Extending the Search
with GMOS
Figure 2.
(Top): Hα evolution
of SN 2011ja during
the first 8 months. The
degredation of the red
peak at ~2,500 km/s is a
sign of dust formation.
(Bottom): Full
spectroscopic evolution
of SN 2011ja over the
first two years.
Over the past decade, our team has been using ground- and space-based optical and IR
imaging and spectroscopy to look for signatures of dust formation in young CCSNe. In
particular the size and sensitivity of GMOS
has allowed us to follow a collection of objects for years after explosion in a search for
the three telltale signs of grain condensation.
First, as dust forms, the optical luminosity
will decrease while almost simultaneously
the near-infrared (NIR) will increase, as the
dust grains absorb the shorter wavelength
light and re-emit it in the IR. Grain formation
will also alter the optical spectrum, creating
asymmetric and blue-shifted lines as the
dust grains attenuate the red (receding) side
of the ejecta preferentially.
And while we initially believed that the dust
grains could only condense 300-600 days after explosion (when the ejecta had expanded and cooled) there have been more and
more confirmed cases of dust forming much
earlier, within 100 days of explosion.
An early onset of dust formation can occur when shocks interact with nearby circumstellar material (CSM), creating an area
known as the cool dense shell (CDS) with
temperatures and densities appropriate for
grain growth. This not only allows a separate
channel for dust formation in CCSNe, but
can also reveal important properties of SN
evolution and progenitor mass loss.
In February 2012, we also began using
GMOS in an extensive observing campaign
on SN 2011ja in NGC 4945 (F