he debate on the progenitors of Type Ia supernovae (SNe) has not been
settled yet. There is consensus on that the SN is a thermonuclear
explosion of
a white dwarf which is in a binary system, but the structure of the
companion
star is heavily debated. One possible scenario is that the companion is a
normal main-sequence or a red giant star, and the white dwarf gains mass
via
mass transfer through the L1 point before exploding. Another possibility
is
that the companion is also a white dwarf and the explosion occurs via
merging
of the two white dwarfs. Alternatively, the collision of two white dwarfs
in a
triple system has also been suggested as a possibility.
I present observations that strongly favor the first scenario, i.e. the
normal
companion + white dwarf system ("single degenerate model"). We observed
signs
of the collision between the SN blast wave and a companion star shortly
after
the explosion of SN 2012cg, a normal Ia supernova. Comparison with models
suggests that the companion was probably a main-sequence star and not a
red
giant. Such an interaction is not expected in the other scenarios invoking
two white dwarfs. I intend to talk about the details of this interesting
discovery and its implications for future studies.
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