A Near-infrared Shift
Although SNe Ia remain the most proven
technique for studying dark energy, we do
not understand the nature of these explosions, and that ultimately limits their accuracy. Fortunately, shifting the observations
to the near-infrared offers a way forward. In
the near-infrared, SN Ia luminosities are less
affected by dust and show much smaller intrinsic scatter than in the optical. A recent
study, also using Gemini data, demonstrated
an amazing distance accuracy of 6 percent
using SN Ia peak luminosity in the near-infrared (Barone-Nugent et al., 2012).
A key ingredient to realizing the full potential
of near-infrared SN Ia cosmology is near-infrared spectroscopy, which allows us to convert
the peak luminosities to the rest frame. With
the limited size of the world’s current sample,
the time evolution and the diversity of the
near-infrared spectral features are poorly understood. These uncertainties directly affect
the determination of the peak luminosity.
To improve our knowledge of this relatively
unexplored wavelength region, the Carnegie
Supernova Project and the CfA Supernova
Group have embarked on a joint program
to obtain a statistically significant sample of
near-infrared spectroscopic observations.
On August 24, 2011, SN 2011fe was detected
within hours of its explosion in M101 (Figure
1; Nugent et al., 2011). Its proximity and early
detection provided a unique opportunity to
make exquisitely detailed observations of a
supernova. SN 2011fe appears to have been
a typical SN Ia in all respects and serves as an
ideal baseline to compare to other objects.
Ten near-infrared spectra of SN 2011fe were
obtained in the span of a month, including
one SpeX spectrum and nine GNIRS spectra.
We present two of the more intriguing findings from our recently published paper on
these near-infrared spectra (Hsiao et al., 2013).
April2013
Primordial Carbon in
Type Ia Supernovae
Figure 2.
During a SN Ia explosion, the thermonuclear
burning front rips through the carbon-oxygen white dwarf, converting carbon and
oxygen into heavier elements. Since oxygen
is also converted from carbon in this process,
carbon provides the most direct probe of
the primordial material from the progenitor carbon-oxygen white dwarf. Because
conditions in the explosion models, such as
the speed of the burning front, sensitively
control the amount of carbon that remains,
the detection of carbon in observed spectra
serves as one of the most important discriminators between explosion models.
The first convincing detection of carbon in a
SN Ia was presented not long ago by Thomas
et al., (2007). Since then, several studies using
large and independent sets of optical spectra have reached the same conclusion that
GeminiFocus
SYNAPPS (Thomas
et al. 2011) model
spectrum fit to the
GNIRS spectra of SN
2011fe around the
near-infrared carbon
line. The observed
spectra are plotted as
solid black curves. The
best-fit model spectra
are plotted as follows:
with all ions, with
carbon only, and with
all ions except carbon.
These are plotted as red
dotted, green dashed,
and blue dash-dotted
curves, respectively.
The vertical dotted lines
mark the locations
of the best-fit carbon
velocity. The phases
relative to maximum
light are noted.
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