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Preprint 06/06

Non-LTE modeling of supernova-fallback disks

K. Werner, T. Nagel, T. Rauch

Institut für Astronomie und Astrophysik, Universität Tübingen, Germany

To be published in: Astrophysics and Space Science

Abstract.
We present a first detailed spectrum synthesis calculation of a
supernova-fallback disk composed of iron. We assume a geometrically thin disk with a radial
structure described by the classical alpha-disk model. The disk is represented by
concentric rings radiating as plane-parallel
slabs. The vertical structure and emission spectrum of each ring is computed in a
fully self-consistent manner by solving the structure equations simultaneously
with the radiation transfer equations under non-LTE conditions. We describe the
properties of a specific disk model and discuss various effects on the emergent
UV/optical spectrum.
We find that strong iron-line blanketing causes broad absorption features over
the whole spectral range. Limb darkening changes the spectral
distribution up to a factor of four depending on the inclination
angle. Consequently, such differences also occur between a blackbody
spectrum and our model. The overall spectral shape is independent of the exact
chemical composition as long as iron is the dominant species. A pure iron
composition cannot be distinguished from silicon-burning ash. Non-LTE effects
are small and restricted to few spectral features.