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We report 4-epoch VLBA observations of 3C 66A at 22GHz. The resulting images show a typical core-jet structure. We combine our results with some previous results to investigate the proper motions of the jet components. The kinematics of 3C 66A is quite complicated; mildly superluminal motions as well as apparent inward motions have been detected for some components. The inward motions may imply position change of the observed core.
The first dedicated space-VLBI project, the VLBI Space Observatory Programme (VSOP), commenced with the successful launch of radio-astronomical satellite HALCA in 1997. Plans for a second generation space-VLBI project have been made by a working group over a number of years. This project, VSOP-2, has now been approved by Japan's space agency, JAXA, as the ASTRO-G project. It is planned for the spacecraft to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, which include important maser lines. It will have a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. Although the VSOP project mainly observed continuum emission from active galactic nuclei (AGN), VSOP-2/ASTRO-G is expected to enable a variety of high angular resolution maser line observations.
We are using a Japanese VLBI network (JVN) for VLBI observations of 6.7-GHz methanol masers associated with massive star-forming regions. Here we present results for Cepheus A (Cep A) from observations taken on September 9, 2006. The distribution of the maser spots indicates either a spherical bubble or a disk having an inclination of several tens degree. We construct a disk model with an inclination of ~70° and a radius of ~700 AU. From a luminosity of 1.7 × 104L⊙ for a source observed in this region, the excitation of the maser is probably radiative.
The Japanese VLBI network (JVN) has begun observations of 6.7-GHz methanol masers associated with massive star-forming regions. The JVN is a newly-established VLBI array with baselines ranging from 50 to 2560 km spread across the Japanese islands. Three observing bands of 6.7, 8.4, and 22 GHz are now available. The array consists of ten antennas: VERA Mizusawa 20 m, VERA Ishigaki 20 m, VERA Iriki 20 m, Usuda 64 m, Yamaguchi 32 m, Tomakomai 11 m, Tsukuba 32 m, Kashima 34 m, VERA Ogasawara 20 m, and Gifu 11 m, the first five of which have 6.7-GHz receiving systems. In summer 2005, we obtained the first fringes at 6.7 GHz, and VLBI images of 12 methanol maser sites including seven that had not previously been imaged with VLBI at this band. In 2006 summer, we obtained phase-reference observations toward several methanol maser sites.
The origin of the straight magnetic filaments in the Radio Arc near the Galactic Center is still controversial: either if they are permanent structure of constant configuration for a galactic-time scale, or they are temporary structure of short life time such as due to a sudden injection of cosmic rays or to sudden shock compression. Measurement of life time of the radio emitting cosmic ray electrons consisting the filaments is one of the crucial methods besides a time variation measurement of the fine structure of the filaments.
In order to investigate possible spatial variation of spectral index at higher frequencies in the filaments, which might give information about the life time of cosmic ray electrons, we have performed high-resolution radio continuum observations at 43 GHz of the GO.18-0.04 region of the radio Arc near the galactic center using the Nobeyama Millimeter-wave Array. A detailed description of this work is given in Sofue et al. (1992).
The conversion factor from the CO line intensity to column density of molecular hydrogen, X = NH2/ICO is one of the most important parameters in mm-wave study of galaxies and their molecular gas (e.g., Maloney 1990). Although the same value as that obtained for our Galactic clouds (e.g. Sanders et al. 1984; Bloemen et al. 1985) has been widely applied to galaxies, it is far from trivial that the conversion factor is universal among various types of galaxies. There have been few attempts to derive the value for galaxies, and the value is still controversial if it is applicable to other galaxies or not: Approximately the same value as that for the Galaxy has been derived for M33 (Wilson and Scoville 1990, 1992), while an order of magnitude larger value is obtained for the LMC and SMC (Cohen et al. 1988; Rubin et al. 1991).
In order to obtain the conversion factor in nearby galaxies, in which individual molecular clouds can be resolved, we are conducting CO-line mapping of M31. In this paper we report a preliminary results from mapping of a north-eastern spiral arm of M31 in the 12CO(J =1 − 0) line emission using the NMA.
The Orion bright bar is a prominent ionization front located approximately 2’ southeast of the Trapezium stars. Because this ionization front is seen almost edge-on, it provides an opportunity to study the interaction between the HII region and the adjacent molecular cloud. The molecular bar has been thought to be a narrow layer of ~ 50” (0.1 pc) in width parallel to the ionization front with enhanced temperature, density and column density. The molecular gas outside the ionization front was redshifted with respect to the ambient molecular cloud by 1-2 kms−1 (Omodaka et al. 1984, 1986, 1992), suggesting that the expanding HII region generated by the Trapezium stars had driven a shock wave into the molecular cloud at the southeast of the bar. This layer is exposed to intense UV radiation from the Trapezium stars, resulting in the formation of photodissociated regions.
We have made aperture synthesis observations of CS(J=1-0) line and 49 GHz continuum in the Orion bright bar with the Nobeyama Millimeter Array. Figure 1, a map of integrated intensities of CS, clearly revealed fine structures of the molecular bar and more than six prominent features are confirmed. It is noted that these features are lined up at 30” from the ionization front inside the molecular cloud.
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