ ’04) (Warren & Hughes ’04)

Ken Shen

vforward shock = 5000 km/s vforward shock = 3000 km/s γ = 1.2 γ = 5/3 Reverse-shocked SN ejecta Forward-shocked ISM

Emission maps

Density2 integrated along line of sight, viewed at 30°

(Shen ‘15b)

Ken Shen

Density Temperature

(Shen ‘15c)

How does the ejecta influence a surviving companion WD?

• If WD companion survives, will be shock heated and polluted with 56Ni

Ken Shen

How does the ejecta influence a surviving companion WD?

• Hydro simulation with FLASH, spherically average and map to MESA for stellar evolution

(e.g. Pan+, Shappee+)!

• q56 = 1017 erg/g ~ qbinding ~ 1017 erg/g (for cold 0.6 Msol WD)

(Shen ‘15c)

SN 2011fe Kepler Tycho SN 1006

MV ∼ 3.1 0.2 M 0.6 M, most Ni removed 0.6 M, max κ 1 10 102 103 1 10 102 103 104 105

Time [yr] Luminosity [L] and Teff [K]

Ken Shen

• Merging double WD systems with primary WD mass > 0.9 Msol likely lead to detonation!
• Companion WD < 0.7 Msol: helium triggers double detonation!
• Companion WD > 0.7 Msol: direct carbon ignition (“violent merger”) can occur!

!

• Helium WD companion not detonated by the SN ejecta if at the proper binary separation!

!

• Supernova remnant consistent with observed SNRs!
• Forward-shocked ISM spherical!
• Reverse-shocked ejecta roughly spherical!

!

• Appearance of surviving WD companion!
• Likely bright and blue, very high proper motion!
• Probably not seen in Tycho or Kepler!
• Suggests WD companion nearly or completely disrupted prior to ignition

Summary

Ken Shen

C/O WD H MS

• r giant

Detonation during double degenerate merger Single degenerate

C/O WD C/O WD

Explode No shock interaction Depending on timescale No H seen Nothing seen pre-explosion Ex-companion not seen post-Ia Rates Circumstellar absorption Okay for some,! but not for all Depending on timescale Depending on clumping SN remnant IGE production

C/O WD He WD C/O WD

• r

Long-lived double degenerate merger

Summary

+ + +

Ken Shen

Questions

• Can IGE production problem be avoided with sub-Chandrasekhar detonations?!

! ! ! ! !

• If WD companion disrupted prior to ignition, is there an observable signature (polarization, SNR

appearance, early-time excess)? If WD companion survives, why don’t we see it?

Ken Shen