Carbon monoxide (CO) emission lines are the principal probe used to investigate the distribution, structure, and kinematics of interstellar molecular gas in the Galaxy. In order to investigate the global structure of extended molecular clouds, a small-aperture telescope has an advantage, because its large beam makes it possible to obtain fully-sampled maps of large regions quickly. The VST-1 60-cm radio survey telescope was constructed by the Institute of Astronomy, the University of Tokyo and the Nobeyama Radio Observatory, the National Astronomical Observatory of Japan during 1988-1989. It is located at Nobeyama Radio Observatory in Japan. The primary purpose of this telescope was a large-scale survey in the 12CO (J = 2-1) emission line to determine the temperature and density distribution of molecular gas in the Galaxy by comparing the 12CO (J = 2-1) data with the 12CO (J = 1-0) data obtained with the Harvard-Smithsonian Center for Astrophysics (CfA) 1.2-m survey. The beam size of the VST-1 was designed to be the same as that of the CfA 1.2-m telescope, so that one can directly compare the data from the two telescopes.
We developed a waveguide-type sideband-separating (2SB) superconductor-insulator-superconductor (SIS) mixer receiver for the 200 GHz band, and installed it in VST-1. The waveguide-type 2SB receiver is free from the quasi-optical single sideband (SSB) filter and has the ability to observe signals in the two sidebands both independently and simultaneously. This important feature of the 2SB receiver should enable us to observe two or more spectral lines that are separated by more than 10 GHz at the same time, and the performance of the observations will be greatly improved. In addition, it is also noteworthy that through simultaneous detection, we can better determine the line-intensity ratios of two molecular lines, e.g., T (12CO)=T (13CO), without being contaminated by errors in pointing. Using the upgraded VST-1 telescope, we initiated a survey of molecular clouds with the 12CO (J = 2-1) and 13CO (J = 2-1) emission lines. These are the first large-scale observations with the waveguide-type 2SB SIS mixer for the 200 GHz band.
Very Small Telescope No.1 (VST-1)
Reference
Nakajima, T. et al., "A New 60-cm Radio Survey Telescope with the Sideband-Separating SIS Receiver for the 200 GHz Band", Publ. Astron. Soc. Japan 59, pp.1005-1016 (2007)
Nakajima, T. et al., "New 60-cm Radio Survey Telescope with the Sideband-Separating SIS Receiver for the 200 GHz Band", Proc. of the 7th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, pp.308-317 (2007)
Nakajima, T., "Development of the Waveguide-Type Sideband-Separating SIS Receiver Systems for the Millimeter Radio Telescopes", doctor thesis (Osaka Pref. Univ. 2008)