1.85-m millimeter/submillimeter telescope

45-m telescope
 We have been developing the 1.85m mm-submm telescope installed at the Nobeyama Radio Observatory. The target frequency bands are 115GHz, 230GHz, and 345 GHz, corresponding to molecular rotational lines of J =1-0, 2-1, and 3-2, respectively, of CO and of the isotopes. The scientific aim is to precisely reveal physical properties of molecular clouds along the Galactic Plane by obtaining a large scale distribution of molecular gas, which also can be compared with large-scale observation data in various wavelengths, e.g., Planck, Herschel, Fermi, and so on. This project is a mutual collaboration among Osaka Prefecture University, Tokyo Gakugei University, the University of Tokyo and Nobeyama Radio Observatory.

The surface accuracy of the main dish was measured to be 19 micron in rms. The telescope is enclosed in a dome covered with a membrane that is transparent at the target frequencies. Although the dome helps a lot to prevent thermal/wind deformation of the telescope, "standing-wave" phenomenon due to the supporting structure seems to damage the quality of the observed spectra, which has already been solved by the installation of a Path Length Modulator. Currently our telescope was equipped with a low-noise 2SB receiver system at 230GHz band. If we set the 1st local frequency at around 225GHz, 12CO, 13CO, and C18O (J =2-1), appear around 5-6 GHz in the IF range, which enables us to obtain these three lines simultaneously. We also installed a Digital Fourier Spectrometer, which has a 1 GHz bandwidth that can be divided into 16384 channels. The three lines are separately fed into the consecutive three frequency ranges of the spectrometer.

We have successfully obtained the molecular data in the three lines in the last September. The mapping data were obtained with the On The Fly (OTF) technique. With the OTF, the telescope continuously slew through the source with time to map it, whose result is a cube of spectra. This minimizes the dead time of the telescope compared with the normal raster scan observations. We are now carrying out the commissioning and science verification by observing several famous star forming regions with the OTF observation mode whose mapping area is 1°×1°or 2°×2°.

Reference
Onishi, T., et al. "A 1.85m Mm-Submm Telescope for Large-Scale Molecular Gas Survey in 12CO, 13CO and C18O (J = 2-1)", Publ. Astron. Soc. Japan 65, pp.78-90 (2013)