A hypothesis or theory is clear, decisive, and positive, but it is believed by no one but the person who created it. Experimental findings, on the other hand, are messy, inexact things, which are believed by everyone except the person who did that work.
Harlow Shapley Through Rugged Ways to the Stars
Smashing White Dwarfs: Book One of the Supernovae Trilogy
Frank Timmes
SPIDERStarlib
THE ASTROPHYSICAL JOURNAL
isotopesproject100
White dwarf supernova play a key role in astronomy:
Distance indicators Element factoriesCosmic-ray acceleratorsKinetic energy sourcesBinary star terminus
Green & Yellow - iron and silicon
Blue - high energy electrons
Red - dust
Tycho Supernova Remnant:
Age: - Nov 1572Distance: ~ 8500 ly Diameter: ~ 18 ly (8 arc min) Expansion: ~ 0.0015 ly/yr
Identification of what is exploding is unknown - this is the outstanding mystery in the field.
NASA’s Spitzer, Chandra, & Spain’s Calar Alto
Constellation:Cassiopeia
Several observational characteristics help in the hunt for the progenitors of the explosions:
1) About 90% of all white dwarf supernova form a homogeneous class in terms of their spectra and light curves.
4000
wavelength in angstroms
5000 6000 7000 8000
silicon II
silicon II
cobalt IImagnesium II
calcium IIiron II
sulfer “W”
oxygen I calcium II
White dwarf supernovae are defined by their spectra: no hydrogen lines and a strong silicon absorption feature.
Kasen 2008
Pereira et al 2013
Near maximum light, spectra are characterized by O-Ca at high velocity (~20k km/s). Late nebular phase spectra are dominated by iron lines.
Pinwheel (M101)
SN 2011fe
0 20 40 60
1010
109
Lum
inosity (
L⊙
)
Time (days since peak)
Optical light curve
56Ni (τ1/2
~ 6 d) +
56Co (τ1/2
~ 77 d)
~0.6 M⊙ of 56Ni
for a typical SNIa
γ-ray escape
Expansion and Diffusion
time scales about equal
Several observational characteristics help in the hunt for the progenitors of the explosions:
1) About 90% of all white dwarf supernova form a homogeneous class in terms of their spectra and light curves.
2) Correlations between different observables, such as the peak luminosity and width of the light curve.
Kim et al 1997
Brighter is wider.
-20 0 20 40 60-17
-18
-19
-20
-20 0 20 40 60-17
-18
-19
-20
as measured
light-curve timescale“stretch-factor”corrected
days
MV
- 5
log(
h/65
)
days
MV
- 5
log(
h/65
)
Calan/Tololo SNe Ia
This empirical fact can be used to correct for variations in the peak luminosity to give a standard candle.
After correction, distances are accurate to ≤ 7% !
Surface Temperature (K)
Color
Hot Cool
Blue Red
Dim
Bright
Lum
inos
ity (
Lsun
)
106
10-4
1
Yellow
Warm50,000 6000 3000
1 Msun
Main Sequence
Red Giant
HeliumIgnites
Helium Burning to Carbon
Planetary Nebula:Tosses off Hydrogenand Helium Layers
Runs out ofHelium fuel
Carbon-OxygenWhite Dwarfin 10 billion years
H → He
He
H
HHe
C+O
C core + H envelope DA WDs
SDSS DR1, Madej et al. 2004
Mass [M⊙]
Num
ber o
f sta
rs
100
50
0
0.2 0.4 0.6 0.8 1.0 1.2
Different main-sequence stars make different white dwarfs.
Pluto White Dwarf
Radius: 1185 km
Mass: 0.18 Earth’s
Radius: 1185 km
Mass: 1.37 Sun’s
105 107 109 10110
.5
1
1.5
Central Density g cm-3
Tota
l Mas
s (M
sun)
Ideal
Ferm
i gas + General Relativity
+ Coulomb Corrections
n=3/
2 po
lytro
pe
n=3 polytrope
NeutronStar
WhiteDwarf
Supernova
A white dwarf can only have so much mass.
Single-Degenerate channel Double-Degenerate channel
Mergers:
Collisions:
The relative frequency of these channels is unknown.
Benz et al 1985
The first white dwarf smashes were calculated in 1985:
3D, 5000 particles with nuclear burning done afterwards and approximate thermodynamics.
Bottom line:Tiny amounts of 56Ni produced.
Message:Nothing here, move along.
0.6 + 0.9 Msun
0.6 + 0.6 M⨀, zero impact parameter,x-y plane,temperature.
