Development of a Transportable Telescope for Galactic Survey at 500 GHz in Antarctica

Abstract

We have developed a transportable 30-cm submillimeter- wave telescope to operate at the Dome Fuji station in the Antarctic plateau. Transportability is an important requirement in the design; the telescope can be divided into several subsystems by hands. The maximum weight of the subsystems is restricted to be below 60 kg, so that the telescope can be assembled without a lifting machine. A small 4 K mechanical cryocooler is used for cooling down a SIS mixer. Total power consumption was designed to be less than 2.5 kW. The optical system was designed to satisfy the frequency independent matching condition at the subreflector and the feed horn of the SIS mixer, so we could accommodate a higher frequency receiver without changing mirrors. A quasi-optical filter was employed for the single sideband operation in observations of the CO (J=4-3) line at 461.04 GHz and the [CI] (P-3(1)-P-3(0)) line at 492.16 GHz. It was equipped with a 1 GHz width spectrometer that covers a velocity width of 600 km/s with a velocity resolution of 0.04 km/s at 461 GHz. We carried out test observations at a 4400-m altitude site in northern Chile during winters of 2010 and 2011. The typical system noise temperature, including atmospheric loss, was 3000 K (SSB) at 461 GHz, that is mainly limited by atmospheric opacity. The beam size of the 30-cm offset Cassegrain antenna at 0.65 mm of wavelength was measured to be 9'.4 +/- 0'.4 by cross scanning of the sun. This angular resolution of the 30-cm telescope is same as those of the Columbia-CfA-U. Chile CO (J=1-3) surveys. We estimated the main beam efficiency to be 87 +/- 5% by observing the new moon. We succeeded in mapping Orion Molecular Cloud A and M17 SW in CO (J=4-3) followed by test observations toward Orion KL in both CO (J=4-3) and [CI] (P-3(1)-P-3(0)).