Supernova Acceleration Probe: Studying Dark Energy with Type Ia Supernovae Page: 4 of 12
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Fig. 2. The SNAP focal plane working concept.
The two-axis symmetry of the imager filters allows
any 90~ rotation to scan a fixed strip of the sky and
measure all objects in all nine filter types. The im-
ager covers 0.7 square degrees. Underlying the fil-
ters, there are 36 2k x 2k HgCdTe NIR devices and
36 3.5k x 3.5k CCDs on a 140K passively-cooled
focal plane. The six CCD filter types and three
NIR filters are arranged so that vertical or hori-
zontal scans of the array through an observation
field will measure all objects in all filters. The false
colors indicate filters with the same bandpass. The
central rectangle and solid circle are the spectro-
graph body and its light access port, respectively.
The spectrum of a supernova is taken by placing
the star in the spectrograph port by steering the
satellite. The four small, isolated squares are the
star guider CCDs. The inner and outer radii are
129 and 284 mm, respectively.Fig. 3. A schematic spectrograph optical de-
sign. The beam is going out from the slicer (on
the bottom right) to a prism disperser back faced
coated by a dichroic. The visible light (blue path)
is reflected and the IR light (in red) continue to a
second prism used to reach the required spectral
dispersion. The two beams are therefore focused
on two detectors. The dimensions of the spectro-
graph are approximately 400 x 80 x 100 mm. See
Ealet et al. (2003) for more details.
dark-energy properties, especially the time vari-
ation of the equation of state.
3.1. Sources of Systematic Uncertainty
High-redshift supernova searches have been
proceeding since the late 1980's (Norgaard-Nielsen
et al. 1989; Couch et al. 1989; Perlmutter et al.
1995, 1997, 1998, 1999; Schmidt et al. 1998; Riess
et al. 1998; Tonry et al. 2003; Knop et al. 2003;
Riess et al. 2004). Particularly since the discov-
ery of the accelerating expansion of the Universe,
the high-redshift supernova methodology for mea-
suring cosmological parameters has been critically
scrutinized for sources of systematic uncertainty.
Below (and summarized in Table 2) is a lists of
these sources where we highlight in bold the fea-
tures specific to SNAP that allow systematic con-
trol. Generically, the need for high signal-to-noise
observations over a broad wavelength range for
0.1 < z < 1.7 supernovae, as well as the truncation
of ground-observatory light curves of high-redshift
supernova at high-Galactic latitude, point to the
necessity of a space mission.4
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Albert, J.; Aldering, G.; Allam, S.; Althouse, W.; Amanullah, R.; Annis, J. et al. Supernova Acceleration Probe: Studying Dark Energy with Type Ia Supernovae, report, August 8, 2005; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc875275/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.