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New Stellar Insights
from Precision
Supernova Data
Lars Bildsten
Kavli Institute for Theoretical
Physics
University of California Santa
Barbara
Type IIP Supernova
•  Single star progenitors of 8-16 M •  Distinctive light curves that reveal the underlying
parameters (Energy, 56Ni mass) of the core collapse.
•  Though the core collapse mechanism remains a
puzzle, once launched, accurate modeling of the
shock wave propagation in the progenitor structure,
light curves and spectra is well underway!
•  Want to use the plethora of observational data to
measure the key parameters and unravel the
uncertain amount of mixing induced during shock
traversals  Maybe one case we fully understand! What they Look like
Dall’Ora et al. 2014
•  Plateau phase that
lasts 100 days
with H present at
the photosphere
•  Collapse to
radioactive
powered tail once
the photosphere
has reached inner
helium/metal
shell=> 56Ni mass
can be measured Progenitors studied in Nearby Galaxies
Smartt 2015
Stellar Luminosity at Time of
Collapse => ZAMS Mass
Smartt 2015
Cantiello, prv. comm (MESA)
Punchlines from IIP Progenitor Studies
Smartt 2015
•  18 detections of precursor objects, all with
luminosities less than 105L
•  Evolution and outcomes presumed to be from single
star evolution
•  IIP’s arise from red supergiants with masses in the
range of 8-16 M important to explosion
modeling. •  Radii range from 500-900R at this phase (see
Gonzalez-Gaitan et al. 2015)
Understanding the Brightness
•  An ejected mass M expanding at v, so R=vt, and
has with Kappa
N⇥
R2
M
tdiff
c
⇥c
Rc
•  Radiation diffusion time is >R/v=age until a time
⇥1/2
M
td ⇥
⇥ (10 20) days
vc
•  But before then the expansion is adiabatic and ⇥
Ro
since it is radiation-dominated=> T
To
R
Estimating the Luminosity
•  The luminosity is
Energy in Radiation
L⇠
Diffusion Time
•  During the adiabatic phase, T goes like 1/R, giving
L
Ro4 acTo4
M
Esn cRo
M
•  A good, rough, estimate for the peak luminosity of
Type IIP SNe (~109 L) where Ro is the initial
radius.
•  Real calculation by Popov and Kasen and Woosley.
Kasen & Woosley ‘09
Understanding the Plateau
•  During the plateau, the photosphere is working
it’s way through the Hydrogen layer, at nearly
constant Teff=6000 K. •  Moves back in Lagrangrian coordinates, taking a
time
tpl = 122 days
• 
56Ni
✓
E
1051 ergs
◆
1/4
✓
M
10M
◆1/2 ✓
R
500R
◆1/6
decay can lengthen the Plateau duration if
very abundant Dessart and Hillier 15 M model
Important work is Well
Underway
SN2012A
Pejcha
& Prieto 2015 •  Velocities evolve as time
passes and deeper parts of the
envelope become revealed.
•  Lots of data on many events
allows for first parameter
estimates to be made.
•  However, true testing of theory
and accurate inferences
requires a stronger coupling of
theory with observation.
What we hope to Learn
•  Are the data from a Type IIP SNe consistent with an
explosion of an 8-16M star? (i.e. are there any surprises?)
•  Are the implied parameters (e.g. mass and radius)
consistent with the known progenitor?
•  Can we make accurate enough inferences of explosion
energy and 56Ni masses to illuminate the core collapse
mechanism? •  What can we learn, really, about the stellar progenitor
structure, or are most details wiped out?
•  Does the mixing induced by reverse shocks deep within the
ejecta confound our work or provide a new probe? Explosion Energy-Ejecta Mass
Pejcha & Prieto 2015 Explosion Energy-56Ni Mass
Pejcha & Prieto 2015 Nebular Line Modeling
•  Late times, optically
Jerkstrand et al. 2014
thin nebular phase
•  Emission powered
by 56Co decay
•  Line intensities
inform us about
amount of elements
deep within the
object.
•  Agrees with the
implied progenitor
mass and consistent
with lightcurve.
MESA is open source:
anyone (over 700
users!) can download
the source code,
compile it, and run it for
their own research or
education purposes. Bill Paxton, Father of MESA
•  MESA now
handles shocks,
allowing for the
ejection of
envelopes from
energy
deposition deep
within
•  Comparison to
the left (Paxton
et al. 2015) is
for a 15M At 20 Days
from MESA
Paxton, prv. Comm. 2015
•  H envelope is in
homologous flow
•  Density profile of
the ejecta is well
calculated. •  Simple light
curves are
straightforward
from radiative
diffusion for the
plateau stage. New Era in Theory and Computation
well timed with the Data Explosion
•  MESA allows for a thorough exploration of progenitor
models •  MESA, SNEC and other codes can be used to run shock
waves through stars, evolve the hot, radiation dominated
ejecta, and calculate lightcurves needed for immediate
inferences. •  SEDONA, CMFGEN . . . can be used for the detailed
radiative transfer required to make accurate comparisons.
•  Combination of these capabilities + analytics with full data
sets should create a new way to probe both the stellar
progenitor and the explosion physics. One Example: Unstable Profiles & Mixing
•  The reverse shock leads
to regions of dense
Helium getting decelerated by light material.
•  Many e-foldings, depending on H envelope mass
Wongwathanarat et al. 2015 Wongwathanarat et al. 2015 Wongwathanarat et al. 2015 Minor mixing is
detectable!
Morozova et al. 2015
Indicators & Impact: Much to Do
•  Physics at H/He reverse shock location allows H to
mix to deeper layers, increasing plateau length.
•  Smoothing of the density and velocity profile will
modify the observed photospheric velocities at late
times in the plateau
•  Mixing at deeper locations can allow 56Ni to reach
higher velocity outer layers, impacting both the
light curve and the later nebula phase. •  Amount of mixing likely dependent on the H
envelope mass, yielding another useful probe of
mass loss prior to explosion. . . .