Raskin et al 2010
2010: 2 million particles with inline burning and realistic thermodynamics.
Message in 2010: Lots of interesting possibilities!
Raskin et al 2010
Equal mass
Equal h
56N
i Yie
ld [M
๏]
00.10.20.30.40.50.6
Particle Count [x1000]0 500 1000 1500 2000
1985result
0.6 + 0.6 M⨀
.4 .6 .8 1 1.20
.5
1
1.5
Mas
s 56
Ni
(M⊙
)
Average White Dwarf Mass (M⊙)
Raskin et al 2010
Kushnir et al 2013
Range of observed 56Ni masses
Average observed mass
Collisions can cover the observed range of 56Ni masses.
Exceptionally bright white dwarf supernova have been interpreted as double-degenerate events.
0.5 1.0 1.5 2.0 2.5 3.0 3.50.0
0.5
1.0
1.5
2.0
Luminosity (1043 erg)
Nic
kel M
ass (
Msu
n)
SN 2009dcSN 2007if
SN 2003fg
SN 2006gz
SN 2005hj
Howell et al 2006
Observations suggest about 5 million white dwarf supernova per year within a redshift of one.
SDSS David Kirkby
Eugene Onegin and Vladimir Lensky’s duel.
Watercolor by Ilya Repin (1899)
An objection to the collision scenario is the perception that such collisions are extremely rare.
Collisions have been believed to predominantly occur in dense stellar environments, such as cores of globular clusters.
Even accounting for gravitational focusing, the collision rate is ~5000 white dwarf supernovae per year within a redshift of one.
σ = πb2 = πR2 1 + vescv
2
Wait! There is a 3rd body in this duel.
Eugene Onegin and Vladimir Lensky’s duel.
Watercolor by Ilya Repin (1899)
Hierarchical triple star systems with white dwarf binary orbital separations of 1-300 AU are known to exist.
3 body problem
e � 0.999999
The white dwarf binary’s ellipticity can be driven to large values in a triple star system because ellipticity can be traded for inclination in the conservation of angular momentum
Lz =�
1 � e2 cos(i)
in Kozai-Lidov oscillations.
0 20
Radii of white dwarfs
Head-on
Collision
40 60 80 100 12010
8
109
1010
1011
1012
1013
10
semimajor axis
pericenter
seperation
m1 = m2 = 0.5 M⊙ white dwarf binary
+ m3 = 0.5 M⊙ perturber
14
1015
time (x 1000 yr)
Dis
tance (
cm
)
Katz & Dong 2013
White dwarfs in a triple star system have a ~3% chance of experiencing a collision within 5 billion years.
If ~20% of white dwarfs are in triplets, the calculated supernova rate is about the same as the inferred rate.
15-20 % of 1M⊙ ≤ M ≤ 8M⊙ stars with a M > 1M⊙ companion makes the collision scenario dominant.
AO Measurements of A-stars, N=121
All binaries
Nu
mb
er
of
bin
arie
s
5
0
5
10
15
50 500 5,000 50,000
Period (years)
Msecondary > 1 M⊙
RV Measurements of red giants in open clusters, N=797
Num
ber o
f Red
Gia
nts
1
10
100
1 2 4 8 16
All Red Giants0.5 < P < 5 yr0.5 < P < 5 yr, Msecondary > 1M⊙
Mprimary (M⊙)
Klein & Katz 2016
Prediction: GAIA will find ~10 new wide orbit double degenerates within 20 pc from the Sun.
This puts a strong constraint on the “triple-assisted” collision model for white dwarf supernovae.
1) Silicon, Sulfur, Calcium ratios
2) Unburned carbon and oxygen
3) Tidal tails
4) Sufficient number of binary WDs
5) Early gamma-rays
6) Narrow hydrogen emission or absorption
7) Circumstellar interaction in radio or x-rays
8) Gravitational wave signatures
9) Frequency as a function of redshift
Advances (plus a little serendipity) over the next decade should enable us to decipher the progenitors of white dwarf supernovae:
0.1 - 1.0 M☉ 56Ni for the light curve
0.2 - 0.4 M☉ Si, S, Ar, Ca for the spectrum
< 0.1 M☉ 54Fe + 58Ni for the nucleosynthesis
Allow for some diversity for the population
A successful model starting from a carbon+oxygen white dwarf must make
Raskin et al 2010
0.8 + 0.6 M⨀, zero impact parameter,density
Raskin et al 2010
0.8 + 0.6 M⨀, zero impact parameter,density, zoomed
Raskin et al 2010
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