We report the current status of the NASCO (NAnten2 Super CO survey as legacy) project which aims to provide all-sky CO data cube of southern hemisphere using the NANTEN2 4-m submillimeter telescope installed at the Atacama Desert through developing a new multi-beam receiver and a new telescope control system. The receiver consists of 5 beams. The four beams, located at the four corners of a square with the beam separation of 720′′, are installed with a 100 GHz band SIS receiver having 2-polarization sideband-separation filter. The other beam, located at the optical axis, is installed with a 200 GHz band SIS receiver having 2-polarization sideband-separation filter. The cooled component is modularized for each beam, and cooled mirrors are used. The IF bandwidths are 8 and 4 GHz for 100 and 200 GHz bands, respectively. Using XFFTS spectrometers with a bandwidth of 2 GHz, the lines of 12CO, 13CO, and C18O of J=1−0 or J=2−1 can be observed simultaneously for each beam. The control system is reconstructed on the ROS architecture, which is an open source framework for robot control, to enable a flexible observation mode and to handle a large amount of data. The framework is commonly used and maintained in a robotic field, and thereby reliability, flexibility, expandability, and efficiency in development are improved as compared with the system previously used. The receiver and control system are installed on the NANTEN2 telescope in December 2019, and its commissioning and science verification are on-going. We are planning to start science operation in early 2021.
Currently, we are performing a large-scale survey of molecular clouds toward the Galactic Plane in 12CO, 13CO, and C18O(J = 2–1) with the 1.85-m mm-submm telescope from Nobeyama Radio Observatory. In addition, we are proceeding with the preparation of a new project to observe several additional molecular lines including higher transitions of CO isotopes, such as 12CO, 13CO, and C18O(J = 2–1, 3–2) simultaneously with a wideband receiver (210–375 GHz). The optics has a Cassegrain reflector antenna with Nasmyth beam-waveguide feed and is composed of Main-reflector, Sub-reflector, ellipsoidal mirrors, and plane mirrors. New wideband optics will be required to achieve this goal. In order to accomplish the optics, we have designed a corrugated horn with a fractional bandwidth of ∼56 %, and frequency independent optics to couple the beam from the telescope onto the horn. The corrugated horn has a conical profile and the variable corrugation depth. It has been optimized by using CHAMP, our targeting return loss of better than −20 dB, cross-polarization loss of better than −25 dB, and far-field good radiation pattern. The simulation of the corrugated horn results in low return loss, low crosspolarization, and symmetric beam pattern in that frequency band. The simulated aperture efficiency of the designed receiver optics on the 1.85-m telescope is above 0.76 at all frequencies by using GRASP. Recently, we have succeeded in simultaneous observation of 12CO, 13CO, and C18O(J = 2–1 and 3–2) toward Orion KL with the optics for the first time.
The 1.85-m mm-submm telescope has been operated at Nobeyama Radio Observatory to observe molecular clouds in the nearby Galactic Plane based on the molecular lines of 12CO, 13CO, C18O(J = 2–1). We are planning to relocate the telescope to a site (∼2,500 m) at the Atacama Desert in Chile and to newly install a dual-band receiver for simultaneous observations of lines of CO isotopes with the transitions of J = 2–1 and J = 3–2. In order to achieve this goal, we have developed a wideband diplexer to separate radio frequency (RF) 211–275 GHz (ALMA Band 6) and 275–373 GHz (ALMA Band 7). We adopted a waveguide type FrequencySeparation Filters (FSF) as the basic concept of the wideband diplexer in 210–375 GHz. The wideband diplexer (α) has already been fabricated and measured as the prototype, and we thus obtained reasonable performance in the CO lines band. On the other hand, the measurement result indicates the return loss is relatively worse in 280–300 GHz, although it doesn’t affect the simultaneous observations of 230 GHz and 345 GHz band. We carried out 3D shape measurement with an optical microscope, and then, found that there are machining errors in the parts of the resonator in High Pass Filter. The analysis based on electromagnetic simulation reveals that the errors significantly affect return loss around cut-off frequency. In this paper, we describes the design of the waveguide diplexer, S-parameter measurement, and detailed analysis to verify the discrepancy between simulation and measurement.
We report the current status of the 1.85-m mm-submm telescope installed at the Nobeyama Radio Observatory (altitude 1400 m) and the future plan. The scientific goal is to reveal the physical/chemical properties of molecular clouds in the Galaxy by obtaining large-scale distributions of molecular gas with an angular resolution of several arcminutes. A semi-automatic observation system created mainly in Python on Linux-PCs enables effective operations. A large-scale CO J =2–1 survey of the molecular clouds (e.g., Orion-A/B, Cygnus-X/OB7, Taurus- California-Perseus complex, and Galactic Plane), and a pilot survey of emission lines from minor molecular species toward Orion clouds have been conducted so far. The telescope also is providing the opportunities for technical demonstrations of new devices and ideas. For example, the practical realizations of PLM (Path Length Modulator) and waveguide-based sideband separating filter, installation of the newly designed waveguide-based circular polarizer and OMT (Orthomode Transducer), and so on. As the next step, we are now planning to relocate the telescope to San Pedro de Atacama in Chile (altitude 2500 m), and are developing very wideband receiver covering 210–375 GHz (corresponding to Bands 6–7 of ALMA) and full-automatic observation system. The new telescope system will provide large-scale data in the spatial and frequency domain of molecular clouds of Galactic plane and Large/Small Magellanic Clouds at the southern hemisphere. The data will be precious for the comparison with those of extra-galactic ones that will be obtained with ALMA as the Bands 6/7 are the most efficient frequency bands for the surveys in extra-galaxies for ALMA.
We are promoting the Hybrid Installation Project in Nobeyama, Triple-band Oriented (HINOTORI), a project aiming at triple-band simultaneous single-dish and VLBI observation in the 22-, 43- and 86-GHz bands using the Nobeyama 45-m Telescope. The triple-band simultaneous observation becomes possible by developing two perforated plates and mounting them in the Nobeyama 45-m Telescope optics. One is a 22/43-GHz-band perforated plate, which transmits the higher frequency (43-GHz) band and reflects the lower frequency (22-GHz) band, and the other is a 43/86-GHz-band perforated plate, which transmits the 86-GHz band and reflects the 43-GHz band or lower. Both plates are designed to be installed in the large telescope optics with a beam diameter as large as 50 cm and insertion/reflection losses are both 0.22 dB (5%) or less in the design. The receivers used in triple-band simultaneous observation system are the H22 and H40 receivers, which are already installed in the Nobeyama 45-m Telescope, and the TZ receiver, which is a 100-GHz-band receiver including the 86-GHz band and reinstalled in the Nobeyama 45-m Telescope. A system of simultaneous observations in the 22- and 43-GHz bands of the Nobeyama 45-m Telescope with the 22/43- GHz-band perforated plate has been completed and commissioned for scientific observations. Also VLBI fringes between the Nobeyama 45-m telescope with the dual-band observation system and the VERA 20-m telescopes at 22 and 43 GHz was detected successfully.
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