Spectrum Synthesis
and Supernovae
Peter Nugent (LBNL)
The acceleration is 6 years
old…
…well more like 6 Gyr, we’re just slow at
figuring it out.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
2
How do we measure it?
The dynamics of space is described by the expansion rate
of the Universe as a function of time.
An astronomical source emits a signal at
time t0 which we detect now at time t1
Over this time the distance between the
source and the observer changes from
d0 to d1.
Comparing the observed and absolute
luminosities of the source tells us
about d1 through the inverse square
law.
Comparing the observed and emitted
wavelengths or the signal tells us about
d1 / d0. This we label the redshift.
Relating d0 to d1 tells us about the integrated expansion rate of the Universe
over that period and repeating this for sources at different distances tells
us how the expansion rate has changed over time.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
3
Distances and Redshifts
Redshifts are easy to measure.
- A simple spectrum gives you the wavelengths.
Distances are very difficult.
- Astronomers typically measure distances with standard candles.
- They need to be seen across the universe, they have to be
bright!
- Their brightnesses need to be well calibrated.
- The objects can't change or evolve as a function of the
universe's
age or expansion history.
All roads lead to Type IaIPAM
Supernovae...
Workshop IV: Transfer
Peter Nugent
Phenomena
4
Type Ia Supernovae
Type Ia Supernovae are
bright:
For a few weeks they are as
bright as the entire galaxy
they originated in.
"Before" and "After" for SN 1999be.
Type Ia Supernovae are very similar:
They give reliable distances to better
than 10% and their brightness don't
appear to change as a function of the
age of the universe.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
5
Lightcurves and Spectra
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
6
Differences Calibrated
In 1993 Mark Phillips
discovered the correlation
between peak brightness and
lightcurve shape.
Brightness
This allowed one to calibrate
SNe Ia to about 8% in
distance.
Peter Nugent
The race was on…..
time
IPAM Workshop IV: Transfer
Phenomena
7
Hubble Diagram
The Calan/Tololo
Survey by Hamuy et al.
pinned the low-z part
of the Hubble diagram,
while the work of
Riess et al. and
Perlmutter et al. got the
high-z end.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
8
Contours
The data showed that SNe Ia were
fainter at their observed redshifts than
they would have been given an ΩM=1
by 10-sigma…
…and in addition they were fainter
than they would have been in an
empty universe, indicating
acceleration.
Theorists rejoice, Dark Energy is born!
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
9
Now What?: The Past 2 Years
Many groups have gone out to test these measurements:
 More, more, more!
 Look for signs of dust.
 Compare subsets in different environments.
Thanks to B. Schmidt, A. Riess and C. Lidman
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
10
Host Galaxy Studies
Sullivan et al. (2003)
Ellipticals
&
Spirals
Over 30 SNe Ia host galaxies at high-z observed with HST/STIS
photometry and with spectroscopy taken at Keck.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
11
Differences are small
Scatter about the Hubble line
was less in the E/S0 galaxies,
and they were, on average,
~0.1 magnitudes brighter than
their spiral counterparts.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
12
More, More, More!
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
13
Precision Measurements
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
14
Higher
Redshift…
Aphrodite (z~1.3)
ACS F850lp
Riess et al.
GOODs SN
Search.
~10 SNe Ia
NICMOS F110W
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
15
Concordance Cosmology
NASA and DOE
have proposed
a
Joint Dark
Energy Mission
to measure the
accelerating
universe.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
16
Where does modeling come
in?
Supernova Spectrum Synthesis Simulations:
-
Discover ways to improve them as distance indicators
-
Eliminate/Constrain systematic uncertainties
-
Real -Time assessment of data
-
Provide the link between the data and hydrodynamical models
-
Determine the nature of the progenitor
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
17
Spectrum Synthesis
1-D, Simplified Physics, Model Atmospheres
(very quick line identification & velocity determination)
SYNOW/MADSYN
3-D, Simplified Physics, Model Atmospheres
(what effects geometry has on determining distances to SNe)
SYNPOL
1-D, Full Physics, Spectrum Synthesis
(can we make SNe better for distances/cosmology)
PHOENIX
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
18
PHOENIX
PHOENIX is a state-of-the-art spectrum synthesis code which is
currently in 1-D. It treats all the applicable micro-physics
appropriately and has been used to model supernovae of all
types, the sun, novae, cool stars, red-giants, quasars and active
galactic nuclei.
Input: Luminosity, Abundances, Density and Velocity Profiles and
Non-Thermal Ionization from radioactive Ni, Co, etc.
Each of the above inputs range by an order of magnitude for SNe.
100 spatial zones, 300k wavelength points, energy conservation
and non-LTE for 50 ionic species.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
19
General Model Assumptions
 full treatment of special relativistic radiative transfer in
spherical geometry for all lines and continua,
 radiative equilibrium in the Lagrangian frame (including
all velocity terms),
 full non-LTE treatment of most ions.
 detailed profiles for the lines, fluorescence effects are
included in the NLTE treatment
 equation of state used includes up to 26 ionization stages of
40 elements as well as up to 206 molecules.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
20
PHOENIX
Radiative Transfer Assumptions:
 spherical symmetry,
 time independence,
 full special relativistic treatment in the Lagrangian frame.
Spherically symmetric, special relativistic equation of
radiative transfer
 partial integro-differential equation,
 telegrapher's equation: boundary value problem in rand
initial value problem in (certain restrictions apply)
Peter Nugent

