In Antarctica the cold and dry air is expected to provide the best observing conditions on the Earth for astronomical
observations from infra-red to sub-millimeter. To enjoy the advantages in Antarctica, we have a plan to make
astronomical observations at Dome Fuji, which is located at inland Antarctica. However, the harsh environment is very
problematic. For example, the temperature comes down to as low as-80 degree Celsius in winter, where instruments
designed for temperate environment would not work. In this context, we have developed a 40 cm infra-red telescope,
which is dedicated for the use even in winter at Dome Fuji. In designing the telescope, we took account of the difference
of the thermal expansion rate among materials, which were used for the telescope. Movable parts like motors were
lubricated with grease which would be effective at -80 degrees. Most parts of the telescope are made of aluminum to
make the telescope as light as possible, so that it makes the transportation from seacoast to inland and assembling at
Dome Fuji easier. We also report the experiment that we have done at Rikubetsu (the coldest city in Japan) in February
2008.
We present the development and first astronomical applications of VPH grisms which are now operated at
cryogenic temperature in MOIRCS, a Cassegrain near-infrared instrument of the Subaru Telescope. We designed
and fabricated the VPH grisms with a resolving power ~3000 for the use in near-infrared bands. The VPH
grating, encapsulated in BK7 glass, is glued between two ZnSe prisms with vertex angle of 20 deg. After
repeating several thermal cycles down to ~100 K carefully enough not to cause irreparable damage on the
grism during cooling, we evaluated the performance at cryogenic temperature in the laboratory and found no
deterioration and no large difference in the performance from that measured in room temperature. Based on
commissioning observations with MOIRCS, we have confirmed the high efficiency (~0.8) and the resolving power
of the original design. Common use of the grisms is due to start in the second semester of 2008.
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