Progress in radiative transfer modelling

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Progress inradiative transfer modelling

• First International Conference on Physics at
  GaißachTeilbereich C5 Type Ia Supernovae and
  Cosmology

Tadziu Hoffmann Universitätssternwarte München
A. W. A. Pauldrach, P. Hultzsch, D. Sauer, W.
Hillebrandt
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SN Ia as distance indicators

• Most important characteristics of Type Ia
  supernovae
• SN Ia are very bright (? visible at
  large distances)
• SN Ia are calibratable standard candles (we know
  their absolute luminosities)

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SN Ia as distance indicators
surprising result Distant SNe Ia appear
fainter than standard candles in an empty
Friedmann model of the universe!
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SN Ia as distance indicators
surprising result Distant SNe Ia appear
fainter than standard candles in an empty
Friedmann model of the universe!
SN Ia luminosity distances indicate
accelerated expansion!
Are SNIa Standard Candles independent of age? Or
is there some evolution of SN Ia luminosity with
age?
Spectroscopy is a powerful tool to search for
differences!
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Observed SN Ia spectra

• Early epochs
• (lt 2 weeks after maximum)
• No H and He lines
• Prominent absorption features of mainly
  intermediate-mass elements embedded in
  anonthermal pseudo-continuum (SiII, OI, SII,
  CaII, MgII, ) ? photospheric epoch
• Characteristic P-Cygni line profiles
• blue-shifted absorption
• red-shifted emission
• broad lines ? high velocities of ejecta

SN 1992A at early phases 5 days after B maximum
HST spectrum, Kirshner et al., ApJ 415, 589 (1993)
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Models for Type Ia Supernovae
Are SNe Ia standard candles in a cosmological
sense? Required Realistic Models and Synthetic
Spectra of Type Ia Supernovae
Comparison
Explosion model v(r), ?(r), composition
NLTE model J?(r), ni(r), synthetic spectrum
Observed spectrum
elaborate theory and sophisticated models required
Hillebrandt et al.
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Different approaches tomodelling spectra

• SYNOW (Branch et al.)
• large number of adjustable parameters(essentially
  each line is fitted separately)
• Monte Carlo (Mazzali Lucy)
• inner boundary assumed to be Planck function
• assumes pseudo-LTE for occupation numbers
• detailed non-LTE (Pauldrach et al.)
• occupation numbers computed consistently with
  radiation field
• previously diffusion approximation at inner
  boundary
• now new (more consistent) approach toinner
  boundary condition (more on this later)

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Theory of expanding atmospheres
key aspects of theoretical activity basic
theoretical ideas Milne E.A., 1926, MNRAS 86,
459 Sobolev V., 1957, Sov. AA J. 1, 678
theoretical basis Lucy L. B., Solomon P., 1970,
ApJ 159, 879 Castor J.I., Abbott D.C., Klein R.,
1975, ApJ 195, 157
X-rays and wind shocks Cassinelli, J., Olson, G.,
1979, ApJ 229, 304 Lucy L. B., White,R., 1980,
ApJ 241, 300 Owocki S., Castor, J., Rybicki, G.
1988, ApJ 335, 914
aspects of radiative transfer Rybicki G.B., 1971,
JQSRT 11, 589 Hummer D.G., Rybicki G.B., 1985,
ApJ 293, 258
basis of our theoretical framework Pauldrach
A.W.A., Puls J., Kudritzki R.P.,1986, AA,164,86
Pauldrach A.W.A., 1987, AA, 183, 295 Puls J.,
Pauldrach A.W.A., 1990, PASPC 7, 203 Pauldrach
A.W.A. et al., 1994, AA, 283, 525 Feldmeier A.
et al., 1997, AA 320, 899 Pauldrach A.W.A. et
al., 1998, ASPCS 131, 258 Pauldrach A.W.A.,
Hoffmann T.L., Lennon M., 2001, AA, 375, 161
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Models for expanding atmospheres
epoch, density, luminosity, abundances
minimalset of inputparameters
synthetic spectrum
observed spectrum
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Models for expanding atmospheres
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Models for expanding atmospheres
EUV line blocking and blanketing drastic
effects on ionization, excitation, and emergent
fluxreason the velocity field shifts at
different radii up to 1000 spectral lines into
the line of sight at the observers frequency
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Observed and synthetic SN Ia spectra
SN 1992A at early phases 5 days after B maximum
Models based on W7 explosion model averaged
chemical composition above the photosphere (Nomoto
et al., 1984, ApJ. 286, 644)
with line blocking
without line blocking
Pauldrach et al., 1996, AA 312, 525
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Spectra and ionizing fluxes
Example ? Puppis
ionization stages depend on ionizing radiation?
influence can be traced by UV spectral lines
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Detailed analysis of O-stars
hot supergiant?? Pup
.
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Observed and synthetic SN Ia spectra
SN 1992A at early phases 5 days after B maximum
Models based on W7 explosion model averaged
chemical composition above the photosphere (Nomoto
et al., 1984, ApJ. 286, 644)
Sauer Pauldrach, 2002, Nuclear Astrophysics,
MPA/P13
Nugent et al., 1997, ApJ 485, 812
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Results (1)
D. Sauer

• Fairly good reproduction of the main features of
  the spectrum esp. in the blue and UV range
• Some features are too deep
• Too much flux towards red and IR range

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Radiation field at inner boundary
Radiation field does not approach the Planck
function even at great depth!
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Opacities at inner boundary
O star
SN Ia
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Reasons for discrepancy

• Problem Inner boundary for radiative transfer
• Optical depth scale remains strongly
  wavelength-dependent even at large mean ?.
• Large optical depths in lines but no true
  continuum! Locally optically thin between lines
  even in great depths. Electron scattering does
  not help!
• No regime where radiative diffusion really valid.
  Diffusion approximation for radiation field does
  not provide a realistic flux.
• However Nebular approach also not valid!

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Modified inner boundary condition for Type Ia
Supernovae
Modifications to the inner boundary that allow
deviations of the radiation field from thermal
equilibrium conditions. The dominating
contribution from Thomson scattering is
explicitly taken into account
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Results new boundary condition
Striking improvement!
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Models for Type Ia Supernovae
Are SNe Ia standard candles in a cosmological
sense? Required Realistic Models and Synthetic
Spectra of Type Ia Supernovae
Comparison
Explosion model v(r), ?(r), composition
NLTE model J?(r), ni(r), synthetic spectrum
Observed spectrum
23
SN Ia as distance indicators
surprising result Distant SNe Ia appear
fainter than standard candles in an empty
Friedmann model of the universe!
SN Ia luminosity distances indicate
accelerated expansion!
Are SNIa Standard Candles independent of age? Or
is there some evolution of SN Ia luminosity with
age?
Spectroscopy is a powerful tool to search for
differences!
24
The End