IPAM Workshop IV: Transfer
Phenomena

21
Radiative Transfer
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
22
Basic Emissivity
More complicated for NLTE but similar in principle.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
23
Numerical Solution
Basic idea: discretize  / and treat the boundary
value problem for each wavelength individually
Operator splitting (OS) method:

 solve along characteristics of the RTE
 iterative method: piecewise parabolic ansatz to calculate I
for given J - iterate to self-consistent solution for J
 eigenvalues of iteration matrix close to unity -> use
operator splitting to reduce eigenvalues of amplification
matrix
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
24
Rate Equations
Where nj is the level population and Rij & Cij are the radiative
and collisional rates, respectively + Saha-Boltzmann.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
25
Atomic Data
Example Grotrian
diagram for Fe II:
617 Levels
1.2 million total lines
The level populations
off all species are
solved simultaneously
as a very large set of
linear equations, in
256-bit precision!
All relevant b-f and f-f transitions are included - atomic line
blanketing: about 2*106 lines dynamically selected from Kurucz
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
26
The Brightness-LC
Correlation
There exists a spectral
sequence of increasing
luminosity that
correlates very nicely
with those of the
lightcurves:
Broader-Brighter-Hotter
Nugent et al. (1995)
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
27
SN Phot-Z Templates
The spectral templates
were created by
homogenizing IUE and
HST observations +
modeling to fill in the
gaps.
Here we have the SN Ia
template every week for
the first 7 weeks. Note
the large color
evolution.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
28
SN Phot-Z Results
SN 2001jm
Best fit z = 0.96+/-0.07
The observed redshift
was z = 0.979
Success rate is ~95%
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
29
Recent Discoveries…
Synthetic spectra from
Lentz et al. (2000),
based on explosion
models by Höflich et al.
(1999).
Metallicity effects the
UV.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
30
Observed Metallicity
Nugent et al.
HST/STIS
studies of the
UV…
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
31
Metallicity and Cosmology
Understanding the
UV has large
implications for
cosmology.
Ω
UV - suppressed
UV - enhanced
Intrinsic color and
corrections for dust
Get intertwined.
ΩM
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
32
SYNPOL & 3-D Effects
SYNPOL is a relatively simple code from the physics
standpoint. A Monte Carlo code (follow the photons out)
incorporating LTE and a 2-level atom. It iteratively solves for
the temperature structure and calculates the polarization due
to electron scattering and scattering off of lines.
Input: Luminosity, Abundances, Density and Velocity Profiles
300x300x300 spatial zones, 2-4k wavelength points, energy
conservation and an atomic linelist of ~500k transitions.
1010 photons to converge in energy
1014 photons for spectropolarimetry
Full runs calculated on NERSC’s IBM SP take ~50,000 hrs.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
33
SYNPOL & 3-D Effects
We need the large number of
photons since:
 Polarization is low < 1%
 Atmosphere changes quickly on
short scales
 Many lines to interact with…
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
34
A Hole in SNe Ia?
A White Dwarf accretes
material from a companion
star, either a main sequence
Star or a Red Giant.
The companion subtends an angle ~40o.
After explosion, the SN ejecta runs over the companion
star in a few minutes to hours.
o
 This may leave a ~40 hole in the SN ejecta .
(Marietta et. al. 2000; c.f. Livne et. al. 1996)

Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
35
A Hole in SNe Ia?
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
36
A Hole in SNe Ia?
QuickTime™ and a YUV420 codec decompressor are needed to see this picture.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
37
A Hole in SNe Ia?
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
38
A Hole in SNe Ia?
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
39
Effect on Cosmology?
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
40
SN Factory
Objective is to improve
our understanding of
Type Ia Supernovae for
cosmology.
Search is carried out at
Palomar and Haleakela
and spectrophotometric
follow-up at UH 2.2-m
and other telescopes
like YALO.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
41
SN Factory
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
42
SN Factory
Not a slur,
they picked it:
FRench
Observing
Group of
Supernova
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
43
SYNOW/MADSYN
SYNOW employs
the Sobolev
approximation for
the line transfer, as
well as a “hard”
photosphere and
equivalent 2-level
atoms in LTE.
Highly
parameterized and
very fast.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
44
SYNOW/MADSYN
Input for the photosphere:
 Temperature
 Velocity
 Density (exp or pwr law)
Input for the lines:
 Optical depth
 Min and Max velocity
 Teff
Runs in < 10 sec, almost all time is spent reading Kurucz linelist.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
45
SYNOW/MADSYN
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
46
Conclusions
 Many great nearby & high-redshift programs underway now
 All will rely on computational modeling to improve our
understanding of supernovae and to constrain systematics.
 Understanding/Constraining 3-D effects will be important for
“precision” cosmology….
Peter Nugent
IPAM Workshop IV: Transfer
Phenomena
47