Astron. Astrophys. 345, 211-220 (1999)

Improved Monte Carlo techniques for the spectral synthesis of supernovae

L.B. Lucy

ST-ECF, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany

Received 15 September 1998 / Accepted 20 November 1998

Abstract

Improvements in Monte Carlo techniques for computing synthetic spectra of supernovae (SNe) are described and tested using a simplified model for the atmosphere of a Type Ia SN. In the first innovation, a procedure is implemented that replaces the previously-assumed line formation by resonance scattering with a branching model using Sobolev escape probabilities, and the resulting improvement is demonstrated by comparison with exact calculations for FeII . In a second innovation, greatly accelerated convergence is achieved in the computation of emergent spectra by replacing the crude procedure of binning escaping Monte Carlo quanta with one based on the formal integral for emergent intensity. This is made possible by extracting line- and continuum source functions from a Monte Carlo simulation. Because of accelerated convergence, the required size of the Monte Carlo simulations is reduced by a factor , thus greatly speeding up the calculation of model spectra and thereby allowing interactive diagnostic analyses of the spectra of newly-discovered SNe.

Key words: radiative transfer methods: numerical stars: atmospheres stars: supernovae: general

Present address: Astrophysics Group, Blackett Laboratory, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BZ

Send offprint requests to: L.B. Lucy

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Contents

• 1. Introduction
• 2. Physical model
• 3. Line lists
• 4. Monte Carlo procedures
  • 4.1. Branching
  • 4.2. Line absorption rate
  • 4.3. Scaling
  • 4.4. Relativistic terms
• 5. Emergent spectrum
  • 5.1. Basic idea
  • 5.2. Line source function
  • 5.3. Continuum source function
  • 5.4. Monte Carlo estimator for
  • 5.5. Formal integral
• 6. Numerical results
  • 6.1. Line formation
  • 6.2. Emergent spectrum
  • 6.3. Implications
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999
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