A new Japanese infrared balloon telescope

We have developed a new 50-cm infrared balloon-borne telescope. The first flight of this telescope system is scheduled for September 1998. We used an offset paraboloidal mirror and used its primary focus to reduce the amount of background emission from the telescope itself in order to perform photometric observation with high sensitivity. The structure of the telescope is made of carbon fiber reinforced plastics (CFRP) to reduce its weight and make the optics free from thermal contraction due to low temperatures during observational flights to retain good focusing of the optics. For the detector, we use our newly developed 4 × 8 stressed Ge:Ga array in order to perform 150–180 μm photometry. The detector is installed in a cryostat and cooled by liquid He down to 2 K. The large format of the detector raises the observational efficiency enabling us to survey a wide area of the sky (up to 10° × 10°) with a high spatial resolution of 1.5′ in one observational flight. In the first flight, we plan to survey the Orion region, W51, etc. and to map some external galaxies.