Dust around Type Ia supernovae Page: 2 of 12
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extinction law, but has to be treated through careful radiative transfer (Witt et al. 1992).
SN 2002ic, as an extreme example, was found to be associated with a massive hydrogen rich
material with mass around 6MO/(n/108crn3) (Hamuy et al. 2003; Wang et al. 2004; Wood-
Vasey et al. 2004; Deng et al. 2004). Wang et al. (2004) deduced from spectropolarimetry
observations that the hydrogen rich materials are distributed in an asymmetric, perhaps disk-
like geometry. Such a massive envelope, if exists in the Galaxy, must be easily observable.
It can in fact be identified with well studied post-AGB objects such as proto-planetary
nebulae (PPNe). The post-AGB phase is very short lived, lasting only on the order of a
few thousand years. This explains why SN 2002ic like events are rare but it also raises the
question of whether SNe Ia can occur in environment in which the surrounding nebulosity is
more diluted. PPNe ultimately evolve to planetary nebulae (PNe) which then disperse into
the interstellar medium (ISM) and leave behind white dwarfs in the center. A large fraction
of white dwarfs inside PNe are found to be likely in binary systems (De Marco et al. 2004).
The PN phase lasts for about ten to a hundred times longer than the PPN phase. Assuming
that the explosion of the central white dwarfs are unrelated to the evolution of nebulosity
outside, one can expect that there are about 10 times more SNe Ia occurring inside PNe
for every SN Ia occurring inside a PPN. Extinction to the central white dwarfs of several
PNe were observed by Wolff et al. (2000), and the dust extinction optical depth is typically
around 1. Assuming that there is no dust creation/destruction after the PPN shell ejection
and homologous expansion of the nebulae, at any later epochs the dust opacity scales as
ia(looooyear)2, where t is the dynamical age of PNe which is typically around 10,000 years.
It thus takes about 105 years for the dust to be diluted to T < 0.01 - a level that is still
sensitive to modern SNe Ia observations. Dusts in PNe are distributed in patchy opaque
clumps such as observed in the Helix nebula (O'Dell et al. 2004). These dusty clumps may
survive even longer time scales. On top of the dust ejected as PPNe during the post-AGB
phase, more dust may be ejected to the CS environment throughout the evolution path
to SNe Ia. This argues that circumstellar dust may be important and has to be analyzed
carefully for precision measurements.
3. Dust scattering and absorptions
The albedo of interstellar dust is around 0.7 in B and V filters, as was found from obser-
vations of reflection nebulae (see Draine (2003) for a review of interstellar dust properties).
This means that scattering dominates the interaction between photons and dust particles.
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Wang, Lifan. Dust around Type Ia supernovae, article, October 20, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc884055/m1/2/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.