The construction of 43GHz VLBI network and the project search for VLBI radio sources of phase-referencing VLBI astrometry with VERA.

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VERA (VLBI Exploration of Radio Astrometry) is a new VLBI ax mainly aimed at study of the structure and dynamics of our Galaxy through high precision phase-referencing VLBI astrometry of astronomical maser sources. VERA, with its dual-beam antenna system, will enable us to observe a galactic maser and an extra-galactic reference source simultaneously in order to remove the atmospheric fluctuation. In order for VERA to achieve a 10μ as level accuracy, allowing us to obtain parallaxes of maser sources in the whole Galaxy, it is required that the maser and reference source must be located within 2°each other. This requires a large number of reference sources spreading over Galactic plane because H2O(22GHz) and SiO(43GHz) masers which are the main targets, are mostly concentrated in the galactic plane. Hence the search for VLBI sources in the galactic plane is indispensable to the success of VERA. In order to search for 43GHz VLBI sources, we started to install the 43GHz cooled receiver to 34m antenna which belongs to Kashima Space Research Center, Communications Research Laboratory in these Funds. By this we will start a 43GHz survey of continuum radio sources in the galactic plane using this 34m telescope and Nobeyama 45m telescope. We constructed small-sized cooled dewar and has succeeded in cooling the receiver. Further, we incorporated the Local oscillator (this Grant-IN-Aid) and installed these components in 34m telescope. The system noise temperature, including atmospheric loss, was 300K. In this test observations, very serious problems arosed. As the antenna inclined, the antenna pointing accuracy become significantly poor due to both the bending and hanging down of the subreflector. This knotty problems was mainly settled by Satoru Morisaki, a graduate student of Kagoshima University. He also set up high-resolution acousto-optical spectrometers.