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.
Figure 2.
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.
20
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, SNe 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.
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).
Primordial Carbon in
Type Ia Supernovae
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 convi